gis technical presentation

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Gas Insulated SwitchgearJuly 16, 2010Kerala State Electricity Board, Kozhikode

1Name : Ankur Aggarwal Division : EPD Category : General

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ContentsIntroductionWhy only SF6 GasMain Drivers for GIS ApplicationProduct Development CycleCharacteristics of Gas Insulated SwitchgearsMain Parts of GIS

Primary ComponentsGas Compartments

Sealing System of GISPressure LevelsEarthing SystemSecondary Control SystemDelivery & StorageErection of GISCommissioning of GISGIS Testing at SiteInspection & Maintenance of GISHybrid Sub StationComparison of AIS & GISLife Cycle Cost AnalysisSafety & Security IssuesPartial DischargeMaintenance (Typical)

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INTRODUCTION

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INTRODUCTION

What is GIS????GIS stands for GAS INSULATED SWITCHGEARA metal enclosed switchgear in which the insulation is obtained, at least partly, by an insulating gas other than airat atmospheric pressure (IEC 62271-203)

This term generally applies to High Voltage SwitchgearsThe gas used is generally SF6 or SF6 mixtures

Considering that the basic aspect of substation design i.e. installation, operation, maintenance and extension is possible with a maximum of one circuit and one section of bus bar out of service simultaneously.

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INTRODUCTION

GIS using SF6 is now a well established technology and have been in service since the 1960’s.GIS Technology is typically of modular design and filled with a minimum quantity of SF6.GIS can have low life cycle cost compared to AIS and can be used for indoor as well as outdoor applications.There has been a rapid growth in the application of this technology with an estimated 80,000 bays now in service and increasing at a rate of over 6,000 bays per year. (Source CIGRE Working Group B3.17 report 381 June 2009)

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INTRODUCTION

The Gas Insulated Switchgear has got hermetically sealed cast aluminum enclosures, flanges, covers and aluminum castings.

The GIS is built up from modular units which are designed not to burn through in the event of an internal arcing in the time limited by the recommendation of IEC 62271-203.

The modules join to each other with flanges.

The live parts are supported by epoxy resin based insulator discs which always can be found between flanges of the neighbor modular units.

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INTRODUCTION

The key advantages that GIS can offer of compactness, immunity from environmental conditions and reliability are well understood and documented.

In today’s environment where assessments of capital projects are made on a total life time basis; there GIS can be the most cost effective solution in comparison with AIS.

Life Cycle Cost (LCC) assessments are enabling the one perceived disadvantages of GIS, i.e. its higher initial cost, to be overcome.

With this background, GIS technology is expected to become the preferred choice of many users in the future.

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WHY ONLY SF6 GAS

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WHY ONLY SF6 GAS

SF6 Gas is a colorless, odourless, non-toxic, non-flammable synthetic gas.SF6 Gas is around 5 times heavier than air and is among one of the heaviest known gases.Under normal conditions SF6 gas is chemically inert & stable; its reactivity is among the lowest of all substances.The excellent insulating properties of SF6 are resulting from tothe strong electron affinity (electro-negativity) of the molecule.This is based on two mechanisms a) resonance capture and b) dissociative attachment of electrons, in accordance with the equations:

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WHY ONLY SF6 GASSF6 Gas break down is possible only at relatively high field strengths.

The breakdown voltage at 50Hz & 1 Bar in a homogenous field is around 2.5 to 3 times higher than the corresponding values of air or nitrogen.

On account of its thermal properties and low ionisation temperature SF6 exhibits outstanding characteristics for extinguishing the electric arcs.

The arc quenching time using SF6 gas is around 100 times less than that using the air.

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MAIN DRIVERS FOR GIS APPLICATION

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MAIN DRIVERS

Short Planning, Delivery & Installation RequirementsHigh Level of Reliability & AvailabilityMinimal Maintenance EffortsHigh Degree of Safety for Operating PersonnelLong Operating Life > 50 YearsFactory Pre Assembled and Tested UnitsProtection from Environmental ConditionsCustomer Tailored Solution due to modular designsExtension of AIS under operation or restricted space availabilitySimple constructionRestricted Space AvailabilityHigh Land Acquisition Costs

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PRODUCT DEVELOPMENT CYCLE

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GIS PRODUCT DEVELOPMENT CYCLE

CIGRE Report on GIS Product Development Cycle

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CHARACTERISTICS OF GIS

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Compact space saving design with uncomplicated foundations.

