Review of ferroresonance in power distribution grids

Ferroresonance is a special case of resonance, which can occur when a non-linear inductive reactance is connected in series with a capacitive reactance. In instances of ferroresonance involving electric power distribution facilities, the inductive reactance will be the magnetizing reactance of a single-phase or three-phase transformer. The capacitive reactance will be due ordinarily to the conductor-to-sheath capacitance of primary cable supplying the transformer under favorable conditions. Ferroresonance may be accompanied by abnormally high or low voltages as a result of single pole switching of one or two phases of the source supply to the transformer. Ferroresonance is capable of producing sustained overvoltages with peak magnitudes approaching, or exceeding twice the rated peak voltage, which is harmful and unsafe for the operation of most equipment. In this paper, the various conditions giving rise to occurrence of ferroresonance will be identified. The most prevalent resonance resulting in undesirable voltage conditions will be addressed and analyzed. Also some possible means of preventing occurrence of unsafe ferroresonance in power transformers will be proposed.