Download - GAS INSULATED SWITCHGEAR

Preface

The GIS offers economic solutions for complex switchgear applications, e.g. in densely populated areas, for aesthetic town planning or under severe environmental impacts. Precisely speaking GIS leads to an effective use of a limited space. Due to the inherent safety and compact layout of a Gas insulated substation, it is the best solution for substations which are to be built in restricted underground spaces.

Since all live parts of GIS are contained in a metal enclosure, they are fully protected against environmental effects, such as salt deposits in coastal regions, sand storms, humidity in the atmosphere, etc.; insulator cleaning is eliminated and, thus, high reliability is achieved.

As the Live parts (e.g. buses and connections) are contained within earthed enclosures of GIS and are inaccessible, as such it ensures maximum operator safety and reduced maintenance.

Besides that GIS meets with recent requirements for aesthetic compatibility with surroundings. More over adoption of GIS offers an excellent solution for environmental protection since it helps in protecting the system from hazards.GIS is considered trouble free and maintenance free installation. However in case of any fault the services of manufacture’s representatives are required to attend and repair the fault since all the modules of GIS comes directly under assembled form and in sealed condition from factory since no technical expertise is available indigenously for repair and maintenance of GIS. A manual on GIS will certainly help the users to understand a brief of GIS regarding the details of inside components of GIS, its installation process and operation and maintenance of GIS. The preparation of manual on GIS is an attempt in this direction it will prove be a guide/recommendatory document for the power station utilities in the country.

CHAPTER-1

1.0 INTENT

The manual is a maiden attempt to consolidate information in a scientifically organized way, so as to engineer a document which should be available to user utilities as a “Manual” on gas insulated switchgear and gas handling aspects. Document incorporates broadly:

Check application of GIS at feasibility stage. Propose complete data and rationalized specifications with techno economic provisions

on spares and effective execution. Develop a GIS station which should give reliable service deliberating specifically with

reference to standard schemes. User interface in engineering, quality assurance and testing Consolidate gas handling, maintenance and testing related equipments/norms. Considerations and decisions to be taken by users considering overall implications High Frequency transients and their controlling measures Provide list of updated standards and codes. Emerging technologies.

The manual shall also touch the options of hybrid switchgear available to users as a techno-economical solution under specific cases.

Besides Technical Aspects, the manual shall also cover safety and training aspects. The manual has been prepared taking into consideration the availability of information from manufacturers, testing organizations, and users etc. This document is to be considered by the user as a recommendatory document and customarization with respect to project specific requirement is essentially required taking into account prevailing standards at the time of application. The gas used in the switchgear needs proper handling on account of environmental considerations. Normally the pressure inside the GIS is kept above four bars and liquefaction of the gas at this pressure could happen on temperatures below (-) 30oC. The application therefore should be carefully done in case the ambient temperature happens to go below this temperature.

GIS internationally is getting acceptance on account of technical merits. It has excellent adaptability in meeting most difficult terrain or space constraints. The land area required for a GIS is in the order of 10% to 20% of that for an AIS 9(Air Insulated Switchgear) substation considering the switchgear bay, the saving in overall land area depends very much on the specific voltage level and the connection to transformers, reactors and incoming and outgoing lines. If the substation is connected to overhead lines, then space will have to be allocated for tower and droppers which might reduce the total land saving, . Indoor and underground GIS is possible even in urban and highly populated areas which will allow building of the substation at the point of consumption which will bring about significant cost savings in the distribution network.. It is upto 220 kV level, transportation conditions permit factory assembled bay which is most attractive and favorable feature for indoor & outdoor application alike due to very short erection and commissioning time. Reduced requirement of maintenance make them suitable option for most reliable operation. In fact quality consciousness of equipment alone makes GIS as favored equipment choice for remote operation. All these factors in totality make GIS one of the attractive equipment options to adopt.GIS is also considered for severe environment condition, where saline pollution near coastal areas of industrial pollution requiring regular cleaning of insulators and corrosion of metallic components and electrical joints. GIS is also adopted when substation is to be installed at very high altitudes or very low temperatures or seismic considerations and hydro station.

CHAPTER- 2

TECHNO ECONOMIC FEASIBILITY

Initial equipment cost price of GIS is usually higher than that of AIS. There are many other merits/ considerations which need to be justified/ evaluated including the higher initial equipment expenditure. Therefore, the choice of GIS with respect to AIS is a techno-economic decision to be made taking into account technical, economical and environmental factors. The main advantages of GIS are as under:-

• Compactness/ Land requirements • Suitable for Mountainous zones • Environmental conditions • Replacement/up gradation of AIS due to growing power demand • Reliability • Safety • Applicability to strategic locations. Less area of land requirement

2.1 Compactness / Land Requirement

GIS compact dimensions and design make it possible to install substations up to 550kV right in the middle of load centers of urban or industrial areas. This compactness of GIS has a direct influence on land requirement and land cost. Compact modular designs offer many possibilities in layout design and allow specific site requirements to be met as compared to AIS. The land requirement for GIS substation (considering switchgear only) is of the order of 8 to 20 percent of that for an AIS substation. The savings in land area depends upon the voltage level and the associated equipments like transformers, reactors and incoming/outgoing lines. The savings could also be maximized by using cable connections and short length GIS trunking applications.

In the case of underground hydroelectric power plants, GIS can be erected close to transformers or near the outdoor yard. A study of cost has to be made considering the space availability, cavern dimension in considerations in terms of height, width and

number of cables required for power evacuation system from the HEP. This is due to the fact that in EHV cables of small current carrying ratings cost is largely governed by insulation requirements. Hence economy has to be studied on case to case basis considering a wide spectrum of parameters.

2.2 Mountainous Zones

For AIS the site preferably should be fairly flat land or maximum it could be in steps. The requirement increases as the altitude increases as compared to plains due to air density correction factor. In mountainous zones, it is difficult to get piece of flat land & it has to be obtained in different terraces. This entails high preparation cost whereas for GIS the space requirement is low and can be housed in a building (leveling of site can be minimized).Precaution is however required to be taken to ensure that natural calamity or collapse of rock etc should not damage the GIS and it continues to perform as envisaged. The stability of land & adjoining rock is required to be kept in view before finalizing switchyard locations.

2.3 Environmental Conditions

Severe environmental considerations, listed below, lead to very high maintenance costs for the AIS.

• Coastal site where saline pollution deposits may be heavy, • Substantial industrial pollution may require frequent/regular (possibly monthly or annual)

insulator cleaning/ hot line washing. • Industrial pollution may cause severe corrosion of metallic components, flanges, electrical

joints etc. • Where substations are installed at very high altitudes the effects of low air density, snow

loading & sub zero temperature need be considered for all equipments of AIS (could require the provision of additional costly insulation) where as for GIS installation only SF6/air bushing need only be considered

• Extreme climatic conditions would also require additional measures to be considered for bushings and GIS parts outside the building,

• Seismic considerations may dictate extensive mechanical support and bracing of AIS in order to meet specified requirements. The physical design of GIS allows seismic criteria to be more readily achieved at a lower overall cost.

GIS enclosed within the building would be immune from these effects except for the SF6/air bushings. GIS therefore becomes an environmental friendly option for both rural and urban areas.

2.4 Replacement/ Up gradation of AIS due to growing Power Demand

Most of the power systems operate with equipment of different ages. Optimal moment for replacement of the equipment is determined by technical, economical, environmental and/or strategic reasons. GIS with higher rating can be used for replacement of AIS in the event of growing power demand/ replacement at the end of the existing equipment’s lifetime or of the need for a higher transmission voltage without the additional land requirements. For example an 8 to 10 bay 132kV AIS could easily be replaced by a 14 to 18 bay 220kV GIS. GIS should be extendable to meet the requirement of additional bays in future for which the required space should be made available in the GIs room.

2.5 Availability and Reliability

Each bay is factory assembled and includes the full completeness of circuit breaker, isolator switches, grounding switches, instrument transformers, control and protection equipment, interlocking and monitoring facilities. A high quality standard is ensured by the fact that all the equipment is produced, routine and site tested by one manufacturer. Further in the case of integrated or prefabricated control cubicles and cabling, all circuits and functions may be factory-tested, which reduces the failure probability on site and the time for erection and commissioning significantly. Modern GIS are expected to perform satisfactorily in service for many years with minimal or even no maintenance due to the fact that deterioration due to weathering is eliminated totally. Unless GIS is subjected to regular and onerous switching duties, maintenance of CBs, disconnectors and earth switches may not be required for many years. Therefore it is expected that the failure rates of the equipments/ components would be very low, GIS would have very high

reliability and availability (low failure frequency rate and long maintenance intervals). Due to enclosed bus bar, bus faults are minimal.

Fig 2 : Reliability of GIS in a country

2.6 Safety

The encapsulation of GIS provides a high degree of safety for operators and other personnel due to the fact that it is impossible to touch any live part of the switchgear inadvertently. Protection against vermin or vandalism is also provided. The consequences of an internal arc are normally contained within the enclosure through rapid operation of the protection. Even under worst-case conditions it is limited to the operation of a pressure relief device or burn through after some time. No GIS part will explode, and the damaged region is limited due to the gas compartmentalization.

2.7 Strategic Locations

The use of indoor GIS is absolutely necessary for strategic locations as it can be installed in a new building, existing building, or even in an underground cavern, or a simple hall. All components such as Busbars.Disconnectors, Circuit Breakers, Instrument Transformers, cable terminations, and joints are contained in earthed enclosures filled with SF6 gas. The enclosures are non -magnetic metallic containers. In indoor stations there is no other requirement whereas in outdoor installations effect of emissivity is required to be considered due to solar radiations.

GIS installations are assembled from variety of standard modules which are assembled together with flanged connections and plug in type of contacts on the conductors, so as to easily disassemble individual components subsequently. The gas tight enclosure surrounds all the live parts, which are supported on spacer (insulators) and insulated from the enclosure by SF6 gas. The barrier insulators divide the bay into separate gas compartments sealed off from each other. This minimizes effect on other components during plant extensions and also enables inspection and maintenance. The flanged joints contain non-ageing gaskets. Leakage of gas can pass only to atmosphere, but not between the compartments.

2.8 Cost (Life Cycle Cost)

Factors affecting life cycle cost :

• GIS/AIS Primary hardware – The capital cost of GIS/AIS including installation cost, land, building, main equipment cost etc and the cost of all secondary control, protection and monitoring equipment.

• Maintenance – The cost of all preventive maintenance, predictive maintenance and repair maintenance.

• Operation Costs -It includes operation & maintenance cost and cost of inventory & spares. • Outage Costs – This includes outage costs like power/energy interruption and repairing &

capital maintenance.

Overall LCC would be the sum of above. If cost analysis is done considering LCC, GIS will become obvious cost effective solution.

2.9 Other Considerations

GIS finds favorable acceptance in case of urban areas , underground power stations, places where environmental considerations are given added favour . It may be important even in case of rural and other areas where space is not a constraint but due to the following factors:

(a) Price of land (b) Cost of acquisition of land (c) Cost of environmental disturbance including crop/tree considerations (d) Developmental cost of land (e) Associated deployment / R&R of affected people (f) Cost of civil works for AIS versus GIS – this could include but not limited to indoor/outdoor GIS and building requirements for associated auxiliaries (g) Cable - supply ,erection and maintenance including selection of higher sizes on account of voltage drop considerations, long lengths in AIS as compared to GIS (h) Operating cost -this could include but not limited to maintaining crushed rock, illumination and lightening protection requirements(i) Maintenance requirements of CBs , CTs , dis-connectors, and bus PTs(j) Probability of bus faults /conductor faults due to over heating.

2.10 Cost Comparison between AIS and GIS

In order to compare the economic viability of a Gas Insulating Sub station Vs the Air Insulated Sub Stations the following three cases have been studied which clearly establish the superiority of GIS over AIS:

420 kV, 6 bay Grid Sub Station

i) Double Bus Bar Vs I type scheme having 4 diameters

ii) Double Bus Bar Vs D type scheme having 4 diameters

220 kV, 6 bay Grid Sub Station

The working details of the above three cases are given in Table 1, 2 and 3 respectively

TABLE –1220 KV

Cost Comparison Between GIS and AISAssumptions:-1. No. of Bays – 6 , 220 KV Grid Substation2. Double Bus Bar Scheme3. Expected normal Life – 25 years (taken same as for AIS for the purpose of comparison)4. Area Required FOR GIS 250 Sqm For AIS 8260

sqm.Initial Cost Rupees

GIS AIS1. Land Cost @ Rs. 250/sqm 62500 20650002. Development Cost @5% 3125 1032503. Environmental Considerations @ 3% 1875 619504. Land Acquisition Cost @ 2% 1250 413005. Oustees Compensation @ 8% 5000 165200

Total Land Cost in Rural Area 73750 2436700

6. Main Equipment Cost 180000000 1080000007. Erection Cost 0 86400008. Cabling Cost 360000 10800009. Earthling Cost 360000 108000010. Illumination Requirements 360000 1080000

Fixed Cost (Total 1-10) 181153750 122316700

11. Operation & Maintenance expenses in 25 yrs. of life Span 22500000 8100000012. Inventory & Spares 2700000 3240000

Variable Cost (11+12) 25200000 84240000

13. Repairing & Capital Maintenance 5400000 10800000

14. Total Cost 189253750 217356700While Comparing the costs, control Room and pothead yard requirements have been excluded as they are same in both the cases. Values shown in the tables are indicative only to bring out the comparison. Capitalization will depend more on application and scheme selection. In case of generating stations the variants could be hydro, thermal etc. However, in grid where system redundancy can take care of outages to avoid interruption the capital loss on this account shall not be significant. Similarly radial feed environmental consideration also can contribute towards power/energy.

1. Since various modules of circuit breakers instrument transformers, bus bar etc. come under factory assembled module so GIS takes very little time in erection, testing & commissioning.

2. GIS is either practically of low maintenance or very little maintenance so once erected does not pose any maintenance problem for years together except some filling of gas in the modules to maintain the required pressure inside the module.

TABLE – 2420 KV

Cost Comparison Between GIS and AISAssumptions:-1. No. of Bays – 6 , 420 KV Grid Substation2. Double Bus Bar Scheme Vs I Type layout having 4 diameter for 6 bays3. Expected normal Life – 25 years (taken same as for AIS the purpose of comparison)4. Area Required For GIS 640 Sqm For AIS 26400

sqm.Initial Cost Rupees

GIS AIS1. Land Cost @ Rs. 250/sqm 160000 66000002. Development Cost @5% 8000 3300003. Environmental Considerations @ 3% 4800 1980004. Land Acquisition Cost @ 2% 3200 1320005. Oustees Compensation @ 8% 12800 528000


6. Main Equipment Cost 360000000 1800000007. Erection Cost 0 144000008. Cabling Cost 720000 18000009. Earthing Cost 720000 180000010. Illumination Requirements 720000 1800000

Fixed Cost (Total 1-10)


Variable Cost (11+12)



1.Since various modules of circuit breakers instrument transformers, bus bar etc. come under factory assembled module so GIS takes very little time in erection, testing & commissioning.

2. GIS is either practically of low maintenance or very little maintenance, so once erected does not pose any maintenance problem for years together except some filling of gas in the modules to maintain the required pressure inside the module.

TABLE – 3420 KV

Cost Comparison Between GIS and AISAssumptions:-1. No. of Bays – 6, 420 KV Grid Substation2. Double Bus Bar Scheme Vs D Type scheme having 4 Diameter 3. Expected normal Life – 25 years (taken same as for AIS for the purpose of comparison)4. Area Required

For GIS 640 SqmFor AIS 48720 sqm.

Initial Cost RupeesGIS AIS

1. Land Cost @ Rs. 250/sqm 160000 121800002. Development Cost @5% 8000 6090003. Environmental Considerations @ 3% 4800 3654004. Land Acquisition Cost @ 2% 3200 2436005. Oustees Compensation @ 8% 12800 974400


6. Main Equipment Cost 360000000 1800000007. Erection Cost 0 144000008. Cabling Cost 720000 18000009. Earthling Cost 720000 180000010. Illumination Requirements 720000 1800000

Fixed Cost (Total 1-10)


Variable Cost (11+12)



1.Since various modules of circuit breakers instrument transformers, bus bar etc. come under factory assembled module so GIS takes very little time in erection, testing & commissioning.

2. GIS is either practically of low maintenance or very little maintenance, so once erected does not pose any maintenance problem for years together except some filling of gas in the modules to maintain the required pressure inside the module.

2.11 Hybrid Options – Comparison of AIS, GIS and comparison of AIS, GIS and Hybrid Options is broadly given below along with single phase enclosure of GIS: -

Comparison table

Criteria AIS GIS Hybrid

Space requirement High Low Middle

Equipment cost Low High Middle

Environmental Influence

High Low Middle

Maintenance requirements

High Low Low

The modular construction of SF6 switchgear has an added advantage to build GIS for all type of layout schemes of EHV substation.

Busbar Disconnector Cable Disconnector

Current Transformer Connection Current

Circuit Breaker Transformer

Circuit Breaker

Fig 3 : Single Phase Enclosure of GIS

SF6 gas is a superior insulation medium, having dielectric strength 3 times that of air at atmospheric pressure. Up to 72.5 kV, SF6 pressure is about 3.5 to 4.5 bar and may go as much as 6-7 bars for high voltage & EHV CB’s.

CHAPTER- 3

SWITCHING SCHEME OPTIONS AND THEIR SINGLE LINE DIAGRAMS

Switching scheme for high and medium voltage GIS are governed by consideration of its operation. Selection of Bus bar numbers, i.e , single or multiple depends upon how the system is to be operated and also keeping in view the need for sectionalisation. Other factors like the need to isolate parts of installation for maintenance purpose, future extensions etc are also taken into account. Following are the major aspects considered while selecting switching schemes:

Number of incoming and outgoing circuits and their effects on outage in terms of

consequential loss. Quantum of revenue loss on account of outage of number of circuits Amount of power to be handled and level of security for each circuit Number of duplicate circuits and alternate supplies towards next Substations Higher degree of flexibility Scope of future expansion without shut-down or with limited shut down Reliability of supply during various possible faults and maintenance. Cost: The selection of the most suitable switching scheme for particular substation is

done after evaluation of technical aspects. Simplicity of operation may not give adequate reliability, whereas very highly reliable scheme will require large number of CBs and likely to cost more.

Maintenance of any desired part of substation without major shut down Selection of scheme depends on the size and importance of the substation.

3.1 Categorization of GIS Schemes

Keeping above aspects into consideration, schemes are normally selected in the following categories:

3.1.1 Distribution GIS - Up to 33 KV

• Single Bus bar System : Where outages can be allowed for all the circuits and can be planned where there is a space constraint. Fig-1a

• Single Sectionalized Bus bar : Where outages in the important feeders are permitted as per

planned shutdown for maintenance. Fig. 1 b

• Double Bus: Where outages in the important feeders, are permitted as per planned shutdown for maintenance as well as built in reliability OF CB/ Bus bar failure. Fig. 2

3.1.2 Medium size GIS- 66KV to 145KV

• Single Bus bar System: Importance of power supply to be ascertained by utility where security & flexibility are of a little concern.

• Double bus: Where maximum security and flexibility is desired to connect feeders in any bus. Maintenance of any bus bar is possible.

• Main and Transfer bus: Where outages in the important feeders are permitted as per planned shutdown for maintenance. Here bus bar maintenance is possible by transferring the important load on transfer bus. Fig-4

Fig 4: Typical Ring for 4 bay Arrangements

3.1.3. Large EHV GIS, both for Generating Stations and Transmission Network- 245 kV and above

• Double bus bars with bus coupler: Suitable for Substation in a highly inter connected

network, in which there are many incoming and outgoing feeders with a possibility of expansion . Bus bar maintenance is possible. Fig-3

• Double main & transfer bus with transfer breaker scheme: This is adopted in those Substations where quantum of power transfer per feeder is high. This scheme provides switching flexibility, high security against bus bar faults and minimum outage during maintenance. Bus bar maintenance and outage of each CB is possible without interruption of flow of power. This scheme is more proffered scheme for AIS, but the scheme is considerably costly .Fig 5

• Breaker and a half scheme: This is adopted in those Substations where quantum of power transfer per feeder is high. This scheme provides enough switching flexibility, high security against bus bar faults, breaker fault. The scheme offers minimum outage during maintenance. Cost is moderately higher. Fig 6

Ring bus/ Inter connected mesh: This is adopted for those substations, where there are up to 5 number of circuits carrying high power. It provides maximum security against bus bar faults and and power flow continuity is maintained. This scheme requires less number of CBs than in breaker and a half scheme. However, it has lesser flexibility in Switching operation.fig-6

Most acceptable switching scheme:Normally double busbar with bus coupler configuration would be most acceptable proposition and is widely used in the substation. However user may opt different schemes depending upon their technical requirement and also on cost consideration.

3.2 Single Line Diagrams ( SLDs)

General details of the single Line Diagrams of GIS are given above. Typical single Line Diagram of the GIS stations of 220 kV Chamera -II H.E. Project and 400 kV Chamera-I level installed on some of the underground Hydro Power Stations in operation are enclosed Chamera-I and typical single line diagram and section diagram of 220 KV power station.

CHAPTER- 4

STUDIES REQUIRED BEFORE APPLICATIONOF GIS (245 KV & ABOVE)

Once techno-economic viability is established and it is decided to use GIS tentative layout is required to be developed. The layout should necessarily consider connection of incoming and outgoing bays for the GIS. The method of connection i.e. cable or overhead connection or a bus duct also has an important bearing on the cost and reliability of the GIS installation. Capacitance of these components varies and adequate care is required to be taken with the help of studies to take precautions for possible resonance or over voltage. It is recommended to get the following studies done as a part of planning first and then based on specific equipment information, adequate protective measures are to be adopted in time to avoid failures. Normally following studies are recommended

4.1 Insulation Co-ordination Studies

These studies would reflect requirements in terms of electrical parameters for the planned system and it will be exposed to power frequency, impulse and switching over voltages. Each study will need system data in terms of immediate interconnecting transmission lines. The outcome would determine the location and parameters of lightening arresters required to be installed on the incoming bays /outgoing bays and the bus bars. In the event of systems having reactors at the ends of the line, the study would also determine neutral reactor arrestor ratings.

4.2 Transient Recovery Voltage Studies

Switching in GIS also generates high frequency transients which get enlarged and are sometimes detrimental to adjoining equipments. Ferro-resonance phenomenon and effects of higher frequency transients & Very Fast Transient Over Voltages (VFTO ) are also required to be studied before system engineering is completed to ensure that reflected transients do not become a cause of Ferro resonance. Users have normally found it difficult to carry out these studies on account of availability of tools and data required for the studies. Normally EMTP group users should be able to manage the studies and data for the studies have to be furnished by the user in respect of system and prospective suppliers of GIS.

