B phase grounding in the secondary of Potential transformer

[Charz]

Hello All,

Can anybody tell me the what is the configuration of PT used in the attachment? It has B phase grounded. I have read that the advantage with this is that the earth fault protection in the generator system can be set without any fear of it maloperating for a phase-to-ground fault in VT secondary circuits. But how come grounding the B- Phase avoids mal operation? The basic principle of PT is it should not be short circuited to
earth. Just for Imagination, if the neutral of the secondary is not grounded and the phase is grounded, Could we relate it to like
a single line to ground fault on ungrounded system. Then even this causes the operation of ground fault relay

 

[rian0201]

B phase grounding in the secondary of Potential transformer

It avoids by not providing a zero sequence path during ground faults on pt sec side.

If you connect it in wye-g wye-g, you need to coordinate your ground relays on the generator (both voltage and current ground elements) to pt sec fuse.

Remember that pts are just transformer in smaller sizes, can you not bank a transformer that way? Grounding the b-phase operate the relay, no zero sequence path.


Sent from Mars

 

[Charz]

It avoids by not providing a zero sequence path during ground faults on pt sec side.

If you connect it in wye-g wye-g, you need to coordinate your ground relays on the generator (both voltage and current ground elements) to pt sec fuse.

Remember that pts are just transformer in smaller sizes, can you not bank a transformer that way? Grounding the b-phase operate the relay, no zero sequence path.


Sent from Mars

Hi Rian,

Thank you!! even phase to ground fault on other phase causes current flow between the b phase and the faulted phases, hence causing the
fuse to blow on the unfaulted phase.