Vibration Triggered Leakage of Surface Charge on Epoxy Insulator Under DC Voltage

Surface charge accumulation is considered as a critical threat to the safe operation of epoxy insulators installed in gas-insulated switchgear (GIS). This article reports on the charge leakage phenomenon of the insulator with the occurrence of impact vibration under dc voltage. A full-sized disk insulator with a multiarc surface profile was employed as the test sample. A vibration system was established to output vibration to the insulator in two modes. In Mode I, the maximum acceleration was 338.9 m/s(2) and the impact frequency was 1.1 Hz. In Mode II, the maximum acceleration decreased to 4.6 m/s(2) but the impact frequency increased to 107.5 Hz. The charge densities on the insulator surface were measured before and after the vibrations. The results indicated that the vibration led to the obvious leakage of homo-charges during the dc stressing process, especially in the nonplanar region. The leakage of homo-charges under positive stressing was more remarkable than that under negative stressing. The reduction of homo-charge quantity was more serious in Mode I than in Mode II. It is suggested that the vibration-triggered charge leakage is mainly due to the charge detrapping caused by microdisplacement of molecular chain occurring in the insulator with the vibration and subsequent charge release to the gas phase under the normal electric field, by which the surface charge accumulation quantity is remarkably reduced.