electrical substations

8/17/2019 Electrical Substations

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Electrical substations: 132 KV

1. 1. 2014 Electrical Substations P roject Report, 132 KV Substation, Purukul,

Dehradun P ower Transmission Corporation of Uttarakhand Limited S ubmitted By:Girish Gupta Id no. 42206, 4th Year, Electrical Engineering, College ofTechnology, Govind Ballabh Pant University of Agriculture & Technology,Pantnagar

2. 2. Project Report 3 Sl. No. INDEX Topic P age N o. 1. Training O rder 2 2.Certicate 4 3. Acknowledgement 5 4. Power Transmission Corporation ofUttarakhand Limited 6 5. 132 KV S/s P urukul, Dehradun 8 6. Substation 10 7.Transformer 16 8. Power Line Carrier Communication 19 9 . Bus B ars 22 10.Circuit Breakers 2 3 11. Isolators 2 7 12. Insulators 2 8 13. Relays 3 0 14. Capacitor

Bank 3 3 15. Protection of Substation 34 16. Conclusion 38 17. Bibliography 393. 3. Project Report 4 CERTIFICATE This i s t o certify t hat Mr. Girish Gupta, student

of 4th year, Electrical Engineering, Bachelor of Technology, College ofTechnology, Govind Ballabh University o f Agriculture & Technology, Pantnagarhas un dergone su mmer training at 132KV Substation, Purukul, Dehradun underPower Transmission Corporation of Uttarakhand Limited (PTCUL) from 7th July,2014 to 7th August, 2014 under the overall guidance of Mr. Prabhash Dabral,S.D.O., Purukul, Dehradun. Mr. Girish Gupta has su ccessfully co mpleted h istraining and submitted the training project report. During the period of training he

was f ound sincere, punctual and regular. His co nduct and behavior was ve rygood. Mr. Prabhash Dabral Sub Division Officer 132 KV Substation PTCULPurukul, Dehradun

4. 4. Project Report 5 ACKNOWLEDGEMENT I am very thankful to Mr. RavindraKumar, Executive E ngineer, Power Transmission C orporation o f UttarakhandLimited who g ave me an opportunity to undergo training at 132KV Substation,Purukul, Dehradun under Power Transmission Corporation of UttarakhandLimited (PTCUL). I am also thankful to Mr. Prabhash Dabral, Sub Division Officer,132 KV Substation, PTCUL who o rganized the training in a systematic m anner

and guided me through the whole training programme. I would also like to thankall officer/officials w ho guided a nd helped me at each and every st ep in thetraining programme. Girish Gupta Id no. 42206 4th year, Electrical Engineering

5. 5. 4. POWER TRANSMISSION CORPORATION OF UTTRAKHAND ProjectReport 6 LIMITED (PTCUL) Power Transmission Corporation of Uttarakhand Ltd.is t he power transmission utility of the state of Uttarakhand formerly known as

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Uttaranchal. On 9 November 2000, this 2 7th state of the Republic o f India wascarved out of the Himalayan and adjoining northwestern districts o f Uttar Pradeshper the Uttar Pradesh State Re-organization Act, 2000. The State of Uttaranchalin exercise of the power granted to it under Section 63(4) of the State Re-

organization Act, 2000, formed two separate companies i n power sector -Uttaranchal Jal Vidyut Nigam Ltd. for generation of hydro-electricity in the stateand Uttaranchal Power Corporation Ltd. for transmission & distribution ofelectricity in the state. Enactment of the Electricity Act, 2003, a distinct watershedin the Indian power sector, as i t introduced innovative concepts l ike powertrading, Open Access, Appellate Tribunal, etc., and special provisions f or the ruralareas, made it mandatory for all the States t o restructure their SEBs. As p er theprovisions o f Electricity Act, 2003, the state government separated powertransmission business from UPCL which was l eft only with distribution of

electricity. A new company b y the n ame & style o f Power TransmissionCorporation of Uttaranchal Ltd. was cr eated to handle power transmissionbusiness an d registered as a G overnment Company under Section 617 ofCompanies A ct, 1956 on 27th May, 2004. It started functioning w.e.f. 1st June,2004. 100% shares o f the Company is he ld by the Government of Uttarakhandeither directly o r through its n ominees. Authorized capital of the Company a t thetime of incorporation was R s. 10 crores d ivided into one lac e quity sh ares o f Rs.1000 each. At present the authorized capital of the company is r upees o nehundred crores. The Company is m anaged by the Board of Directors w ho meet

frequently a t least once in every q uarter. The day to day management of theCompany is l ooked after by the Managing Director and other full time Directors o fthe Company a long with o ther senior officers. The Corporate a nd RegisteredOffice of the company is at Vidyut Bhawan, Near ISBT Crossing, SaharanpurRoad, Majra, Dehradun. Following given is t he power line map of Uttarakhandwhich shows v arious i nstalled substations o f different capacities a nd transmissionlines i n Uttarakhand. It also indicates the position of the new upcomingsubstations i n the different regions.

