ISOLATOR TESTING

1. SUPPORT INSULATOR INSULATION RESISTANCE TEST:

                        This test is done on porcelain support insulators of the isolator. In Horizontal Centre Break isolators there are two poles per phase each having three support insulators. All insulators need to be checked for insulation resistance with 5 KV motorized megger and the IR value should be greater than 10000 MΩ.

2. INSULATION RESISTANCE TEST FOR CONTACTS:

                        This test is done on contacts of the isolator with respect to earth. In Horizontal Centre Break isolators there are two contacts, one is called male contact and other is female. Both contacts need to be checked for insulation resistance with 5 KV motorized megger separately and the IR value should be greater than 10000 MΩ.

3. INSULATION RESISTANCE TEST FOR MOTOR:

                        This test is done on Drive Motor of the isolator with respect to earth. In Horizontal Centre Break isolators there is one Motor. It needs to be checked for insulation resistance with 500 V motorized megger and the IR value should be greater than 100 MΩ. Similarly if any earthing switch is there with isolator then its drive motor IR value also need to check by same procedure as for isolator.

4. CURRENT MEASUREMENT TEST FOR MOTOR:

                        This test is done on Drive Motors of the isolator and earth switch. In Horizontal Centre Break isolators there is one Motor per phase. It needs to be checked for load current that it should be in limit or not. If it is found more than rated current then there might be jamming in the drive mechanism or there might be excessive load of jumpers connected to it.

5. CONTACT RESISTANCE MEASUREMENT OF ISOLATOR:

                        Contact resistance measurement is carried out on the contacts of isolator when isolator is in closed position. 100 Amps. D.C. is provided to both ends of the isolator in close condition through the CRM kit and Voltage across the ends is measure by milli Voltmeter. Then by ohms law the resistance of close contact is calculated. It is to be come in micro Ohms & the value should not increase 150 micro Ohms.

      Some of the manufacturers made the CRM kit which directly measures the resistance of contacts. 

Similarly CRM of earthing switch is to be done on earthing rod after closing it with the contact of isolator.

6. CLOSING AND OPENING TIME MEASUREMENT OF ISOLATOR:

Closing and opening time of isolator contacts is needed to check whether they are operating within specified permissible time limit or not. For this purpose we can use stopwatch.