Coordination of ground fault protection

[noside]

Hello everyone, we have utility supplied distribution transformer, having a three phase connection YY with both neutral grounded,
My question is
1. Does ground fault current magnitude in the secondary will be the same in primary, since the star point of two sides have common ground connection?
2. Does coordination of ground fault is possible?
3. Where to place the CT for 51N, at the primary or secondary side? or to have CT both in primary and secondary side.

Thank you in advance, for your unlimited sharing of expertise!

 

[cranky108]

1. Only if the transformer windings are of the same voltage, and the transformer has zero impedance.....No.
2. Likely the utility has any ground only protection set very high. Use the utility's phase protection as what you are coordination with.
Unless you know for sure there is a utility added ground device.
3. Use the secondary side for a ground CT.

The utility likely has many of these transformers, and buys them in bulk (unless it is very large to them) so the cost of replacing it is very low. So the utility likely has minimum in the way of protecting it. Use your own protection for your equipment.