Abstract

Ferroresonance is a nonlinear electrical phenomenon that can damage transformers, surge arresters, cable insulation, and switchgear — and create dangerous backfeed voltages on conductors that should be de-energized. Although relatively rare, the conditions that make ferroresonance possible are becoming more common as utilities install more underground cable, adopt high-efficiency low-loss transformers, and interconnect distributed generation. This paper provides a practical overview of ferroresonance for distribution engineers and field crews: what causes it, how to recognize it, what it does to equipment, and how to reduce the odds of occurrence through proper switching practices and system design.