Zinc oxide ZnO surge arresters are developed in the 70 's a new arrester, which is mainly formed by the zinc oxide varistor. Every piece of pressure-sensitive resistors made from it when certain switches voltage (varistor), under normal operating voltage (that is, less than the breakdown voltage) pressure-sensitive resistor value is equivalent to insulation, but under impulse voltage (greater than the breakdown voltage), penetrated the varistor is a low value, equivalent to a short circuit. Varistor hits, however, are transient recovery when higher than the breakdown voltage o