4.3 Ferro-Resonance Phenomenon:

Ferro-resonance is basically a low frequency phenomenon which is non-linear in nature and may cause sudden change of the state of the system resulting in excessive switching over voltages and/or currents. Abnormal levels of harmonics, over voltages/ currents, either as stable oscillation or as transients caused by Ferro-resonance often represent risk for electrical equipment. Ferro-resonance is a complex phenomenon that can occur in electric circuits having a nonlinear inductance, capacitance and a voltage source. Power system networks are made up of large number of inductances (power transformers, voltage transformers, shunt reactors) as well as capacitors (cables, long lines, CVT’s, capacitor banks) etc. thus presenting situations under which Ferro-resonance can occur. Switching transients, energizing or de-energizing transformers or loads, occurrence or removal of faults may initiate Ferro-resonance.

4.3.1 Studies for predicting Ferro-resonance

Ferro resonance problems can be studied by simulation techniques involving the modeling of power systems to ensure that the over voltages due to Ferro-resonance are lower than the rated power frequency withstand voltage levels . Time Domain digital simulation in transient state : based on a reduced three-phase model representation of the power system with correct parameter values and initial condition a long time simulation study is to be carried out with the help of transient simulation packages.

4.4 Seismic Studies:

Probable failures that could happen during an earthquake are: GIS modules can fall from their elevated platforms and can get severely damaged due to

inadequately anchored rail-supports. Damage/Leakage in GIS bushings. Rigid connectors can transfer force to damage studs/connectors of the bushing Current transformers, capacitive coupled voltage transformers, surge arrestors and line

traps can get damaged;

4.4.1 One of the main difficulties when substation equipment is damaged is that there is limited number of spare parts or spare replacement equipment available. Repair and replacement of damaged equipment is a time-consuming and labour-intensive task hence seismic considerations are to be kept in mind while engineering GIS application. IEEE Standard 693, “recommended Practice for Seismic Design of Substations,” clearly defines qualification seismic levels, qualification procedures, and acceptance criteria. This standard recommends that sites with projected ground motions above 0.1g should have their equipment seismically qualified. Thus power utilities with service areas in seismic Zone III,IV and V (as per BIS 1893:2000) should have their substation equipment seismically qualified.

4.4.2 Following are some of the considerations utilities must evaluate when deciding seismic level:

Expected magnitude of an earthquake at the substation; The criticality of the substation with respect to the utility's total system; The speed at which equipment can be replaced; Safety considerations; The possibility and acceptability of bypassing the equipment should the equipment fail; The overall reliability of the system.

For these reasons, zone maps are provided in BIS 1893 as an aid to guide the utility in selecting the appropriate level, not as a requirement. The utility must evaluate the site and all the other considerations to determine which level is appropriate.

Fig 5 : Seismic Test set up

4.4.3 Seismic Analysis

Before starting seismic calculations, static calculations can be carried out taking into account the static effects on the structure and the foundations. The analysis can be carried out with two different load cases:

1. Static Load Case:

Weight Thermal Expansion Wind Load--is considered only in case the GIS is planed to be located in outdoor.

2. Dynamic or seismic load case – This analysis is to be performed in two orthogonal directions :

Seismic specification in the X direction Seismic specification in the Y direction

Equipment and supporting structures of substations located in seismically sensitive regions / zones have to be designed to withstand possible earthquakes. Procedure used to verify the seismic design of equipment includes simulations based on the finite element method combined with either response spectrum or time history analysis and shake table testing.

One of the most effective ways of reducing earthquake damage for new installations is to use equipment that has been seismically qualified. Central Power Research Institute (CPRI), Bangalore can help both develop the system performance criteria and evaluate equipment seismic withstand capability. CPRI can carry out structural analysis on civil structures and electrical equipment to determine seismic withstand capability. Time history response and spectrum analyses of equipment are carried out using the Finite Element Method. CPRI is equipped with the state-of-the-art facilities for model or real size testing of structures, components and electrical equipment using as seismic shake-table.

CHAPTER - 5

STANDARD LAYOUT EQUIPMENT ARRANGEMENT & SIZE OF BUILDING

5.0 Strategic Locations

The use of indoor GIS is absolutely necessary for strategic locations as it can be installed in a new building, existing building, an underground cavern, or a simple hall. All components such as Busbar, Disconnector, Circuit Breaker, Instrument Transformers, Cable terminations and joints are contained in earth enclosure filled with SF6 gas at a pressure above 3kg/sq.cm. The enclosure are of non-magnetic and corrosion resistant cast aluminium or weld aluminium sheet or stainless steel sheet.

The GIS installations are assembled from variety of standard modules which are Joined together by flange connections and plug contacts on the conductors, so as to

easily dissemble individual component subsequently. The gas tight enclosure of high grade aluminum and surrounds all the live parts, which are supported on spacer(insulator) and insulated from the enclosure by SF6 gas. The barrier insulators divide the bay in to separate gas compartments sealed off from each other. This minimizes effect of other components during plant extensions and also enables inspection and maintenance. The flanged joints contain non-ageing gaskets. Leakage of gas can pass only to the outside, but not between the compartments.

5.1 Layout Of GIS

Modular SF6 GIS can be tailor made to suit the particular site requirement. GIS could be suitably erected on any floor or basement and ducts could be taken through walls via SF6 gas insulated busbar /cable. GIS is suitably located and accommodated in various types of applications including following:

• In switchgear room of Hydro Electric power station near turbine-generator hall or at a distance where pothead yard could be made .• Basement of multistoried building. • terrace/top floor of multi-storied building • under ground substation • In a building to receive outdoor transmission line termination.

Irrespective of space consideration,the location of GIS and associated components should be so placed that any change in adjoining hills etc. should not have impact on the GIS. This will avoid prolonged outages due to limited availability of spares in the country and equipment generally is tailor made.

In GIS installation, all basic substation Busbar schemes as explained in earlier chapter of “Switching scheme options” can be realized with the help of standard modules. The modular construction offers the following advantages:

i. Quick Installationii. Simple stocking of sparesiii. Easy transportationiv. No risk of pollution and corrosionv. Occupies less spacevi. No threat of securityvii. Easy extension viii. Standardization of components

The bus bars are laid longitudinally in indoor hall to which incoming and outgoing bays are connected. The bays are connected to bus bars cross-wise. Bus bars are partitioned at each bay with an objective to isolate Busbar compartments for the purpose of extension and at the same time avoid damage to adjacent bays in the event of fault.

i. The enclosure of GIS may be of aluminum alloy or stainless steel. The selection of material largely depends on temperature rise consideration and permissible limit depending on emissivity (solar radiation) and / or temperature rise of conductor.

ii. It is found economical to adopt 3 phase enclosures up to 145KV system voltage. For system voltage above 145KV single - phase enclosure design are preferred

iii. The GIS component like circuit breaker, load break switches, earthing switches, isolators, voltage transformers, current transformers, surge arrestors and connectors are functionally separate modules of a standardized modular system

GIS could be in common enclosure or phase segregated (single phase) depending upon customer requirement and cost consideration. For higher voltages i.e. 220 KV and above, phase segregated construction is adopted.

5.1.1 Building Space Requirement

Layout of GIS and consequently requirement of building space depends upon following factors:

5.1.1.1 External termination with overhead lines:

• Overhead line exit require spreading of GIS bus arrangement to meet phase to phase clearances in air.

• In case external termination of lines are only at one side of building, these are usually at intervals of 3 to 4 bays to maintain required clearances between bushings.

• In case external termination of lines are on both sides of building or are taken some distance by means of SF6 bus connections, the respective bays can be next to each other.

• Connection of overhead line with GIS rigid busbar is made through outdoor condenser bushings

5.1.1.2 Location and type of connection with Transformer:

• Unlike overhead line connection, wherein conductor is taken through bushing, the GIS conductor directly terminates at transformer bushing terminal with the help of lateral mounting unit and barrier insulator. A flexible bellow takes care of thermal expansion & erection tolerances and prevents transfer of tank vibration to switchgear enclosure.

• In case, there is difficulty in connecting GIS directly on to transformer bushing terminal, we can adopt external termination method by connecting transformer bushing terminal to outdoor condenser bushing. In such cases, Surge Arrester is accommodated below outdoor condenser bushing.

5.1.1.3 Termination of feeders through high voltage Cable: • The connection between GIS and high voltage cable is done through cable termination /

cable sealing end. • Plug in cable sealing ends for XLPE/Oil Filled cables could be through SF6/XLPE, SF6/Oil

cable termination also be a good option. They consist of gas tight plug in sockets, which are installed in the switchgear, and prefabricated plugs with grading elements of silicone rubber.

• A separate cable basement is provided for cable entry, its distribution and installation. 5.1.1.4 Location of Surge Arrestor to suit connection with Line and Transformer:

• The arrangement as discussed above for termination of line and transformer decide the location of Surge Arrester inside the GIS building or outside.

• Location of Surge arrester depends upon distance between GIS and incoming termination, particularly as it depends upon the calculated distance as per system studies.

5.1.1.5 Future expansion – with a view to have minimum downtime, it should be necessary on the part of user to specifically mention the possibility and requirement of expansion clearly.

5.1.1.6 Erection and Maintenance aspects- Gangways of sufficient dimension must allow unhindered access to the components for erection and maintenance. To achieve maximum flexibility for break down and routine maintenance, additional area at the end of installation is preferred for storing SF6 gas handling plant and vital T&P and spare numbers of SF6 cylinders to be provided.

5.1.1.7 Height of building is governed by the maintenance clearances required for the assembly/module of GIS to be lifted by crane . However the opinion of manufacturer may be sought.

5.1.1.8. The clearance between breaker poles

5.1.1.9 Mounting of Circuit Breaker- Vertical or horizontal

Considering high reliability of GIS components, simplified arrangement with less redundancy could be given preference to reduce cost.

Various Equipment Modules of GIS are described as under.

5.2 Busbar Modules

• Main conductors are Aluminium or Copper tubes and its dimension depends upon mechanical strength corresponding to short circuit forces.

• The conductors are provided with silver plated finger contact assembly mounted on support Insulator. These sliding contacts allow tubular conductors to expand axially with temperature rise without additional stress on support insulators.

• The shape of support insulator for tubular conductor normally ensures that field distribution is

uniform

For easy assembly and any type of design configuration, busbar modules are standardized in various forms, like L-unit(90 degree junction), four way junction, angle unit(120-180 degree junction), T-unit with flange for earthing switch.

5.3 Circuit Breaker Module

The circuit breakers shall be phase segregated & have duplicate trip coils for 220 KV and above. In 132 KV and below three phase configuration of CB can be with one trip coil These shall be trip free, and anti-pumping with either or both of the duplicate trip circuits connected. A manual emergency trip facility could add to flexibility to meet contingency needs to trip the CB. Pole discrepancy tripping shall be provided.

Each 220 KV level or above circuit breaker shall be equipped with electrically separate two shunt trip systems per mechanism. Two trip coils are arranged to share a common magnetic circuit, the operation of either coil shall be independent of other, i.e., if one of the trip coils has been damaged or destroyed, it shall not affect the operation of the other.Facilities shall be ensured so as to enable timing tests of the circuit breaker to be carried out after switchgear has been energized with SF6 gas. It should not be necessary to open up any gas section to make test connections to the circuit breaker primary terminals for this test.

5.3.1 Operating Mechanism

Circuit breakers shall be power operated either by a motor charged spring operated mechanism or by hydraulic mechanism. Main poles of the breaker shall be such that the design shall ensure a close pole spread with a maximum of 5 ms closing.

Optimally user can opt for two type of mechanisms one suitable for A/R and one for generator/transformer switching. Operating mechanism of first type shall be suitable for high speed enclosing. It shall be anti-pumping electrically and mechanically under every method of closing (except during manual closing of a breaker for maintenance). A latch checking switch shall be provided on mechanically trip free mechanisms to prevent reclosure before the breaker latches have reset.

Main poles shall operate simultaneously. There shall be no objectionable rebound and the mechanism shall not require any critical adjustment. It shall be strong, rigid, positive and fast in operation.

A closing release shall operate correctly at all values of control voltage between 80% and 110% of the rated voltage. A shunt trip shall operate correctly under all operating conditions of the circuit breaker up to the rated breaking capacity of the circuit breaker and at all values of control supply voltage between 70% and 110% of rated voltage.

Working parts of the mechanism shall be of corrosion resisting material. Bearings which require grease shall be equipped with pressure type grease fittings. Bearing pin, bolts, nuts and other parts shall be adequately pinned or locked to prevent loosening or changing of adjustment with repeated operation of the breaker. Self lubricating dry type bearing should be accepted

Provision shall be ensured for attaching an operation analyser to perform speed tests after installation of the CB at site.

5..3.2 Spring Operated Mechanism

Spring operated mechanism shall be complete with motor, opening spring, closing spring with limit switch for automatic charging and all necessary accessories to make the mechanism a complete operating unit.

As long as power is available to the motor, a continuous sequence of closing and opening operations shall be possible.

After failure of power supply to the motor, at least two close-open (C-O) operations of the circuit breaker shall be possible.

Breaker operation shall be independent of the motor which shall be used solely for compressing the closing spring.

Motor rating shall be such that it requires only about 30 seconds for fully charging the closing spring.

Closing action of the circuit breaker shall compress the opening spring ready for tripping. When closing springs are discharged after closing a breaker, closing springs shall

automatically be charged for the next operation.

Spring operated mechanisms have very low operating energy, simplified drives, enhanced operation reliability ,easy erection at site ,simple in principle construction, ease of handling with minimal maintenance. It gives a high accuracy along with very high mechanical endurance.

5.3.2.1 Hydraulic Operated Mechanism

Hydraulic operated mechanism shall comprise self contained operating unit with power cylinder, control valves, high and low pressure reservoir, motor, etc. A portable pump set shall also be provided for emergency operation.

The oil pressure controlling the oil pump and pressure in the high pressure reservoir shall be continuously monitored. Necessary hardware to achieve this, including the loose pressure gauge, instruments and interconnecting piping etc shall form integral part of this mechanism

The mechanism shall be suitable for at least two close-open operations after failure of AC supply to the motor.

It is up to the user to specify both above mechanisms or select any one depending upon merits and requirements of operation of GIS.

5.3.2.2 Operating Mechanism and accessories Housing

Common marshalling box with necessary tubing and interconnecting cables are required for trouble free operation. A light point with door switch and one 3 pin 240V AC 15A socket outlet can be provided in the housing.

5.3.3 Duty Cycle of Operating Mechanism

Normally o-c-o cycle would be an acceptable proposition. irrespective of the type of operating mechanism the breaker has even after the failure of auxiliary supply.

5.3.4 Circuit Breaker Performances

The maximum interrupting time at the minimum operating pressure of the mechanism shall be specified by the user utility. This is normally governed by stability requirements of fault clearance total time.

5.3.5 Auto Reclosing Equipment

This will govern number of operating mechanisms per CB. High speed, single shot auto reclosing could be single or three phase. All relays, timers, controls and interlocks required for auto reclosing along with a selector switch for single pole and three pole auto reclosure and all the associated hardware shall be required .

The duty cycle of the auto reclosing breakers shall be O-t-CO-t'-CO, where the dead time interval (t) shall be adjustable. User shall clearly state the minimum dead time interval (t) & (t’) that can be used and the range of adjustment for the same. IEC 62271 part-100 could be referred for selection .

Auto reclosing equipment shall be suitable for operation on the DC control voltage specified. Control circuitry shall be such that the reclosing sequence shall not come into operation if the breaker is opened by hand (healthy trip) and also if the breaker is closed on to a short circuit.

5.4 Disconnector (Isolators) and Earth Switches

5.4.1 Disconnector : They are either on-load break switch or no-current break type (for isolation only).

Disconnector for isolation contains following features: • Mechanism which operates with or without remote control • Necessary inter-locks feature with CB, dis-connectors, PTs and earth switches. • Mechanically coupled position indicator Some of the users specify a viewing glass for physically inspecting the position of dis-connector. It is considered not to be a technical requirement but more of a statutory consideration. In fact providing a glass window adds to possibility of gas leakage and weak points prone to damage during transportation handling. Some times due to flash overs/ arching, it has been noticed that impurity deposited on the window lead to defeating the function

5.4.2 Earthling Switch

They are normally mounted or integrated in the isolator housing. They can be hand or motor operated with necessary interlocks/ capacitive tap to operate only when high voltage part is dead.

Fast acting earth switches for overhead lines must be capable of interrupting capacitive and inductive currents. Normally due to standardization the values in this regard are

adopted in accordance with IEC. Transformer connected to long cable should also have Fast acting Earthling switch.

5.4.3 Construction Features

The isolator and earthling switch shall be provided with high current carrying contacts on the hinge and jaw ends and all contact surfaces shall be of silver faced copper.

Each isolator shall have an individual gas compartment. Associated earth switch should be in the gas compartment of the isolator except for bus bar side isolator earth switch which will have a separate and independent gas compartment to avoid shut down to both bus bars in the event of failure of junction gas barrier.

Motor operated high speed earthling switch shall be designed in a manner to prevent transmitting of impact to earth switch bushing.

Provision shall be made to padlock the hand operated earth switch in both the open and closed positions.

Earthling switches on the line-side of incoming feeders shall have make proof contacts and stored energy high speed operating mechanisms that make them suitable to close on a fault. These motor operated earthing switches on incoming lines shall be of high speed closing (quick make action) type.

All earth switches shall be insulated from the enclosure and connected to the enclosure by a removable link to facilitate current injection

High speed earthing switches on the line/cable entrance side shall be capable of interrupting line capacitive currents upon opening and in worst conditions of closing.

5.4.4 Operating Mechanism and Controls

The isolator shall be provided with positive continuous control throughout the entire cycle of operation. The operating pipes and rods shall be sufficiently rigid to maintain positive control under most adverse conditions and when operated in tension or compression for isolator closing. They shall also be capable of withstanding all torsional and bending stresses due to operation of the isolator.

It shall not be possible, after final adjustment has been made, for any part of the mechanism to be displaced at any point in the travel sufficiently to allow improper functioning of the isolator when the isolator is opened or closed at any speed. All holes in cracks, linkages, etc., having pins shall be drilled to accurate fit so as to maintain the minimum amount of slack and lost motion in the entire mechanism.

The operating mechanism design shall be such that during the operation of the isolator (especially manual operation), once the moving blades reach the sparking distance, springs shall take over to give a quick, snap action closing so that the isolator closing is independent of manual efforts. Similarly, the springs must assist during the opening operation to give quick breaking feature.

Disconnector and high speed motor operated earthing switch mechanisms shall be provided with a mechanism with stored energy to always assure completed operations.

5.4.5 Interlocks

Interlocking devices must provide absolute and positive protection against potentially harmful maloperations of the switchgear. The following functions interlocks are to be provided:

To ensure that safe and logic sequence to actuate breakers, switches, isolators and grounding switches.

Checking the actual fully closed or fully open position of all switching elements before and after each move.

Providing the logical checks and issuing the resulting PERMISSIVE or BLOCKED signals for the switchgear.

Indicating positively the absolute condition/position of the supervised equipment. Local manual and remote electrical operation of all essential functions. Local emergency unlocking facilities via safety-key switches under the full responsibility

of the operator.

Intrabay and interbay interlocking should normally be provided by the GIS manufacturer until unless specifically excluded from the scope. Electrical interlocking for circuit breaker and isolator shall be provided and it shall be fail –safe type. Mechanical interlocks for isolator & Earthing Switch shall be fail-safe type.

5.4.6 Short Circuit Requirements

The rated peak short-circuit current or the rated short time current carried by an isolator or earthing switch for the rated maximum duration of short circuit shall not cause: Mechanical damage to any part of the isolator or earthing switch. Separation of the contacts or contact welding. A temperature rise likely to damage insulation.

5..5 Current and Voltage Transformers

5..5.1 Current Transformers module

They are toroidal-core type and arranged before or after CB’s depending upon measuring and protection concept of the user. The numbers of cores is not a limitation as the length can be suitably increased to adopt required no. of CTs.

5..5.2 Voltage Transformers

Voltage transformers shall be of the metal enclosed, gas-insulated inductive type, mounted directly on the high voltage enclosure.

Secondary terminals must be located in accessible grounded terminal boxes on the PT enclosure itself. The secondary connections must be wired to the terminal strip in the respective bay marshalling cubicle.

PTs should be in segregated compartment and not forming a part of bus bar.

5..5.3 General Requirements

Secondary terminals of each voltage and current transformers should be brought out in a weatherproof terminal box. Short circuiting and earthing the CT secondary at the terminal box should be ensured as a good practice. The star point whenever required shall be formed at the terminal box only.

Terminal and polarity marks should be indelibly marked on each VT & CT on the associated terminals and these marks shall be in accordance with relevant standards.

Each VT & CT shall be provided with a rating plate showing the particulars as required by the relevant standard.

Each CT shall, when called for in specific requirements be equipped with an over voltage protective device to limit the voltage developed across the secondary terminals to a safe value not exceeding 3kV.

The secondary terminal box for the voltage transformers shall also include necessary HRC fuses for protecting the secondary circuit. Further, for the purpose of fuse supervision on remote panel both terminals of fuse shall be brought out to the terminal box.

Whenever a VT secondary winding is used for both measurement and protection application, it shall have accuracy class of 0.2 /0.5/3.0 as required .

All CT cores in this specification shall be of low reactance type.

No turns compensation shall be used in case of 'Class-PX CTs.

In case of multi ratio CTs, the minimum specified requirements in respect of VA, accuracy and knee point Voltage (KPV) and maximum secondary resistance specified shall be met at all taps.

Voltage transformers shall be of electromagnetic type.

Voltage and current transformers shall be given tropicalised treatment for satisfactory operation in hot and humid climate.

5.6 Surge arrester

Gap-less ZnO arresters are provided either outdoor or indoor depending upon distance between GIS and incoming termination from overhead line/transformer. Normally isolable outdoor surge arrestors on the bus bar should be used. This will facilitate quick isolation and coupling whenever bus bars are required to be exposed to high voltage test.

Surge arresters shall be of the hermetically sealed, Gapless (Metal Oxide), suitable for use with gas insulated switchgear. They shall have adequate thermal discharge capacity for severe switching surges, long duration surges and multiple strokes. The surge arresters when provided with pressure relief devices shall be capable of withstanding the internal pressures developed during the above discharges without operation of the pressure relief devices.

5.6.1 Discharge Counter

Self contained discharge counter shall be provided for each single pole unit.

A leakage current detector as an integral part of the discharge counter shall be supplied. The counter along with the detector shall be so arranged that it will be possible to read the leakage current values from outside the cubicle. The value of leakage current beyond which the operation is abnormal shall be clearly marked in red colour on the detector.

