EQUIPMENTS IN SUB-STATION

EQUIPMENTS IN SUB-STATION

ISOLATOR : It used for supporting live conductor and bus bars. For 66 kv switch yard stack, mounted horizontal or vertical as per condition.

CONDUCTOR : Generally copper / Aluminium material used. Now a days Aluminium conductor used for its higher conductivity on weight basis, low cost for same current capacity and excellent corrosion resistance and formability, for reliable connection they can be coted with silver.

OIL CIRCUIT BREAKER AND RECLOSER : The HV Circuit breaker are intended for making/breaking high voltage circuits when they carry the normal load current/break circuit in case of fault. Generally pneumatic/hydraulic/mechanically operated breaker should be used instead of solenoid mechanisum. The re-closers used on low voltage bus structure columns and thus separate structure can be avoided.

AIR BREAK/DISCONNECTED SWITCH : They are manually operated but can also be mounted if they are to be of remote controlled type. Now a days automatic sectionalization switches used.

The disconnect switch for 46 kV and below are generally of single pole and have hook stick operated mechanism but they can also be of group-operated mechanism.

The 110 kv and higher voltage disconnected switches are group operated. However, these air break switches are opened only after the circuit breaker had made the circuit dead.

TRANSFORMERS : The use of 3 phase transformers, because of the advantages of 3 transformer is that in case of fault in one of them it could be completely replaced by new one. The main advantage of 3 phase transformer need only one 3 phase load tap changing mechanism could be used. Further the installation of a single 3 phase transformer is much simpler than 3 phase transformer. The 3 phase transformer generally installed over a flat concrete slab foundation In order to provide ventilation the large transformer are placed upon length of rail.

CARRIER CURRENT EQUIPMENT : Such equipment is used for communication, relaying tele metering or for supervisory control. This equipment is suitably mounted and connected to the high voltage power circuit. The communication equipment is mounted adjacent to the breaker and connected above the breaker termination.

PROTECHTIVE FUSE AND RELAYS : The fuses are very commonly provided on the high voltage side Alongwith the other protection device. It serves to protect the transformer from the system or it can also be said that the fuse protects the system from transformer. Its also used to protects the power system equipment from damage against fault at any point enroute.

CONTROL CABLE AND CONDUIT SYSTEM : The modern power complex has made it all most necessary to provide automatic operation/interlocks. Control cables and conduits are necessary for effecting such automatic controls. The control supply 110 or 220 volt and cable used is multi conductor havinf 10 / 37 or 61 conductors as per requirement. For laying this cables generally ducts are run from control house basement to centerally located junction boxes from where the conduits are to the required point.

SWITCH BOARD : It consists of meters, relays and control equipment. The essential meters are placed as the top end. Relay and nonessential meters are placed at the bottom, so as to facilitate their operation.

CONTROL ROOM : All equipment such as switch board carrier current equipment, batteries etc. Generally 2 X 1.5 Mtr. Basement hatch way left in floor for facilitating the installation. Below the switch board a slot of about 10 cm. Provided for control room cable.

EquipmentFunctionRemarks

1.BusbarsVarious incoming and out going circuits are connected to bus bars. Bus bars receive power from incoming circuits and deliver power to outgoing circuits.Either Rigid Aluminium Tubular bus bars supported on post insulators.

OR

Flexible ASCR or All aluminium stranded bus bars supported from two ends by strain insulators.

Two levels or three levels Indoor or outdoor.

2. Surge Arresters

(Lightning Arresters)Surge Arresters discharge the over voltage surges to earth and protect the equipment insulation from switching surges and lighting surges.

(Word `Surge refers to impulse wave is transmission of distribution systems.)

- Connected generally between phase conductor and ground.

- Located as the first equipment as seen from the incoming overhead line and also near transformer terminals phase to ground.

- Two types : Gapped Arresters and Gapless zinc-Oxide Arrestors.

3. Isolators ( Disconnecting

Switch )To provide isolation from live parts for the purpose of maintenance.- Located at each side of circuit breaker.

- Does not have any rating for current breaking or current making.

- Types :

1. Center rotating horizontal swing.

2. Center-break

3. Vertical swing

4. Pantograph type

- Interlocked with circuit breaker.

4. Earthing SwitchDischarging the voltage on the circuit to each for safety.- Mounted on the frame of the isolators.

- Location generally for each incomer and each bus bar Section.

5. Current Transformer Stepping down current measurement, protection and control.-1. Protective CT

-2. Measuring CT

-Location decided by protective zone measurement requirement.

6. Voltage TransformerStepping down current for measurements, protection and control.- Types :

1. Electro magnetic

2. Capacitive VT (CVT)

- Location on feeder side of circuit breaker.

7. Circuit breakerSwitching during normal and abnormal operating condition. To interrupt short circuit currents.

Operations include :

- closing

- opening

- auto-reclosing

Located near every switching point. Located at both end as every protected zone.

- types : Depending on rated voltage : Low voltages, medium high voltage, high voltage, extra high voltage.

- Types : Depending on medium of are quenching :

1. SF

2. Vacuum

3. Air blast

4. Minimum Oil.

8. Power TransformerTo step-up or step-down A.C. voltages and to transfer electrical power from one voltage level to another.- Usually oil filled for outdoor use.

- two winding or three winding.

Tap changers used for voltage control. For every large transformers, Transportation, rail permit etc. should be decided in advance.- Three single phase units to form a three bank used when single three phase unit becomes too large to transport.

- Provided with coolers.

- Provided with tamp-changers.

