Power Systems Protection
Power Systems Protection
(OP)
I came across an MCSU relay(GEC) setting which puzzled me. The Core balance CT ratio is 0.5/0.0075 and the pick up was set at 1.5 with a plug setting of 1. What is the actual primary pick-up current in this case?
I thought it would be 1.5x CTR(66.67)= 100A, but the source of the feeder where the relay is installed has a secondary winding neutral earthing impedance that limit the EF current to 25A. I would not have thought that any protection engineer would have missed that out. Please help?
I thought it would be 1.5x CTR(66.67)= 100A, but the source of the feeder where the relay is installed has a secondary winding neutral earthing impedance that limit the EF current to 25A. I would not have thought that any protection engineer would have missed that out. Please help?






RE: Power Systems Protection
If In = 1 Amp, the pickup is 0.015 Amps secondary, which is 1 Amp primary with that CT Ratio.
RE: Power Systems Protection
I was forced to increase the pick up settings on cables feeders with shorter cables of the same size before. I am still amazed by the setting and I did not physically check if the relay is activated.