The aging criterion of ZnO varistors based on leakage current harmonic characteristics

Zinc oxide (ZnO) varistors are widely used in power systems to limit overvoltage, and their quality directly affects the safety of the entire protected system. In this paper, the current parameters of ZnO varistors during the whole life aging period under different types of impulse current were studied. The results showed that after multiple pulse tests, the proportion of higher harmonics in the leakage current rises quickly, and the higher harmonic currents are more sensitive to impact. The voltage gradient of the varistor also undergoes a significant change before failure. Harmonic characteristics and varistor voltage were the key parameters to measure the aging level of varistor.