6. 6. Power and Transmission Line Map of Uttarakhand P roject Report 77. 7. 5. 132 KV SUBSTATION, PURUKUL, DEHRADUN The 132 KV substation was

commissioned in the year 27th March, 1983. There a re two main 132 KV busincoming for the substation. These buses a re:- 1. 132 KV Purukul-Dhalipur Line2. 132 KV Purukul-Majra Line Now the transmission line rst parallel connectedwith lightning arrester to diverge surge, followed by C VT connected parallel. CVTmeasures voltage and steeps d own from 132KV to 63.5 Volts A .C. for control

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panel, at the location a wave trap is co nnected to carrier communication a t higherfrequencies. A current transformer is co nnected in series w ith line which measurecurrent and step down current at ratio 800:400:200:1 for control panel.Switchgear equipment is p rovided, which is t he combination of a circuit breaker

having an isolator at each end. Two transformers a re connected to main bus. Themain bus h as t otal capability o f 60 MVA for 132 KV, which is su bdivided into twotransformer capacity of 60 MVA (40MVA + 20MVA) parallel connected for 132KV.In addition to the Main bus, Transfer Bus i s a lso provided in the substation incase any m aintenance work is t o be c arried out on the main bus o r there is aglitch in the main bus. After the Main bus, lightning arresters, currenttransformers, isolators a nd circuit breakers before the transformers are provided.Current Transformers s teps d own current at ratio 400:200:1 for control panel.Then Transformer step downs vo ltage from 132KV to 33KV. The main bus i s then

again provided with switchgear equipment & a current transformer. This g ivesway to six feeders t ransmitting power to various p laces. The main bus i sconnected to jack b us o r transfer bus t hrough a bus co upler & 33KV is p rovidedwith switchgear equipment. This g ives w ay to feeders t ransmitting power toProject Report 8 1. Opto Electronics 2. Anarwala I 3. Anarwala II 4. Mussoorie I5. Mussoorie II 6. I.T. Park 7 . GEMES A step down transformer of 33KV/440V isconnected to control panel to provide supply to the equipments o f the substation.Capacitor bank is co nnected to main bus o f 33KV. It is p rovided to improve powerfactor & voltage prole. Capacitor Bank co mprises o f two units o f 5 MVAR

making total capacity of 10 MVAR.8. 8. At present, an extra 20 MVA transformer is being currently installed at the

substation. Also an additional 132 KV Purukul-Bindal Line is n ow beingconnected to the substation. Project Report 9

9. 9. Pole mounted substation TRANSFORMER SUBSTATION They are known astransformer substations a s b ecause transformer is t he main componentemployed to change the voltage level, depending upon the purposed servedtransformer substations m ay be • Underground substation • Outdoor substation • Indoor substation • S witching Substation 2. According to the constructionalfeatures: • Convertor Substation • Collector Substation • Industrial substation • Converting substation • Frequency ch ange substation • P ower factor correctionsubstation • Switch substation • Transformer substation • Project Report 10 6.SUBSTATIONS A substation is a part of an e lectrical generation, transmissionand distribution system. Substations transform voltage from high to low, or thereverse, or perform any o f several other important functions. Between the



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generating station and consumer, electric p ower may ow through severalsubstations a t different voltage levels. Substations m ay be owned and operatedby a n electrical utility, or may b e owned by a large industrial or commercialcustomer. Generally su bstations a re unattended, relying on SCADA for remote

supervision and control. A substation may include transformers t o change voltagelevels between high transmission voltages and lower distribution voltages, or atthe interconnection of two different transmission voltages. Substations areclassied by two broad categories:- 1. According to the service requirement:

10. 10. Project Report 11 classied into: a) STEP UP SUBSTATION The generationvoltage is s teeped up to high voltage to affect economy in transmission of electricpower. These are generally located in the power houses a nd are of outdoor type.b) PRIMARY GRID SUBSTATION Here, electric power is received by p rimarysubstation which reduces t he voltage level to 33KV for secondary t ransmission.

The p rimary gr id su bstation is ge nerally of outdoor type. c) SECONDARYSUBSTATIONS At a secondary su bstation, the voltage is further steeped down to11KV. The 11KV lines r uns a long the important road of the city. The secondarysubstations ar e also o f outdoor type. d) DISTRIBUTION SUBSTATION Thesesubstations a re located near the consumer’s l ocalities a nd step down to 400V, 3-phase, 4-wire for supplying to the consumers. The voltage b etween any t wophases i s 400 V & between a ny phase a nd neutral it is 230 V. SUBSTATIONCHARACTERISTICS 1. Each circuit is p rotected by its ow n c ircuit breaker andhence plant outage does not necessarily r esult in loss of supply. 2. A fault on the

feeder or transformer circuit breaker causes l oss of the transformer and feedercircuit, one of which may be restored after isolating the faulty circuit breaker. 3. Afault on the bus s ection circuit breaker causes c omplete shutdown of thesubstation. All circuits may be restored after isolating the faulty circuit breaker. 4.Maintenance of a feeder or transformer circuit breaker involves loss of the circuit.5. Introduction of bypass isolators b etween bus b ar and circuit isolator allowscircuit breaker maintenance facilities without loss of that circuit.

