Discharge Characteristics on the Surface of an Insulating Plate with Accumulated Charge in SF6

Gas insulated equipment inevitably employs various kinds of solid dielectrics. Surface electrification (charging) on the solid surface may significantly reduce the insulating ability of the equipment. This paper reports the results of the experimental work carried out to clarify the characteristics and mechanism of discharge propagation on the surface of an insulating plate which have been electrified by a preceding surface discharge. Oscillating lightning impulse corresponding to disconnector-induced surge was employed in the test together with fundamental square voltage. A streak camera and a still camera were used to examine the mechanism of the surface discharge as well as to measure the length of discharge channel. While the length of discharge channels is scarcely affected by the preceding discharge for the square voltage, there occurs a distinct change of the length with each voltage application in the case of the oscillating impulse. When positive and negative voltages of the same height are applied by turns, the maximum length appears at the application of the first positive voltage. These characteristics are discussed by measuring the charge quantity during the propagation of surface discharge.