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open delta PT connection

open delta PT connection

open delta PT connection

(OP)
Is Open delta PT connection unreliable for directionality?

RE: open delta PT connection

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

RE: open delta PT connection

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.

RE: open delta PT connection

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.

RE: open delta PT connection

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

RE: open delta PT connection

If you do it right, yes.
 

RE: open delta PT connection

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

RE: open delta PT connection

(OP)
Thank you guys very much

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