Minimal weight by light weight construction through the use of aluminum housings and use of computer aided design tools to optimize the shape and size.

Complete safety to the personnel under all operating and fault conditions based on new manufacturing methods and quality control procedures.

• Environmental compatibility enables no restrictions on choice of location by means of minimum space requirement, low noise emission and effective gas tightness using sealing systems with guaranteed leakage rates < 0.5% p.a. per gas compartment.

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Economical transport of several bays connected together as maximum possible shipping unit.

Minimal operating cost of practically maintenance free equipment, designed for extremely long service life up to 50 years. This ensures that first inspection will not be necessary until after 25 years of operation, however depending upon the status of the switchgear.

Highest reliability by a product concept which includes most modern design tools, development programs and appropriate quality control measures.

Easy and efficient installation and commissioning with transport units already fully assembled and tested in the factory, pre-filled with SF6 gas at reduced pressure.

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CHARACTERISTIC OF GIS

Technology Design

Insulation Insulating Medium

Enclosure

AIS Technology

External Insulation

Air, SF6 Gas Live PorcelainOr

Composite InsulatorsGIS

TechnologyGas

InsulationSF6 or SF6

MixturesMetal Enclosures

(Aluminum) effectively earthed

Hybrid Technology

Mixed Insulation

SF6 or Sf6 Mixtures and

Air

Permutation & Combination of all

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MAIN PARTS OF GIS

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PRIMARY COMPONENTS

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PRIMARY COMPONENTS

Isolator

CB PT

CT

Bus Bar

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PRIMARY COMPONENTS

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PRIMARY COMPONENTS

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PRIMARY COMPONENTS

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PRIMARY COMPONENTS

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PRIMARY COMPONENTS

1-Phase Bus Bar with Connecting Element

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PRIMARY COMPONENTS

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PRIMARY COMPONENTS

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PRIMARY COMPONENTS

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PRIMARY COMPONENTS

3131

GAS COMPARTMENTS

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GAS COMPARTMENTS

GIS contains several independent gas compartments.

The internal barriers between the gas compartments are provided by solid insulator discs.

The system gives possibility

For decreasing gas losses

For restriction of damages caused by fault arc

For reducing the time of gas manipulations

Different gas compartments contains usually different gas volumes

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GAS COMPARTMENTS

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GAS COMPARTMENTS

All the gas compartments include the following basic parts:

A Metal Rupture disc assembly with deflector cover (as PRD)

A temperature compensated contact manometer for continuous monitoring of internal gas pressure

A set of gas connection valves

A set of gas filters

These basic parts basically act as safety and security devices for satisfactory performance of GIS during actual site conditions.

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SEALING SYSTEM OF GIS

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GIS represents closed pressure system

Gas leakage rates are < 0.5% p.a. i.e. a undisturbed life of 20 years is guaranteed for GIS before the gas has to be replenished.

GIS is built in modular units (for single phase design) which are joined with each other through flanges.

Epoxy resin insulator discs are placed between the flanges of the neighboring units to support the live parts.

To ensure static gas tight sealing ethylene-propylene rubber rings are placed.

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PRESSURE LEVELS

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PRESSURE LEVELS

GIS uses SF6 gas as insulation & arc quenching material.

Therefore pressure in puffer type circuit breaker is high because of better arc quenching properties.

The figure shown below depicts the various pressure levels and their relationship as specified and governed by various IEC and IN Standards.

However, the exact pressure values are not fixed and vary from manufacturer to manufacturer and specifically design wise orientation in pressure values is also more or less applicable.

