Space Charge Characteristics of ZnO Varistors after Pulse Degradation

ZnO varistors are wildly used in power system and electronic system to protect equipments against surges and over-voltage. As there is none series gap in ZnO arresters, the ageing phenomenon of ZnO varistors has attracted great attention. In order to study the principle of pulse degradation of ZnO varistors, the thermally stimulated current (TSC) characteristic, voltage-current (U-I) and pulse electro-acoustic (PEA) characteristic of aged ZnO varistors have been investigated. The experimental results show that the trap level and trap charge increase as the impact time or impulse current increased; the TSC results show that there is ion migration during pulse degradation process of ZnO varistors, which is account for the drift of U-I characteristic curves. Based on the research results, a conclusion can be drawn that the pulse degradation of ZnO varistors is the consequence of thermal ageing and ion migration. The space charge characteristics of ZnO varistors provide a new view to study the pulse degradation mechanism of ZnO varistors.