5.6.2 Control Cabinets

5.6.2.1 The elements for control, indication and alarms are contained in local control cabinets mounted close to bays. The elements normally mounted in the control cabinets consist of the following:

(i) Mimic diagram with control switches for electrically operated breakers, load break switches, disconnects and earthing switches and indicators for all components provided with auxiliary switches.

(ii) Local/Remote Selector Switches.(iii) Alarm facia with indicating lamps for monitoring operating system, gas

density and auxiliary supplies.(iv) Contactors, timing relays etc.(v) Terminal blocks.(vi) Interior lighting, heater, cable glands.(vii) Lockable bypass switches for defeating the interlocks to facilitate

maintenance work.

5.7 SAFETY LOCKS

5.7.1 Safety locks for locking the disconnects and earthing switches in the positions “Operation” or “Maintenance” are also provided. In the “Maintenance” position these locks interrupt the control circuits of motor drives for disconnects and earhing switches. In the manually operated earthing switches, these locks in the “Operation” position do not permit engagement of manual operating handle with the earthing switches operating shaft.

5.8 INTERLOCKS

5.8.1 GIS control cabinet includes electrical interlocks to prevent incorrect switching sequence and ensure correct operation of isolators, circuit breakers and earthing switches from local control cabinet or from the control room.

5.9 SF6 GAS DENSITY

5.9.1 Density of SF6 affects the dielectric strength of GIS and breaking strength of SF6 circuit breaker. Since the gas pressure is influenced by temperature, it is the density of gas which is monitored. For this purpose temperature compensated gas density monitors are provided in the bus bar, circuit breaker and isolator compartments formed by the provision of barrier insulators. The compartments are fitted with non-return valve connections for installing density monitors, evacuation and for filling gas.

5.9.2 SF6 is five times as dense as air. It is used in GIS on pressure from 3.5-7 bars absolute. The pressure is so selected such that gas will not condense into liquid at the lowest temperature, the equipment could experience. The is about 100 times superior than air in terms of interrupting arc.

5.10 SUPPORTING STRUCTURES

5.10.1 Depending on the design of installation, the GIS can be self supporting or erected on steel supporting structures of simple design anchored to the substation floor.

5.11 GIS Terminations

GIS terminations could be any of the following:

- SF6 to air bushings- SF6 to cable termination- SF6 to oil bushings for direct connection to transformer- SF6 bus duct

All termination modules are commonly used to connect the GIS with transformer. Overhead lines could be connected to GIS either though cables or through SF6 to air bushings. Type of terminations has also bearing on the size of substations. If cable or SF6 bus ducts are used, substation can be kept quite compact. SF6 to air bushings, on the other hand, requires minimum clearance in air and thus requires more space and in addition, they are subject to environmental conditions. Especially in cities/ industrial areas where space is both restricted & expensive and the surrounding environment has impact on type of termination, preference should be for cable termination or S6 bus duct. Selection of cable termination will have to be judiciously done keeping in view the specific requirement.

CHAPTER-6 EARTHING OF GIS

All enclosures of all the GIS should be grounded at several points so that there should be

grounded gauge all live parts. All conduits and cables sheaths should be connected to the

ground bus, to be provided, in the control cubicles and the marshalling boxes. The three enclosures of single phase GIS are required to be bonded to each other at the ends of GIS to ensure flow of circulating currents. These circulating currents cancel the magnetic field that would otherwise exist outside the enclosure. GIS does not have circulating currents but does have eddy currents in the enclosure and should also be multi point grounded. Although multi point grounding leads to some losses in the enclosure due to circulating current multi point grounding results in many parallel paths for the current from an internal path to flow to the switchyard ground grid. All steel structures should be grounded.1 All wirings to GIS should be shielded and grounded.2 Subassembly to subassembly ground conductors should be provided to assure safe voltage gradients.The recommendations of manufacturers and multi point grounding concept normally ensures touch and step potentials within safe levels prescribed by IEEE 80-2000.

The GIS should be extendable to meet the requirement of addition of bays in future. The side on which the extension should be provided with suitable extension bellows /flanges with blanking plates. The building that is to house the GIS should have space provision for future extension.

6.1 Definitions:

Most important terms relating to earthing systems are summarized below:

• Earth – refers both to earth as a place and to earth as a substance e.g. humus, clay, sand, gravel, rock

• Reference earth – is that part of earth, particularly the ground surface outside the sphere of influence of an earth electrode or earthing system, between two random points in which there occur no perceptible voltages resulting from the earthing current.

• Earth electrode – is a conductor which is embedded in the ground and electrically connected to it, or a conductor embedded in concrete which is in contact with the earth over a large area (e.g. Foundation earth)

• Earthing conductor – is a conductor connecting a piece of equipment to an earthing electrode provided it is not in the ground, or in the ground but insulated.

• Main earthing conductor – is an earthing conductor to which a number of earthing conductors are connected.

• Earthing system – is the located delimited sum total of conductivity interconnected earth electrodes or metal parts acting in the same manner and earthing conductors.

• Earth resistivity – is the specific electrical resistivity of the earth. • Dissipation resistance – of an earth electrode is the resistance of the earth between the

electrode and the reference earth. • Earthing impedance – is the a.c. impedance between an earthing system and the reference

earth at operating frequency. • Impulse earthing resistance – is the resistance presented to the passage of lighting /

currents between a point of an earthing system and the reference earth. • Protective earthing – is the earthing of a conductive component not forming part of the

normal electrical circuit in order to protect people from unacceptable touch voltages. • System earthing – is the earthing of a point in the normal electrical circuit in order that

apparatus or systems can be maintained properly. • Lightening protection earthing – is the earthing of a conductive part not forming part of the

normal electrical circuit in order to avoid as far as possible flashover to the normally live conductors as a result of lightening strokes (back flashovers)

• Earthing voltage – is the voltage occurring between an earthing system and reference earth.

• Earth Surface Potential – is the voltage between a point on the earth’s surface and reference earth.

• Touch voltage – is the part of the earthing voltage, which can be shunted through the human body, the current path passing from hand to foot (horizontal distance from touchable part about 1 m) or from hand to hand.

• Step voltage – is that part of earthing voltage, which can be shunted by a person with a stride 1 m long, the current path passing from foot to foot.

• Potential control – consists in influencing the earth potential, in particular the earth surface potential, by earth electrodes.

• Earth Fault – is electrical connection between one conductor of the normal electrical circuit and the earth or an earthed part due to a defect. The electrical connection can also be by way of an arc.

• Earth Fault current – is the current passing to earth or to earthed parts when an earth fault exists at only one point at the site of defect.

• Earthing current – is the total current flowing to earth by way of the earthing impedance. • TRANSIENT ENCLOSURE VOLTAGE (TEV): Very fast transient phenomena, which are

found on the grounded enclosure of GIS systems. The phenomenon is also known as transient ground rise (TGR) or transient ground potential rise (TGPR).

• VERY FAST TRANSIENT (VFT): A class of transients generated internally within GIS characterized by short duration and very high frequency. VFT is generated by the rapid collapse of voltage during breakdown of the insulating gas, either across the contacts of a switching device or line-to-ground during a fault

Fig 6 : Typical Earthing Arrangement of GIS

6.2 Codes and Standards on Earthing

DIN VDE 0141/7/7.76 VDE specification for earthing systems in a.c. installations for rated voltages above 1 kV

DIN VDE 0151/6.86. Materials & Minimum dimensions of earth electrodes with regards to corrosion.

IEC 621-2A/1981. First supplement to publication 621-2(1978). Electrical installations for outdoor sites under heavy conditions (including open cast mines and quarries). Part 2: General Protection requirements.

IEC 364-5-54/1980. Amendment No.1 July 1982. Electrical installations of buildings. Part-5: Selection & erection of electrical equipment. Chapter 54: Earthing arrangements and protective conductors.

IEC-479-1/1994. Effects of current passing through the human body. IEEE std 80-2000 IEEE Guide for Safety in AC Substation Grounding IS:3043-1987 “Code of Practice for Earthing”

6.3 Materials for Earthling Systems

Earth electrodes (underground) and earth conductors (above ground) must conform to certain minimum dimensions for mechanical strength and to withstand possible corrosive attack.

Selection of material, size of conductors, primary electrodes depends on following factors:

Material should have sufficient conductivity It must carry and dissipate fault current without excessive temperature rise. Material should have high resistance to corrosion.

The enclosures of GIS should be properly designed and adequately grounded so as to limit the potential difference between individual sections within the allowable limit of 65-130 V during faults.

6.4 Dimensioning of Earthling Systems

The cross-section of earth electrodes and earthing conductors must be such that the material’s strength is not reduced in the event of a fault current.

6.5 Measurements for Earthling Systems

The specific resistance of the soil is important for calculating earthing systems.

6.6 Design Principles

The earthing system of the sub station buildings, especially of buildings with gas – insulated switchgear (GIS) must be capable to carry power – frequency short circuit currents (earth fault currents) and high frequency currents from switching and lighting. The requirements from the high frequency currents determine the layout of the earthing system, which can be characterized as a meshed network (or a cage shaped network) in order to give low impedance across it. Some special conductors of this cage are rated to fulfill the power frequency requirements.

GIS are subjected to same magnitude of ground fault current. The basic requirements of an earthing system of GIS are similar to that of Air Insulated Switchgear .However due to availability of less area (about 10-20%) as compared to conventional outdoor substations and compactness of the equipment, it is difficult to achieve the adequate grounding by conventional methods.

In the fault condition or during the normal operation, due to high frequency currents generated, electric breakdown in the insulating gas occurs. This electric breakdown generates very high frequency transients (Transient Enclosure Voltage (TEV)), which can be passed on to the GIS grounding system. These transients may have to be considered in the design of the grounding system.

In addition to these transients, external magnetic field produced by the main circuit current of large capacity GIS is strong. This magnetic field creates problems like local overheating of structures around the GIS, electromagnetic vibration, increased induction to control cables etc. Excessive currents should not be induced into adjacent frames, structures or reinforcing steel, establishment of current loops via other station equipments.

In GIS the use of cathodic protection may be required. Normally it is required to protect facilities external to the GIS e.g. pressurized type cables etc.

6.7 Touch & Step Voltage in GIS

Touch & Step voltages have to be considered mainly in outdoor substations. GIS buildings have an elaborated meshed earthing system, which comprises all metal parts like foundation earth electrode, earthing conductors and the GIS housing. In case of a power frequency earth fault the total of this earthing system assumes an earth potential rise versus the distant references earth. However the voltage differences between the metal parts of the building are very small. Dangerous touch or step voltages do not exist.

6.8 Grounding of Enclosures

Because of availability of return path for induced currents in continuous enclosure type design of GIS, a shielding to internal field exists. However, under asymmetrical faults, the D.C component is not shielded and causes an external voltage drop due to enclosure resistance.

To limit the undesirable effects caused by circulating currents the following precautions should be taken:

Grounding of the enclosure should ensure that significant voltage difference does not exist between individual enclosure sections

Particular attention should be given to the metallic enclosures of the GIS assembly. All metallic enclosures should be grounded properly through the base frame of the GIS so as to ensure the minimum flow of circulating currents.

To avoid the circulation of enclosure currents beyond regular return path, power cable sheath should be grounded directly without involving the enclosure in the grounding path. To facilitate this isolation, design of cable terminations should be such that an isolating air gap or proper insulating elements are provided.

Proper care should be taken to ensure that current transformers mounted on GIS should not carry the enclosure return current.

Wherever there are discontinuities in enclosures / changes in the medium e.g. at cable terminations or transformer connections, special care should be taken to limit very fast transient over voltages and to prevent circulating currents in circuit breakers and transformer tanks.

GIS cable terminations and other discontinuities in the enclosures are significant sources of Transient Ground Potential Rise phenomenon. The isolation between the directly grounded power cable sheath and the enclosure may give rise to Transient Ground Potential Rise phenomenon. Particular attention should be given to limit the Transient Ground Potential Rise phenomenon

6.9 Grounding of GIS Foundation In the GIS substations, concrete foundations may cause irregularities in current discharge path. In this respect, a simple monolithic concrete steel reinforced slab is advantageous, both as auxiliary grounding device and for seismic reasons

CHAPTER- 7

ESSENTIAL AUXILIARIES

Essential auxiliaries required for GIS application are normally same as that of AIS. The testing equipment however, is required to a limited extent due to reduced maintenance. Essential auxiliaries have been listed below but their application is not discussed in detail since these have been covered in the manual elsewhere. The list for the user is as under:

DC supply :

This has already been discussed in “General Information in clause No.12.1 Essential Parameter.

AC supply This has already been discussed in “General Information in clause No.12.1 Essential Parameter.

Gas handling cart- vacuum, filling and purification. Testing instruments

Air / gas humidity tester, Gas. purity detector for SO2,H2O,CF4,AIR etc., Gas leakage tester, Breaker timing measurement kit, Set of equipment for pressure measurement and gas density meter

Crane for erection -Selection of Crane capacity depends upon weight of heaviest part of the GIS modules to be lifted. EOT crane2.5 Ton is required for indoor type GIS and mobile crane for outdoor type GIS.

CHAPTER- 8

GAS HANDLING SYSTEM

8.1 Sulfur Hexafluoride

SF6 gas is an inert, stable, colorless, odorless, nontoxic, nonflammable gas approximately five times heavier than air and will displace air in confined area Gas contains no oxygen and will not support life. Confined areas must be force ventilated

when working with SF6 gas The Occupational Safety and Health Administration (OSHA) regulation on air

contaminants, 29 CFR 1910.1000, establishes that SF6 gas has no adverse effects when inhaled in the air at a Threshold Limit Value (TLV) of 1,000 ppm.

Extremely stable gas with high dielectric strength and excellent arc-quenching properties The Environmental Protection Agency has identified Sulfur Hexafluoride as a greenhouse

gas with a global warming potential 23,900 times the effect of an equal mass of Carbon Dioxide and an atmospheric lifetime of 3,200 years.

Fig 7: Quenching Capacity of SF6

8.2 GAS Specification

Pure Sulphur hexafluoride is absolutely non-toxic. The bi-products arising during production of the gas are removed during subsequent purification operations IEC 60376 provides recommendations for SF6 gas as under: SF6 > 99.90 % by weight Air < 500 ppm by weight (0.25 vol.-%) CF4 < 500 ppm by weight (0.1 vol.-%) H2O < 15 ppm by weight (0.012 Vol-%) Mineral oil < 10 ppm by weight Acidity,in terms of HF < 0.3 ppm by weight Hydrolysable fluorides, In terms of HF < 1 ppm by weight

Wherever gas is handled there must be no open place or welding or hot metal surfaces such as infrared equipment. Eating, drinking and smoking while working with gas is to be strictly avoided. Although this gas is recognized as physiologically safe, certain precautions have to be taken in order to ensure safe handling of gas.

8.3 Permanent Gas Treatment Devices

• Means shall be provided inside each enclosure for treating the SF6 gas by the use of desiccants, driers, filters, etc. to remove impurities in the gas.

• All gas compartments shall be fitted with static filter material containers that will absorb residual and entering moisture inside the high voltage enclosures. Filters inside the breaker compartment shall also be capable of absorbing gas decomposition products resulting from the switching arc.

8.4 SF6 Gas Monitoring Devices

All gas compartments must have their own independent gas supervision and alarm systems. Each gas supervision circuit shall be equipped with a temperature compensated pressure gauge, test connection point and maintenance connection point and the same shall be easily accessible. One should monitor at least the following locally and on remote

• “Gas Refill” Level-This will be used to annunciate the need for gas refilling. • “Breaker Block” Level-This is the minimum gas density at which the manufacturer will

guarantee the rated fault interrupting capability of the breaker. At this level the device contact shall trip the breaker and block the closing circuits.

• Over pressure alarm level-This alarm level shall be provided to indicate abnormal pressure rise in the gas compartment.

It shall be possible to test all gas monitoring relays without de-energising the primary equipment and without reducing pressure in the main section. Disconnecting type plugs and sockets shall be used for test purposes; the pressure/density device shall be suitable for connecting to the male portion of the plug.

Two potential free electrical contacts shall be provided with each and every alarm.

8.5 SF6 Gas Maintenance Plant

Fig 8 : Gas Maintenance Plant

The entire plant necessary for filling and evacuating the SF6 gas in the switchgear equipment shall be supplied with the contract to enable erection and maintenance work to be carried out. This shall include all the necessary gas receivers for temporarily storing the evacuated SF6 gas as well as any other gases which may be used in the process. The capacity of the temporary storage facilities shall at least be sufficient for storing the maximum quantity of gas that could be removed from the largest compartment of GIS and associated compartments on either side +10% extra SF6 gas when carrying out maintenance or repair work on any pieces of the switchgear and associated equipment. The necessary compressor to remove SF6 gas from the compartments, vacuum pump to create vacuum inside the compartment before SF6 gas filling operation, dust and moisture filter shall form a part of the plant.

The plant shall have facilities for drying air and SF6 gas or any other gases with which the switchgear compartment may be temporarily filled during the process of filling with SF6 gas.

Each of the gas compartments shall be fitted with permanent valves through which the gas is pumped into or evacuated from the compartments.

The Mobile auxiliary plant complete with necessary hoses and couplings etc. for purifying (SO2,H2O,CF4,AIR) and drying SF6 gas in the switchgear gas compartments .

The auxiliary gas purification and drying plant shall be combined as a single unit with the gas filling and evacuating plant.

8.6 SF6 Gas Detecting Instruments

The portable SF6 gas detector shall be light weight and provided with long flexible probe to enable detection of SF6 gas leakage from hard to reach areas.

8.7 Maintenance of Gas Handling System

The life of GIS largely depends on the quality of gas. Depending on the size of switchgear appropriate equipment with sufficient storage capacity and performance is selected based on two largest gas section capacity in the installation. The handling equipment for the gas should consist of main components such as SF6 compressor, vacuum pump , storage tank , evaporator and filter unit which are connected together with valves and fitting . Every component within closed cycle are to undergo dry running and therefore, absolutely oil free without a chance of gas getting contaminated. The built in filters provide for the drawing and cleaning of gas during each gas operation. In fact gas valves couplings and fittings themselves ensure a high degree of leak tightness and operational safety. When selecting equipment, it should be ensured that couplings are self closing type in order to avoid air and moisture penetrating due to the lines. Maintenance equipment with automatic sequences could be the state of art and should be referred because of its high degree of operational safety. It is necessary, to monitor parameters of gas filled in the GIS.

CHAPTER- 9.

LIST OF STANDARDS, MANUALS, CODES AND REFERENCES

• The design, material and commissioning of switchgears and accessories shall comply with all currently applicable statutes, regulations and safety codes in the locality where these will be installed. The material shall also conform to the latest applicable standards.

• Except as noted, all the equipments offered shall conform to the requirements of the latest editions of relevant standards.

• National standards will be acceptable only if they are established to be equal or superior to referred standards. In all such cases, copies of English translation of all such standards shall be enclosed with the bid.

• In the event of any conflict between the codes and standards referred to in this specification and the requirement of this specification, the latter shall govern.

Sr.No.

Title Standard Reference

1. International Electro-Technical Vocabulary IEC-60050 2. High Voltage Alternating Current Circuit Breakers IEC-62271-

100 3. Gas-Insulated Metal-Enclosed Switchgear For Rated Voltages

Above 52kv IEC 62271-203

4. Insulation Co-Ordination IEC 600715. Cable Connections For Gis For Rated Voltages OF 72 kV &

aboveIEC 60859

6. High Voltage Test Techniques IEC-60060 7. Recommendation For Heat Teated Aluminium Alloy Busbar

Material Of The Aluminium-Magnesium-Silicon TypeIEC-60114

8. Alternating Current Disconnectors And Eathing Switches IEC-62271-102

9. Bushing For Alternating Vatages Above 1000 Volts

IEC-60137

10. Current Transformers IEC-6004411. Voltage Transformers IEC-6018612. Electrical Relays IEC-6025513. Low Voltage Fuses IEC-6026914. Low Voltage Motor Staters IEC-6029215. Specification And Acceptance Of New Sulphurefxafloride IEC-6037616. First And Second Supplement To Iec Pub-376 (1971) IEC-60376

A&B17. Synthetic Testing Of High Voltage Alternating Current Circuit

BreakersIEC-60427

18. Guide For Checking Sf-6 Gas Taken From Electrical Equipment IEC-6048019. Artificial Pollution Test On Hv Insulators To Be Used On Ac

SystemIEC-60507

20. Gas Insulated Metal Enclosed Switchgear For Rated Voltages Of 72.5 Kv And Above

IEC-60517

21. Classification Of Degree Of Protection Provided By Enclosures IEC-6052922. Common Clauses For HV Switchgear And Controlgear

StandardsIEC-60694

23. Addl. Requirement For Enclosed Switchgear And Control Gear Form 1 Kv To 72.5 Kv For Use In Severe Climate Conditions

IEC-60932

24. Guide For Selection Of Insulators In Respect Of Polluted Conditions

IEC-60815

25. Gas Insulated Mental Enclosed Switchgear For Rated Voltages 72.5 Kv And Above Requirements For Switching Of Bus

IEC-61259

Charging Circuit By Disconnectors26. IEEE Recommended Practice For Seismic Design Of

SubstationsIEEE 693

27. High-Voltage Switchgear And Controlgear Part 2: Seismic Qualification For Rated Voltages Of 72,5 Kv And Above

IEC 62271-2

28. Specification For Transportable Gas Containers. Seamless Steel Containers

BS-5045-1

29. IEEE Guide For Safety In Ac Std.80 Substation Grounding ANSI/ IEEE30. Circuit Breakers ANSI-C3731. Quality System-Model For Quality Assurance In Final Inspection

And TestISO-9003

32. European Standard-Cast Aluminium Alloy Enclosures For Gas Gilled High Voltage

EN-50052

33. Wrought Aluminium And Aluminium; Alloy Enclosure For Gas Filled High Voltage Switchgear And Control Gear

EN-50064

34. Welded Composite Enclosures Of Cast And Wrought Aluminium Alloys For Gas Filled

EN-50069

CHAPTER- 10

EMERGING TECHNOLOGIES

This chapter shall incorporate based on inputs from the manufacturers in respect of following

10.1 HYBRID SWITCHGEAR

i) Hybrid switchgear-With the advent of GIS a number of manufacturers have come out with models which are in between AIS and GIS. This could be a very healthy and cost economic solution to the users in terms of constraints they face during application of substations /pothead yards. Combining disconnector, breaker and CTs is commonly available but tailor made configurations to meet the site specific needs are very much possible. Compaction of AIS is, therefore, possible with the use of hybrid switchgear.

