Electrical High Voltage Circuit Breakers

8/4/2019 Electrical High Voltage Circuit Breakers

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ELECTRICAL HIGH VOLTAGE CIRCUIT

BREAKERS

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132kV High Voltage circuit breaker

Electrical power transmission networks are protected and controlled by high-voltage breakers. Insubstations the protection relay scheme can be complex, protecting equipment and busses fromvarious types of overload or ground/earth fault. Electrical protection should be provided against

the following abnormal conditions:

1. overloading (excessive currents not due to faults)2. transformer faults3. short-circuit faults between phases4. short-circuit faults to earth

These breakers are available for indoor or outdoor applications and High-voltage breakers arebroadly classified by as follows.

1. Oil circuit breakers (OCBs)2. Vacuum circuit breaker (VCB)
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3. SF6 Circuit Breakers4. Air circuit breakers

Brief detail of above types are given in bellow

Oil Minimum Circuit Breakers (OMCB)

Nowadays OMCBs are very popular in sub stations and power stations. In oil minimum circuit

breakers the current breaker takes place inside of the interrupter. The enclosure of the interrupter

is made of insulating material like porcelain. Hence the clearance between the live parts and theenclosure can be reduced and lesser quantity of oil require for internal insulation. This type of

circuit breaker is used widely in outdoor sub station, rated even up to 66 kV. The type of oil

circuit breaker is bulky.

Vacuum circuit breaker (VCB)

In this breaker vacuum is used as insulator and as an arc-quenching medium VCB also used as ahigh voltage control switch. There is no oil. Therefore will not occurring any fire problems in

this kind of circuit breaker. Vacuum circuit breakers in particular are useful for controlling andprotecting electrical systems. Vacuum circuit breakers offer many advantages as compared to

other types of circuit breakers.

Air Circuit Breaker (ACB)

ACB is used against very high current. Air circuit breakers are commonly used in electricaldistribution systems. Air circuit breakers which include operating mechanisms that are mainly

exposed to the environment. ACB is also protecting for over load, short circuit and earth fault.

Most of air circuit breakers are use in indoor type substations.

SF6 Circuit Breakers

Sulfur hexafluoride (SF6) gas is an alternative to air as an interrupting medium. SF6 is a

colorless nontoxic gas, with good thermal conductivity and density approximately five times that

of air. The principle of operation is similar to the air blast breakers, except that the SF6 gas is notdischarged into the atmosphere. A closed circuit completely sealed and self-contained

construction is used. SF6 Circuit Breakers are mostly use in Indoor type Primary sub stations in

Sri Lanka and other countries because of its convenience.SF6 Gas has good qualities as bellow.

1.

Good heat transfer quantity.2. Pressure can be checked easily3. Short arcing time4. Compartmented SF6 HV load-break isolating switch


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Circuit breakers have their contacts immersed in oil. Current disconnect takes place in oil which

cools the arc developed and thereby cool the arc. There are three poles in this oil circuit breakerwhich use to protect 3 phases. The poles of small oil circuit breakers can be placed in one oil

tank however; the large high-voltage circuit breakers have each pole in a separate oil tank. The

oil tanks in oil circuit breakers are normally sealed. The Electrical connections between the

contacts and external circuits are made through porcelain bushings. If we are using oil as an arc-quenching medium we have to consider advantage of oil so followings are advantages of oil as

an arc-quenching medium.

1. Oil is very good insulator2. Has a high dielectric strength3. Cold oil is able to act as an insulator

Oil circuit breakers are comprises of a tank filled with insulating oil. There are 2 kinds of OCBs.

Those are.

1. Oil Circuit breakers2. OilMinimum Circuit breakers (OMCB)

In OCBs there are fixed and movable contacts. It has 3 porcelain bushings, 3-phase line currentset to fixed contacts. When the circuit breaker is closed, the line current of each phase penetrate

the tank by means of a porcelain bushing, flow through the first fixed contact to the second fixed

contact, and then out by second bushing .

OVERHEAD TRANSMISSION LINESA transmission line has three constants R, L and C distributed uniformly along the whole

length of the line. The resistance and inductance form the series impedance. Thecapacitance existing between...

INSTRUMENT TRANSFORMESThese can be classified in to two parts. They are, Current Transformers and Potential
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Transformers. These transformers are generally used to measure the high voltages and

high currents. In power stations and...

Cooling and Losses of TransformersPower transformers rated up to a few KVA can be adequately cooled by natural

convective air-cooling, sometimes assisted by fans. Some power transformers are

immersed in specialized transformer oil that acts...
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Electrical High Voltage Circuit Breakers