11. 11. Project Report 12 STEPS IN DESIGNING SUBSTATION The First Step indesigning a Substation is to d esign a n E arthing Earthing Materials • S ubstationEarthing C alculation Methodology Calculations for earth impedances, touch andstep potentials a re based on site measurements o f ground resistivity a nd systemfault levels. A grid layout with particular conductors is then analyzed to determinethe effective substation earthing resistance, from which the earthing voltage iscalculated. In practice, it is normal to take the highest fault level for substationearth grid calculation purposes. Additionally, it is n ecessary t o ensure a sufficient



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margin such that expansion of the system is ca tered for. To determine the earthresistivity, probe tests are carried out on the site. These tests are best performedin dry w eather such that conservative resistivity r eadings a re obtained. • Earthingand Bonding The function o f an e arthing a nd b onding system is to p rovide a n

earthing s ystem connection to which transformer neutrals o r earthingimpedances m ay b e connected in order to pass t he maximum fault current. Theearthing system also ensures that no thermal or mechanical damage occurs o nthe equipment within the substation, thereby resulting in safety to operation andmaintenance personnel. The e arthing s ystem also guarantees e quipotentbonding such that there are no dangerous p otential gradients d eveloped in thesubstation. In designing the substation, three voltages h ave to be consideredthese are: 1. Touch Voltage This i s t he difference in potential between the surfacepotential and the potential at earthed equipment whilst a man is s tanding and

touching the earthed structure. 2. Step Voltage This i s t he potential differencedeveloped when a man bridges a distance of 1m with his feet while not touchingany other earthed e quipment. 3. Mesh Voltage This is the maximum touchvoltage that is d eveloped in the mesh of the earthing grid. • and Bonding System.

12. 12. Switchyard F ence Earthing The s witchyard fence earthing p ractices a repossible and are used by different utilities. These are: a) Extend the substationearth grid 0.5m-1.5m beyond the fence perimeter. The fence is t hen bonded tothe grid at regular intervals. b) Place the fence beyond the perimeter of theswitchyard earthing grid and bond the fence to its o wn earthing rod system. This

earthing rod system is n ot coupled to the main substation earthing grid.CONDUCTORS USED IN SUBSTATION DESIGN An ideal conductor shouldfulll the following requirements: a) Should be capable of carrying the speciedload currents a nd short time currents. b) Should be able to withstand forces o n itdue to its si tuation. These forces c omprise self-weight, and weight of otherconductors a nd equipment, short circuit forces a nd atmospheric forces su ch aswind and ice loading. c) Should be corona free at rated voltage. d) Should havethe minimum number of joints. e) Should need the minimum number ofsupporting insulators. • Project Report 13 1. Conductors B are copper conductor isusually u sed for the substation earthing grid. The copper bars t hemselves u suallyhave a cross-sectional area of 95 square millimeters, and they a re laid at ashallow depth of 0.25-0.5m, in 3-7m squares. In addition to the buried potentialearth grid, a separate above ground earthing ring is u sually p rovided, to which allmetallic su bstation p lant is b onded. 2. Connections C onnections t o the grid andother earthing joints sh ould not be soldered because the heat generated during

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fault conditions could cause a soldered joint to fail. Joints are usually bolted. 3.Earthing R ods T he e arthing g rid m ust be su pplemented by e arthing rods to a ssistin the dissipation of earth fault currents and further reduce the overall substationearthing resistance. These rods a re usually m ade of solid copper, or copper clad

steel.13. 13. Project Report 14 f) Should be economical. The most suitable material for the

conductor system is co pper or aluminums. Steel may be used but has l imitationsof poor conductivity a nd high susceptibility t o corrosion. In an effort to make theconductor ideal, three different types h ave been utilized, and these include: Flatsurfaced Conductors, Stranded Conductors, and Tubular Conductors .OVERHEAD LINE TERMINATIONS Two methods are used to terminateoverhead lines at a substation. a) Tensioning conductors to substation structuresor buildings b ) Tensioning conductors t o ground winches. The choice is

inuenced by the height of towers and the proximity to the substation. Thefollowing clearances should be obs erved: VOLTAGE LEVEL MINIMUM GROUNDCLEARANCE less than 11kV 6.1m 11kV - 20kV 6.4m 20kV - 30kV 6.7m greaterthan 30kV 7.0m Clearance in accordance with voltage value

14. 14. STANDARD SIZES OF CONDUCTOR FOR LINES OF VARIOUS VOLTAGESThe following s izes h ave now been standardized by CEA for transmission lines o fdifferent voltages:- Project Report 15 1 . For 440 KV Lines Tw in 'Moose' ACSRhaving 7 -Strands o f steel of dia 3.53 mm and 54-Strands o f Aluminum of dia 3.53mm. 2. For 220 KV Lines 'Zebra' ACSR having 7-strand of steel of dia 3 .18 mm

and 5 4-Strands of Aluminum of dia 3.18 mm. 3. For 132 KV Lines ' Panther'ACSR having 7-strands o f steel of dia 3 .00 mm and 30-Strands of Aluminum ofdia 3.00 mm.

