AUTORECLOSER TRIP

[PUNGLU]

We recently replaced an 11kV aurocloser with a smrc type of autorecloser having an R6 controller. All the pre-commissioning tests were ok but when we put it into service it tripped on an earth-fault.

I decided to disable the ground fault and closed the bypass swith. There were currents of 100A, 0 & 30A on the A, B & C phases respectvely.

The former switchgear failed after one of the leads to its bushing terminals snapped burning the porcelain insulators(the controller had been accidentally switched off by an operator and it was apparently left off. Before the breaker behind operated, serious overheating of the porcelain insulators (especially on the B phase) on which the taplin isolators are mounted.

Could there be a problem with the CT wiring or could overheating have affected the insulators, reducing their creepage distances and thus causing some leakage to the steel channel on which they are mounted?

 

[JensenDrive]

Gee, 0A on phase B? Something seems really strange. Even 100A and 30A on A and C seems pretty strange. Those currents, if real, imply a lot of ground current, and if they are in the CT leads, then the recloser is sure going to think there is a ground fault. I do not know if bushings can open internally without it being obvious, but sounds like there is an open or short somewhere.

 

[jghrist]

Maybe you have an open in the B phase CT, causing both the zero current measurement and arcing and heating from the high open-circuit voltage.

 

[PUNGLU]

The auto-recolser, if put into service without the bypass switch, trips on very high currents (500Amps on B and neutral.). I hane been suspecting that the porcelain insulator onwhich the taplin isolator rests(B-pahse) has some leakage and as such the current flowing to the B-Phase autorecloser terminal is diverted to ground.