Fig 9 : Hybrid Switchgear

Hybrid solutions combines’ five functions of traditional AIS substation namely Circuit Breaker, Disconnector, Earth Switch, Current Transformer and Voltage Transformer into one module encapsulated in SF6 gas compartment. It has following advantages:

Space saving upto 50-60% can be achieved compared to an AIS station. It has high reliability due to usage of mature GIS components & technology. Installation is fast and easy. It allows flexibility in layout design.

Fig-10

In order to adopt this course of option the bidding documents will have to be functional without detailing of items and single line diagram along with space available could be supported with the system requirements in terms of electrical parameters. In such cases the optimum use of hybrid switchgear could be possible and the specification would not be limited to a manufacturer

10.2 Controlled switching requirements – Experiments have proven that in case of

switching on i.e. closing of CB is carried out on or near zero crossing of sine waves, the switching surges would be extremely small and it will be providing least stress on insulation of GIS as well as other connected equipments. Similarly tripping of CBs could also be ensured near zero crossing to limit the over-voltages. The implementation of control switching needs an operating drive immune to variations in operating voltage and frequency. The thyristor control for point of wave switching would be a phenomenon required to achieve control switching requirements. It is understood that relays are available for the purpose but information to what extent CB manufacturers/GIS manufacturers are geared up to adopt this technology remains a point of concern.

10.3 Gas Mixtures extent and possibility – Impurities in GIS are yet to be proven. In fact in chambers where no switching is required as also in gas bays transmission lines experiments are going on and mixing of nitrogen is being considered increasingly feasible. Trials are going on where SF6 and nitrogen mixtures are also being used for switching functions and insulation in electrical equipment. The major application however is commercially limited to gas insulated transmission line as far as SF6 and nitrogen mixtures are concerned.

10.4 Enclosure options – The GIS enclosure should essentially be divided into several sections separated by gas tight barrier insulators. Each section should be provided with the necessary piping and valves to allow isolation, evacuation and refill of gas without evacuation of any other section. Location of gas barriers insulators is to be clearly discernable outside the enclosure by a band of distinct colour normally used for safety purpose. Two options further could arise in respect of enclosure provision i.e. bus disconnectors arranged in a separate gas compartment or arranged in a common gas compartment. Although manufacturers of both technologies are available but majority is towards separate gas compartment. In fact the user need not necessarily stress upon the enclosure options as outage of bus bar disconnectors would in any case lead to outage of bus bar. Similarly the leakage of the gas from the main bus bar chambers are also of little relevance once monitoring equipment is installed.

10.5 Bus trunking. -Trunking at bus bars is used for extending the GIS connection out of a

building or to meet specific lay out requirements. In fact truncated bus sections once clearly shown provide advantageous flexibility in optimizing space and cost with special reference to outdoor applications of GIS. Co-ordination with pot head yard equipment and integration with the lay out is an advantage which alone bus trunking gives with respect to high voltage cables.

10.6 Composite bushings- Along with porcelain, glass, the silicon rubber bushings have been

developed and are progressively being used. These bushings have found use in transmission lines and in stray cases at sub-stations. Techno-economics however, is not deliberated in technical documents published. Although technically composite bushings in a GIS would be facing SF6 atmosphere but not many examples are available where composite bushings have been used in GIS as well as for end terminations.

10.7 Gas based transmission lines-GIL is the latest technology being used by GIS

manufacturers in India for short lines. Technically speaking the GIL is an acceptable proposition where mixture of SF6 and nitrogen gas is used . Application however, needs to be techno-economically studied with reference to AIS and XLPE options available. Areas having constraints and where XLPE option is not feasible the possibility of GIL could be studied and applied. It is purely on terrain and ecological conditions which would necessitate use of GIL as an option on power stations. Besides other options as and when available may be considered :

CHAPTER- 11

TRAINING ASPECTS

Normally for any major repair /replacement of any GIS components services of the experts of manufactures are required however for general understanding and minor maintenance for any initial handling of the problem short duration of training shall be very useful. The training is to be arrange in the following manner.a) Four week on site training during erection. b) Two week training on GIS at manufacturer’s works

Curriculum for GIS Training

General Explanation for GIS Layout and Architecture of GIS Gas Sectionalization of GIS Construction of CB Operating Mechanism of CB Maintenance of CB Overhaul of CB (Interrupting chamber ) Overhaul of CB (Operating Unit) Construction of DS/ES Maintenance of DS/ES Overhaul of DS/ ES Construction of Bus/ Cable head/ SF6 – air bushing Maintenance of Bus/ Cable head/ SF6 – air bushing Overhaul of Bus/ Cable head Overhaul of Tr.connection/ SF6 – air bushing Maintenance & Construction of Oil-gas bushing Maintenance & Construction of Lightning Arrester Maintenance & Construction of VT/CT Maintenance & Construction of Local control panel Erection of GIS at site. Installation & Testing of GIS at site Type tests of GIS Routine tests of GIS. Faults simulation of GIS Localization of GIS fault.

CHAPTER- 12

ESSENTIAL PARAMETERS TO BE SPECIFIED DURING FLOATING AN ENQUIRY

Generally specifies requirements for gas insulated, metal enclosed switchgear in which the insulation is obtained, at least partly, by an insulating gas other than air at atmospheric pressure.

12.1 ESSENTIAL PARAMETERS

In the manual these aspects are specifically covered which are required to be specified to ensure reliable service of GIS in a tropical country like India and also which are not specified by IEC but are important from utility point of view. Some of these are:

Design & Performance requirements –operating duty, reliability class Architecture of the GIS Specification of gas Philosophy of Gas sectionalisation Fault / replacement of any component in the GIS should not lead to complete shut down

of the station Future extension should not lead to complete shut down of the station. 3 phase Vs 1 phase enclosures Special provision for earthling Special arrangements for testing due to non accessibility to the current carrying parts Interface with cables/ transformers/ overhead lines/ Terminal point of supply Special maximum ambient air temperature & system particulars Type of operating drive for CBs No. of interrupters in case of preference* Spare parts & maintenance equipment Training Space availability & time schedule Packing, marking & transport instructions Tests at site Provision of view ports* Material of containers*

Some of the parameters are governed by technical requirements but items marked ‘*’ are not mandatory as far as bidding document is concerned.

The essential requirement of the specification are given in detail as under:

General specificationThe specification covers design, engineering manufacture assembly, testing at manufacturer's works, supply, delivery and installation, testing and commissioning of the metal encapsulated SF6 Gas insulated indoor switchgear(GIS).

The switchgear shall be complete with all fittings, components and accessories. Materials and components not specifically stated in this specification but which are necessary for satisfactory operation of the equipment shall be deemed to be included unless specifically excluded and shall be supplied without any extra cost.

GENERAL INFORMATION

The design and workmanship shall be in accordance with the best engineering practice to ensure satisfactory performance and service during the life of the equipment as specified. All similar parts of any equipment shall be interchangeable.All deviations from the specification shall be brought out clearly in the respective schedule of deviations forming part of the tender. Unless brought out clearly, the tender shall be deemed to conform to the specifications scrupulously. Any deviation between the specification and the catalogues of the offer if not clearly brought out in the schedule of deviation will not be considered as valid deviation and the equipment shall be deemed to be conforming to specifications.Following auxiliary supplies shall be available at site.

Normal Variation in Frequency Phase Neutral voltage voltage (Hz) Connection(Volts)

415 +/-10% 50+/-5% 3 Solidly earthed

240 +/-10% 50+/-5% 1 Solidly earthed

220 190V to 240V DC Isolated system

Combined variation of frequency and voltage shall be 10%. Fault level for the 415V AC Power distribution system of the owner shall be 32 MVA or less.

The GIS equipment and its axillaries service shall conform to as per applicable Indian standard or international standards. In case manufacturer wants to adopt any other standard then he should specifically mention and take the approval from the owner in writing.

12.2 TESTS All equipment furnished shall confirm to the type tests and shall be subject to routine tests in accordance with the requirements stipulated under respective equipment heads. Owner reserves the option for getting any or all of the type tests conducted on the equipment within a reasonable period say up to six months after the award of contract. The Bidder shall ensure and confirm that the equipment offered is exactly similar to the equipment which has already been type tested.

The Owner reserves the right to witness any or all of type, routine & acceptance tests specified, for which at least 30 days advance notice shall be given by the Contractor.

Before the type test commences, the Owner shall be informed well in advance. The Contractor shall furnish the type test procedure and schedule along with venues, within 3 months of award for approval. Contractor shall ensure that all drawings and quality plans are approved before the type test commences.

The owner will have the right of having, at his own expense, any other test(s) of reasonable nature carried out at Contractor premises or at site or in any other place in addition to the aforesaid type and routine tests, to satisfy himself that the material complies with the specification.

All deviations from the specification shall be clearly brought out in the respective schedule of deviations. Unless brought out clearly, the bidder shall be deemed to conform to the specification scrupulously.

The Owner reserves the right to have any field tests conducted on the completely assembled equipment at site.

12.3 MANDATORY MAINTENANCE EQUIPMENT

The Bidder shall include in his bid spare parts and maintenance equipment considered necessary, by him for a reasonable period say for three (3) years of satisfactory operation of the equipment.

The Bidder shall also include in his bid any special erection and maintenance tools required for his equipment.

12.4 INSPECTION Inspection and acceptance of any equipment under the specification by the Owner or his authorized representative shall not relieve the contractor of his obligation of furnishing equipment in accordance with the specification and shall not prevent subsequent rejection, if such equipment is later found to be defective. A Material Despatch Clearance Certificate(MDCC) shall be issued by the owner after the inspection of the equipment. The MDCC will be issued only after approval of test reports.

All equipment furnished shall confirm to the type tests and shall be subject to routine tests in accordance with the requirements stipulated under respective equipment heads. Owner reserves the option for getting any or all of the type tests conducted on the equipment.

The Engineer, his duly authorised representative and/or an outside inspection agency acting on behalf of the Owner shall have, at all reasonable times access to the Contractor's premises or works and shall have the power to inspect and examine the equipment/materials and workmanship of the works during its manufacture or prior to despatch.

12.5 QUALITY ASSURANCE To ensure that the equipment and services under the scope of this Contract, whether

manufactured or performed within the Contractor's works or at his sub-contractor's premises are at the Owner's site or at any other place of work, the contractor shall adopt a suitable quality assurance programme to control such activities at all necessary points. Such programmes shall be outlined by the Contractor and shall be finally accepted by the Engineer after discussions before the award of Contract.

12.6 PACKING & SHIPMENT

After satisfactory final inspection/tests and receiving despatch clearance from the purchaser; the tendered shall adequately pack the equipment for transportation to designated site through Rail and/or Road, Sea transport.

The Contractor shall be responsible for any loss or damage during transportation and handling.

The detailed despatch schedule for each equipment shall be supplied well in advance. The packing list shall indicate complete details of the equipment being despatched.

12.7 INSURANCE

The contractor at his cost shall arrange, secure and maintain all insurance to protect his interest and interests of the owner. Any loss or damage to the equipment during handling, transportation, till sixty days after receipt of the equipment and material at site and also during storage, erection, putting into satisfactory operation and all activities to be performed till such time the station is "Taken Over" by the owner shall be to the account of contractor.

12.8 STORAGE

All the equipment furnished under the contract and arriving at site shall be promptly received, unloaded and transported and stored in the storage spaces by the contractor.

The contractor shall maintain an accurate and exhaustive record of all the equipment received by him and keep such record open for the inspection of the Engineer.

All equipment shall be handled very carefully to prevent any damage or loss. The Contractor shall have total responsibility for all equipment and materials in his custody. The Contractor shall make suitable security arrangements to ensure the protection of all materials, equipment and works from theft, fire, pilferage and any other damages and loss.

The owner shall have lien on all equipment including those brought to the site for the purpose of erection, testing and commissioning of the Plant.

12.9 GAS ENCLOSURES

The metal enclosures for the SF(, gas insulated equipment modules shall be made from nonmagnetic material which does not require protective painting either internal or external. The gas filled enclosures shall conform to the Pressure Vessel code applied at the country of manufacturer or ASME.

The metal enclosures shall be designed for the mechanical loads to which they are subjected in service. The modular design of the switchgear shall offer maximum flexibility from the point of view of design, operation & maintenance.The enclosures must be sectionalised with gas tight barriers between sections or compartments. The arrangement of sections shall be such that it is possible to extend the existing bus bars without having to take out of service the available bus bar.

12.10 SUPPORT INSULATORS & SECTION BARRIERS The support insulators and section barriers/insulators shall be free from voids and shall

be so designed so as to reduce the electrical stresses in the insulators to a minimum. Gas section barriers and enclosure walls shall be gas tight and capable of withstanding the maximum pressure differential that could occur across the barrier i.e. with a vaccum Pressure Relief device

Pressure Relief device Pressure relief devices shall be provided in each gas section to protect the main gas

enclosures from damage or distortion during the occurrence of abnormal pressure increase or shock waves generated by internal electrical fault arcs.

Pressure relief shall be achieved either by means of rupture diaphragms venting directly into the atmosphere. Suitable guards and deflectors shall be provided to prevent pieces of diaphragm from flying out or any dangerous SF6 arc product gases escaping, in a manner that could endanger personnel who may be present.

Suitable guards and deflectors shall be provided to prevent pieces of the diaphragm or plug from flying out or any dangerous SF6 arc product gases escaping, in a manner that could endanger personnel who may be present.

The enclosure and barrier insulators shall be designed to prevent rupturing in the event of a service failure. Each insulator shall withstand the pressure rise due to an internal arcing fault on one side and with vacuum on the other side.

drawn on one side of the barrier and the maximum gas pressure on the other side.

Gas Leakage

The guaranteed maximum gas leakage shall be less than 0.5% per year for any individual gas compartment and less than 0.5% per year for the whole equipment.

12.11 EQUIPMENT GROUNDINGThe grounding arrangement shall ensure that the touch and step potential are within the

safe limits. The ground continuity between the enclosures of the GIS Switchgear shall be affected through flanges.

12.12 SUPERVISION OF ERECTION

The tenderer shall quote for providing the supervision services for the various stages of work.

All skilled and unskilled labour and all tools, materials & testing apparatus will be provided by the purchaser. Any specialized tools & equipment required for erection, testing & commissioning of the switchgear shall be arranged by the contractor free of cost.

It must be generally possible to remove a single circuit element (breaker, disconnect switch, bus insulator) without removing another element. Circuit breakers interrupter unit shall be removable from its tank without moving the tank or any other element. Further, Disconnect switch contacts shall be accessible through manholes. It will be permissible to remove a short piece of bus between elements in order to remove an element.

For routine inspection and possible repairs, all elements should be accessible without removing support structures. The removal of individual enclosure parts, or entire breaker bays, shall be possible without disturbing the enclosures of neighboring bays.

• The station shall be complete with all necessary supports, platforms, ladders, staircases, catwalks, mechanism cabinets and internal cable raceways etc. Suitable maintenance/ operation platforms shall be provided between each bay and at the end bays.

• The bus duct may be of bolted flange . • Two main bus bars shall be provided with a gas barrier in the middle with provision of

independent gas monitoring & filling etc. In addition, provision shall be made in the two main buses of the GIS, so that in the event of a fault in one part of one of the main buses, other part of this bus can be sectionalised by means of detachable device and taken back in service (by means of installing end covers in the healthy part of the main bus).

• The arrangement of gas sections or compartments shall be such that it is possible to extend existing busbars without having to take out of service more than one busbar at any given time.

12.13 Model / Technical Specification for GIS

The model Technical Specification for 400KV GIS, with a double bus bar scheme with bus coupler 3 nos in coming from generators 2 nos outgoing transmission lines covering all aspects including the technical parameters of associated equipment of GIS in are detailed in Annexture-1. The model technical specification describes the technical parameters of all the main and auxiliary equipments, testing requirement of GIS and guaranty technical parameter. The concerned organization/ agencies may utilize the model technical specification after incorporating necessary modification & details etc. suiting to their requirement.

12.4 Guaranteed Technical Particulars (GTPs): Essential Parameters to be specified during floating of an enquiry have been detailed above. During the process of tendering, negotiations, award, manufacturing, inspection etc. some of the parameters are revised to some extent. As a part of the guarantee, the manufacturer supplies the guaranteed technical particulars. Actual GTPs of 220KV GIS of Dhauliganga and 400 KV GIS of Chamera-I are given on Annexture -2 and 3 respectivly

Annexture-1Model Technical Specifications for GIS

1. GAS INSULATED SWITCHGEAR

1.1. Scope of Work

Provision of labour, tools, plants, materials and performance of work necessary for the design, manufacture, quality assurance, quality control, shop assembly, shop testing, delivery at site, site storage and preservation, installation, commissioning, performance testing, acceptance testing, guarantee for two years of 400 kV GIS System as per the specifications hereunder, complete with all auxiliaries, accessories, spare parts and warranting a trouble free safe operation of the installation.

The scope of work shall be a comprehensive functional system covering all supply and services including but not be limited to following:

1.1.1. 400 kV GIS

Metal-enclosed phase segregated type SF6 gas insulated switchgear system rated for 400kV, 3 phases, 50 Hz consisting of following major items for a model power house having 3 machines and two lines:

i) Two (2) 3-phases, 2000/4000 A SF6 gas insulated metal enclosed bus bars complete in all respects, comprising of:

Six (6), individual bus bars enclosures running the length of the switchgear,

Six (6) single-phase surge arrestors, three in each bus ,

Six (6) single-phase, 2-core voltage transformers, three in each bus,

Six (6) single-phase disconnector complete with manual and motor driven operating mechanisms, one in each bus for isolation of voltage transformer,

Six (6) single-phase safety earthling switches complete with manual and motor driven operating mechanisms, one with each single-phase disconnector.

ii) One (1) bus-coupler bay modules, each comprising of:

One (1), 3-pole SF6 gas insulated circuit breaker, complete with dedicated operating mechanism,

4-core, multi ratio, 3-pole current transformers,

Two (2), 3-phase, single-pole group-operated disconnector complete with manual and motor driven operating mechanisms,

Two (2), 3-phase, single-pole group-operated safety earthing switches complete with manual and motor driven operating mechanisms,

One (1), local control cubicle for control of coupler bay, bus bar VT and disconnector including bay controller.

iii) Three (3) generator bay modules, each comprising of:

One (1), 3-pole SF6 gas insulated circuit breaker, complete with dedicated operating mechanism for each pole,

One (1), 5-core, multi ratio, 3-pole current transformer,

Three (3) single-phase surge arrestors,

Three (3), 3-phase, single-pole group-operated disconnector, complete with manual and motor driven operating mechanisms,

Three (3), 3-phase, single-pole group-operated safety earthing switches, complete with manual and motor driven operating mechanisms,

Three (3), bushings,

One (1), local control cubicle for control including bay controller.

iv) Two (2) transmission line bay modules, each comprising of:

One (1), 3-pole SF6 gas insulated circuit breaker, complete with individual operating mechanism

One (1), 5-core, multi ratio, 3-pole current transformer,

Three (3), 3-phase, single-pole group-operated disconnectors, complete with manual and motor driven operating mechanisms,

Two (2), 3-phase, single-pole group-operated safety earthing switches, complete with manual and motor driven operating mechanisms,

One (1), 3-phase, single-pole group-operated high-speed earthing switch, complete with manual and motor driven operating mechanism,

Three (3), SF6 / air bushings for outdoor connections,

One (1), local control cubicle for control including bay controller.

v) All necessary terminal boxes, SF6 gas filling, interconnecting power and control wiring, earthing connections, gas monitoring equipment and piping support structures etc,

vi) The first filling of SF6 gas for the equipment supplied plus an additional quantity sufficient for conducting all tests on equipment at the site before placing it into successful operation. SF6 gas shall be supplied in returnable cylinders. In addition about 10 % spare gas (of total used for GIS) by weight shall be supplied in 40 litre non returnable cylinders,

vii) Continuous on-line monitoring and diagnostic systems to monitor gas density, gas pressure, leakage, moisture (offline) etc., operating parameters such as current, voltage, temperature etc. complete with sensors, control/processor units, wiring/cabling in all respect and integration of the systems with plant SCADA system,

viii) Coordination and provision of necessary contacts and/or ports for integration with plant SCADA system.

Any other item(s) not mentioned specifically but necessary for the satisfactory completion of scope of work defined above, as per accepted standard(s) / best international practices.

1.2. Specific Parameters

The switchgear shall have double bus bar arrangement. The rated capacity of switchgear including bus bar and all feeders shall be 2000/4000 A.

Each bus shall be capable of evacuating full station capacity including overload.

The single line diagram for …… kV GIS is given in drawing no. ………….

1.3. Rating and Functional Characteristics

System Description

Location Indoor/Outdoor

Scheme Double Bus bar arrangement

No. of Bays 6

System Requirement

Rated voltage kV 420 KV

Rated frequency, Hz 50

Rated withstand Voltage to earth

- Power Frequency 520kV

- Lightening Impulse (peak value) 1425kV

- Switching Impulse 1050kV

Rated short time withstand current (r.m.s) for 1 Sec

40/63kA

Rated Peak withstand current 100/157.5kA

Rated normal current, A, r.m.s 2000/4000A

Control voltage DC 220 V + 10% / -10%

-20% for trip coils

Auxiliary AC supply, 3 phase 415 ± 10% V

Partial discharge of switchgear assembly at highest voltage for equipment, pc

<10

Maximum Gas leakage rate (%) of the respective volume, per year

1 % individual section and 0.5%on overall basis per phase

Circuit Breaker

Type SF6

Description Three separate pole equipped with single pole operating mechanism

First-pole-to clear factor 1.3

Rated short circuit breaking capacity, kA (r.m.s)

40/63kA

Rated short circuit making capacity, kA (peak)

100/157.5KA

Rated line charging breaking current capacity, A

400A

Rated cable charging breaking current capacity, A

400A

Duty Cycle

- Line Breakers O-0.3s-CO-3 min– CO

- Generator feeder and bus coupler breaker

O-3min-CO-3 min–CO

Closing Time Less than or equal to 100 ms

Breaking Time Less than or equal to 50 ms

Small inductive current breaking capability (without producing excessive over voltages)

10 A

Disconnector

TypeThree separate pole mechanically coupled and group-operated

Operation Motor as well as manual

Rated withstand voltage across isolating distance

- Power frequency 610kV

- Lightening Impulse

(Peak)1425kV

Rated capacitive current make and break capacity

0.50A

Rated Bus Transfer Current 80% of rated normal current

Rated Bus Transfer Voltage 20V r.m.s

Earthing Switch

Making Capacity kA (peak) 100/157.5 kA

Rated short-time current 40/63kA

Rated Induced Current/Voltage for Electromagnetic coupling(rms)

160 A / 10kV

Rated Induced Current/Voltage for Electrostatic coupling(rms)

18A/20kV

Current Transformers

Current ratio

Generator/Bus coupler ………………

Line bay ………………

Accuracy class

- For protection PS

- For metering 0.2

Surge Arrestor

Type Gapless metal Oxide station type

Rated arrestor voltage 336 KV rms

Nominal discharge Current (8/20s wave) 20 KA

Energy dissipation capability Not less than 10 KJ/kV

Partial Discharge at highest level <10

Bus Voltage Transformer

Type Inductive type, single phase, two core

Location R,Y,B phase

Purpose Synchronising, and Metering

Voltage ratio (400/3) kV/ (110/3) V/ (110/3) V

Accuracy class

- Metering

- Protection

0.2

3P

Voltage factor 1.5 for 30 s,

1.2 for continuous

1.4. Performance Guarantee

The GIS system along with all auxiliaries and accessories shall be capable of performing intended duties under specified conditions. There should be guarantee for the reliability and performance of the individual equipment as well as of the complete system.

