Studies On Aging Characteristics Of ZnO Varistor By Space Charge

ZnO varistors are highly non-ohmic resistor and they are widely utilized in protecting electric power transmission line and electronic device against the dangerous overvoltage or voltage surge, and the ac voltage aging characteristic of ZnO varistors is one of the most concerning performance parameters. In this paper, the power features, V-I characteristics, thermally stimulated current (TSC) performance and the space charge distributions tested by pulsed electro-acoustic method (PEA) of ZnO samples, which was prepared with a common formula, has been investigated before and after an accelerated aging test. The experimental results show that with the increasing of aging time, the power loss increases and the V-I characteristic curves drift symmetrically. The space charge characteristics tested by TSC and PEA show the trapped charges increase and the trap level becomes deeper. The analysis on these experimental results reveales that the migration of interstitial zinc ions change the space charge distributions and decrease the schottky barrier heights, which ieads the aging of ZnO varistors. Consequently, the space charge test is a powerful method for evaluating the aging characteristic and life of ZnO varistors.