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 (1977). 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.