Influence of nonuniformity of ZnO varistors on their energy absorption capability

A simple thermo-mechanical model is applied to evaluate the influence of th e nonuniformity of ZnO varistor disks used in surge arresters on their ener gy handling capability. Puncture is the dominating failure mode for slightl y nonuniform disks, but cracking becomes more likely as the degree of nonun iformities increases. It is shown that minimization of the chance of a fail ure of varistor disks at high-current pulses can be achieved by adjusting t heir resistivity in the upturn region of the I-V characteristic. Simulation of the behavior of varistor disks under high-current 4/10 mus pulses requi red by the ANSI standard tests shows that these tests provide very little i nformation about the actual energy handling capability of the disks. This c onclusion suggests that alternate test methods should be developed and incl uded in the relevant standards.