15. 15. Project Report 16 7. TRANSFORMERS Transformer is a static m achine,which transforms t he potential of alternating current at same frequency. It meansthe transformer transforms t he low voltage into high voltage & high voltage to lowvoltage at same frequency. It works on the principle of static i nduction principle.When the energy is t ransformed into a higher voltage, the transformer is ca lledstep up transformer but in case of other is kn own as st ep down transformer.TYPES OF TRANSFORMERS 1. Power Transformer It is used for thetransmission purpose at heavy l oad, high voltage greater than 33 KV & 100%efficiency. It also having a big in size as compare to distribution transformer, itused in generating station and Transmission substation at high insulation level.They ca n be o f two types: Single P hase Transformers an d Multi PhaseTransformers. 2. Instrument Transformers T hese transformers a re used for the

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measurement purposes at that points where st andard voltmeters an d a mmeterscannot be used. They are of two types:- a) CURRENT TRANSFORMER Acurrent transformer (CT) is u sed for measurement of alternating electric c urrents.When current in a circuit is t oo high to apply d irectly t o measuring instruments, a

current transformer produces a reduced current accurately p roportional to thecurrent in the circuit, which can be conveniently c onnected to measuring andrecording instruments. A current transformer isolates t he

16. 16. measuring instruments from what may b e ve ry high vo ltage in the m onitoredcircuit. Project Report 17 b) POTENTIAL OR VOLTAGE TRANSFORMERVoltage transformers (VT) (also called potential transformers (PT)) are a parallelconnected type of instrument transformer, used for metering and protection inhigh-voltage circuits or phasor phase shift isolation. They are designed to presentnegligible load to the supply b eing measured and to have an accurate voltage

ratio to enable accurate metering. A potential transformer may h ave severalsecondary windings o n the same core as a primary winding, for use in differentmetering or protection circuits. 3. Auto Transformers An autotransformer is a nelectrical transformer with only o ne winding. The "auto" prex refers to the singlecoil acting on itself and not to any k ind of automatic m echanism. In anautotransformer, portions o f the same winding act as b oth the primary a ndsecondary si des o f the transformer. The winding has a t least three taps w hereelectrical connections a re made. Autotransformers h ave the

17. 17. advantages o f often being smaller, lighter, and cheaper than typical dual-

winding transformers, but the disadvantage of not providing electrical isolation.Project Report 18 4. On the basis o f working On the above basis, transformersare of two types: Step up Transformer and Step down Transformer. 5. DistributionTransformers A distribution transformer is a transformer that provides t he nalvoltage transmission in the electrical power distribution system, stepping downvoltage to the level used by cu stomers.

18. 18. 8. POWER LINE CARRIER COMMUNICATION (PLCC) Reliable & fastcommunication is n ecessary for safe efficient & economic p ower supply. Toreduce the power failure in extent & time, to maintain the interconnected gridsystem in optimum working condition; to coordinate the operation of variousgenerating unit communication network is i ndispensable for state electricityboard. In state electricity boards, the generating & distribution stations aregenerally located at a far distance from cities w here P & T communicationprovided through long overhead lines i n neither reliable nor quick. Power-linecommunication (PLC) carries d ata on a conductor that is a lso used



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simultaneously for AC electric power transmission or electric p ower distribution toconsumers. By using the existing AC power lines a s a medium to transfer theinformation, it becomes e asy t o connect the houses w ith a high s peed n etworkaccess point without installing new wirings. This technology has been in wide use

since 1950 and was m ainly u sed by the grid stations t o transmit information athigh spe ed. PRINCIPLE OF PLCC Power-line com munications systems oper ateby adding a modulated carrier signal to the wiring system. All type of informationis m odulated on carried wave a t frequency 5 0Hz to 500 KHz. The modulated HFcarrier fed into the power line conductor at the sending end and ltered out againat the respective stations. Long earlier system double side band a mplitudemodulation was m ore co mmon but the present amplitude m odulated system.Since high voltage power lines a re designed to carry large quantities o f energyon the high vo ltage and the c ommunication s ystem at low voltage, they c annot be

directly c onnected to high voltage lines. Suitably d esigned coupling equipmentshave therefore to be employed which will permit the injection of high frequencycarrier signal without undue loss a nd with absolute protection of communicationequipments o r operating p ersonal from high voltage h azard. Project Report 19Therefore, the coupling equipment essentially comprises the following: 1. WaveTrap or Line Trap Wave trap is co nnected in series w ith power line between thepoint of connection of coupling capacitor and S/S. Wave trap offers n egligibleimpedance to HF carrier. Wave trap stands e lectromechanically a nd thermally forshort circuit current in the event of fault on the line. On the basis of blocking

frequency b ank, the wave trap can be following type: a) All wave19. 19. Project Report 20 b) Single Frequency c) Double Frequency’ d) Broad Band

