1 Transformers

8/11/2019 1 Transformers

1/8

List of Content TransformersPower TransformerCurrent Transformer

V oltage Transformer Capacitive V oltage Transformer RelaysCircuit BreakersCapacitor BankInsulatorIsolator

Power System ProtectionSurge ArrestorsSingle line diagramReferencesTransformers Static device which converts electrical energy from one voltage toanother.Transformers at Sahibabad Sub Station-1. 160 MVA 220/132 KV (BHEL)2. 160 MVA 220/132 KV (AREVA)3. 40 MVA 132/33 KV (KANOHAR)4. 40 MVA 132/33 KV (ALSTOM)5. 20 M

They are used to change the amplitude of high frequency pulses by the turns ratio and to provide isolation betweencircuits.Itsmain parts are:-Core:-Manufactured from laminations of CRGO(ColdRolled GrainOriented)Silicon Steel. It gives very low specific loss at operatingflux densities. Windings:- They are made from paper insulatedcopperconductors which are transposed at


2/8

regularintervalsthroughout the winding. It provides equal fluxlinkage andcurrent distribution between strands. Bushing:-They use a maximum amount of conductormaterial to provide therequired shape and physicalstrength, and use a minimum amountof insulatingmaterial to provide only the insulating function.Pressure Relief Valve:-Transformers are provided with pressure relief valve whichoperates in case of suddenpressure formation inside thetransformer.

Cooling System:-

Transformers are provided withcooling bank. These are provided with fans and pumps.These fans and pumps automaticallyoperate, dependingupon the settings of winding temperature .

Protective Relays .Current Transformers A current transformer (CT) is used for the measurementof electric currents.

W hen current in a circuit is too high to directly apply tomeasuring instruments, a currenttransformer produces a reducedcurrentaccurately proportional to the current in thecircuit, whichcan be connected to measuringand recording instruments.

Voltage Transformers V oltage transformers ( V T) are another type ofinstrumenttransformer, used for metering and protection in high-

voltage circuits. They are designed to present negligible load to the supply beingmeasured and to have a precise voltage ratio toaccurately stepdown high voltages so that metering andprotective relayequipment can be operated at a lowerpotential.


3/8

V Ts are typically used for higher voltages (for example,765 k Vfor power transmission), or where isolation isdesired between themeter and the measured circuit.

Relays

A relay is an electrically operated switch.These are used to protect electrical circuits from overloador faults.Relays find applications where it is necessary to control acircuit bya low-power signal, or where several circuitsmust be controlled byone signal.

Operation W hen an electric current is passed through the coil, theresultingmagnetic field attracts the armature. The consequent movement of the movable contacts eithermakesor breaks a connection with a fixed contact.If the set of contacts were closed when the relay was de-energized,

then the movement opens the contacts and breaks the connection,and vice versa if the contacts wereopen. W hen the current to the coil is switched off, thearmature isreturned by a force, approximately half as strong asthemagnetic force, to its relaxed position. This force is provided by a spring.

Circuit Breaker A circuit breaker is an automatically-operated electricalswitch.It is designed to protect an electrical circuit from damagecaused by overload or short circuit.Its basic function is to detect a fault condition, interruptthecontinuity, and immediately discontinue electricalflow.


4/8

Operation of a C.B. Circuit breakers for large currents or high voltages areusuallyarranged with pilot devices.It senses a fault current and operate the trip openingmechanism.The trip solenoid that releases the latch is usually energized by aseparate battery.Once a fault is detected, contacts within the circuit breakeropen tointerrupt the circuit.Some mechanically-stored energy (using something suchassprings or compressed air) contained within the breakeris used toseparate the contacts.Circuit breakers have solenoids to trip the mechanism, andelectric

motors to restore energy to the springs.The circuit breaker contacts carry the load current withoutexcessive heating, and also withstand the heat of the arc produced when interrupting the circuit.Contacts are made of copper or copper alloys, silveralloys, andother materials.

W hen a current is interrupted, an arc is generated. This arc is contained, cooled, and extinguished in acontrolled way,so that the gap between the contacts canagain withstand the voltage in the circuit.Once the fault condition has been cleared, the contacts areagainclosed to restore power to the interrupted circuit.

TYPES OF CIRCUIT BREAKER Medium-voltage circuit breakersMedium-voltage circuit breakers can be classified by themedium

used to extinguish the arc: V acuum circuit breaker Air circuit breakerSF6circuit breakers


5/8

High-voltage circuit breakerHigh-voltage breakers are broadly classified by the mediumusedto extinguish the arc.

Bulk oilMinimum oil Air blast

V acuum SF6

INSULATOR Types of insulators:Pin-Type- Used up t o 3 3 kvSuspension-Type-Used for insulatingO/H lines against higher voltagesStrain or Tension Type- strings are placed in horizontal plane

P OW E R SYSTEM P RO TECTI O

N

Powersystem


6/8

protectionis a branch of electricalpower engineeringthat deals with theprotection of electrical power systems from faults.

The objective of a protection scheme is to keep the powersystemstable by isolating only the components that areunder fault, while

leaving as much of the network aspossible still in operation.

Components Protection systems usually comprise five components:

Currentand voltage transformers to step down the high voltagesand currents of the electrical power system toconvenient levels forthe relays to deal with;

Relaysto sense the fault and initiate a trip, ordisconnection,order;

Circuit breakersto open/close the system based onrelay and auto-reclosercommands;

Batteriesto provide power in case of power disconnectioninthe system.


7/8

Communication channelsto allow analysis of currentand voltage at remote terminals of a line and to allowremotetripping of equipment.


8/8

Documents

1 Transformers