Circuit Breaker Testing

Testing of Circuit Breaker is not so easy as other equipment such as Transformer, Motor, Generator etc. As short circuit current is very large for Circuit Breaker testing of these is difficult. Also there is no satisfactory methods to do it at reduce power.

All testing plant of Circuit Breaker consist a specially designed alternator capable of giving about 2000 MVA (Mega Volt Ampere)  under short circuit condition. The Prime over of alternator is about 750 KW (killo watt).

Process: Circuit Breaker Testing

Motor is just disconnected before short circuit is done. The Kinetic energy of rotor is sufficient to give the desire energy for testing. The exciter of alternator is driven separately, with a large voltage output so it may withstand the current increasing during short circuit condition.  External device such as Transformer, Resistor, Reactors are used to control the current and voltage.

Testing of Circuit Breaker classified into Two main groups. 

1.      TYPES TESTS

2.      ROUTINE TEST

TYPES TESTS OF CIRCUIT BREAKERS:

These tests are conducted on first few prototype circuit breakers of each type for the purpose of providing the capabilities and confirming the rated characteristics of the circuit breaker design. Tests are conducted in specially built testing laboratories.

Types Tests are performed as per recommendation of standards IEC or IS.

Type Tests classified as follows:

MECHANICAL TESTS OF CIRCUIT BREAKERS: 

These are mechanical endurance type tests involving repeated opening and closing of the Circuit Breaker. a Circuit Breaker must open and close at the correct speed and perform its designated duty and operation without mechanical failure.

DIELECTRIC TESTS OF CIRCUIT BREAKERS: 

These test are performed to check power frequency and impulse voltage capacity.

Power Frequency tests are conducted on a new Circuit Breaker, the voltage varies with Circuit Breaker rated voltage. The test voltage with a frequency between 15 Hz- 100 Hz is applied as follows:

(a) between poles with Circuit Breaker closed, (b) between poles and earth with Circuit Breaker open, (c) Across terminals with Circuit Breaker open.

The voltage is gradually increased and maintained at test voltage for one minute.

In Impulse Tests impulse voltage of specific shape and magnitude is applied to the Circuit Breaker for outdoor circuit dry and wet test are conducted.

THERMAL TEST OF CIRCUIT BREAKERS:

Thermal Tests are performed to check the thermal behavior of the Circuit Breaker. Circuit Breaker under test is subjected to steady state temperature rise due to flow of current. The temperature rise for rated current should not exceed 40ºC for current less than 800A normal current and 50ºC for normal value of current 800A and above.

SHORT CIRCUIT TEST OF CIRCUIT BREAKERS:  

Circuit Breaker are subjected to sudden short circuits in test laboratories and oscillograms are taken to know the behavior of the Circuit Breaker at the time of switching in, During contact breaking, and after arc extinction. The oscillograms are studied with particular reference to the making and breaking currents, both symmetrical and asymmetrical re-striking voltages, and switch-gears are tested a number of times at rated conditions.

ROUTINE TESTS OF CIRCUIT BREAKERS:

Once type tests are conducted and particular design is found to be satisfactory the product becomes prototype and a large number of Circuit Breaker of similar design are manufactured. Each and every Circuit Breaker is still subjected to few more tests before commissioning. These tests are called ROUTINE TEST.

Routine Tests are performed as per recommendations of the standards IEC or IS. These test are performed in the manufacture's premises.

Routine Test include (a) Power frequency voltage test, (b) milli-volt drop test and (c) Operational tests.

• Power frequency test is same as done for Type Tests Dielectric Test.
• Milli-volt drop test is performed in order to determine the voltage drops within the current path of the breaking mechanism.
• Operation test is performed on the breaker by simulating its tripping by artificially closing the contacts of the relays.

IF ANY OTHER TEST USING FOR CIRCUIT BREAKER TEST,  PLEASE WRITE IN THE COMMENT BOX.

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