Summer Training Presentation

ELECTRICITY DISTRIBUTION SYSTEMAT

220 KV SUB-STATION,SAHIBABAD

Presented By – NAMRATA PATHAKE.N. 4th YrSec- FRoll No.- 0702721066

List of Content• Transformers• Power Transformer• Current Transformer• Voltage Transformer• Capacitive Voltage Transformer• Relays• Circuit Breakers• Capacitor Bank• Insulator• Isolator• Power System Protection• Surge Arrestors• Single line diagram• References

Transformers• Static device which converts electrical energy

from one voltage to another.

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 MVA 132/11 KV (JEUMONT)

Power Transformer• They basically work only on high voltages and

currents .• They are used to change the amplitude of high

frequency pulses by the turns ratio and to provide isolation between circuits.

Its main parts are:- Core:- Manufactured from laminations of

CRGO(Cold Rolled Grain Oriented)Silicon Steel. It gives very low specific loss at operating flux densities.

Windings:-They are made from paper insulated copper conductors which are transposed at regular intervals throughout the winding. It provides equal flux linkage and current distribution between strands.

Bushing :- They use a maximum amount of conductor material to provide the required shape and physical strength, and use a minimum amount of insulating material to provide only the insulating function.

Pressure Relief Valve :- Transformers are provided with pressure relief valve which operates in case of sudden pressure formation inside the transformer.

Cooling System :-Transformers are provided with cooling bank. These are provided with fans and pumps. These fans and pumps automatically operate, depending upon the settings of winding temperature .

Protective Relays .

Current Transformers

• A current transformer (CT) is used for the measurement of electric currents.

• When current in a circuit is too high to directly apply to measuring instruments, a current transformer produces a reduced current accurately proportional to the current in the circuit, which can be connected to measuring and recording instruments.

Voltage Transformers

• Voltage transformers (VT) are another type of instrument transformer, used for metering and protection in high-voltage circuits.

• They are designed to present negligible load to the supply being measured and to have a precise voltage ratio to accurately step down high voltages so that metering and protective relay equipment can be operated at a lower potential.

• VTs are typically used for higher voltages (for example, 765 kV for power transmission), or where isolation is desired between the meter and the measured circuit.

Capacitive Voltage Transformers(CVT)

• Capacitive voltage transformers are used for line voltmeters synchroscopes, protective relays, tariff meter. They are used for voltages higher than 66kV.

Relays• A relay is an electrically operated switch.• These are used to protect electrical circuits from

overload or faults.• Relays find applications where it is necessary to

control a circuit by a low-power signal, or where several circuits must be controlled by one signal.

Operation• When an electric current is passed through the coil,

the resulting magnetic field attracts the armature.• The consequent movement of the movable contacts

either makes or 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 were open.

• When the current to the coil is switched off, the armature is returned by a force, approximately half as strong as the magnetic force, to its relaxed position.

• This force is provided by a spring.

Circuit Breaker• A circuit breaker is an automatically-operated

electrical switch.• It is designed to protect an electrical circuit from

damage caused by overload or short circuit.• Its basic function is to detect a fault condition,

interrupt the continuity, and immediately discontinue electrical flow.

Operation of a C.B. • Circuit breakers for large currents or high voltages

are usually arranged with pilot devices.• It senses a fault current and operate the trip

opening mechanism.• The trip solenoid that releases the latch is usually

energized by a separate battery.• Once a fault is detected, contacts within the circuit

breaker open to interrupt the circuit.• Some mechanically-stored energy (using something

such as springs or compressed air) contained within the breaker is used to separate the contacts.

• Circuit breakers have solenoids to trip the mechanism, and electric motors to restore energy to the springs.

• The circuit breaker contacts carry the load current without excessive heating, and also withstand the heat of the arc produced when interrupting the circuit.

• Contacts are made of copper or copper alloys, silver alloys, and other materials.

• When a current is interrupted, an arc is generated.

• This arc is contained, cooled, and extinguished in a controlled way, so that the gap between the contacts can again withstand the voltage in the circuit.

• Once the fault condition has been cleared, the contacts are again closed to restore power to the interrupted circuit.

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

medium used to extinguish the arc:• Vacuum circuit breaker• Air circuit breaker • SF6 circuit breakers

High-voltage circuit breakerHigh-voltage breakers are broadly classified by the medium

used to extinguish the arc.• Bulk oil• Minimum oil• Air blast• Vacuum• SF6

CAPACITOR BANK• Capacitor banks can improve the power factor if the load

is leading, which is unusual. Typically in substations capacitor banks are employed to reduce over voltage.

INSULATOR

• Types of insulators: Pin-Type- Used upto 33kv Suspension-Type- used for insulating O/H lines against higher voltages Strain or Tension Type- strings are placed in horizontal plane

ISOLATOR• A disconnector or isolator switch is used to make sure that an

electrical circuit can be completely de-energized for service or maintenance.

POWER SYSTEM PROTECTION• Power system protection is a branch of

electrical power engineering that deals with the protection of electrical power systems from faults.

• The objective of a protection scheme is to keep the power system stable by isolating only the components that are under fault, while leaving as much of the network as possible still in operation.

Components

Protection systems usually comprise five components:• Current and voltage transformers to step down the

high voltages and currents of the electrical power system to convenient levels for the relays to deal with;

• Relays to sense the fault and initiate a trip, or disconnection, order;

• Circuit breakers to open/close the system based on relay and auto-recloser commands;

• Batteries to provide power in case of power disconnection in the system.

• Communication channels to allow analysis of current and voltage at remote terminals of a line and to allow remote tripping of equipment.

SURGE ARRESTORS• The protection against transient voltage surges

is provided by surge arrestors.• They are usually connected between phase and

ground.• Surge arrestor discharges current impulse

surge to earth and dissipates energy in the form of heat.

• The equipment has certain assigned lightning impulse voltage withstand level.

References•www.ieee.com•www.upptcl.com•Upptcl training manual.

Thank You