Following should be stated and guaranteed:

The maximum yearly gas loss in every monitored compartment, In the event of loss of gas exceeding 1.0 percent in any section measured in the first two years after commissioning of GIS.

Number of mechanical and fault current operation of circuit breaker interrupter unit before it is opened for inspection and maintenance,

Number of operation of operating mechanism before it is opened for inspection and maintenance.

1.5. Design and Construction

1.5.1. Standards

The system and equipment shall be designed, built, tested and installed to the latest revisions of the following applicable standards. In the event of other standards being applicable they will be compared for specific requirement and specifically approved during detailed engineering for the purpose:

Sl. No.

Standards Description

1 IEC 62271(All Parts) “High voltage switchgear and control gear”,

2 IEEE C37.122-1993 IEEE Standard for Gas-Insulated Sub-stations (GIS)

3 IEEE C37.123-1996 IEEE Guide to specifications for Gas-Insulated, Electric Power Substation Equipment

4 IEC 60694 1996 Edition Common Clauses for high-voltage switchgear and control gear standards

5 IEC 60376 – 2005 Edition Specification of technical grade sulphur hexafluoride (SF6) for use in electrical equipment

1.5.2. General

It is understood that each manufacturer has its own particular design concept and it is not the purpose of this specification to impose unreasonable restrictions. However, in the interest of safety, reliability and maintainability, the switchgear offered shall meet the following minimum modular concept and design requirements:

1. Fail safe inter and intra bay Inter locking scheme

2. Maintenance of one bus bar with the other bus bar in service,

3. Interchangeability of similar parts,

4. Future extension of bays, with maximum one bus outage at a time

5. Possible to remove and replace the fully assembled parts of circuit breaker,

6. Pressure relief device for each pressurised section,

7. Gas density monitoring device for each isolated section/module,

All mechanical parts, which are outside of gas filled compartment, must be externally accessible and serviceable without disconnecting the main bus bar or feeder circuits.

All current carrying components of the equipment specified shall be capable of continuous operation at the specified rated current without exceeding the maximum temperature rises specified in the relevant IEC standards.

1.5.3. Arrangement and assembly

The arrangement shall be single-phase enclosed. The assembly shall consist of completely separate pressurized sections designed to minimize the risk of damage to personnel or adjacent sections in the event of a failure occurring within the equipment. Rupture diaphragms shall be provided to prevent the enclosures from uncontrolled bursting and suitable deflectors provide protection for the operating personnel. In order to achieve maximum operating reliability, no internal relief devices shall be installed because adjacent compartments would be affected. Modular design, complete segregation, arc-proof bushings and “plug-in” connection pieces shall allow ready removal of any section and replacement with minimum disturbance of the remaining pressurized switchgear.

1.5.4. Metal enclosed Bus bar

The bus bars shall be single-phase segregated metal-enclosed type. The enclosure design shall essentially be based on following considerations

Temperature and solar radiations

Thermal cycling, vibration, shock and seismic

Design Pressure on normal and abnormal conditions

Conductors and live part shall be mounted on moulded epoxy resin insulators specially made for the EHV application. The conductors shall be made of tubular aluminium. Silver plated finger contacts at the ends of conductor or mounted on support insulators shall be provided to form sliding contact permitting the conductor to expand axially on a temperature rise, without imposing any mechanically stresses on the supporting insulators. Metal bellows compensators shall be provided on enclosure for permitting longitudinal expansion. The enclosure shall be dimensioned for the full return current. Compensators shall be bypassed by copper straps.

1.5.5. Circuit breakers

The circuit breaker shall be designed to minimize switching over voltages and also to be suitable for out-of-phase switching. The specified arc interruption performance must be consistent over the entire operating range, from line-charging currents to full short-circuit currents. The complete contact system (fingers, clusters, jets, SF6 gas) shall be designed to withstand at least twenty (20) operations at full short-circuit rating without the necessity to open the circuit breaker for service or maintenance.

The interrupter and operating drive should be simple and sturdy conforming to C2 & M2 class complying with T100 & L75 without maintenance respectively as per IEC 62271-100.

The operating mechanism shall be spring / spring or hydraulic / spring type.

The circuit breakers shall comprise three single-phase metal clad breakers poles. Each pole shall consist of the operating mechanism, interrupter unit and the enclosure with basic supporting structure. The mechanism shall be trip free mechanically or electrically with anti pumping device. Grading capacitors shall be provided to ensure uniform voltage distribution between interrupting elements. SF6

circuit breakers shall conform to IEC-62271-100. Auxiliary contacts of the breakers shall be provided for the local and remote indications, the performance of various control and protection schemes and the interlocking scheme. Alarm and cut-off contacts for mechanism faults and gas pressure loss shall also be provided. The circuit breaker shall be capable of being operated locally or from remote.

1.5.6. Current transformers

The current transformers shall be of single phase inductive type and shall have multi core with multi ratio, which shall be changeable by means of taps on secondary side. Independent cores shall be used for different purposes as per drawing no. …….

1.5.7. Voltage transformers

The voltage transformers shall be of single phase inductive type with secondary windings Independent cores shall be used for different purposes as mentioned in GTP.

The voltage transformer shall be located in a separate module and shall be connected phase to ground to the phase buses.

1.5.8. Disconnector

The three-phase disconnector shall comprise of three separate pole and all the three poles shall be mechanically coupled via robust mechanical link. All three poles shall be group-operated manually as well as through motor driven mechanisms.

The disconnector shall have provision for visual indication of switching position. Disconnector shall conform to IEC 62271-102. Sufficient auxiliary contacts shall be

provided for indications (local and remote), interlocking schemes and the performance of various control and protection schemes.

1.5.9. Earthing switch

The 3-phase earthing switch shall comprise of three separate pole and all the three poles shall be mechanically coupled via robust mechanical link. All three poles shall be group-operated manually as well as through motor driven mechanisms.

Each earthing switch shall be electrically and mechanically interlocked with its associated disconnector and circuit breaker. Sufficient auxiliary contacts for indications and interlocking shall be provided. Inspection window shall be provided in the enclosure.

1.5.10. High speed earthing switch

The three-phase high-speed make-proof type-earthing switch shall comprise of three separate pole and all the three poles shall be mechanically coupled via robust mechanical link. All three poles shall be group-operated manually as well as through motor driven mechanisms. It shall be used to discharge the respective charging current in addition to their safety earthing functions.

Each earthing switch shall be electrically and mechanically interlocked with its associated disconnector and circuit breaker. Sufficient auxiliary contacts for indications and interlocking shall be provided. Inspection window shall be provided in the enclosure.

1.5.11. Surge arrestor

The surge arrestor shall be of gap-less heavy-duty station type and the live part shall comprise of non-linear metal oxide resistors without spark gap. Provision shall be made for measurement of leakage current and connection of discharge counter.

The arrestors shall be either the plug in construction or the disconnect link type and be attached to the GIS in such a manner that they can be readily disconnected during the dielectric tests. The metal housing of the arrestor should be connected to the metal enclosure of the GIS through the flanged or bolted joints.

1.5.12. Name Plate

Each auxiliary control cubicle must be identified with the feeder designation to which it is assigned.

Each instrument transformer must have its own rating plate with the information as required in IEC 60044-1 and IEC 60186.

1.5.13. Earthing

The enclosures of all the GIS shall be grounded at several points so that there shall be a grounded gauge around all live parts. All conduits and cables sheaths shall be connected to the ground bus, to be provided, in the control cubicles and the marshalling boxes. All steel structures shall be grounded. The manufacturer shall recommended earthing requirements during engineering in the first submission of drawings

All wirings to GIS shall be shielded and grounded at both ends.

Subassembly to subassembly ground conductors shall be provided to assure safe voltage gradients.

1.5.14. SF6 GAS

The gas shall generally conform to IEC 60376 – 2005 edition but for following

Water < 5 ppm by weight

Carbon Tetra Fluoride < 250 ppm by weight

Air < 250 ppm by weight

1.5.15. On-line monitoring

Continuous on line monitoring system shall be provided to monitor conditions such as gas density, gas pressure, gas leakage, moisture (offline) etc. and operating parameters such as current, voltage, temperature etc. of GIS for smooth operation and detection of any changes in insulation at an early stage during normal operation to take appropriate remedial action .

Each system shall be complete with sensors, input/output module, control/processor unit, relays, junction boxes, cabling and associated accessories for measuring, monitoring and data acquisition of intended parameters to be monitored.

1.5.15.1. Gas monitoring system

Each gas-filled compartment shall have its own SF6 gas density / pressure monitoring system, each comprising of a temperature compensated SF6 gas density monitoring unit and pressure gauge having alarm/trip contacts.

Gas pressure and density shall be continuously monitored and displayed by a suitable temperature compensated instrument, which will provide an alarm signal in case of pressure drop before the allowable minimum pressure is reached.

1.5.16. Local control cubicle

The Local control cubicle shall contain all the equipment required for controlling and monitoring the bay. Each bay’s local control cubicle shall have at least the following main function:

8. The mimic diagram with control switches for electrically operated circuit breakers, disconnector and earthing switches as well as the position indication of all components provided with auxiliary switches,

9. Alarm facia with indicating lamps for monitoring of gas density,

10. Trip circuit healthiness,

11. Electric interlocking between devices,

12. Interface between central control and the switchgear,

13. Interior lighting, safety shrouding, heating to prevent condensation etc.

All the switchgear bay module shall be supplied with a local control cubicle of the floor standing type. The cubicle shall have full height, hinged, gasket lockable double doors. One door shall have safety glass window through which various controls can be viewed without opening the door. The cubicle shall be utilized as both the switchgear bay local control module and as the terminating centre for all power supply, control, annunciation and supervisory wiring interfacing with the system. Adequate no. of potential free contact shall be made available for providing necessary input/output interface.

Implemented technology for control shall be digital and local control cubicle shall incorporate bay control unit for integration to plant SCADA system through local control Board for GIS.

1.6. Design Calculations

Design calculation should be submitted covering at least the following, for review / acceptance.

14. Calculation of power requirement for operating mechanism of breakers, disconnector and earthing switches.

15. Data/calculations in regard to the loads under severe short circuit conditions to be transferred to civil structures for designing of GIS hall accordingly.

1.7. Spare Parts

S. No. Description Quantity

1 SF6 gas for use during operation and maintenance in non-returnable cylinders.

10% of total quantity in 40 kg cylinders

2 One pole of complete Interrupter unit of circuit breaker with operating mechanism and tie rod etc

one phase

3 Complete drive mechanism including motor for disconnector switches and earthing switches

1 no.

4 Complete drive mechanism including motor for fast acting earthing switches.

1 no.

5 Trip coils for circuit breakers 6 nos.

6 Closing coils for circuit breakers 6 nos.

7 Complete set of rupture disc 2 sets

8 Pressure switch/gas pressure transmitter

2 sets of each used type

9 Pressure gauge 2 sets of each used type

10 Gas density relay 2 sets of each used type

11 Gas tight bushing of each type used 2 nos. of each used type

One set would be applicable for one phase of one feeder bay

1.8. Tools and Instruments

1.8.1. Special tools

The list of special tools must include the following:

One (1), gas processing unit and filling units, along with tools and spares to handle gas quantity in at least two largest gas sections, with provision to check SF6 moisture and acidity content,

One (1), set of handling devices and tools for assembling and dismantling of bays / complete GIS modules,

One (1) set of handling devices and tools for assembling and dismantling each type of operating mechanism of circuit breakers, disconnectors and earthing switches,

1.8.2. Testing instruments

The list of testing instruments shall include following mandatory items:

One (1) no. air / gas humidity tester,

One (1) no. gas. purity detector for SO2,H2O,CF4,AIR etc.,

One (1) no. gas leakage tester,

One (1) no. breaker timing measurement kit,

One (1) set of equipment for pressure measurement and gas tightness testing.

1.9. Quality Assurance and Testing

Quality assurance and testing requirements specified separately in “Quality assurance and Testing Specifications (QTS)” should be strictly followed.

Annexture-2GAS INSULATED SWITCHGEAR

Guaranteed Technical Particulars (220KV)

Item/Clause No.

Parameter Units Contractor's Data

1 General 1.1 Type Designation

During Detail Engg.

1 Performance Data 1.1 Nominal Voltage Un kV 2201.2 Highest Voltage for Equipment Um kV 2451.3 Rated Frequency

Normal Condition Hz. 50 Exceptional Condition Hz. As per IEC

Standard1.1 Power Frequency withstand Voltage, (One) 1

Minute

Phase to Ground KVrms 460 Phase to Phase KVrms N/A

1.2 Power Frequency withstand Voltage at Atmospheric SF6 Gas Pressure

Continuously KVrms N/A For (One) 1 Minute KVrms 141

1.3 Lightening Impulse withstand Voltage Against Ground kVpeak 1050 Over Isolating Distance of Isolators kVpeak 1050-150 Over Isolating Distance of Circuit Breaker kVpeak 1050

1.4 Switching Impulse withstand Voltage Against Ground kVpeak N/A to 245 KV

According to IEC 60694

Over Isolating Distances of Apparatus kVpeak N/A to 245 KV According to IEC 60694

1.5 Maximum Partial Discharge of Swtichgrear Assembly at Highest Voltage for Equipment Um

pC <10

1.6 Maximum Leakage Rate in Percent of the Respective Volume per Year

% 0.5

1.7 Temperature Rise oC 30

2 Characteristic Data 2.1 Minimum Symmetrical Short-Time withstand

Current (One) 1 SecondK Arms 40

2.2 Minimum Dynamic Short-Circuit withstand Current

KA Peak 100

2.3 Corone Extinction Voltage kVrms 2002.4 Circuit Breaker

2.4.1 Rated Continuous Current A 20002.4.2 Rated Short-time withstand Current KA Peak 100

GAS INSULATED SWITCHGEARGuaranteed Technical Particulars(220 KV)

Item/Clause No.


2.4.3 Rated Symmetrical Short-Circuit Breaking Current

K Arms 40

2.4.4 Rated Asymmetrical Short-Circuit Breaking Current

K Arms 40

2.4.5 Rated Short-Circuit Making Current K Arms 1002.4.6 Line Charging Current Breaking Capability A 1252.4.7 Small Inductive Current Breaking Capability

(Without Producing Excessive Over Voltages)A 10

2.4.8 Operating Sequence Line Breakers

0.03 S-CO-3 Min CO

Generator Feeder & Tie Breakers

0-3 Min-CO-3 Min.CO

2.4.9 Mechanical Opening Time ms <302.4.10 Total Breaking Time ms <502.4.11 Total Closing Time ms <1152.4.12 First Pole to Clear Factor 1.3

2.5 Isolator 2.5.1 Rated Continuous Current A 20002.5.2 Minimum Make and Break Capability for

Capability for Capacity Current A0.25

2.5.3 Total Operating Time (Closing or Opening Cycle)

s <4

2.5.4 Temperature Rise oC 34

2.6 Fast acting Grounding Switch 2.6.1 Rated Short-Circuit Making Current KA Peak 1002.6.2 Rated Switching Capacity

Inductive Currents A 80 Capacitive Currents A 0.25

2.6.3 Operating Time Changing Time of Stored Energy Mechanism s 14 Fast Facing Time ms <100

2.7 Safety Grounding Switch 2.7.1 Rate Short Time withstand Current (One) 1

Sec. kA40

2.7.2 Total Operating Time (Closing or Opening Cycle) s

4

2.8 Bus Voltage Transformers 2.8.1 Rated Transformation Ratio

For Protection kV/V 220/v3/110v3 For Metering kV/V 220/v3/110/v3

2.8.2 Accuracy Class/Rated Burden For Protection

VAClass 3P/50-100VA

For MeteringVA

Class 0.2/50-100VA

GAS INSULATED SWITCHGEAR

Guaranteed Technical Particulars(220 KV)

Item/Clause No.


2.9 Surge Arrestor 2.9.1 System Voltage kV 2452.9.2 Rated Arrestor Voltage kV 1982.9.3 Rated Nominal Discharge Current A 102.9.4 Minimum Thermal Capacity 10kJ/kV of Ur2.9.5 Continuous Operating Voltage (COV) kV 1682.9.6 MCOV as per ANSI Test kV Not Tested as per

ANSI Standard

2.9.7 Temporary Over Voltage (TOV) 1 Sec. KV 218 10 Sec. KV 208

2.9.8 One Minute (Dry) Power Frequency withstand Voltage of Arrestor Housing

kV 460

2.9.9 Impuse withstand Voltage of Arrestor Housing with 1.2/50 ms Wave

kV 1050

2.9.10 Discharge Voltage kV 2.9.11 Switching Surgas

1 kA 366 2 kA 400 3 KA 418

2.9.12 8/2D MS 5 kA 432 10 kA 460 20 kA 497 40 kA 547

Annexture-3

GTPs of GIS (400 KV)GIS Technical Data

Type designation - 8DQ1

Applicable standards - IEC694,517

No. of bays - 8

1. Main data of switchgear system

Nominal voltage UN kV 420

Highest voltage for equipment Um

kV

Rated frequency Hz 50

Power frequency withstand voltage, 1 minute at min operating SF6 gas density

kVrms 520 Phase to Ground

kVrms 610 Across Isolating distance

kVrms 610 Across open circuit breaker

Lightning impulse withstand voltage (1.2/50 ms)

- against ground kVpeak 1425

- over isolating distance of isolators

kVpeak 1425 +240

- over isolating distance of circuit breakers

kVpeak 1425 +240 Open circuit breaker

Switching impulse withstand voltage (250/2500 ms)

- against ground kVpeak 1050 Phase to Earth

- over isolating distances of apparatus

kVpeak 900

Rated continuous current

- busbars and bus tie A 2000

- feeder circuits A 2000

Minimum symmetrical short-time withstand current, 1 second

kArms 63

Minimum dynamic short-circuit withstand current

kApeak 170(Rated peak withstand current)

Nominal insulating SF6 gas pressure at 20°C (minimum

operating pressure)

- enclosures BAR 3.8

- circuit breaker BAR 4.5

Filling SF6 gas pressure at 20°C

- enclosures BAR 4.3

- circuit breaker BAR 6.5

2. Circuit breaker

Rated continuous current A 2000

Rated symmetrical short-circuit breaking current

kArms 63

Rated asymmetrical short-circuit breaking current

kArms

Rated short-circuit making current

kApeak 170

Number of quenching chambers

- 2

Operating sequence - O-0.3s-CO-3min-CO

Mechanical opening time ms 38(+/- 3)

Total breaking time ms 59(+/- 3)

Total closing time ms 85(+/- 5)

First pole to clear factor - 1.5

Command duration ms 50

Arcing time ms 21

3. Isolator

Rated continuous current A 2000

Total operating time (closing or opening cycle)

s </= 6.5 For both opening & closing

4. Fast acting grounding switch

Rated short-circuit making current

kApeak 63

Rated shorttime withstand current

kA 63

Operating times

- charging time of s 6

stored energy mechanism

- fast acting time ms 100 (+/-10)

5. Safety grounding switch

Rated short time withstand current, 1 s

kA 63

Total operating time s <5 (opening/closing)

6. Current transformers

Manufacturer - Siemens

Type designation - AMT 420

Generator / transformer feeder CT’s

- number of current transformers

- 1/phase in each feeder

- rated primary current A 1500&375 1500forcore4&5, 375 forcore1,2&3

- rated secondary current

A 1

- accuracy class/burden of core 1

-/VA 5P 10/30VA


-/VA 5P 10/30VA


-/VA 5P 10/40VA


-/VA 5P 30VA


-/VA 5P 30VA

- rated short-time thermal current, 1 s

kArms 31.5

- rated dynamic current

kApeak 100

Line feeder CT’s


- 1 in each feeder

- rated primary current A 1500&1000 1500 FOR CORE2,3,4&5 AND 1000 FOR CORE1

- rated secondary A 1

current- accuracy

class/burden of core 1-/VA 5P 10/40VA


-/VA 5P 10/30VA


-/VA 0.5FS5/30VA


-/VA 5P 10/30VA


-/VA 5P 10/30VA


kArms 31.5


kApeak 100

7. Bus tie CT’s


- 2

- rated primary current A 1500

- rated secondary current

A 1


-/VA 5P 10/30VA

-' accuracy class/burden of core 2

T1 0.5FS5/30VA

T2 5P 10/30VA


kArms 31.5


kApeak 100

8. Potential transformers

Manufacturer - Siemens AG

Type designation - Phase- Neutral

Number of potential transformers

- 2

Number of windings per PT - 2

Rated transformation ratio

-' for SYNCHRONISATION

kV/V 400:1.732/110:1.732

- for metering kV/V 400:1.732/110:1.733

Accuracy class/rated burden

- for protection -/VA 0.5/200

- for metering -/VA 0.5/200

- for protection -/VA 0.5/200

- for metering -/VA 0.5/200

9. Gas system / General

1.1SF6 gas pressure alarm level

- enclosures Bar 3.7

- circuit breaker Bar 5.7

10. SF6 gas processing unit

- make - DILO

- type - 3-020-R500

- power supply voltage V 415

- power consumption kW 18

Total power consumption of heating elements of CB Module &Hydraulic Mech.

per feeder W 1(15 W), 1(30 W) Control unit

1(15 W) Oil Tank

1(15 W) Operating Mechanism

1(30 W) Auxiliary switch box

at supply voltage V 220

11. Circuit breaker

Circuit breaker operating mechanism

- kind of stored energy mechanism

- pressurized oil

- power consumption of charging motor

W 1100

at supply voltage V 415

Closing coil

- number of coils - 1

- power consumption W 300W

at voltage V 220

Trip coil

- number of coils - 2

- power consumption W 300

at voltage V 220

12. Isolator

Power consumption of

drive motor W 200

at voltage V 220

13. Fast acting grounding switch

Operating mechanism

- kind of stored energy mechanism

- spring snap action

- power consumption

of charging motor W 220

at voltage V 220

14. Safety grounding switch

Power consumption of

drive motor W 200

at voltage V 220

CHAPTER- 13

INSPECTION AND QUALITY ASSURANCE

Gas insulated switchgear (GIS) is accepted world wide with many superior features due to highest reliability and reduced maintenance. This is achieved through very high QA/QC adopted at each component level, assembly level, which goes into manufacturing of GIS.

