Performance of metal-oxide arresters exposed to ferroresonance in padmount transformers

Ferroresonant overvoltages have been recognized as a threat to arresters installed on underground distribution systems. Extensive tests have been performed to evaluate the thermal and electrical performance of MOV arresters exposed to this duty. Arrester discharge currents were found to be small and arrester heating is slow. The eventual temperature rise and the potential for thermal instability depends greatly on the type of arrester. Arrester designs which promote better heat dissipation to the ambient are shown to reach an acceptable steady-state temperature when exposed to ferroresonance of indefinite duration