Grounding transformer capacitive current compensation

[usercan]

There are cases in which star-delta step down transformer, with delta side grounded through zig zag grounding transformer, connected to the cable distribution network. When there is a phase to ground fault on a cable feeder , compensation occurs between the capacitive current of cables and inductive current of grounding transformer. So feeder relays can not detect the fault. Have you ever experienced something like that? Do you have any technical explanation? I thought compensation would occur with Peterson coils.

 

[RRaghunath]

We are supposed to select the grounding transformer zero sequence impedance and the neutral grounding resistor so as to allow ground fault current in excess of Capacitive current in the system (in case of Single Phase to Ground fault). Higher ground fault current ensures there is no resonance between transformer inductance and the system capacitance.