3V0 via broken delta connection or numerically derived within a protection relay
3V0 via broken delta connection or numerically derived within a protection relay
(OP)
I was reading through this old thread trying to find an answer to my question.
http://www.eng-tips.com/viewthread.cfm?qid=216248
I work a protection engineer and I'm doing a bit of reading into the merits of Neutral Voltage Displacement (NVD) or Residual Voltage Protection being based on either numerically derived 3V0 or via a Broken Delta connection.
The system to which I'm applying NVD is a normally resistively earthed network but with the possibility of being back-livened via a delta winding of transformer in contingent situations. The NVD is there to detect and trip.
Ferroresonance can be an issue so loading the 'broken-delta' connection helps. But equally an auxiliary VT with a broken delta can assist here.
Any comment to why a 'broken delta' connection could be superior to numerically derived 3V0?
Regards,
Chris
http://www.eng-tips.com/viewthread.cfm?qid=216248
I work a protection engineer and I'm doing a bit of reading into the merits of Neutral Voltage Displacement (NVD) or Residual Voltage Protection being based on either numerically derived 3V0 or via a Broken Delta connection.
The system to which I'm applying NVD is a normally resistively earthed network but with the possibility of being back-livened via a delta winding of transformer in contingent situations. The NVD is there to detect and trip.
Ferroresonance can be an issue so loading the 'broken-delta' connection helps. But equally an auxiliary VT with a broken delta can assist here.
Any comment to why a 'broken delta' connection could be superior to numerically derived 3V0?
Regards,
Chris






RE: 3V0 via broken delta connection or numerically derived within a protection relay
RE: 3V0 via broken delta connection or numerically derived within a protection relay
This is a good paper on unexpected delta sources:
Protection for Unexpected Delta Sources, by Ken Behrendt
RE: 3V0 via broken delta connection or numerically derived within a protection relay
I hadn't come across the idea of switching the VT loading resistor before, I've normally applied burden resistors in the past as a permanent connection. An advantage with broken delta is the loading only generate heat when there is a voltage imbalance or the frequency on the secondary is not cancelled by the other phases. 99.99% of the time, the voltages will be balanced. That 0.01% of the time is when the remote end CB opens disconnecting the earth reference.
Thanks very much for the paper reference. I had a quick read and it looks worth rereading in detail.
Regards,
Chris