A. Circuit breaker is a device which will isolate the circuit under the fault condition in order to protect healthy part from faulty part by the command of Relay.It also used for switching operation under normal condition. So breaker is a device which can be operated at normal condition and abnormal conditions also.
When any fault occurs in electrical system it is necessary to isolate the fault part, other wise healthy part also effected by fault part. But while performing switching operation on circuit there is occurrence of arc for MV and HV voltages.
There are some points should keep in mind
1.Breaker can capable to open under fault condition.
2.Breaker can able to close when fault exist.
3.The Arc quenching medium should be capable to clear the arc other wise arc will re strike.
SF6 Circuit breaker (400kv, India)
In order to find healthiness of breaker we have to do following test at field.
1.INSULATION RESISTANCE TEST...
2.CONTACT RESISTANCE MEASUREMENT...
3.TIMING TEST...
4.COIL RESISTANCE TEST...
Measure trip coil and close coil resistance by using multimeter.
5.INSULATION RESISTANCE TEST FOR MOTOR and COILS...
Measure insulation resistance for motor winding and trip coil and close coil separately by removing all external connections by applying 500volts dc.
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