Failure modes and energy absorption capability of ZnO varistors

Thermal and mechanical behavior of ZnO varistors used in surge arresters is simulated for current pulses of various magnitude and duration. Time depen dence of the temperature profile and of the distribution of thermal stresse s is computed by solving heat transfer equations for varistor disks with no nuniform electrical properties. The simulations identify failure processes and determine energy absorption capability of varistor elements. The result s are in excellent agreement with experiment and provide fundamental explan ation of the energy handling dependence upon current surge intensity and du ration.