9. Shunt ReactorsUsed for long E H V transmission lines to control voltage during low-load period. To compensate shunt capacitance of transmission line during low load periods.- Usually oil filled, gapped core, shielded.

- Usually unswitched.

10. Shunt CapacitorFor compensating reactive power of lagging power factor. To improve power factor. For voltage control during heavy lagging power factor loads.- Located at receiving stations and Distribution Sub-stations.

- Banks rated 132 kV, 66 kV, 33 kV, 11 kV, 6.6 kV etc.

- Switched in during heavy loads, switched off during low loads.

11. Sales CapacitorUsed for some long E H V A. C. lines to improve power transferability.- Capacitor bank located at sending-end and/or receiving-end of line.

- Provided with by-pass circuit-breaker and protective spark-gaps.

12. Carrier Equipment

Line trap unit

- Coupling Capacitor

- Electronic EquipmentUsed for protection and communication signaling, voice communication, protection signaling, telex channel, control and monitoring signals.- Line trap unit usually mounted above C V T or on separate structure.

- Coupling capacitor mounted on structure.

- Tunning unit.

- P L C C panels located in Control room.

13. Marshalling Kiosks To mount monitoring instruments, control equipment and to provide access to various transducers. Control and protective cable are laid between Marshalling Kiosks located in switchyard and corresponding indoor control panels.- Located switchyard near every power transformer ; a group of equipment in a bay.

14. Metering Panels,

Control and Relay

Panels (Indoor)To house various Measuring Instruments, Control Instruments, Protective Relays.- Located in air-conditioned building. Control cables and laid between switchyard equipment and these panels.

15. Medium Voltage A. C.

switchgear and Low

Voltage A. C.

Switchgear (Indoor).To provide A. C. power to auxiliaries, station lightning system etc. at respective voltage levels.- Located inside switchgear building.

16. Station Earthing SystemTo provide a low resistance Earthing for

- discharging currents from surge arrestors, overhead shielding, Earthing switches.

- For equipment body Earthing

- for safe touch potential and step potential in substation.- Earth-mat and earth electrodes placed below ground level. Connected to equipment structures, neutral points for purpose of Equipment Earthing and Neutral Point Earthing.

- for providing path for neutral to ground currents for earth fault protection.

17. Lightning ProtectionTo protect substation equipment from direct lightning strokes.-Lightning Masts located in outdoor yard.

- Alternatively, overhead shieding wires to cover entire outdoor yard.

18. Series Reactors (Current

Limiting Reactor)To limit short-circuit current and to limit current surges associated with fluctuating loads.- Located at strategic locations such that fault levels are reduced. Now no more preferred.

19. Isolated Phase Bus

SystemProvides connection between generator and main transformer. High normal currents.- Aluminium enclosures for each phase conductor. Can withstand high.

To provide connection between L V side of power transformer and indoor metal clad switchgear.Short-circuit currents due to magnetic shielding provided by enclosures.

20. Neutral Grounding

Equipment

-Resistor

- Reactor To limit short-circuit current during ground fault.-Short-time rated. Connected between neutral point and ground.

21. Static Var Sources (SVS)To provide stepless, variable shunt compensation for voltage control.-Thyristor controlled shunt reactor and shunt capacitor

- Rapid control of voltage.

22. Line trapInductive coil usually outdoor.-Connected in outdoor yard incoming line.

- Past of PLCC requirement.

23. Power Cables Single core

- Three core-P V C insulated

-X L P E insulated

-for power flow

24. Control Cables Multi core-P V C insulated

Shiclded

For protection, Controlmeasurements etc.

Low voltage

25. Insulators

Procelain

Glass

Epoxy for

Indoor use String Insulators

1. Tension

2. Suspension

Post insulators

Solid care For Flexible ASCR conductors

For tublar conductors

For apparatus

LIST OF EQUIPMENTS IN SUB STATIONS

1. Circuit breaker 66/132 kV: a) Bulk oil (b) Minimum oil c) SF 6

2. Isolaters

3. Transformer a) Power b) Distribution

4. Earth Switches

5. Potential Transformers : a) Current b) Potential

6. Circuit breaker 11 kV a) Bulk b) Minimuum oil c) SF-6

d) Vacuum

7. Power line carrier communication equipment

8. Wire less set

9. Telephone

10. Batteries

11. Battery Charger

12. A C Distribution Board

13. D C Distribution Board

14. Neutral Resistance

15. Neutral Resistance

16. Capacitor Bank

17. Earting Transformer

18. Fire Extingusher

19. Lighting Arestor

PERMISSIBLE CONTINOUS RATING OF FEEDERS

SYSTEM VOLTAGESIZE OF CABLE/CONDUCTORCURRENT CAPACITY

132 kV0.2 Sq.inch.450 A

132 kV0.125 Sq.inch.280 A

66 kV0.2 Sq.inch.450 A

66 kV0.175 Sq.inch380 A

66 kV0.5 Sq.inch.255.Sq.inch.

66 kV0.1 Sq.inch.210 A

66 kV240 Sq.mm966 A

11 kV1.25 Sq.inch.230 A

11 kV0.2 Sq.inch.220 A

11 kV240.Sq.mm254 A

RATING OF TRANSFORMERS :

5 MVA 66/11 kV 48.8/262.5 A

12.5 MVA66/11 kV109/656 A

15 MVA66/11 kV131/787.5 A

20 MVA66/11 kV175/1050 A

30 MVA132/11kV131/1575 A

50 MVA132/66 kV218.7/437.4 A

65 MVA132/66 kV284.3/568.6 A

100 kVA11 kV/ 440 V5.25/133.34 A

160 kVA11 kV/440 V8.4/2133 A