In order to achieve trouble free and reliable service of GIS in operation, it is essential to follow strict environmental conditions e.g. dust free and pressurized atmosphere during the manufacturing of GIS at vendor’s works as well as during assembly at site..

13.1 TESTS ON ASSEMBLIES AND SUB ASSEMBALIES

Inspection includes mainly various tests on assemblies and sub-assemblies during the manufacture of GIS which are categorized into following types:-

Type/Design tests Production/ routine tests Site tests to be mutually agreed between manufacturer and user.

The above tests are generally to be carried out as per IEC standard 62271-203.

Special arrangements need to be provided in the GIS to enable routine tests and also carry out dielectric tests to confirm dielectric integrity of GIS and detect presence of foreign particles and verify correctness of connections after erection at site.

Tests at site include tests during installation; pre-commissioning, commissioning, field acceptance tests.

Procedure to be adopted for conducting the operational, pre-commissioning, commissioning, performance and field acceptance test should ideally be finalized well in advance, at least six(6) months before start of relevant testing.

All field tests shall be carried out under the supervision of Manufacturer.

Following field tests shall be performed:

• Visual inspection, checks and verifications, • Mechanical operation tests of circuit breakers, disconnectors and earthing switches and

high-speed earthing switches, • Gas leakage test, • Insulation resistance measurement, • DC resistance measurement of the main circuit, • Gas density monitor check, • Inter lock test, • Measurement of moisture content in gas before filling • Test of auxiliary devices. • CT and PT testing • High voltage tests on the main circuit on complete assembly. • Power frequency test of auxiliary and control circuit (2 kV r.m.s for 1 minute), • Partial discharge measurement test, before commissioning • Testing of on line monitoring systems and verification and calibration of various sensors, • Recording of leakage current in the surge counters. • Recording and analyzing of base line data of gas density, gas pressure, moisture, CF4 and

air in gas (offline) in CB sections. • Power frequency test on site assembled GIS • Other tests not mentioned specifically but required by IEC/IEEE.

13.2 Quality Assurance

Superior quality control system will assure high product quality. Only raw materials of the best commercial grade quality and high reliability are to be used in the manufacture of GIS. High reliability of materials ensures that maintenance work is kept to a minimum. A typical quality plan will have major components such as breakers, disconnecting switches, lightning arrestors, earth switches, etc. with in process inspection methods, tests, records, etc. Customer hold points will also be included in the quality plan, which shall be mutually agreed by the PURCHASER and VENDOR and approved.

13.2. Model Quality Assurence Plan

Model quality assurance plan document consist of formats which incorporate assembly, sub assembly and component wise tests/ checks to be carried out. % of such tests/ checks, reference to concerned documents, record formats, whether the tests are to be performed, witnessed or verified and what are the customer hold points (chps). these formats are placed at Annexure 4

Annexure 4 (Page 4/7)QUALITY ASSURANCE PLAN (MODEL)

PROJECT: ……………………………………………. CLIENT:NAME OF EQUIPMENT: Gas Insulated Switchgear VENDOR:

NIT/P.O. REFERENCE:

SR. NO.

ITEM/COMPONENTS & CHARACTERISTICS

NATURE OF CHECKS

QUANTUM OF CHECKS

REFERENCE DOCUMENTS/ ACCEPTANCE NORMS

RECORD FORMAT

Perform

A)

12

3a)b)c)

4a)

b)

c)

d)

CIRCUIT BREAKERRoutine TestsPressure Test on EnclosureGas Leakage Test

Auxiliary & Control CircuitWiring CheckHV Test (2kV for One Minute)IR Management

Mechanical Operation Test5 Open & 5 Close Operation at Minimum Supply Voltage and Minimum Pressure5 Open & 5 Close Operation at Minimum Supply Voltage and Minimum Pressure5 Close-Open Operating Cycles at Rated Supply Voltage and Rated PressureMeasurements of Operating Times.

Test-do-

VisualElectrical

-do-

Funtional

-do-

-do-

Measurement

100%-do-

-do--do--do-

-do-

-do-

-do-

-do-

Tech.Spec/ IEC:517-do-

Tech.Spec./Appd.Drg./IEC:517Tech.Spec./IEC:56 & 517

Tech.Spec./IEC:204

Tech.Spec./IEC:56 & 517

-do-

-do-

Tech.Spec./Appd.Drg.

JIRJIR

JIRJIRJIR

JIR

JIR

JIR

JIR

2/32/3

2/32/32/3

2/3

2/3

2/3

2/3

Note: a. In ‘Inspection Agency’ column figure 1,2, or 3 to be filled. 1-will indicate ‘Client’, 2-will indicate ‘supplier’ & 3-will indicate ‘sub-supplier’.

b. In ‘Remarks’ column following abbreviations shall be used – RR-Review of Records, T.C. – Test Certificate Submission & CHP – Customer Hold Point.

c. Test certificates shall be submitted at the time of final inspection.*CHP for 20% TC for 100%

Signature Signature & Seal(I&QA DEPT.) (VENDORS Q.C. DEPT. OR REPRESENTATIVE)



NIT/P.O. REFERENCE:

SR. NO.


NATURE OF CHECKS

QUANTUM OF CHECKS


RECORD FORMAT

Perform

5a)

b)

c)

d)e)

f)g)

Electrical TestsPower Frequency Voltage Dry Test on Main CircuitMeasurement of Contact Resistance of Main CircuitMeasurement of Resistance of Circuit Breaker Closing and Trip CoilsPartial Discharge MeasurementMeasurement of Power Consumption of Motor Operated Mechanism at Rated Supply VoltageOperational & Interlocks Check.Operational Check of Pressure Density Monitoring Switches

Electrical

Electrical

-do-

-do-Electrical

-do--do-

100%

-do-

-do-

-do--do-

-do--do-

-do-


Tech.Spec./Appd. Drg.

Tech.Spec./Appd. Drg.Tech.Spec./Appd. Drg.

Tech.Spec./IEC:517Tech.Spec./Appd. Drg.

JIR

JIR

JIR

JIRJIR

JIRJIR

2/3

2/3

2/3

2/32/3

2/32/3





Annexure 4 (Page3/7)QUALITY ASSURANCE PLAN (MODEL)


NIT/P.O. REFERENCE:

SR. NO.


NATURE OF CHECKS

QUANTUM OF CHECKS


RECORD FORMAT

Perform

B)

12

3a)b)c)

4a)

b)

c)

d)

5a)

b)

DISCONNECTORS & EARTHING SWITCHESRoutine TestsPressure Test on EnclosureGas Leakage Test

Auxiliary & Control CircuitWiring CheckHV Test (2kV for One Minute)IR Management

Mechanical Operation Test50 Operating Cycle at Rated Voltage 10 Operating Cycle at Minimum Voltage 10 Operating Cycle at Maximum Voltage Opening/ Closing Time

Electrical TestsPower Frequency Voltage Tests of the Main Circuit and Partial Discharge MeasurementMeasurement of the Resistance of Main Circuit

Test-do-

VisualElectrical

-do-

Electrical

-do-

-do-

Measurement

Electrical

-do-

100%-do-

-do--do--do-

-do-

-do-

-do-

-do-

-do-

-do-

Tech.Spec/ IEC:517-do-

Tech.Spec./Appd.Drg./IEC:517-do-

Tech.Spec./IEC:204


-do-

-do-

IEC: 56



JIRJIR

JIRJIRJIR

JIR

JIR

JIR

JIR

JIR

2/32/3

2/32/32/3

2/3

2/3

2/3

2/3

2/3




Signature Signature & Seal (I&QA DEPT.) (VENDORS Q.C. DEPT. OR REPRESENTATIVE)



NIT/P.O. REFERENCE:

SR. NO.


NATURE OF CHECKS

QUANTUM OF CHECKS


RECORD FORMAT

Perform

c)d)e)

6

C)

1

2345

6

Operation & Interlock check IR MeasurementMeasurement of Power Consumption of Motor

Driving Mechanism of Dis-connector & Earthing SwitchesRoutine Tests

CURRENT TRANSFORMERRoutine TestsVerification of Terminals Marketings.

Inter-Turn Over voltage Test.Test for AccuracyComposite Error TestPower Frequency Withstand Tests on Primary Winding and Partial Discharge MeasurementPower Frequency withstand Between Sections of Primary and Secondary Winding and on Secondary Winding

VisualElectrical

-do-

-do-

Visual

-do-Measurement

-do-Electrical

Electrical

100%-do--do-

-do-

100%

-do--do--do--do-

-do-

Tech.Spec./Appd.Drg.Tech.Spec./IEC:204

Tech.Spec./Appd.Drg.

Tech.Spec./Appd.Drg./IEC

Tech.Spec./Appd.Drg.IEC:44-1 & 185

-do--do--do--do-

-do-

JIRJIRJIR

TC

TC

TCTCTCTC

TC

2/32/32/3

2/3

2/3

2/32/32/32/3

2/3







NIT/P.O. REFERENCE:

SR. NO.


NATURE OF CHECKS

QUANTUM OF CHECKS


RECORD FORMAT

Perform

D)

12

3

4

5

6

E)

1

23

45

VOLTAGE TRANFORMER Routine TestsPressure & Gas Leakage TestVerification of Terminals Markings.

Power Frequency Withstand Tests on Primary Winding and Partial Discharge Measurement (150 % of rated max. phase voltage)Power Frequency Withstand Tests Between Sections and on Secondary Windings.Induced Over-voltage Withstand TestTest for Accuracy

SURGE ARRESTORRoutine TestsMeasurement of Reference VoltageResidual Voltage TestPartial Discharge & Contact Noise TestLeakage TestCurrent Distribution Test(For Multi Column Arrestor)

TestVisual

Electrical

-do-

-do-

Measurement

Electrical

-do--do-

TestElectrical

100%-do-

-do-

-do-

-do-

-do-

100%

-do--do-

-do--do-

Tech.Spec./IEC:517Tech.Spec./Appd.Drg./

IEC:44-2 & 186

Tech.Spec./IEC:44-2 & 186

-do-

-do-

Tech.Spec./IEC:44-2 & 186

Tech.Spec./IEC:99-4

-do--do-

-do--do-

TCTC

TC

TC

TC

TC

TC

TCTC

TCTC

2/32/3

2/3

2/3

2/3

2/3

2/3

2/32/3

2/32/3





Annexure 4 (Page 6/7)

QUALITY ASSURANCE PLAN (MODEL)


NIT/P.O. REFERENCE:

SR. NO.


NATURE OF CHECKS

QUANTUM OF CHECKS


RECORD FORMAT

Perform

12

3

4

F)1

23456

G)123

H)1

Acceptance TestsPressure Test on EnclosureLightning Impulse Redidual Voltage Test.Measurement of Power Frequency VoltagePartial Discharge Measurement

Local Control CubicleVisual & Dimensional Check

Checking of BOM and LayoutVerification of Correct WiringDielectric TestsIR MeasurementFunctional Tests by Simulation

EnclosureDimensionMechanical TestChemical Test

Aluminum for ConductorDimension

TestElectrical

-do-

Electrical

Visual/ Measurement

VisualElectrical

-do--do--do-

MeasurementMechanicalChemical

Measurement

-do--do-

-do-

100%

100%

-do--do--do--do--do-

100%Sample Plan

-do-

-do-

Tech.Spec./IEC:517Tech.Spec./IEC:99-4

-do-

Tech.Spec./IEC:99-4

Tech.Spec./Appd.Drg./IEC

-do--do--do--do--do-

-do--do--do-

-do-

TCTC

TC

TC

JIR

JIRJIRJIRJIR

TCTCTC

TC

2/32/3

2/3

2/3

2/3

2/32/32/32/3

2/32/32/3

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Annexure 4 (Page 7/7)

QUALITY ASSURANCE PLAN (MODEL)


NIT/P.O. REFERENCE:

SR. NO.


NATURE OF CHECKS

QUANTUM OF CHECKS


RECORD FORMAT

Perform

234I)12

3

J)123

4

K)

L)

Mechanical Test Chemical TestConductivityEpoxy InsulatorCreepage DistanceDry Power frequency withstand test & IR testBending Resistance Test

Other EquipmentsSF6 Gas Filling StationOn-line Gas Monitoring SystemMonitoring Equipment for Internal Arcing of Contacts.PRD for each Pressurized Section.

Checking of provision for necessary contact/ port for integration with plant SCADA.

Field TestsAs per Technical Specification

MechanicalChemicalElectrical

MeasurementElectrical

Mechanical

Test-do--do-

-do-

Visual

Test

Sample Plan-do--do-

-do--do-

-do-

100%-do--do-

-do-

-do-

-do-

-do--do-

-do--do-

-do-

-do--do-

-do-

-do-

-do-

TCTC

TCTC

TC

TCTC

TC

JIR

JIR

2/32/3

2/32/3

2/3

2/32/3

2/3

2/3

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Chapter-14As brought earlier, The GIS is practically trouble free and maintenance free. GIS requires only visual and external inspection till 20 years. Although negligible but few faults have occurred in GIS stations. Case studies of such incidents are listed in the following section

(Case Studies)

14.1 Chamera-1 Power Station

14.1.1 Description of the Project Chamera-1 is located at khairi about 30km away from Dalhousie in District Chamba of Himachal Pradesh. Project consist of three machines of 180MW each. This is a poundage runoff river scheme and utilise the water of Ravi river . The power generated by chamera project is evacuated through 400KVdouble circuit to Kishanpur. Chamera Power Station is provided with 400 KV GIS with 3 nos incoming from 3 nos generating Units of 180 MW each and 2 nos transmission lines emaninating from GIS and connecting to 400 KV Kishanpur Substation. GIS is provided with double bus bar scheme with a bus coupler. The project has been commissioned in 1994

The rated electrical parameters of GIS are as under:

Rated Voltage : 420KVRated Frequency : 50HzL.I withstand voltage : 1425KVP.F withstand voltage : 520KVL.I. withstand voltage : 1050KVRated current busbar : 2000ARated current bays : 2000ARated short time for 01 sec. : 40KARated short circuit breaking current 40KA

The no. of operations of circuit breakers installed at various bays till date of failure were as followsUnit #1 321 nosUnit #2 374 nosUnit#3 257 nosBus coupler 082nosLine # 1 307 nosLine # 2 343 nosThese operations of breakers have been performed during running of machines for hours as follows:Unit # 1 : 8648 hrs.Unit # 2 : 10479 hrs.Unit # 3 : 8682 hrs.

14.1.2 The Incident Details On 05.02.1996 Gen. - 2was stopped at 11:08 hrs. it was again started at 17:02 hours to meet the peek demand. Only this machine i.e. unit no. 2 was in operation due to less inflow. The generator was synchronized at 17:12 hrs on bus bar no. 2. At the time of synchronization both the 400KV lines were on this bus –bars At 17:00 hrs the voltage at line-1, line-2 and bus-2 was 400KV. Only generation was 90MW as the water available was only for this generation. At 17:26hrs. hose are connected 400KV breakers i.e. line 1, line 2 and generator #2. Tripped through bus bar differential protection. machine also tripped due to operation of generator lock out relay (86G and 86S2) which operated consequent to operation of generator transformer REF relay as well as the busbar differential protection relay.

Investigation of fault: As a first check the IR valves of section were taken.The details of which are as under

Busbar (with 5kv megger)R-Phase : 8000MOhmY-Phase : 3200MohmB-Phase : 3200Mohm

Transformer HV + 400kv oil filled cable transformer neutral disconnected.\

All three phases together: 5000Mohm

Generator-2 stator winding + bus duct + transformer LV (General neutral disconnecting and all P.T’s disconnected.

8Mohm at 5KV40Mohm at 1KV

On next morning an alarm Generator-2 SF6 gas chamber trouble appeared at SER. It was found by maintenance crew that SF6 gas is leaking from Generator-2 CT isolator junction. So, generator -3 which was running was closed and Line-1 and Line-2 were also tripped. After ensuring whole GIS is dead, gas pressure of various chambers were taken and it was found that gas pressure of breaker chamber and isolator chambers is equal at 6:00 kg/cm2 against normal value of 6.5 kg/cm2

To further investigate, the cause of fault circuit breaker contact resistance of all three phases were measured. The values observed are as follows :R-Phase: 300 micro ohm.Y-Phase: 520 micro ohm.B-Phase: 300 micro ohm.These values were compared with resistance value of identical Generator-3 circuit

breaker and it was inferred that some arcing might have taken place in Y-Phase of Generator-2 circuit breaker which showed higher contact resistance. It was decided that faulty section calls for inspection and there is definite indication of a fault.

14.1.3 Observations/Extent of Damage- DetailsA. CT/ISOLATOR MODULE, POLE-Y i Gas Tight Bushing

The inspection cover of isolator module was opened first, to inspect the top side of the bushing. Only minor traces of white decomposition produce of SF6 at open patch were observed. Otherwise, it looked normal from top side.After this, front side cover of CB chamber was opened. From this side bottom portion of the bushing was visible. It was found burnt and looked completely black. Burnt-out material from bushing had fallen on the bottom surface of circuit breaker housing, on the interrupter casing (break vessel) and capacitor.After disconnecting the flexible connection between CB & CT the CT- isolator module was isolated by dismantling it from the rest of GIS. Thereafter, gas tight bushing was removed after dismantling the CT -isolator module. The bushing was then inspected minutely. A hairline crack was observed on top side of bushing running few millimeters away from conductor to bottom side

of bushing had two characteristic flashover paths due to flashover. Two channels has been formed along these characteristic flashover paths due to burning of epoxy. These channels started from conductor and ended near outer flange. Flashover signs were found on outer flange. The burnt epoxy busted away intact leaving behind a smooth

surface as if it had no bond with channel surface. A third flashover mark was also found, however, epoxy was intact there. Crack on this side was more thicker than that on top side. To observe further, bushing was radiographically examined and it was found that crack has developed in angled plane. O-rings on both sides of bushing were found O.K.

ii Current TransformerWhole of the CT was covered with black epoxy ash due to burning of epoxy. Flashover signs on CT electrode and conductor were observed. However no major damage was noticed and it needed rectification only by cleaning and polishing of flash over points.

B. CIRCUIT BREAKER MODULE, POLE-Yi Lot of ash/black dust of burnt material fallen from the burnt gas tight bushing was found on the surface of circuit breaker housing. Flash-over marks at the bottom of housing as well as on the top of housing near the flexible connector between CT & CB were observed. After cleaning, it was observed that damage due to flashover was not severe and housing could be used after with proper cleaning, polishing and painting.ii Outer surface of break vessel of circuit breaker interrupter unit of CT side (unit end) found damaged due to burning and required to be replaced.iii Capacitor circuit breaker interrupter unit was found burnt on outside surface. However its capacitance value was to be normal. Due to burning on outside surface, the dialectic strength of capacitor was not known required replacement.iv Deep flashover marks at shields of circuit breaker interrupter unit of CT side were observed. These shields required to be replaced.v After opening CT interrupter unit assembly it was observed that Circuit Breaker contacts were normal and there was no sign of flash over on mese contacts. The damaged components of the circuit breaker modules are marked a.vi Burnt epoxy in powder form found on post insulator mounting arrangement after removal of it and required cleaning.

C. R&B POLE MODULES OF CB & ISOLATORR&B poles of circuit breaker module as well as isolator module were inspected by opening rupture diaphragm of circuit breaker and inspection cover of isolator. There was no trace of any flashover or carbon deposits over these modules and no smell was noticed suggesting that mese poles were healthy.It appears that fault had initiated on account of failure of gas tight bushing in Y-pole. The burnt material from this bushing had called on the CB interrupter assembly and this material has caused further flash over between Circuit Breaker shields and between liver parts and earth.

8.1.4 FAULT ANALYSISAll the records and observations were analyzed to establish the reason of fault. The analysis of records and observations with specific reference to GIS are discussed below:

8.1.4.1 The behavior of protection was analyzed and found in conformity to the schemes implemented.14.1.4.2 Analysis of SF6 Gas Leakage:

The gas leakage was detected next day in morning when the related alarm appeared on SER. Before that no leakage of gas or any smell was noticed by maintenance crew trying to find out the reasons of trippings. Log book records of gas pressure readings also read the pressure normal even after 12 hours of tripping. Due to crack gas started seeping to isolator chamber from circuit breaker chamber because of differential pressure between chambers. As the crack was hairline crack, it took a longer time to reach the equilibrium and alarm appeared when gas pressure in chamber reached alarm level of 5.7 kg/cm2. The movement of gas might have displaced the O-ring on circuit breaker side near crack point resulting in leakage of gas to atmosphere through flange joint. The point at this location must have fissured with this leakage with time and leakage became appreciable. The smell of gas indicated that gas has been composed due to arcing as normal SF6 gas was colourless.

14.1.4.3 Analysis of observations after opening of faulty section:It was observed that maximum burning took place in the gas tight bushing which is located just above the CT isolating the gas tight chambers. The flashover caused formation of two channels along the flashover characteristic path as seen in photograph. The separation of burnt epoxy from the bushing might have taken place due to arc

travelling few millimeters below the CT side surface of bushing in turn bursting out the epoxy. Crack which runs from the conductor upto the metallic flange had also consequently developed in the bushing. It was found from the inspection of interrupter unit that, no flashover had taken place inside the interrupter unit and the contacts of the interrupter were healthy. Therefore, it was concluded mat fault was not initiated inside the circuit breaker. Burning over the outside surface of breaker vessel of interrupter unit and the flash over marks on the shields of breaker were due to falling of burnt material from the gas tight bushing. That is why burning over the surface of break vessel has taken on plate just below the gas tight bushing only. The two flash over right from the conductor upto the metallic flange (earthed part) indicate the path of arc travel from live part to earth. Due to heat of the arc the epoxy insulation has burnt and deep cavities have been formed on CT side of gas tight bushing. Initial flashover must have occurred along these two paths only. Therefore, it can be said with reasonable certainty that fault must have started from the failure of gas tight bushing only. Once the arcing started at the gas tight bushing, the gas near the CT area must have got ionized immediately. The falling burnt material too must have caused sparking/flashover over the surface of CT electrodes and over the circuit breaker shields and grading capacitor. Due to this faults had developed on both sides of generator CT and the relays which are looking towards 400 kv bus bar (BB differential relay) as well as towards generator transformer (transformer REF and 400 kv cable differential relay) operated. Analysis based on SER record also corroborates this analysis. Due to cracking of gas tight bushing leakage of SF6 gas from circuit breaker chamber to isolator chamber took place.