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PRESSURE LEVELS (IEC 62271-203)

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PRESSURE LEVELS GAI3 245 kV

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PRESSURE LEVELS GT01 145 kV

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PRESSURE LEVELS

• Design Pressure:– Abstract value used at determining the wall

thickness of enclosure elements.– It is valid at the design temperature which is the

average of the permissible temperatures of the active parts and the enclosures.

– According to IEC 62271- 1, the maximum temperature for silver coated contacts in SF6 is 105 deg C and for accessible parts expected to be touched in normal operation is 70 deg C.

– Therefore the design temperature shall be (105+70)/2 = 87.5 deg C

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PRESSURE LEVELS

• Rated Filling Pressure:– This is the actual working value on which the

equipment is filled up under normal conditions.– It is valid at 20 deg C gas temperature– Some Type Tests are performed at rated gas

pressure like gas tightness test, mechanical endurance test, internal arc test and inductive current breaking capacity test.

• Alarm Pressure:– This value is approximately 90% of the rated value.– This is basically the setting level for the first step of

gas protection– At this value the gas monitoring device and relay

gives alarm signal for refilling.

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PRESSURE LEVELS

• Minimum Functional/ Lock Out Pressure:– The minimum permissible pressure of the equipment.– Dielectric Test, Switching Test & Temperature rise test

are performed at this value.– If the pressure falls under this value the second level of

gas protection has to provide the electrical isolation of the defected gas compartment.

• Routine Test & Bursting Test Pressure:– RTP = k x Design Pressure– Where k = 1.3 for welded and 2 for cast aluminum

enclosures– This is dominated by IEC 62271-203.– BTP = m x Design Pressure– Where m = 3 for welded and 5 for cast aluminum casing

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EARTHING SYSTEM

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EARTHING SYSTEM

GIS Earthing System is designed according to IEEE Guide for safety in AC Substation grounding (IEEE Std 80).

Earthing eliminates all the hazardous potential differences caused by:

Fault Situation (Short Circuit) or

Return Currents (electromagnetically induced among the phases during normal operation)

Earthing also protects the personnel from shock hazard voltage by maintaining low touch/ step voltage among the different parts ofswitchgear.

Earthing of GIS is established by using two different types of earthing conductors i.e. interconnecting earthing bars among the phases and earthing conductors between the enclosure and Earth Mat.

From Safety point of view, LCC and Structural elements are also earthed.

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EARTHING SYSTEM

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SECONDARY CONTROL SYSTEM

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Secondary Cables: For Controlling, power supply of drives, and GIS signaling.

LCC (Local Control Cubicle): Connection between substation control system and GIS.

LCC gives possibilities to check the service conditions and healthiness of switches and devices. Position signal of all the switches appear in mimic diagram of LCC.

Operation of switches is possible either from control room or locally through LCC.

In normal service the LOCAL/ REMOTE Selector switch are in REMOTE control position to operate the GIS from Control room. If the selector switch is turned to LOCAL position, the switches of theconcerned bay can be operated from LCC.

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DELIVERY & STORAGE

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DELIVERY & STORAGE

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Delivery & Storage

• Packing:– GIS Unit and all other parts and materials required for

erection & operation are seaworthy packed in wooden cases &

– Packing is provided with signs for transport & storage as well as instructions for proper handling.

• Storage of Shipping Units:– If GIS is not planned to assemble immediately after delivery it

is recommended to leave the shipping units in weatherproof transport packing.

– Wooden cases can be stored either in open air or in ware houses.

– To safeguard the packing unit from ground moisture and for better ventilation, the unit is raised on planks and covered with waterproof sheets.

– The temperature of storage shall be in the range of -15 deg C to +25 deg C and humidity shall be < 50%

– SF6 gas cylinders shall be handled and stored carefully in a cool, dry and away from flames and sunlight.

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DELIVERY & STORAGE

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ERECTION OF GIS

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SAFETY PRECAUTIONS FOR ERECTION

To prevent accidents, fire hazards, shocks the utility operator to ensure that:

A responsible person and supervisor caries out the erection

Only qualified and trained personnel are designated for the work

Installation and operation manual (manufacturer specific) shall be strictly followed.

