Laboratory studies of the effects of multiple lightning currents on low voltage zinc oxide varistors

The authors report on experiments in which multipulse lightning currents were applied to varistors to simulate the effects of multistroke lightning currents. Multipulse currents cause more damage than standard single-impulse current tests. Seven out of eight varistors failed the multiple current test at 75% of maximum rated current. Of these, three were destroyed by short-circuit and were physically damaged, while another three exhibited gross changes in their I-V characteristics. Devices subjected to single impulse currents survived. The multipulse tests used are representative of the surges caused by multiple stroke lightning in the field, and it is concluded that the adequacy of the standard impulse tests currently specified for low voltage AC power circuits should be reassessed