Harmonic Characteristics of Leakage Currents of ZnO Varistors Under Impulse Aging

The zinc-oxide (ZnO) varistor is widely used to limit the overvoltage in the power systems, and its quality is closely related to the safety of the entire protected system. In this paper, accelerated aging experiments under different current levels were carried out on the ZnO varistors to study the harmonic characteristics of the leakage currents in the aging process. It is found that the proportions of higher order harmonics in leakage currents increase faster after several impulse tests and then a sudden decrease appears before the varistor fails, which is caused by the decrease of the varistor voltage. And based on this, a new criterion for the aging of the ZnO varistor is put forward.