Tools, tackles and other devices for installation are available

Only manufacturer approved lubricants, materials, fillers, degassers etc are used.

Death, severe injuries and considerable damage to property and environmental damages may result if the safety and erection procedures are not followed.

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SAFETY PRECAUTIONS FOR ERECTION

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PREPERATORY WORK FOR ERECTION

Since for GIS erection an absolute cleanliness is required, no installation work of any kind may be carried out at the same time.

The following aspects are substantial:

Foundations and Earthing System

Cables and Cable Ducts

Transport Routes & Lifting arrangements

Tools, devices and consumables

Lighting, power & water supplies

Civil Works

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COMMISSIONING OF GIS

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GIS Commissioning should not commence before:

GIS erection is complete

Auxiliary and control cables have been connected

All auxiliary and control voltages are available at the switches

SF6 gas filling has been completed

GIS is connected to earthing system.

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Checks and Verifications:

Switchgear conformity with manufacturer drawings and instructions

Conformity of secondary control & protection circuits

Conformity of earthing system

Sealing of all enclosure flanges and tightness of bolts & connections

Proper functioning of AC & DC auxiliary supply systems

Proper operation, alarm and position indication of each drive

Proper function of electrical interlocks between LCC & GIS

Proper filling pressure of each gas compartment

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GIS Testing at Site

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GIS Testing at Site

Before putting into service the GIS shall be tested to check the correct operation and dielectric strength of the equipment.

These tests comprise:

Dielectric tests on auxiliary circuits

Measurement of the resistance of the main circuits

Measurement of gas condition

Gas Tightness Test

Checking the ratio and polarity of the CT

High Voltage AC Test on Main Circuits

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GIS Testing at Site

Dielectric Test on Auxiliary Circuits:

After the site erection is completed, the auxiliary cables that were not tested in the factory have to be tested for checking the correct wiring.

The test is performed with HV AC Test Equipment

1 kV AC Voltage shall be applied between the terminal blocks and the earth points for 1 sec with neutral points of the circuit to be removed during testing

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GIS Testing at Site

Measurement of Resistance of Main Circuit:

During the erection the resultant resistance of all bays between the bus bar and the outgoing terminal shall be checked.

The resistance shall be calculated from the voltage drop measured at min 100 A DC loading current.

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GIS Testing at Site

Measurement of Gas Condition:

The moisture content of SF6 gas should be measured with dew point measuring device

Similarly the gas percentage measurement shall also be carried out using gas measuring device. SF6 percentage should be > 95%.

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GIS Testing at Site

Gas Tightness Test:

Generally gas leakage test with gas leak detector is being done at site to ensure that there is practically no gas leakage after erection and commissioning of GIS and before putting it into service.

CT Ratio & Polarity Test:

The ratio and polarity of the current transformer is checked using primary current injection method.

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GIS Testing at Site

High Voltage Test of GIS (AC Test):

This test is carried out to ensure the dielectric strength of the switchgear which if unhealthy can lead to an internal fault in future thereby leading to Partial Discharges.

The test voltage to be applied as per IEC 62271-203 is 380 kV rms for 1 minute.

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INSPECTION & MAINTENANCE OF GIS

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INSPECTION OF GIS

GIS Life Cycle is ~ 50 years. There is a small risk of failure which can often be avoided by proper monitoring and inspection of GIS

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MAINTENANCE OF GIS

GIS is hermetically closed system.

Primary contacts and conductors are under protective gas atmosphere and therefore no corrosion may occur due to humidity

No internal or external parts are designed to be replaced withinthe life cycle of GIS.

Practically GIS is maintenance free since the same is tested forhigher number of operations viz 10000 for circuit breakers.

However, within the scope of general overhauling only checking and replacing of contacts, nozzles etc is carried out till the time GIS operations are in prescribed limit of the IEC recommendations and Type Test Certifications.

