open delta PT connection

[Uquresh1]

Is Open delta PT connection unreliable for directionality?

 

[rbulsara]

Check the relay manual. Three wye connected PT are often needed (or easier to implement) to get the polarizing element (zero sequence voltage in this case) for directional neutral (ground) overcurrent function.

Alternatively you can use current polarization, usually much more cumbersome or even not feasible if the source transformer is not near by.

Rafiq Bulsara

http://www.srengineersct.com

 

[davidbeach]

There is no zero sequence in the secondary of an open delta VT. So nothing in the relay that works on zero sequence voltage or zero sequence impedance will function correctly.

 

[cranky108]

There are relays that do support open delta directionalty. But you do have to give up something for it. Like said above zero sequence anything.

Some people don't use zero sequence for directinality any way. We use negative sequence.

 

[Uquresh1]

@ Cranky: so -ve seq. can be used reliably with open delta conxn for phase and ground faults?

 

[cranky108]

If you do it right, yes.

 

[davidbeach]

My preference is negative sequence, but I'd never willingly give up zero sequence as a back up. Decent relays will use both.

 

[Uquresh1]

Thank you guys very much