impedance corner grounds
impedance corner grounds
(OP)
There has been much discussion in the forum regarding ungrounded delta versus grounded wye systems. Grounds provide voltage stability and fault clearing, ungrounded delta allows you to ride out the first ground fault. Impedance grounded wye systems seem to allow the best of both worlds. But why have I never heard of an impedance corner grounded delta? Seems like it would allow an existing delta system to stabilize their voltages with little expense. Can't find a prohibition in the NEC. I cannot be the first to have thought of this. Is such a thing ever used? Just wondering.






RE: impedance corner grounds
RE: impedance corner grounds
RE: impedance corner grounds
RE: impedance corner grounds
I don't think there would actually be an increase in short circuit currents that the transformer would face when one corner of a delta is grounded. Sure, ground fault currents would be larger but a line-to-ground fault is just equivalent to a line-to-line fault to which the equipment is already braced for.
One advantage on the protection side is there would be one less fuse, breaker, etc. needed for a corner-grounded system than an ungrounded delta system.
RE: impedance corner grounds
It may work. Offhand, the only thing would be dealing with some continuous ‘grounding’-resistor heat dissipation from dissymmetry. It is sort of like one simplified means of ground detection—look at a single phase-to-ground voltage and monitor it for both under- and over-voltage.
RE: impedance corner grounds
This system would be unigrounded at the transformer. The grounded phase would connect on the transformer side of the resister. There would be no path through the resister for load current under normal conditions. The only non-fault continuous current the resister would carry would be due to capacitive coupling.
jbartos and mvcjr,
The resister or reactor would be sized to limit ground fault currents to acceptable continuous levels just like with an impedance grounded neutral system.
RE: impedance corner grounds
RE: impedance corner grounds