SOLUTION

Routine Tests

The routine tests are performed on each individual circuit breaker of proven design; the purpose is to prove the correctness of the assembly and the material used and to check the proper functioning of the Circuit Breaker.

The routine tests include the following tests:

(a) Operational tests.

(b) Measurement of resistance of the main circuits.

(c) One-minute power frequency voltage dry withstand tests.

The test procedures, methods of finding results, tests to be performed, etc. are specified by Standards Organizations. 

It is commonly accepted and provided in various standards that the certificates of type tests shall be considered as evidence of the compliance of the circuit breakers with the relevant clauses of the specifications and the manufacturer shall make available such certificates together with the detailed drawings of the circuit breakers and a record of any alteration that may have been made in the subsequent to the type tests.

Type tests can be broadly classified as:

1. Mechanical tests.
2. Thermal tests.
3. Dielectric tests.
4. Short-circuit tests:
   1. Making capacity test
   2. Breaking capacity tests
   3. Duty cycle tests
   4. Short time current tests.

Short circuit tests are of utmost importance and will be dealt with in detail in the next section. However, a brief account of other tests is given below,

(a) Mechanical tests: These are mechanical endurance type-tests involving repeated opening and closing of the breaker. The circuit breaker is opened and closed several times (500) without any current in the current-carrying parts. Some operations (50) are by energizing the relays, the remaining are by closing the trip circuit by other means. No adjustments are permissible during testing. After the test, there should be no distortion or wear of the parts.

(b) Thermal tests: These are conducted by passing an alternating current of normal frequency through the current-carrying parts of the circuit breaker. The temperature is measured by thermometers or thermocouples with temperature indicators or self-resistance methods. The temperature rises for rated current should not exceed 40°C for currents less than 800 A normal current and 50°C for the normal value of current 800 A and above.

(c) Dielectric tests: These are conducted for testing the insulators of the breaker. These can be classified as:

 Power frequency tests: Conducted on a clean new circuit breaker, the test voltage varies with a circuit breaker rated voltage. The test voltage with a frequency between 15-100 Hz is applied as follows:

(i) Between poles with circuit breaker closed,

(ii) Between poles and earth with circuit breaker open

(iii) Across terminals with circuit breaker open.

The voltage is gradually increased and maintained at the test value for 1 minute.

Impulse tests: in this test impulse voltage of specified shape and magnitude is applied to the breaker. For the outdoor circuit, dry and wet tests are conducted.

(d) Short-circuit test: These are conducted in short-circuit testing stations and are mainly meant to prove the ratings of the circuit breaker. Before discussing the tests properly, it would be worthwhile to discuss the short-circuit testing stations.