120kV OCB Contact resistance
120kV OCB Contact resistance
(OP)
Anyone have some expected ranges of contact resisnces for a 1200A 120kV OCB? I am seeing some lower than expected values, verified with 2 different microhmeters. Breakers were cycled 10 times before tests.






RE: 120kV OCB Contact resistance
OCB's can do some strange things with the low voltages used in microohmmeters.
old field guy
RE: 120kV OCB Contact resistance
We cycled the breaker 10 times before the test so that could be a factor, still seems a little low to what I have seen before. All other tests, PF, Time travel, etc... were all good. This is pretty new for an oil breaker 1985 vintage.
RE: 120kV OCB Contact resistance
The closest match we have in our system would be General Electric type KSO breakers. They are 1200 Amp, 138 kV, bulk oil circuit breakers with three phases in one tank, two breaks per phase. I checked a number of test records for these breakers and typical contact resistances measured bushing to bushing with a 100 AMP instrument were 450-550 microhms.
A typical 4000 Amp, 345 kV, air blast breaker had contact resistances in the range of 100-175 microhms bushing to bushing. Not sure what to think about your readings?