The above analysis establishes that the fault had occurred due to failure of gas tight bushing between circuit breaker and isolator chamber.

14.1.5 Probable reasons of failure of gas tight bushingAs described earlier, two zig-zag cavities have been formed on bottom side of bushing between live part and earth due to fiashover along the fiashover characteristic path. It is not certain how and why the bushing failed. Some of the probable causes of failure are discussed as below:i) Failure due to over voltage,ii) Mai- operationiii) SF6 Gas Qualityiv) Manufacturing defect.All these causes and their possibilities are discussed in detail as below:

Failure due to over-voltageBushing can fail due to application of over voltage more than its withstand voltage level. However this reason for failure was ruled out as this bushings was rated for 550 kv system voltage. These were tested for 5 minute power frequency withstands voltage of 740 kv (phase to earth). There was no over voltage at the time of fault as confirmed by the following :

- Voltage recorded by the DR indicates normal voltage.

- No overvoltage relay operated though following overvoltage relays were in circuit:

L-1 O/V Relay - Setting - 1.1 pu Time 5 Sec.L-2 O/V Relay - Setting - 1.1 pu Time 5 Sec.Gen-2 O/L Relay Setting - 1.1 pu Time 3.1Sec.- Instantaneous O/V.- on both lines did not operate.- Since generator was on bar, surge arrestors provided on busbar were in circuit.- No high voltage were recorded by DFR of remote end of the line.

Mal-operationThe tripping occurred while machine was on bar at 90 mw in synchronization with the grid for about 14 minutes. Since, no operation was carried out after the synchronization, chances of any mal-operation are ruled-out.

Quality of SF6 gas (Initial & as filled)Failure may also occur if the moisture content in the SF6 gas is more than the prescribed limit or if the filters provided in the circuit breaker chamber are not effective in absorbing moisture and decomposition products of SF6 gas. Some of decomposition products of SF6 gas does not recombine and are absorbed by the filters provided in the circuit breaker chamber was noticed that dew point of the circuit breaker chambers were low at the time of handing over of G1S for charging and of this particular chamber was less than the prescribed level (- 5 deg. C as against - 7 deg. C minimum and - 15 deg. C normal at working pressure i.e. 6.5 kg./cm2). The manufacturer representative released this for as safe for charging the system. The dew points were measured after 3 mondts for further action. These values were found safe and supplied filters were working. Dew point of the leftover gas in CB chamber (at 0.6 kg/cm2), was also measured after fault & draining off of gas, was found to be - 22 deg. C at 0.6 kg/cm2 which equivalents to - 14 deg. C at working pressure i.e. 6.5 kg/cm2.The ambient temperature at GIS Hall does not fall below 10 deg. C and hence dew point of value of even - 5 deg. C at working pressure was considered good enough and could not be attributed to be a reason of failure.

Manufacturing defectThis appears to be most probable cause of bushing failure. Either inherent manufacturing defect or poor composition of epoxy resin has caused the premature fatigue failure of the bushing. Radiographic examination of the bushing was done at site which showed that crack developed in bushing is through out from central conductor to few millimeters before outer flange and at an angled plane to the bushing surface. No other abnormalities could be noticed from the X-ray prints.The isolator and CT modules came in assembled condition and this bushing was factory assembled. The bushing had passed all factory tests successfully and had withstood 740 kv for 5 minutes and particle discharge intensity at 605 kv was less than 1 pC.

14.1.6 ACTION TAKEN FOR RESTORATIONIt became clear that there is a fault inside the Y-phase of Unit-2 GIS breaker and gas leakage was observed from the CT/lsolator flange joint in between which gas tight bushing is sandwiched.On dismantling the faulty section, it was observed that gas tight bushing had failed and required replacement the faulty section was isolated. Break vessel of circuit breaker interrupter unit and grading capacitor connected across this interrupter had also got burnt due to flash over.The faulty portios were replaced and assembly of the dismantled sections was completed thereafter and after filling of gas the bay was tested and charged successfully.

14.1.7 RecommendationsThe analysis has established that failure of gas tight bushing was the reason leading to the fault. However, exact cause of failure of bushing is still to be ascertained for which foiled bushing was examined. It was the first failure of such kind of bushing known. Though probability of such failure is very very low but cannot be ruled out in totality. However, to minimize the chances of such kind of failure following remedial measures are suggested :

(a) SF6 gas acts as an insulation as well as arc-quenching medium and its proper quality is a must to avoid any kind of failure.

(b) Density monitor is to be provided for eachchamber for detection of leakage of gas.

(c) As Chambers are sealed, manufacturedprescribe checking of gas quality only afterten years when first "routine inspection"becomes due.

d) Quite a few leakage's though very minor way noticed after commissioning which way result in frequent topping-up of with gas in affected chamber till the leakage is checked, once leakage starts chances of ingress of moisture cannot be ruled-out as partial pressure of water vapour in atmosphere remains quite high in comparison to that of inside in chamber dew point of affected chamber should be taken periodically.

e) It would be advisable to measure dew point of each chamber annually and dry out the gas if necessary.

(I) Gas should also be checked annually for SF6percentage and decomposition products and corrective measures taken if necessary. However there should be a considerable time gap between last switching operation and measurement. Monitoring of health and deterioration of insulation is a possible way which can be done by periodical partial discharge measurement. Partial discharge measurement is an important part of the quality assurance system in the production process but on-site measurement was not practicable till then.

(g) The diagnostic method for on-line partialdischarge measurement now in use is VHP (30-300 MHz), UHF (300-3000 MHz) and acoustic methods instead of conventional electrical measurement with coupling capacitor. Feasibility of installing the on-line monitoring system in GIS in the view of authors should not be ignored.Besides, there are several other vital points/factors which need due attention to avoid/minimize chances of occurrence of similar kind of faults and reduce shutdown period in case of a fault/breakdown These points/factors are discussed in details along with remedial measures as below :

A. Monitoring, Logging & Recording of data/eventsi) There was no time synchronization between DFR and SER. As a result, co-relationbetween events recorded by DFR and SER at me time of fault become time consuming and confusing. Master clock which was provided in the CMR panel for time synchronization could be commissioned by the manufacturer's engineer only at a later date.

ii) It was noticed that the exact time of occurrence of "SF6 gas pressure rising" alarm was not recorded at GIS or at control room. Print outs of,SER was also not taken though it is a vital alarm. The SER has memory to record 1999 events and it washes-off the first event, on occurrence of 2000m event. It would be better if daily print out of events are taken after 24 hrs and hard copy kept in record. Possibility of installing additional memory/drive to make back-up should also be considered so that events of past can be retrieved easily for reference and analysis.

iii) Leakage of gas which was notices through smell and was a vital event was not found recorded in shift instruction book being maintained at control room. Such kind of occurrence is abnormal and shift engineers should taken due attention of any such incident and record it in instruction book.

iv) The occurrence of "Gas filled chamber SF6 pressure rising" alarm was acknowledged and hooter was silenced but this was not recorded in log book./shift instruction register. Time of appearance of vital alarms at facia and their acknowledgement should be recorded in long book/shift instruction register.

v) Cumulative no. of operations of each circuit breakers should be recorded at control room at each time of breaker operation besides its recording through counter at GIS panel for cross check and reference in future. In case of fault trippings, the magnitude of fault further permissible number of interruptions of that breaker(s). this is required to determine when "contact system check" of breaker contacts id due as no. of interruptions and interrupted fault current determine the extent of deterioration of breaker contacts.

vi) The recording of data in various log books being maintained at power house should be checked in each shift by the shift engineer for correctness of proper entry. These log books should also be scrutinized periodically by respective maintenance engineer to ensure that log books are properly maintained and serve the purpose they are intended for.

vii) History sheet/book for each equipment/panel installed at power house should be maintained mentioning the running hours, down time, planned/forced maintenance done, spare parts consumed etc., in chronological

viii) Order for reference and use: to investigate/establish the reason of fault/breakdown occurring to equipment/components, inferred to cause of trouble etc., to taken preventive maintenance on basis of

ix) Statistical data base developed for the equipment/plan. It will also help in planning of spares required for O&M of equipment and plant.

14.2 DHAULIGANGA POWER STATION

14.2.1 Brief Description of Power Station:

Dhauliganga Power Station is the first big power station in Kumaon Region of Uttarakhand. The Power Station is situated in Tehsil Dharchula, Pithoragarh district in the state of Uttarakhand, about 370 Kms. from Bareilly and 315 Kms. from Haldwani by road. The power station with an installed capacity of 4x70 MW, is a run-of –the river with pondage scheme on the river Dhauliganga which is a tributary of the river Kali. Brief description of the major components of the power station is given below:

Power house :

It is an underground power house having four vertical type generating units of 70 MW. The Francis type turbines utilize a net head of 297 m with rated output of 73 MW at a design discharge 26.75 cumecs, rotating at a rated speed of 428.6 rpm. 78 MVA, 0.9 pf, 50 Hz, 14 poles generator is coupled to the turbine shaft, generating power at a voltage of 11 KV. This voltage is stepped up to 220 KV by 12 nos. Single phase 29 MVA power transformers located in transformer cavern. 220 KV GIS with double busbar arrangement is installed for switching operation. Power is evacuated through 233 Km. double circuit transmission line to Bareilly, connected to Northern Grid. The GIS is connected to outdoor potyard through 220 KV XLPE cables. Water after turning the turbine is discharged through in to Relugad nallah through four nos. draft tubes and 445 m long 6.5 m dia Tail race tunnel.

14.2.2 Details of Gas Insulated Switchgear:

A 220 KV SF6, Gas-Insulated Switchgear having double bus bar arrangement is installed in the GIS hall for switching operation from generating unit to transmission lines.

The GIS includes

o Four Unit bays

o Two Line bays

o One Bus coupler bay

o One two core Voltage transformer 220 KV/√3 / 110/√3 in each bus bar for synchronization purpose.

o Earthing switches – Normal & High speed type

o Isolators

o Multi core, 1A sec., single phase Current transformers

o Surge arrestors for unit bays

Main specifications are:-

o Manufacturer : Areva Ltd., France

o GIS Type : B105

o Rated voltage, rms : 245 KV

o Rated frequency, Hz : 50

o Rated continuous current, rms : 2000 A

o Rated short circuit current . : 40 KA for 1 s

o Power frequency 1 minute withstand voltage : 460 KV

o Rated lightning impulse with stand voltage : 1050 KV (peak)

o Gas Pressure Rated/Alarm/Trip, bar : 6.3 / 5.8 / 5.5 (20oC)

14.2.3 Major Faults

Major fault has occurred twice in the GIS system of Dhauliganga Power station.

The first fault occurred on 21.06.2006, in the Y phase pole of Circuit breaker of Unit – 4. During normal stopping of the unit, the breaker failed to interrupt the flow of current even though its pole has opened.

The second fault occurred on 20.03.2008, in the bus bar – 1 underneath the bellow portion belonging to Unit – 3. A flashover occurred in the busbar leading to creation of a hole in the bellow causing leakage of SF6 gas.

14.2.4.1 REPORT ON GIS CIRCUIT BREAKER FAILIURE - UNIT 4

Date of Fault - 21.06.2006Component failed - Circuit Breaker of Unit – 4 Y Phase.

14.2.4.1.1 Nature of fault Unit – 4 was running and given stopping command as per grid schedule. The load got gradually reduced and unit circuit breaker opened at about 3 MW load. Filed

breaker also opened subsequently. Suddenly emergency tripping was issued by protection relays. All the other units & line

synchronized in the same busbar as of unit – 4 were tripped by bus bar differential relay.

14.2.4.1.2 Details of Tripping Generator protection relays (two nos.) - Micom P343 initiated the unit tripping through ‘Field

failure’ protection. Feeder management relay - Micom P141 initiated the ‘Breaker failure’ trip. On reception of ‘Breaker failure’ trip signal, the Bus bar Protection relay – DIFB issued

tripping signals to all the Units & Line synchronized with the same bus bar as of Unit – 4.

14.2.4.1.3 Preliminary Observations: All the three poles are shown as ‘Open’ in the UCB local position indicator. Auxiliary contacts of CB also indicated CB ‘Open’ status. Generator protection relays has recorded current in two phases viz. Y & B, whereas, no flow

was recorded in R phase. Bus bar protection relay detected fault in the Bus bar on reception of ‘Breaker failure’ signal

from Micom P141 relay. IR value measurement of circuit breaker was done for all the three phases. The IR value of Y

phase was found very less, indicating a breaker failure. Remaining two phases showed a high IR value.

This suggested that CB has failed to open on receiving the trip signal. The poles are fully opened, but some loose / broken material inside the compartment is maintaining the contact.

The ‘Field failure’ tripping was issued by the relay because, as the field breaker was opened (as per stopping sequence) but stator is connected to grid through failed CB contacts. The rotor was drawing the reactive power from stator, leading to excitation failure condition.

14.2.4.1.4 Rectification WorksThe following rectification works were carried out by the OEM, M/s Areva T&D Ltd. The circuit breaker active part (Y phase) was removed from the compartment after emptying

the SF6 gas. It was found that nozzle of the active part of CB was broken. This has caused the continuous

flow of current in spite of opened pole condition.

As no spare CB was available, to ensure early restoration of unit, it was decided to replace the damaged unit CB with the B Ph. pole of Bus coupler CB.

Accordingly, the Bus coupler bay was taken under planned shutdown. The active part the Unit-4 Y Ph. CB was replaced entirely with active part of Buscoupler B Ph.

Gas was re-filled in the Unit – 4 Y-Ph. compartments as per filling procedure. IR value measurement was done for repaired Unit – 4 Y phase pole and found Ok.

Circuit breaker was operated 50 times manually as a testing procedure. Gas was emptied again and visual inspection of active part was done by removing the rupture disc. No loose materials or abnormal was found inside the compartment.

Gas was re-filled in the CB compartment. CB closing & opening times were recorded for all the three phases and found within limits.

Restoration of Unit – 4 was done after conditioning the CB compartment for one hour by charging from the bus bar end. Visual checks were done around the breaker and no abnormal was found / heard during this conditioning period.

Unit-4 was started and synchronized through Bus bar – 1 successfully on 06.07.2006..

M/s Areva informed that all the three poles of the Unit – 4 CB shall be replaced by them to eliminate any doubts regarding the condition of balance two poles. Accordingly, after receipt of 3 nos. new active parts at site later, all the three poles of Unit – 4 were replaced with new active parts. Bus coupler B-Ph pole was refitted with its original active part removed from Unit-4. Contact resistance of the CB of Unit – 4 & Bus coupler was measured and found within limits.

Bus coupler bay was restored after filling of gas and measurement of IR.

14.2.4.1.5 Cause of FaultFollowing conclusion was given by Areva Ltd., for the causes of failure, after detailed investigation on the faulty CB sent to their factory,:

Several indices show that the rupture of nozzle would have been caused by abnormally high mechanical constraints in torsion on the level of fixing for the transmission of movement.

The chamber has traces and impacts of shocks testifying to a nontraditional operation at the time of CB operation.

The origin of the defect is difficult to determine and investigation report is in conclusive.

14.2.4.2 DETAILS OF FAULTS:

Flash-over of GIS bus bar- unit 3 occurred on 20.03.2008 with the result Isolator compartment of Y- phase of Bus bar-1 of Unit 3 failed.

14.2.4.2.1 Nature of fault

Line 2, Unit 1, & Unit 2 were closed & synchronized through Bus 1. Line 1 & Unit 4 were closed & synchronized through Bus 2. Unit – 3 was in stop condition with Bus 1 Isolator closed. Fault was detected by Bus bar protection relay – DIFB in Bus -1. Subsequently Unit-1, Unit-2 & Line-2 was tripped by bus bar protection relay.

14.2.4.2.2 Details of Tripping

Fault was detected by Bus bar protection relay DIFBCL in Zone1 (Bus 1) Trip command issued from Bus bar Diff. protection to Unit - 1 Trip command issued from Bus bar Diff. protection to Unit – 2 Trip command issued from Bus bar Diff. protection to Line – 2 Trip command issued from Bus bar Diff. protection to Bus coupler SF6 pressure Stage – 1 level (5.8 bar) fault detected in Unit 3 G1 Compartment indicated

by GIS Local control cubicle. SF6 pressure Stage – 2 level (5.5 bar) Fault detected in Unit 3 G1 Compartment

indicated by GIS Local control cubicle.

14.2.4.2.3 Preliminary observations

Immediately after the occurrence of fault the following were noticed.

Heavy leakage of SF6 gas from Busbar 1 Isolator compartment of unit 3 was felt by noise and pungent smell.

Local Control Cubicle (LCC) of unit – 3 in GIS has issued SF6 stage - 1 & 2 Fault alarm for G1 compartment.

On checking the gas alarm in LCC, it was found that alarm is issued from Yph. Isolator of Bus 1.

Alarms read on Line protection relay Micom P442 also indicated fault has occurred in Y ph.

Deposition of decomposed material was observed through the sight glass window in Yph. G1 compartment.

14.2.4.2.4 Investigations done by Manufacturer (Areva Ltd.)

Investigation was done by M/s Areva T&D Ltd., the OEM from 24/03/2008 and following were observed.

Rupture disc of faulty compartment G1 found in good condition & not broken, suggesting that no undue rise in gas pressure in the compartment has occurred & leakage has not taken place through rupture disc.

A small hole was found in the top side of the expansion BELLOW installed in the G1 compartment of Y Phase – Unit-3. This suggested that arcing has occurred underneath the bellow portion creating a hole and gas has leaked through.

On 30/03/2008, further checks were done and following activities were carried out: Acidity test & moisture content test in the adjacent compartments viz. U#4 G1 Y-phase,

U#3 G9 Y phase and U#2 G1 Y phase was done to check occurrence of any leakage in the cone insulator which may lead to mixing of gases belonging to two different compartments. The tests results were good and found within limits.

Gas Pressure in the adjacent compartments were measured and found within limits. The damaged bellow assembly along with the enclosure was dismantled for inspection of

bus bar. Checks revealed that arcing has occurred in the sleeve connecting fixed electrode and

bus bar. Two no. closed insulators, bus bars and fixed electrodes were also found damaged. The compartments where the assembly has been dismantled were covered by blank

plates. This initial investigation suggested that bad contact between bus bar joining sleeve and

fixed electrode might have caused the arcing leading to flashover through bellow.

14.2.4.2.5 Repair works done: The repair works started from 25.04.2008 after receipt of replacement spare parts & HV

testing kit. Damaged parts were replaced.

HV test of Bus bar1, Y phase was conducted successfully on 09.05.2008. Restoration of Bus bar 1 done and charged on 10.05.2008.

Components replacedFollowing GIS components in Bus bar 1, Y Phase were replaced.a. Disconnector for Unit-3 G1 compartment.b. Active part / contact of Disconnector for Unit-4 G1 compartment.c. Closed cone/insulator & fixed contacts near bellow of Unit-3 bus G1 compartment.d. Closed cone/insulator, fixed contacts & tulip contacts for Unit-3 disconnector.e. Bus bar & sleeves in Unit-3 bus G1 compartment.f. Expansion bellow in Y Phase.

Special Tools & instruments used:1. Gas handling equipment2. SF6 decomposition tester3. SF6 Dew point measurement meter4. SF6 purity tester5. Contact resistance measurement kit (250 Amp.)6. Digital pressure gauge.7. Standard tools for GIS maintenance.

14.2.4.2.6 Cause of Fault:After detailed investigation, Areva T&D Ltd. has stated that the root cause for the flash

over is:

1. The flash was clearly due to bad electrical contact between sleeve and fixed electrode.

2. The lack of electrical contact was due to wrong location of the sleeve to fixed electrode.

3. Assembling mistake is most likely the reason for this defect caused by wrong location of the sleeve.

14.2.4.2.7 Preventive measures taken:

As part of preventive action, the busbar sleeves located inside the bellow of R & B phases of Bus bar – 1 were inspected, after removing the gas. The sleeve junction was found in good condition and showed no sign of movement.

Checking of the sleeve condition in the bus bar- 2 of R, Y & B phases were also done and found in good condition.

Date of restorationAfter the completion of rectification works, Unit – 3 was restored & synchronized on 06.05.2008 through bus bar – 2.

CHAPTER- 15

MONITORING OPERATION AND MAINTENANCE

As per manufactures Gas Insulated Switchgear is supposed to be maintenance free for initial 20 years or atleast 20000 of operation but the instances have come that GIS also have maintenance problem even before 20 years. In order to keep the GIS in healthy condition the monitoring of GIS has to be carried out sincerely which will enhance the performance of GIS .

15.1 Monitoring 15.1.1 Monitoring during manufacturing, QA records/test and inspection requirements

a) It is required to be ensured that type tests have been successfully carried out and have been suitably documented for the model of switchgear proposed for adoption . The co-relation of model of CB and MOM mechanism is required to be ensured while adopting typical configuration

b) Routine tests as per applicable standards are to be successfully carried out if not specified w.r.t IEC provisions. Special tests need be decided between the manufacturer and the purchaser prior to placement of award. Routine factory tests required to be ensured for a quality GIS would include

- Pressure test on each enclosure . At two times for cast housings and 1.5 times for welded housings of the design pressure.

- Gas type bushings between the gas compartments must be able to withstand twice the service gas pressure at one side and zero bar (absolute on the other)

- At least 10% of all welds must be subjected to non destructive ultrasonic or equivalent testing .

- Partial Discharge test on each insulator before installation in the switchgear ensuring less than 10pC on the insulator at 110% rated voltage

- Gas leakage test on each transport unit before dispatch.

15.1.2 Monitoring during storage

Sulphur hexafluoride is transported as a pressurized liquefied gas. The containers ideally should not be exposed to direct sunlight and must be secured against over turning or rolling. Storage and work areas must be well ventilated in particular ventilation must be affected at ground level on account of fact that gas vapour is heavier than air . If the gas is stored underground appropriate forced ventilation should be provided . The packages immediately after receipt are to be checked for soundness and kept in secured area. It is recommended to open the material in the containers in front of the supervisory engineer in a desired sequence to ensure smooth erection . Six bay 400 KV GIS having double bus scheme as an example was packed in 73 containers . In case the sequence and packing details are seen carefully the erection time for the GIS could be about 3-4 months.

