Degradation of ZnO ceramic varistors induced by water and AC voltages

ZnO-based ceramic varistors were immersed in 0.01 M NaOH solution and 50Hz AC voltages were applied between the electrodes of each varistor and a counter electrode in the solution. After the treatment, the leakage current of the varistors was increased by more than two orders of magnitude while the switch voltage remained unchanged, and the dielectric loss was markedly increased in the low-frequency region. The degradation induced by water and AC voltages was similar to that induced by water and DC voltages, indicating that water-induced degradation is important for ZnO ceramic varistors regardless of whether they operate under DC or AC voltages.