2. Coupling Capacitor The modulated carrier is l et into power line throughcoupling capacitor specially d esigned to with stand line voltage under all-weathercondition. The upper end of the coupling capacitor is c onnected directly t o theline and the lower end is co nnected to the ground through a carrier frequencychock c oil or drain coil. Thus co upling capacitor forms t he link b etween the PLCCequipment and power line. The coupling ca pacitor used in UPSEB is 22 00pfcapacitance. The coupling capacitor are designed for outdoor use and hence towithstand normal atmospheric ph enomenon such as t emperature & humiditychanges, rain, snow, anticipated wind load, nominal wire tension etc. at full ratedvoltage. In some case capacitive voltage transformers ( CVT) used as a source ofline voltage for metering and protection as a lso used coupling capacitor forPLCC. 3. Protective D evice of Coarse Voltage Arrestor This is co nnected a crossthe primary o f the coupling lter i.e. one end is c onnected to the bottom of the

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coupling capacitor and other end is e arthed. This is provided to protect thecoupling lter against line surges. An air gap is p rovided, where voltage of theorder of 1.8 to 2KV as o bserved across due to lighting etc. on line. 4. Coupling ofFilter The coupling lter is i nserted between the low voltage terminal of the

coupling capacitor and the carrier frequency connection of the carrier terminal.Sometime an earth switch is a lso provided with this u nit. This u nit mainlyperforms t wo functions; rstly it isolates t he connection of equipment from thepower line. Secondly it serves t o match characteristic impedance of the powerline to that of the H.F. cable to connection equipments. 5. H. F. Cable H.F. cablenormally u sed to connect the coupling lter to another coupling terminal. Thecable is i nsulated to withstand the test voltage of 4KV. The impedance of this H .F.cable is so as t o match with the output of the PLCC terminal and secondaryimpedance of coupling lter.

20. 20. Project Report 21 APPLICATION OF PLCC PLCC technology can bedeployed into different types o f applications i n order to provide economicnetworking solutions. Hence merging with other technologies i t proves u seful indifferent areas. These are few key areas w here PLC communications a re utilized:a. Transmission & Distribution Network: PLCC was rst adopted in the electricaltransmission and distribution system to transmit information at a fast rate. b.Home control and Automation: PLCC technology is use d in home co ntrol andautomation. This t echnology ca n reduce the resources a s w ell as e fforts f oractivities l ike power management, energy c onservation, etc. c. Entertainment:

PLCC is u sed to distribute the multimedia content throughout the home. d.Telecommunication: Data transmission for different types o f communications l iketelephonic co mmunication, audio, video communication can be made with theuse of PLCC technology. e. Security S ystems: In monitoring houses o rbusinesses through surveillance cameras, PLCC technology i s far useful. f.Automatic Meter Reading – Automatic Meter reading applications u se t he PLCCtechnology to send the data from home meters t o Host Central Station. WaveTrap

21. 21. Duplicate bus b ar system In large stations i t is i mportant that break d ownsand maintenance should interfere as l ittle as possible with continuity of supply toachieve this, duplicate bus b ar system is u sed. Such a system consists o f twobus b ars, a m ain bus b ar and a spare b us b ar with the h elp of bus co upler, whichconsist of the circuit breaker and isolator. In substations, it is often desired todisconnect a part of the system for general maintenance and repairs. An isolatingswitch or isolator accomplishes this. Isolator operates under no load condition. It



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does n ot have any s pecied current breaking c apacity o r current making capacity.In some cases i solators a re used to breaking charging currents o r transmissionlines. While opening a circuit, the circuit breaker is opened rst then isolator whileclosing a circuit the isolator is closed rst, then circuit breakers. Isolators are

neces s ary o n supply s ide of circuit breakers, in order to ensure isolation of thecircuit breaker from live parts for the purpose of maintenance. A transfer isolatoris u sed to transfer main supply from main b us t o transfer bus b y using buscoupler (combination of a circuit breaker with two isolators), if repairing ormaintenance of any section is r equired. Bus B ars • S ingle bus b ar system withsection alisation. • S ingle bus ba r system • Project Report 22 9. BUSBARS Whennumbers o f generators o r feeders o perating a t the s ame voltage h ave to bedirectly c onnected electrically, bus b ar is u sed as t he common electricalcomponent. Bus b ars a re made up of copper rods o perate at constant voltage.

The following a re the important bus b ars a rrangements u sed at substations:22. 22. Project Report 23 10. CIRCUIT BREAKERS A circuit breaker is an

automatically operated electrical switch designed to protect an electrical circuitfrom damage caused by o verload or short circuit. Its b asic f unction is t o detect afault condition and interrupt current ow. Unlike a fuse, which operates o nce andthen must be replaced, a circuit breaker can be reset (either manually o rautomatically) to resume normal operation. Circuit breakers a re made in varyingsizes, from small devices t hat protect an individual household appliance up tolarge switchgear designed to protect high voltage circuits f eeding an entire city.