15.1.3 Monitoring during installation

For, handling the switchgear during installation a 2 ton crane or hoist is usually considered sufficient . Although, the engineering itself could minimize installation/assembly work at site preference is required to be given to completely factory assembled switchgear bays which require connection of cables or overhead line on site only. In fact 220KV bay with double bus configuration duly assembled can be transported on a normal trailer to site of erection Precautions against ingress of impurities are required to be taken during installation and hence the packing of material is required to be commensurate with type of installation indoor or outdoor. In case of indoor installation where packing is not suitable for outdoor

applications, it is recommended to have filtered pressurized air in the GIS hall during installation

The handling equipment for the gas should consist of main components such as SF6 compressor, vacuum pump, storage tank, evaporator and filter unit, which are connected together with valves and fitting. Depending upon the size of switchgear appropriate equipment with sufficient storage capacity and performance is selected based on two largest gas section capacity in the installation. SF6 gas in GIS is carried out in closed cycles. The life of GIS is largely depend on quality of gas. Every component with in closed cycle are to undergo dry running and therefore, absolutely oil free without a chance of gas getting contaminated. The build in filters provide for the drying and cleaning of gas during each gas operation. In fact gas valve couplings and fittings themselves ensure a high degree of leak tightness and operational safety. When selecting an equipment, it should be ensured that couplings are self closing type in order to avoid air and moisture penetrating due to the lines. A maintenance equipment with automatic sequence could be the state of art and should be referred because of its high degree of operational safety. It is necessary, to monitor parameters of gas filled in the GIS.

15.2 Maintenance of GIS

15.2.1 Before taking up the maintenance of GIS, recommended safety rules from the manufacturer are required to be adhered to. Some of them are listed below but, it is recommended to integrate with recommendations of manufacturer of GIS.

(a) The maintenance programme and time based intervals specified/no. of operations whichever is earlier to form the basis of maintenance. A schedule as recommended by one of GIS supplier showing the interval of visual/minor/major/Preventive maintenance inspection is given as under.

INSPECTION OVERVIEW

Action SF6-Gas Circuit Breaker

Disconnector earthing switch

Make-Proof earthing switch

Performed by

Visual Inspection

Once a year Once a year Once a year Station personnel

Minor Inspection

Every 4 to 6 years

Every 4 to 6 years

Every 4 to 6 years

Every 4 to 6 years

Station personnel

Major Inspection

-

Every 12 to 18 years or after 5000 switching cycles

-Every 12 to 18 years or after 5000 switching cycles

Manufacturer or specially trained personnel of station operator

Preventive Maintenance

Depending on the result of the above inspection

-Depending on the result of the above inspection-Every 15 to 20 years -After cumulated short-circuit current

-Depending on the result of above the inspection-After 10,000 operation-After completion of 100 closr/open cycles by bus transfer current switching by disconnector.

-Depending on the result of above the inspection-After 5,000 operation-After closing on short circuit current-After completion of 100 closr/open cycles by current inducted through parallel lines.

Manufacturer or specially trained personnel of station operator

Manufacturer’s Recommendations

To keep a GIS substation in good working condition , following is recommended for inspection and maintenance:-M1 : Every Year , a visual inspection of the energized substation must be performed.-M2 : Every 4 to 6 years , a minor examination (Control and Cleaning) .-M4 : Every 12 to 18 Years , a minor examination ( Controls, adjustments, lubrication and eventual replacement of parts easy of access) must be performed.-M5 : The fifth level maintenance (equipment repair ) is exceptional ,as the type tests performed in laboratory have shown the GIS equipment could be used for almost 25 years without reaching the wear limits.

It is recommended the manufacturer be referred to carry out fifth level maintenance on the following.

Circuit breakers: Repair depends on the number of operations performed and of the value of breaking currents. Manufacturer to open the circuit –breaker and to repair contacts when the operations number or when electrical wear limits which are indicated in the circuit-breaker maintenance section are reached.

Disconnectors : Checking of contacts and replacement of fuse pins when the number of operations which is indicated in the disconnector maintenance section is reached.

(b) Whenever maintenance is taken up, it is essential to employ the authorized personal: -

Define and discuss in advance the maintenance to be performed and the relative hazards. Proper formatted record sheets to be prepared.

Use parts only supplied by Original Equipment Manufacturers (OEM). It is necessary to identify the equipment which is required to be maintained. Ensure that it

is in de-energized/degassed condition. It is essential to make sure that the equipment is earthed on all sides of the work-zone. The work-zone should be barricated and operator should have necessary protective

clothing and recommended safety devices. It is required to be ensured that necessary maintenance equipment such as slings,

platforms, scaffoldings and electrical equipments/tools are in proper shape.

15.2.2 Condition Monitoring of GIS

Generally GIS requires no or very little maintenance and monitoring the SF6 gas pressure and quality is considered sufficient. For maintenance of the GIS, regular inspections, routine scheduled maintenance and overhaul maintenance are specified by the manufacturers.

The maintenance to be carried out and their periodicity is indicated in the “Maintenance Schedule” given below Manufacturer’s instructions are to be followed for special tests, if any, for that particular make of GIS substation.

Recommended Maintenance Schedule is given at as under below

MAINTENANCE SCHEDULE OF GAS INSULATED SWITCHGEAR

Yearly Visual Inspection

Following visual inspection of the energized substation must be performed:

Activity

(i) SF6 pressure with permanent manometer (if applicable)

(ii) Oil level in tank (Operating mechanism)

(iii) Hydraulic circuits tightness (Operating mechanism)

(iv)

Oil level in damping device (CB with spring operating mechanism and earthing switch with making capacity (if applicable))

(v) Heating of cubicles

(vi) Counters

FIVE YEARLY EXAMINATION

Five yearly examination of the GIS is considered as minor examination and shall include but not limited to:

Activity

(i) Checking of pressure with tool

(ii) Dew point of SF6 gas in CB chamber.

(iii) Density switch operation

(iv) Gas leakages

(v) Operating time of main and auxiliary contacts of CB, mechanical operation of dis-connector and earth switch

(vi) Cleaning of air bushings

(vii) Checking optical indicators and signalling contacts

(viii) Labelling of operating mechanisms and gas filling valves

(ix) Checking of alarm functions

(x) Checking of operating rods for torques in CB poles dis-connectors, earth switches

(xi) Maintenance of gas handling device

(xii) Check hydraulic oil in drives (if applicable).

If the compartment is not provided with an absorber

Ten Yearly Maintenance

It is considered as major examination with small outage and shall include but not limited to:

Activity

(i) Dew point of gas

(ii) Replace filters in operating mechanism

(iii) Replace oil in operating mechanism

(iv) Lubricate the rams

(v) Lubrication of dis-connector operating mechanism

(vi) Lubrication of earth switch operating mechanism

(vii) CB operating arm linkage torque adjustment

(viii) Torque adjustments for disconnector operating rods.

(ix) Cubicle tightness

(x) Accoustic partial discharge measurement

Twenty Yearly or Later

It is considered major examination with prolonged outage and shall include the following but not limited to:

Activity

(i) Open CB pole and check

(ii) Spring and pin replacement

(iii) Maintenance of rams

(iv) Open diasconnector pole

(v) Open E/s pole

Notes:

Normally depending on specifications all GIS CB’s comply with IEC 62271-100 and would have been tested for about 10,000 operating cycles of mechanical duty without significant wear and tear. A random inspection could be done at every 5000 close-open cycles for CB’s, 3000 for disconnector and 1000 nos. for earth switches.

For electrical wear and tear depending on fault level the manufacturer recommendation should be adhered to.

PD measuring facility could be available but experience proves it to be expensive and on account of high reliability of GIS, it is not essentially warranted. In fact acoustic measurement offers better option for existing GIS for monitoring particle content and impurities, should the utilities essentially feel the need of such measurement.

GIS condition monitoring is to be implemented for the achievement of the following objectives:

To monitor the status of the equipment, in association with the digital control system. To reduce the operating costs of the equipment by preventive maintenance To improve, overall, equipment availability.

The condition monitoring equipment will detect any abnormality and an alarm will be raised at the remote dispatch centre, in a predicitive form to inform of a possible future failure.

Once informed, the operator’s maintenance department can acquire more detailed data from the predictive maintenance and diagnostic software. Based on this information, the operator can decide of the level of maintenance to be carried out. One of the main applications where condition monitoring can assist the users in SF6 density monitoring and internal arc localization.

Optional functions like circuit breaker travel curve analysis or electrical wear should be considered mainly for cases where very high availability of the switchgear is required.

15.2.3 SF6 Gas

As SF6 gas is used in all chambers of GIS the monitoring of pressure and quality is of the importance. As per IEC 62271-203/2003 the leakage rate from any single compartment of GIS to atmosphere and between compartments shall not exceed 0.5% per year for the service life of the equipment. The pressure inside a GIS may vary from the rated filling pressure level due to different service conditions. Pressure increase due to temperature and leakage between compartments may impose additional mechanical stresses. Pressure decrease due to leakage may reduce the insulation properties. Further the

quality and dew point of it SF6 gas should also be monitored as the property of SF6 is related to insulation quality.

15.2.4 Partial Discharge Measurement

Electrical Ultra High Frequency (UHF) or Acoustic PD measurement techniques are being employed. Electrical UHF technique gives higher sensitivity and PD detection necessitates the installation of sensors inside the gas compartment during manufacture. Acoustic methods employ sensors which are fixed outside the enclosure. For both the methods the sensitivity depends on the distance between the defect and the sensor.

15.2.5 UHF Partial Discharge Measurement

The partial discharge signals in the range of 1000 MHz to 2 GHz can be detected in the time domain or frequency domain by means of installing sensors usually installed inside the chambers. Due to the complexity of the resonance pattern, the magnitude of the detected PD signal depends strongly on the location.

15.2.6 Acoustic Partial Discharge Measurement

Acoustic signals are emitted from defects in a GIS mainly by the floating particles emitting a mechanical wave in the enclosure when they impinge on it. Discharges from the fixed defects create a pressure wave in the gas, which is then transferred to the enclosure. The resulting signal will depend on the source and the propagating path. As the enclosures are normally made of aluminium or steel, the damping of the signals is quite small.

Acoustic signals can be picked up by means of externally mounted sensors. The location of the defect can be found by searching for the acoustic signal with highest amplitude or time travel measurements with two sensors. Bouncing particles producing discharges in the 5pC range can be detected with a high signal to noise ratio. Sensitivity decreases with distance because the acoustic signals are absorbed and attenuated as they propagate in the GIS. Acoustic measurement is immune to electromagnetic noise in the substation. The acoustic sensitivity to bouncing particles is much higher than the sensitivity of any other method. PD measurement in a GIS installation is recommended once in 5 years.

In GIS substation some of the equipments like Bushings, Surge Arresters, Transformers shall be provided outside the GIS area. Condition monitoring of these equipment is to be carried out as followed for AIS substation equipment.

15.3 Fault Reporting Formats

After commissioning of first GIS in India in 1988, due to its physical compactness and reliability it has been widely applied at various locations. Objective of this format is to obtain and exchange information on the availability and reliability of the GIS and means to improve the same.

To ensure consistent reporting, definition of significant terms will be included and the GIS will be categorized by voltage class.

The failures will be categorized as major and minor failures which will be further sub divided into:

• Initial failure • Generic failure

Dielectric defects can be introduced during shipment/ transportation assembly and can cause faults/ failures in service. Hence, causes of failures viz. contamination or free conducting particles, damage during transport, defective erection at site etc. will be categorized. Details of tests conducted at factory, at site (after assembly) will also be

obtained to co-relate whether the tests at site were adequate or could have been improved upon.

It is recommended to send first information report in a format in a structured way.

The information obtained will help the users and the manufacturers to determine the causes of faults/ failures and recommendations/ precautions to be taken in future manufacturing/ installations to minimize the failures.

In addition, after the repairs, utilities/ manufacturers should familiarize other users to take necessary precautions.

15.4 Spare Parts Management

GIS requires relatively very low maintenance as compared to AIS. Due to the tailor made designs maintenance requirement becomes manufacturer specific. The maintenance personnel should have knowledge of safety rules which are required to be adhered to. The maintenance programme and time based intervals specified /number of operations which ever is earlier should form the basis of maintenance.

Fig. 12 : Progress of Maintenance/Inspection Activities

Each alarm of density meter is required to be analyzed to find out root cause and the defect is to be addressed in the right perspective under guidance of manufacturer.

Recommended spare parts :

Sl No

Description Quantity

1 SF6 gas for use during operation and maintenance in non-returnable cylinders.

10% of total quantity of gas required for filling GIS in 40 kg cylinders

2 One operating mechanism for circuit breaker one phase 3 Complete drive mechanism including motor

for disconnector switches and earthing switches

1 nos.

4Trip coils for circuit breakers 6 nos.

5Closing coils for circuit breakers 6 nos.

6

Complete set of rupture disc 2 sets7

Pressure switch/gas pressure transmitter 2 sets of each used type

8 Gas tight bushing of each type used 2 nos of each type used

9 Gas density relay 2 sets of each type used

One set would be applicable for one phase of one feeder bay

These spares are normally manufacturer specific and as such cannot be used in case of other make of equipment. Users ideally should keep close liaison with other utilities where similar models are installed to have a higher redundancy in availability of spares without increasing inventory. This will ensure less down time in case of outages on account of procurement of spares.

GIS is designed to have a life of about 35 years. It is to be understood that life could be increased by way of condition monitoring and taking corrective action on time. The spares mentioned above are based on the experience of utilities and are considered barest minimum to keep the system healthy.

It is also required to be stressed here that procurement of spares of high inventory is alone not sufficient. In fact it is important to keep / store them in a condition from which they can be used to meet a contingency. Proper preservation norms may therefore, be adopted to perform periodic condition monitoring tests on spares therefore , keep them healthy and stable.

It is common practice of removing defective assemblies from the main spares to meet emergency needs. Any components removed in such contingencies are required to be replenished in a defined schedule so that main spares are always kept complete.

10 years operation in one of the cases called for only torque adjustment in the tie rods and topping up of gas in disconnector and earth switch requirements.

CHAPTER-16

TRANSPORTAION, STORAGE, ERECTION, TESTING AND COMMISSIONING AT SITE

16.1 Transportation

Gas insulated switchgear (GIS) shall be properly packed to protect during ocean shipment, to inland transport, carriage to site and outdoor storage during transit and at the site. Completely assembled bays (subject to transport limitations) of the GIS shall be transported as one shipment unit.

Packing materials shall be dust free and waterproof. All packages shall be clearly, legibly and durably marked with uniform block letters on at least three sides. Fragile items like bushings, CTs, VTs, LAs and fully assembled bays shall be securely packaged and shipped in containers. Silica gel or approved equivalent moisture absorbing material in small cotton bags shall be placed and tied at various points on the equipment wherever necessary.

As far as possible, transshipment should be avoided.

Impact recorders (Accelerometers) shall be provided on the packages to confirm that GIS has not suffered any shocks during shipment, transport, handling, etc. The impact recorders readings are to be taken on receipt of equipment at site and sent to GIS manufacturers in case the readings are exceeding the permissible values.

Transportation from Factory to Port and Port to installation site should be done by means of special hydraulic trailers to avoid transmit jerks. The wooden cases should be fitted with shock absorber by supplier.

Sulphur hexafluoride is transported as a pressurized liquefied gas . The containers ideally should not be exposed to direct sunlight and must be secured against over turning or rolling .

Physical Inspection: Physical inspection should be carried out by the owner in the presence of supplier representative and ensure that every consignment have been received at site in good condition. In case some consignment is damage or missing during transit a report is to be prepared and sent immediately to suppliers with a copy to the representative available at site. A report is also to be sent to insurance company.

16.2 Storage

Storage of GIS at site shall be done as per storage instructions from the SUPPLIER and well protected against dust and moisture.

Storage and work areas must be well ventilated in particular ventilation must be affected at ground level on account of fact that gas vapour is heavier than air. If the gas is stored underground appropriate forced ventilation should be provided.

16.2.1 Storage – Assembled & Tested

It has come to notice at some hydro power stations where GIS stands erected & commissioned that due to other reasons not attributed to GIS the system has to remain idle & wait for energisation, it is recommended to operate all the mechanisms once in six months for one close and open operation to ensure that the gaskets/O-rings do not get dried out and remain lubricated

Fig. 11 : Shipping and Transportation

16.3 Erection Testing & Commissioning

Erection should be carried out under the supervision of supplier’s engineer under the clean & dust free environment. Adequate attention shall be given for proper alignment of GIS bays. For this a care should be taken that a very prestige foundation is require to be made. The accuracy level require for the foundation base is of the order of +/- 3 mm so GIS floor slab is prepared only after obtaining the exact foundation detail from the GIS supplier. The base plate of the GIS bays shall be imbedded at the time of casting of floor slab. Only the special tools and tackles supplied by GIS manufacturer shall be used for the erection of the GIS.

A special trolley to keep the tools with the identification marks on the trolley should be arrange this will help for locating the right tool and collecting it back after the completed.

Testing of GIS:Test procedure runs parallel to the assembly activity, as many of the intermediate test are required to be carried out before the next stage of the assembly is taken in hand. Following are the tests carried out in various stages.

Contact Resistance Test: Soon after the mechanical erection contact resistance of the electric circuit is checked in order to ensure proper alignment and grip of the bus bar. This is very vital stage test as many insecure connection can be detected at this stag easily. This test is conducted by Micro-ohmmeter by passing 100 Amps D.C. current and measuring the voltage drop across the circuit. The access to the current carrying part is made through the earthing switches.

GIS piping , gas charging and gas leakage test: Only after above test result are satisfactory , gas piping work is done and the GIS is charged with the gas leakage test is carried out.

Insulation Resistance Test: This resistance is carried out on the main circuit and control circuit . 1000 V motor operated megger is used to measure the insulation resistance of the main circuit, while a 500 V megger is used for measuring the insulation resistance of the control circuit.

Mechanical Operation test: The gas circuit breaker spring is charged manually to ensure the smooth functioning of the moving parts. The gas mechanism of drive motor is checked for its operation. Similarly the disconnector and earthing switches are checked for their mechanical manual operations. The mechanical operations are carried for five times each for closing and opening of gas circuit breaker, disconnectors and earthing switches.

Operation Timing Test: The operation timings of circuit breaker, disconnecting and earthing switches are verified.

Polarity Test: The CTs and PTs are verified for their polarity and ratio and their connection as per the wiring schedule and checked.

Extra High Voltage Test: finally the entire installation is put for final test.which include the following:

• Pre-commissioning checks & tests, • Initial operation, • Trial operation, • Performance tests.

Chapter -17

GIS Installation in the Country

Due to growing demand of power and evacuation of large amount of power the corresponding large transmission corridor is required. A considerable large built up area is required in the generating station for setting up a sub-station for transferring this large quantum of power through EHV transmission lines. The land built up area is generally not available on hilly terrain. Now days the trend is to go for Gas Insulated Switchgear which occupies very less space and suitable in the areas of pollution associated in the industrial as well as costal areas and gives the better aesthetic views of power station. GIS is only the solution transferring the power from underground power station. Moreover GIS is also maintenance free and is suitable for indoor application as well as mountainous region. In view of this nos. of GIS are coming up in hydro power station as well as on the location where land space is not available.The 1st GIS was commissioned in BEST, Bombay and Carnec Project, TEC Bombay in 1988 at the level of 110 and 245 KV respectively. Since than Nos. of GIS have been installed in the country from the voltage level of 33 KV to 400 KV. A list of few GIS installation in the country is given as under

GIS Installation in IndiaSl. No

Name of S/Stn.

RatedVoltage

Short Ckt. rating

Switching Arrangement

Type of enclosure

No. of Bays

Name of Supplier

Commissioning date

Transmission projects

I TEC Bombay

1 Grant Road

123kV 40KA Double Bus 3 Phase 3 MerlinGerinFrance

2 Salsette 245kV 40KA Double Bus 1 Phase 9 ToshibaJapan

1995

3 Dharavi 245kV 40KA Double Bus 1 Phase 13 ToshibaJapan

4 Backbay 123kV 40KA Double Bus 1 Phase 11 ToshibaJapan

5 Carnac 245kV 40KA Double Bus 1 phase 2 MerlinGerinFrance

Jan. 1988

123kV 40KA Double Bus 1 Phase 11 MerlinGerinFrance

II Best, Bombay

110kV 40KA Double Bus 1 Phase 7 ToshibaJapan

May, 1988

Best, BombayBackbay,Receiving Stn.

145kV33kV

40KA40KA

Double BusDouble Bus

1 Phase1 Phase

1216

Nissin, Japan ABB, Germany

1998

III Desu, Delhi

1. Park Street

220kV 31.5KA

Double Bus 1 Phase 9 ABB,Sweden

March,1994

2 Kashmere Gate

220kV 31.5KA

Double Bus 1 Phase 9 ABBSweden

1997

3 Kashmere Gate

33kV 31.5KA

Double Bus 1 phase ABB, Germany

2003

4 Subzi Mandi

33kV 31.5KA

Double bus 1 Phase SchneiderMarlynGerin Italy

Hydro Power Projects

IV HPSEB1 Bhaba

power House (Under Sanjay Gandhi Vidyut Pariyojna), Bhaba Nagar Kinnaur

245kV 40KA Double Bus 1 phase 7 BBC,Switzerland

April,1989

V Power Grid

1 Kayamkulam

220kV 40KA Double Bus 3 Phase 10 Hyundai,Korea

Oct. 1998

VI NHPC1 Chamera

-I400kV 40KA Double Bus 1 Phase 6 Siemens 1994

2 Chamera-II

220kV 40KA Doble Bus 1 phase Alstomes

3 Uri 400kV 40KA Double Bus 1 Phase 7 ABB,Sweden

1997

4 Dhauliganga

220kV 40KA Double bus 1 Phase Alstome

5 Dulhasti 400kV 40KA Double Bus 1 Phase

VII TNEB

Mylapore

230kV Single Bus with Sectionalizing Btreaker

230kV-1 Phase 110kV-3 Phase

5 1998

VIII Andhra Prdesh Transmission (APTRANSCO)

1 James Street Sub stn.

33kV Single Bus 1 Phase BHEL 1995

Photographs of 220 KV GIS of Dhauliganga , 400 KV GIS ,Chamera-II , 400KV GIS URI and 400KV GIS Chamera-I H.E. Project are given on at fig. 1(a,b), 2(a,b),3(a,b) and Fig. 4 respectively.

Fig. 1 a- Photograph of 220 KV GIS of Dhauliganga H.E. Project.

Fig. 1 b- Photograph of 220 KV GIS of Dhauliganga H.E. Project.

Fig. 2 a- Photograph of 400 KV GIS of Chamera-II H.E. Project

Fig. 2 b- Photograph of 400 KV GIS Chamera –II H.E. Project

Fig. 3 a- Photograph of 400 KV GIS URI H.E. Project

Fig. 3 b- Photograph of 400 KV GIS URI H.E. Project

Fig. 4 - Photograph of 400 KV GIS Chamer-I H.E. Project

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