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HYBRID SUB STATION

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HYBRID SUB STATION

A sub station of which the bays are made from a mix of GIS and AIS technology components and interconnections, i.e. a sub station that consists of bays where some of the bays are made of a mix of AISand GIS technology components or some of bays are made of GIS technology components and their interconnections only are considered as HYBRID SUB STATIONS.

There are two exceptions from this rule:

If the only one component in AIS technology is the HV connection(bushing, box) to O/H line, cable or transformer then the S/s isconsidered as GIS S/s.

AIS where only one component is in GIS technology or where additional elements have a mixture of Air & Gas Insulation but the primary insulation to earth is still air (as in dead tank) they are still considered as AIS S/s.

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COMPARISON AIS & GIS

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LAND

Less as compared to AIS.

App. 70% Land Reduction for a 400 kV GIS S/s wrt AIS

ENGINEERING

Less Engineering Required for GIS wrt AIS.

Engineering Standardization is a continuous process.

Project Specific influence (Cabling, Connections, Soil)

CIVIL WORKS

Involved in both, however, substantial reduction for GIS

AIS requires Equipment and Tower Foundations, cable trenches etc

GIS required GIS Room.

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EQUIPMENT

Equipment Cost AIS viz a viz GIS is nearly double.

With Auxiliaries GIS cost is 1.2 to 1.5 times of AIS

AUXILIARIES (EARTHING, LIGHTING, FIRE FIGHTING etc)

AIS has more area means more requirement

More Fencing, More Earthing, More Lighting

More Cables required for AIS since HV equipments are a distance apart and therefore the distances are longer.

Site preparation, mobilization cost, earth leveling, fencing androads cost are more in AIS compared to GIS.

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ERECTION & COMMISSIONING

Assemblies pre tested at factory and dispatched as single unit in form of complete bays

Time required is < 40% of the time required for erection & commissioning of AIS

Very few cable requirement i.e. between LCC to GIS and between GIS to CRP.

OPERATION & MAINTENANCE

Time for AIS O&M > 2 x Time for GIS O&M

GIS O&M requires only some preliminary checks.

No Environmental Issues

GIS Room and floor are always kept clean.

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ENVIRONMENTAL ASPECTS

No Pollution, Moisture or Temperature Difference Issues.

Less Ecological disturbances since land used is less

Sealed System with optimum earthing, thus no EMF emission

No RIV Interference due to sealed system

ASTHETIC VALUES

GIS is better compared to AIS

All housed beautifully in a room

High profile appearance.

No acoustic load on environment

Less corona discharges

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COMPARISON AIS & GIS (145 kV)

8181

LIFE CYCLE COST ANALYSIS

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Life Cycle costing is a process to determine the sum of all the costs associated with an asset or a part thereof including acquisition, installation, operation & maintenance, refurbishment and disposal costs.

LCC = Acq. Cost + Ownership Cost + O&M Cost + Disposal Cost

GIS Primary Hardware (Acquisition Cost)

When comparing the equivalent primary HV components, GIS is moreexpensive than AIS. However if the prices of the gantries, supports, conductors, earthing, illumination, fire fighting for AIS s/s are included in the comparison, the difference between GIS and AIS can be significantly reduced, because they are already included in the GIS System. Comparison including the cost of land, installation, building etc as well as the cost of secondary control & protection and monitoring equipment is also very important and can lead to more cost attractive solution for GIS in any circumstances.

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Maintenance (Ownership Cost)

In comparison of the failure rate, GIS has better features than AIS. In general, failure rate of GIS components are 0.25 times that of AIS components (viz. CB, CT, CVT, ISO) and especially 0.10 times in case of bus bar. Thus, GIS needs less repair maintenance cost through out its lifetime. The cost of preventive and predictive maintenance are well reduced, because of less possibility of failure.

Operation Cost (Ownership Cost)

Operating cost including the maintenance cost of GIS shall be substantially low as compared to AIS. However, the cost of training, spare holding for new GIS installation is high as compared to AIS.

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Outage Cost (Operating Cost)

Since failure rate of GIS components is lower than that of AIS and therefore, outage cost of AIS including the possible loss ofrevenue by the outage shall be bigger.

