CT Sizing
CT Sizing
(OP)
We have several 6.9kV - 480V (delta/wye) transformers. These transformer neutral bushing CTs are sized at 2000/5 to which we tie to a 51G relay. However, I need to understand the basis for sizing such a CT as the potential phase to ground current (in the event of a ground fault) would far exceed the rating of the CT or am I missing something?






RE: CT Sizing
If you size the CT for the maximum fault current, it will not be sensitive to low level currents.
RE: CT Sizing
Alan
RE: CT Sizing
To determine whether the NCT is oversized one should know the maximum allowable ground fault current at 480 V level.
What is your calculated or allowable ground fault current at 480 V level?