Degradation of the ZnO surge arrester voltampere characteristics under the combined influence of alternate and impulse currents

This paper reports the results of studies on the degradation of ZnO surge arrester characteristics in laboratory and in field. The metal oxide ZnO varistor stability depends on the operating voltage level and the temperature of the environment. Short-term investigations with the appliance of relatively nonforcing operating voltage and temperature levels could not give convincing arguments of existence of Voltampere (VA) characteristics degradation. Switching current impulses can also significantly influence the ZnO varistor VA-characteristics stability because they can change the ZnO ceramic boundary zone structure. In as much as both of these causes act simultaneously and mutually influence each other, it is very important to model both of them in laboratory