Grounding detection 1

[prc]

In a 800 MVA 765/400/33 kV Transformer bank, the tertiary is formed by using 33kV cables. With such an arrangement, how to give grounding detection for tertiary side. Earlier days we used to provide single phase PTs on 33 kV side with broken delta secondary to detect cable fault on tertiary side. I read in this forum that today digital relays can detect zero sequence voltages and such elaborate PT arrangement is not necessary. Can some one give details of such relay and how the desired function is achieved.

 

[davidbeach]

You still need a VT connected from each phase of the tertiary to ground. But instead of a broken delta with one voltage, you take all three voltages to a numeric relay that can calculate 3V0. It will also be able to tell you which phase is grounded while that old broken delta can only tell you that you have a ground somewhere.