Aging characteristics and mechanisms of ZnO nonlinear varistors

The aging threatens the operation stability of ZnO nonlinear varistors. Ordinary, the aging characteristics of ZnO varistors is measured by the power loss changing with time. Analyzing a lot of experimental results, we observed the characteristics of power losses of ZnO varistors can be classified into three types according to applied experimental temperature and applied voltage: (1) the power loss steeply rises with the time and leads to thermal breakdown, when ZnO varistor has a bad performance; (2) the power loss first quickly rises with the time, and then slowly increases with the time, and at last sharply rises with the time and leads to thermal breakdown; (3) the power loss first rises with the time, and then decreases and slowly reaches a stable value with the time. The aging mechanisms for three different aging types of ZnO varistors were discussed based on the changing of Schottky barrier and the migration of zinc interstitials inside ZnO grains, and heat treatment effect