Surface flashovers on metal-oxide varistor blocks

Extensive studies have been made of surface flashovers on varistor blocks using multipulse (MP) currents which simulate multiple stroke lightning ground flashes. The MP results are compared with those obtained with single-pulse (SP) currents and with high temporary overvoltages (TOV) at 50 Hz. The blocks used were mostly of 5 kA rating as commonly used in distribution surge arresters. MP can cause flashovers not evident with standard SP tests; they are very dependent on the quality of the dielectric on the surface and are independent of the surrounding gas.