Directional EF and cable networks
Directional EF and cable networks
(OP)
I have a 22kV extensive cable network fed from a 22kV bus via several outgoing feeders. The current EF settings is 6A, 0.5s on all the feeders. System is resistively earthed limiting the EF current to 25A. If there is a fault on A-phase of feeder A, will there be an infeed from the A-phase on the adjacent feeders into the fault? If so will it necessitate directional protection for the feeders?






RE: Directional EF and cable networks
Somehow, I think that your description and my picture of it don't actually go together. Perhaps a one-line diagram could help.
RE: Directional EF and cable networks
Let's say that the cable capacitance does produce current IB, IC and ID contributions to the fault. I see no need for directional EF protection on these feeders for several reasons.
1) Duration of IB, IC and ID will be typically < 5 cycles.
2) These currents are literally at the threshold of the zero torque line, in fact just outside it as the zero torque line is usually concave. But they could lie just within the operate zone due to resistance resulting in unwanted operation.
RE: Directional EF and cable networks
If not the only way I can see feeders B,C & D affecting the earth fault current seen by the relay on feeder A is if they have a coincident earth fault, for example a cross country earth fault. Any stored charge in the cable capacitance or system inductance creates a DC current at the instant of fault.
Regards
Marmite
RE: Directional EF and cable networks
RE: Directional EF and cable networks
RE: Directional EF and cable networks
Regards
Marmite