Negative sequence current from delta source?
Negative sequence current from delta source?
(OP)
I have an application where I need to apply ground fault protection on the HV side of a customer's delta-wye transformer in the event of loss of the HV utility source (which is supplied from a solidly grounded wye connected transormer). There is a generator connected to the LV side of the transformer. The utility has suggested that either zero sequence voltage or directional negative sequence current tripping of the cutomer's generator source be applied in the event of an HV ground fault. I have heard from others that negative sequence current cannot be produced by the delta connected source. Who is correct?






RE: Negative sequence current from delta source?
See IEEE C37.95.
RE: Negative sequence current from delta source?
I have an application where I need to apply ground fault protection on the HV side of a customer's delta-wye transformer in the event of loss of the HV utility source (which is supplied from a solidly grounded wye connected transormer). There is a generator connected to the LV side of the transformer. The utility has suggested that either zero sequence voltage or directional negative sequence current tripping of the cutomer's generator source be applied in the event of an HV ground fault.
///The Utility suggestion applies to the high voltage transformer side that solidly grounded wye transformer secondary. The Utility suggestion is viable.\\\
I have heard from others that negative sequence current cannot be produced by the delta connected source.
///To the contrary, the negative sequence current may be produced by the delta connected source by any asymmetrical fault.\\\
Who is correct?
///In what? In which sense is question posed?\\\
RE: Negative sequence current from delta source?
See Protection for Unexpected Delta Sources, by Ken Behrendt, at http://www.selinc.com/techpprs/6143.pdf
RE: Negative sequence current from delta source?
RE: Negative sequence current from delta source?
There could be a misunderstanding that negative sequence current cannot be produced by the delta... Zero-sequence current cannot be produced in a delta winding.
Offhand, if wye-wye PTs are available, a 59G/zero-sequence overvoltage function can sensitively and reliably sense faults. Negative-sequence directional current can too, but is slightly more complex to incorporate with single-function relay components. If there are minimal upstream contingencies, I'd go with the simpler 59G.
RE: Negative sequence current from delta source?