Analysis of treeing phenomena by discharge magnitude and discharge luminescence in each phase angle

This paper reports on the investigation of the treeing phenomena by measuring discharge magnitude and discharge luminescence. Treeing experiments were conducted using a PMMA block which has a needle shape void on the tip of needle electrode. One cycle of the ac applied voltage was divided into twenty equal phase angle areas, and they were named φ1~20 in order from the negative peak point of the applied voltage. The ac voltage was applied to the needle electrode, and the discharge pulses and discharge luminescence were measured at the same time in each phase angle area. In this paper, the discharges at φ4 and φ7 phase angle area were especially given attention and the discharge pulse and discharge luminescence caused by only one partial discharge were measured at the same time. As a result, the discharge luminescence at φ4 occurred mainly in the void area independently of the discharge pulse magnitude. At φ7, the discharge luminescence was observed in the void area when the discharge pulse was small, and observed in the tree area when it was comparatively large