However, it shall also be considered that the outage time for GIS can be longer than that of AIS, in case of certain failures.

Disposal Cost

Cost of decommissioning and disposal after use and after subtracting earnings which can be received by selling the reusable materials like aluminum, copper etc have to be capitalized. Now a days CIGRE is studying the feasibility on re usage of SF6 gas up to 99%.

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SAFETY & SECURITY ISSUES

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Substation Security has always been important factor.

Importance of a secure and uninterrupted electricity supply continues to increase.

Outages and failures due to insufficient substation security becomes less and less acceptable to customers.

Substation security is important to:

Maintain the availability of the power supply

Prevent public access to the plants, for the purpose of safety of general public, prevention of vandalism and intruders

Protect other parts and components in a S/s against violent deterioration of high voltage equipment caused by failures.

Prevent and minimize the financial risk due to all the occurrences mentioned above

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Protection Measures to obtain an adequate security level include:

Protection against intruders

Outdoor substations: Fence design (height, shape, minimum clearance to ground, mechanical strength, reduction of height due to snow depth)

Indoor Substations: Building design (windows, doors, access control).

Protect other parts and components in S/s against violent deterioration of HV equipment caused by failures

Outdoor parts: Fence Design, Passive protection of components by concrete structures

Indoor parts: Quality of building material, wall thickness

GIS is inherently well placed to meet these demands and considerations in an excellent way due to:

Small space requirements, these s/s are easier to protect.

The enclosure gives protection against access to live parts

GIS are often located indoor to give additional security compared to outdoor substations.

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CIGRE Report on Power Supply Network with GIS Technology Report 381 Working Group B3.17 Jun 2009

0%

20%

40%60%

80%

100%

PrimaryEnergy

SpaceConsumption

GlobalWarmingPotential

Acid RainPotential

NutrificationPotential

AIS GIS

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PARTIAL DISCHARGE

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PARTIAL DISCHARGE - AN OVERVIEW

Partial Discharge is

Localized Electrical Break down

Of a small portion of electrical insulation system

Under High Voltage Stresses

Which does not bridge the space b/w conductors

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PARTIAL DISCHARGE – AN OVERVIEW

Expectations from GIS

High Reliability

Long Life Space Economization

Maintenance Free

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Preventive Maintenance is required for GIS to ensure maintenance free.

Most Important aspect of Preventive Maintenance is to analyze the type & location of internal fault.

Internal Faults in GIS:

Insulation

Loose Particles

Arcing

Thus Partial Discharge Measurement are very much helpful to evaluate the integrity of the equipment.

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PD Measurement can be taken:

Continuously

Intermittently

On-Line

Off-Line

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MAINTENANCE (TYPICAL)

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GIS General

General Conditions of Equipments

Support Structures

Earthing Connections

Gas Pressure Density/ Level & Trend Analysis

Calibration of Pressure Transmitter/ Transducer/ Pressure Gauges/ Manometers

Alarm Setting & Operations

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CIRCUIT BREAKER

Number of Operations

Trial Operations

Contact Timing. Travel Record

Mechanism Type (i.e. Spring/ Hydraulic/ Pneumatic)

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DISCONNECTOR & EARTHING SWITCHES

Number of Operations

Trial Operations

Motor Operating Time & Current

Operation of position indicating valve

Condition of auxiliary switches, wiring & connections

Conditions of gears, linkages, lubrication

Interlocking operation

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THANK YOU

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CGL CONTACTS

For Further Information, Please Contact

Crompton Greaves Ltd.

Engineering Projects Division

3rd Floor, Tower A, DLF Cyber Greens, DLF Phase III,

Gurgaon (Haryana) – 122 002

Contact Persons:a) Mr. Reshu Madan – Dy. General Manager (+91-9711206415) [email protected]

b) Mr. Kapil Verma – Dy. Manager (+91-9711206425) [email protected]

c) Mr. Ankur Aggarwal – Dy. Manager (+91-9711206437) [email protected]

mailto:[email protected]



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