There are different types of circuit breakers which are:- 1. Low-voltage circuitbreakers L ow-voltage (less t han 1,000 VAC) types a re common in domestic,commercial and industrial application, and include Miniature Circuit Breaker(MCB) and Molded Case Circuit Breaker (MCCB). 2. Magnetic ci rcuit breakersMagnetic ci rcuit breakers u se a solenoid (electromagnet) whose pulling forceincreases with the current. Certain designs utilize electromagnetic forces inaddition to those of the solenoid.

23. 23. Project Report 24 3. Thermal magnetic ci rcuit breakers T hermal magneticcircuit breakers, which are the type found in most distribution boards, incorporateboth techniques w ith the electromagnet responding instantaneously t o largesurges i n current (short circuits) and the bimetallic strip responding to lessextreme but longer-term over-current conditions. The thermal portion of the circuitbreaker provides a n "inverse time" response feature, which trips t he circuitbreaker sooner for larger over currents. 4. Common trip breakers T hree-polecommon trip breaker for supplying a three-phase device. This b reaker has a 2A



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rating. When supplying a branch circuit with more than one live conductor, eachlive conductor must be protected by a breaker pole. To ensure that all liveconductors a re interrupted when a ny p ole t rips, a "common trip" breaker must beused. These may either contain two or three tripping mechanisms w ithin one

case, or for small breakers, may externally tie the poles together via theiroperating handles.

24. 24. Project Report 25 5. Air circuit breakers R ated current up to 6,300 A andhigher for generator circuit breakers. Trip characteristics are often fully adjustableincluding congurable trip thresholds and delays. Usually electronicallycontrolled, though some models are microprocessor controlled via an integralelectronic t rip unit. Often used for main power distribution in large industrial plant,where the breakers a re arranged in draw-out enclosures f or ease ofmaintenance. 6. Vacuum circuit breakers W ith rated current up to 6,300 A, and

higher for generator circuit breakers. These breakers i nterrupt the current bycreating and extinguishing the arc i n a vacuum container. 7. Oil circuit breakers Ahigh-voltage circuit breaker in which the arc i s d rawn in oil to dissipate the heatand extinguish the arc; the intense heat of the arc d ecomposes t he oil,generating a gas w hose high pressure produces a ow of fresh uid through thearc t hat furnishes t he necessary insulation to prevent a restrike of the arc. Thearc i s then extinguished, both because of its e longation upon parting of contactsand because of intensive cooling by the gases a nd oil vapor. They are further oftwo

25. 25. types: Bulk Oil Circuit Breaker (BOCB) and Minimum Oil Circuit Breaker(MOCB). Project Report 26 8. Sulfur hexauoride (Sf6) high-voltage circuitbreakers A sulfur hexauoride circuit breaker uses co ntacts su rrounded by su lfurhexauoride gas t o quench the arc. They are most often used for transmission-level voltages a nd may be incorporated into compact gas-insulated switchgear.

26. 26. Project Report 27 11. ISOLATERS In electrical engineering, a disconnector,disconnect switch or isolator switch is used to ensure that an electrical circuit iscompletely de-energized for service or maintenance. Such switches a re oftenfound in electrical distribution and industrial applications, where machinery musthave its s ource of driving power removed for adjustment or repair. High-voltageisolation switches a re used in electrical substations t o allow isolation of apparatussuch as circuit breakers, transformers, and transmission lines, for maintenance.The disconnector is usually not intended for normal control of the circuit, but onlyfor safety isolation. Disconnector can be operated either manually orautomatically (motorized disconnector). Unlike load b reak sw itches a nd circuit



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breakers, disconnectors l ack a mechanism for suppression of electric a rc, whichoccurs w hen conductors c arrying high currents a re electrically interrupted. Thus,they are off-load devices, intended to be opened only a fter current has b eeninterrupted by some other control device. Safety regulations of the utility must

prevent any a ttempt to open the disconnector while it supplies a circuit.Standards i n some countries f or safety m ay r equire either local motor isolators o rlockable overloads ( which can be padlocked). Disconnectors h ave provisions f ora padlock so that inadvertent operation is not possible (lockout-tag out). In high-voltage o r complex sys tems, these p adlocks m ay b e p art of a t rapped-keyinterlock s ystem to ensure p roper sequence of operation. In some designs, theisolator switch has the additional ability to earth the isolated circuit therebyproviding additional safety. Such an arrangement would apply to circuits w hichinter-connect power distribution systems w here both ends o f the circuit need to

be isolated.27. 27. Suspension insulator For voltages g reater than 33 kV, it is a usual practice to

use suspension type insulators sh own in Figure. Consist of a number of porcelaindiscs c onnected in series by m etal links in the form of a string. The conductor issuspended at the bottom end of this s tring while the other end of the string issecured to the c ross - arm of the t ower. The number of disc u nits u sed dependson the voltage. • P in type insulator As t he name suggests, the pin type insulator ismounted o n a pin on the cross - arm on the pole. There is a groove o n the upperend of the insulator. The conductor passes t hrough this g roove and is t ied to the

insulator with annealed w ire of the same m aterial as t he c onductor. Pin t ypeinsulators are used for transmission and distribution of electric power at voltagesup to 33 kV. Beyond operating voltage of 33 kV, the pin type insulators b ecometoo bulky an d hence uneconomical. • Project Report 28 12. INSULATORS Anelectrical insulator is a material whose internal electric c harges d o not ow freely,and therefore make it very h ard to conduct an electric c urrent under the inuenceof an electric e ld. The insulator serves t wo purposes. They s upport theconductors ( bus b ar) and conne the current to the conductors. The mostcommon used material for the manufacture of insulator is p orcelain. There areseveral types o f insulators (e. g. pin type, suspension type, post insulator etc.)and their use in substation w ill depend upon the service requirement. Differenttypes of insulator are:-

