Absence on zero sequence polarising voltage
Absence on zero sequence polarising voltage
(OP)
Folks recently we had maloperation of a directional blocking scheme.The directional element on the 22kV faulty outgoing feeder did not pickup due to absence of zero sequence polarising voltage even though the relay did record single phase to ground fault current of 500Amp.Could any body suggest possible scenarios where Io could flow without accompaniny Vo ?






RE: Absence on zero sequence polarising voltage
Bung
Life is non-linear...
RE: Absence on zero sequence polarising voltage
RE: Absence on zero sequence polarising voltage
3 limb VTs will not produce any Vo
RE: Absence on zero sequence polarising voltage
RE: Absence on zero sequence polarising voltage
http://www.abb.com/GLOBAL/SEITP/seitp161.nsf/viewunid/5867EA5AEDAD3CB685256CDC006BA914/$file/IndustrialIT+EMS+-+Power+Management+Handout+A4.pdf
where ABB applied several REF541 on 6kV feeders
RE: Absence on zero sequence polarising voltage
RE: Absence on zero sequence polarising voltage
RE: Absence on zero sequence polarising voltage
I see that you have a very high fault resistance (only 500 A fault current). According to your information the "normal" ground fault level should be 400 MVA. This denotes a very high fault resistance.
In such cases the measured Vo = 1/3 (Vr+Vs+Vt) could be very low, not reaching the minimum required polarizing level.
I suggest for such cases to set the protection for "cross polarization", that means, for phase r to ground fault the s-t voltage shall be used for directional discrimination ( unfaulted phases are less affected by voltage drops caused by the short circuit current).
Best regards