STUDIES ON DEGRADATION OF ZNO VARISTORS BY DIELECTRIC-RELAXATION

Pulse-degradation of ZnO varistors has been studied by the changes of frequency spectra of dielectric loss before/after being stressed by impulse current. The experiments show that the frequency spectra of dielectric loss obey the universal law proposed by Jonscher. The gradient factor m can be used both as a measure of the degradation of ZnO varistors macroscopically and a reflection of the changes of microstructure in the ZnO varistors microscopically. The present paper reveals the relationship between the pulse-degradation mechanism of ZnO varistors and their dielectric response.