Ground Fault Protection on Substation

[living2learn]

I have a substation that is fed from the utility at 12kV. On the 12kV main it has a ground fault relay 51G. The circuit then splits to (3) different substations with 1500kVA transformers. All transformers have primary load interupter switches with fuses. The secondary of the transformers do not have a secondary disconnect switch and has as many as (8) feeder breakers.

Q1) If my 12kV system has ground fault protection does my low voltage need it in addition? I know 230.95 applies, but that is only for services and this would be a seperatly derived source?

Q2) Even if a ground fault was experienced on the secondary side of the transformer, the 12kV 51G relay would not even see it?

 

[Joaopato]

In general i would say that if a ground foult occurs in the secundary of the transformer the ground protection won't "see" the zero sequence component of the fault. A severe fault in the secondary will probably motivate de fuse in the primary of the transformer to blow/trip.

 

[inpran]

Living2learn
What is the vector group of the transformer?