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Runsor, No Petersen coils; there are LCs for reactive power compensation and harmonics filtering. You are right; in our case 67N is set as Cap because it is isolated. After we saw the damaged joint where it was the short to earth, it looks that it was a very thin path short current path...

slavag, Relay is vamp 255, www.vamp.fi , very nice and friendly for setting, programming, comms, disturbance record and protecting of course.

An electrical authority requires for HV and MV energy meters that CT and VT are tested with primary current and voltage injection each four years. Does any authority accept “online” or “live” calibration for CT and VT, and if such standards are developed by some certified body or lab? This is...

slavag, I did not made the engineering, and the protection report did not say nothing about this. I will check with designer and come back. Regarding angle pickup, I think this is the setting of current direction in 67N relay module.

burnt2x, 67N is 100 ms, 8A. Angle is also ok because when we had the problem operator tried to reconnect and the cable joint developed a full short circuit to earth and 67N tripped ok. Yes, both 59N and 67N are connected to same open delta for Uo.

% of Uon, voltage of open delta measurement 100 V, also VT secondary are 100 V. 48N, 67N and 51N are all DT. There are generator and utility incomers. Generator has 51N and utility has 67N but direction utility side looking for incomer transformer.

burnt2x, 59N is 10% 0.5s alarm and 25% 0.8s trip incoming. 67N Uo = 10%. Thanks everybody for valuable comments

AMBMI, The engineering decided to use 67N for the outgoing feeders with longer cables, and 51N for those with shorter ones. I was thinking if at least in the 67N we have to try with lower Io setting. Anyway the designers say that two phase short circuit after second earth fault is very risky...

Thanks for your answers, alehman, First it open the utility CB, because of 59N. After operator's reconnection a different CB open. It was a feeder CB because 67N, who downstream the CB afterwards we found a dammaged cable joint. The MV system is neutral insulated, and only distribution...

In a 33 kV isolated industrial installation, there had been a trip from busbar residual voltage protection which opens the utility circuit breaker, leading to total blackout. After busbar inspection nothing was found, so after reconnection from utility one feeder circuit breaker because of...