New England Electric's 30 Years of Experience with Resonant Neutral Grounding of Unit-Connected Generators

Abstract

Since 1951, all unit-connected generators of New England Electric have been grounded using a ground fault neutralizer. The total experience to date, which amounts to over 72 million kVA years, indicates that this grounding method is reliable, effective, and superior to other commonly used techniques. In addition to high sensitivity of ground fault detection, which is illustrated by an actual experience, the ground fault neutralizer also greatly reduces the residual current at the fault location. The claim has been made that the fault current is small enough so as to practically eliminate the danger of iron damage, thus permitting the continued operation of the generator until an orderly shutdown can be arranged. This claim has now been substantiated by experience. A generator winding fault on a 75MVA generator is described, which was allowed to persist for 89 minutes before clearing, with no detectable iron burning in evidence and with very little loss of copper.