The Influence of Electron Emission from the Electrode Materials on the Arcing Current in Inclined-plane Test

It was well recognized that the voltage type has a significant influence on the sample behaviour in the inclined-plane test. Generally, under the same voltage level and contaminant flow rate, the degree of material degradation in the DC test was more severe than that in AC test. And the material behaves the worst in the positive DC test. The amplitude of arcing current usually follows $I$ (+) > $I$ (∼) > $I$ (-). At present, there is no widely accepted explanation on these phenomena. In this paper, the difference between the arcing current of positive and negative half cycles in the AC inclined-plane test was analyzed. Then three types of metal materials with different work functions, i.e. aluminum, stainless steel and copper, were used as the bottom electrode. The influence of work function of the bottom electrode material on the difference between positive and negative half cycles and the material degradation was then studied. The results indicated that electron emission by cathode material should be one of the reasons of larger arcing current and more severe material degradation in positive DC tests. The findings could also explain the observation that material degradation of the specimen under negative DC voltage was more severe than that under positive DC voltage in tracking and erosion tests on composite insulators (such as tracking wheel test, 1000 h salt fog test and 5000 h test).