28. 28. Shackle insulator In early d ays, the shackle insulators w ere used as s traininsulators. But now a day, they a re frequently u sed for low voltage distributionlines. Such insulators c an be used either in a horizontal position or in a vertical



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position. They c an be directly xed to the pole with a bolt or to the cross arm. • Strain insulator A dead end or anchor pole or tower is u sed where a straightsection of line ends, or angles o ff in another direction. These poles m ustwithstand the lateral (horizontal) tension of the long straight section of wire. In

order to support this lateral load, strain insulators are used. For low voltage lines(less than 11 kV), shackle insulators a re used as s train insulators. However, forhigh voltage transmission lines, strings of cap-and-pin (disc) insulators are used,attached to the crossarm in a horizontal direction. When the tension load in linesis e xceedingly h igh, such as a t long river spans, two or more strings a re used inparallel. • Project Report 29

29. 29. Project Report 30 13. RELAYS In a power system it is i nevitable thatimmediately o r later some failure does occur somewhere in the system. When afailure occurs o n any p art of the system, it must be quickly d etected and

disconnected from the s ystem. Rapid d isconnection of faulted apparatus l imitsthe amount of damage to it and prevents t he effects o f fault from spreading intothe system. For high voltage circuits r elays a re employed to serve the desiredfunction of automatic p rotective gear. The relays detect the fault and supply t heinformation to the circuit breaker. Differential Relay A differential relay i s o ne thatoperates w hen vector difference of the two or more electrical quantities e xceedsa predetermined value. If this d ifferential quantity is e qual or greater than thepickup value, the relay will operate and open the circuit breaker to isolate thefaulty section. • Electromagnetic Induction RELAY USED IN CONTROLLING

PANEL OF SUBSTATION • Electromagnetic Attraction • The electrical quantitieswhich may change under fault condition are voltage, frequency, current, phaseangle. When a short circuit occurs a t any p oint on the transmission line thecurrent owing in the line increases t o the enormous va lue. This r esult in a heavycurrent ow through the relay c oil, causing the relay t o operate by c losing itscontacts. This in turn closes the trip circuit of the breaker making the circuitbreaker open and isolating the faulty s ection from the rest of the system. In thisway, the relay ensures t he safety o f the circuit equipment from the damage andnormal working of the healthy portion of the system. Relay works o n two mainoperating principles:-

30. 30. Tripping Relay T his t ype of relay is i n the conjunction with main relay. Whenmain relay s ense any fault in the system, it immediately o perates t he trip relay t odisconnect the faulty s ection from the section. • Earth Fault Relay This t ype ofrelay se nse the fault between the lines a nd the earth. It checks t he vector sum ofall the line currents. If it is not equal to zero, it trips. • O ver Current Relay This



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type of relay works w hen current in the circuit exceeds t he predetermined value.The actuating source is the current in the circuit supplied to the relay f rom acurrent transformer. These relay a re used on A.C. circuit only a nd can operate forfault ow in the either direction. This r elay operates w hen phase to phase fault

occurs.•

Project Report 3131. 31. Auxiliary Relay An auxiliary relay is used to indicate the fault by glowing bulb

or showing various a gs. • Project Report 3232. 32. Improve P ower Factor • Improve Terminal Voltage • Supply Reactive P ower

• Project Report 33 14. CAPACITOR BANK The load on the power system isvarying being h igh during morning a nd e vening which increases t hemagnetization current. This r esult in the decreased power factor. The low powerfactor is m ainly d ue to the fact most of the power loads a re inductive andtherefore take lagging currents. The low power factor is h ighly u ndesirable as i t

causes i ncreases in current, resulting in additional losses. So in order to ensuremost favorable conditions for a supply syst em from engineering and economicstand point it is i mportant to have power factor as c lose to unity a s possible. Inorder to improve the power factor come d evice taking leading power should beconnected in parallel with the load. One of such device can be capacitor bank.The capacitors d raw a leading current and partly o r completely n eutralize thelagging reactive component of load current. Main functions o f Capacitor Bankare:-

