Insulation resistance of high voltage circuit breakers is  carried out when

Insulation resistance of high voltage circuit breakers is  carried out when

Right Answer is:

Any of the above

SOLUTION

Insulation Resistance Measurement Test

The insulation resistance measurement test may be conducted on all types of electrical switchgear using the insulation resistance megohmmeter commonly known as the MEGGER.

The insulation resistance test consists of applying voltage (600-l0,000V DC) to the apparatus to determine the megohm value of resistance. This test does not indicate the quality of primary insulation. Several factors should be remembered when performing this test. The first is that this test can indicate low values of insulation resistance because of many parallel paths. The other is that an insulation system having low dielectric strength may indicate high resistance values. In view of this, the test results should only be interpreted for comparative purposes. This does not indicate the quality of the primary insulation system from the point of view of dielectric withstand ability. The connection diagram for making this test on a power circuit breaker is shown in Figure. When performing insulation testing, it is recommended that auxiliary equipment, such as potential transformers and lightning arresters, be removed from the stationary switchgear.

Insulation resistance tests are made with the circuit breaker in the open and closed position, whereas the insulation test for the switchgear bus is made with one phase to ground at a time, with the other two phases grounded. The procedure for this test is as follows:

  • Circuit breaker opens: Connect HV lead to pole 1. Ground all other poles. Repeat for poles 2 through 6, in turn, with other poles grounded.
  • Circuit breaker dosed: Connect HV lead to pole 1 or 2, as convenient, with either pole of phase 2 and 3 grounded. Repeat for phases 2 and 3 with other phases grounded.
  • Stationary gear (buses): Connect HV lead to phase 1 with phases 2 and 3 ground. Repeat the same for phases 2 and 3 with other phases grounded. Also, perform IR tests between phase 1 and 2 with phase 3.

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