33. 33. Buchholz R elay Buchholz r elay is a safety d evice mounted on some oil-lled

power transformers a nd reactors, equipped with an external overhead oilreservoir called a conservator. The Buchholz R elay is used as a protective devicesensitive to the effects o f dielectric f ailure inside the equipment. Depending onthe model, the relay h as m ultiple methods t o detect a failing transformer. On aslow accumulation of gas, due perhaps t o slight overload, gas p roduced bydecomposition of insulating oil accumulates in the top of the relay a nd forces theoil level down. A oat switch in the relay is u sed to initiate an alarm signal.Depending on design, a s econd oat may also serve to detect slow oil leaks. If anarc forms, gas a ccumulation is r apid, and oil ows r apidly into the conservator.This o w of oil operates a switch attached to a vane located in the path of themoving oil. This s witch normally w ill operate a circuit breaker to isolate theapparatus b efore t he fault causes a dditional damage. • Project Report 34 15.PROTECTION OF SUBSTATION LIGHTNING ARRESTORS A lightning arrestoris a d evice used in p ower systems a nd telecommunications syst ems to protectthe insulation and conductors o f the system from the damaging effects o f



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lightning. The typical lightning arrester has a high-voltage terminal and a groundterminal. When a lightning surge (or switching surge, which is v ery s imilar) travelsalong the power line to the arrester, the current from the surge is d iverted throughthe arrestor, in most cases to ea rth. TRANSFORMER PROTECTION

Transformers a re totally e nclosed static d evices a nd generally o il immersed.Therefore chances o f fault occurring on them are very e asy rare, however theconsequences o f even a rare fault may be very se rious u nless t he transformer isquickly d isconnected from the system. This p rovides a dequate automaticprotection for transformers a gainst possible faults. Various p rotection methodsused for transformers a re:-

34. 34. Conservator and Breather When the oil expands o r contacts by t he changein the temperature, the oil level goes e ither up or down in main tank. Aconservator is u sed to maintain the oil level up to predetermined value in the

transformer main tank b y p lacing it above the level of the top of the tank. Breatheris c onnected to conservator tank for the purpose of extracting moisture as i tspoils t he insulating properties o f the oil. During the contraction and expansion ofoil air is d rawn in or out through breather silica gel crystals i mpregnated withcobalt chloride. Silica gel is c hecked regularly a nd dried and replaced whennecessary. • Project Report 35

35. 35. Transformer cooling When the transformer is i n operation heat is g enerateddue to iron losses t he removal of heat is c alled cooling. There are several typesof cooling methods, they are as follows: 1. Air natural cooling In a dry type of self-

cooled transformers, the natural circulation of surrounding air is used for itscooling. This t ype of cooling is s atisfactory for low voltage small transformers. 2.Air blast cooling It is similar to that of dry type self-cooled transformers with toaddition that continuous b last of ltered cool air is f orced through the core andwinding for better cooling. A fan produces t he blast. 3. Oil natural cooling Mediumand large rating transformers have their winding and core immersed in oil, whichact both as a co oling medium and an insulating medium. The heat produce in thecores a nd winding is p assed to the oil becomes l ighter and rises t o the top andplace is • Marshalling box It has t wo meter which indicate the temperature of theoil and winding of main tank. If temperature of oil or winding exceeds t hanspecied value, relay o perates t o sound an alarm. If there is f urther increase intemperature then relay c ompletes the trip circuit to open the circuit breakercontrolling the transformer. • Project Report 36

36. 36. Project Report 37 taken by c ool oil from the bottom of the cooling tank. 4. Oilblast cooling In this t ype of cooling, forced air is d irected over cooling elements o f



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transformers i mmersed in oil. 5. Forced oil and forced air ow (OFB) cooling Oilis c irculated from the top of the transformers t ank t o a cooling tank t o a coolingplant. Oil is t hen returned to the bottom of the tank. 6. Forced oil and water(OWF) cooling In this t ype of cooling oil ow with water cooling of the oil in

external water heat exchanger takes p lace. The water is c irculated in coolingtubes i n the heat exchanger.

37. 37. Project Report 38 16. CONCLUSION Now from this report one can concludethat electricity plays an important role in our life. At the end of the training, I cameto know about the various p arts o f substations a nd how they are operated. Also Ilearnt about how transmission is d one in various p arts o f Uttarakhand. As e videntfrom the report, a substation plays a very important role in the transmissionsystem. That’s w hy various p rotective measures a re taken to protect thesubstations f rom various faults a nd its sm ooth functioning. Power Transmission

Corporation of Uttarakhand Limited takes su ch steps so that a uniform and stablesupply of electricity can reach in every part of this state.

38. 38. Project Report 39 17. BIBLIOGRAPHY 1. Energy efficiency in e lectricalutilities, Guide book for National certication examination for energy managersand energy a uditors, Bureau of energy efficiency, Ministry o f Power, Govt. ofIndia, 2003. 2. General aspect of energy management and e nergy a udit, Guidebook for National certication examination for energy m anagers a nd energyauditors, Bureau of energy efficiency, Ministry o f Power, Govt. of India, 2003. 3.www.wikepedia.com 4. www.slideshare.com 5. www.electrical-installation.org 6 .

www.home-energy-metering.com 7. www.enspecpower.com 8.www.allaboutcircuits.com

electrical substations

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