The Luminous Characteristics of the SF6 Gap and Spacer Stressed by FOI and LI

Luminous signals emitted during predischarge and the breakdown over the spacer in SF6 was investigated by using a photomultiplier tube under Fast Oscillating Impulse (FOI) and Lightning Impulse (LI). The results show that the waveform and polarity have a prominent effect on the luminous characteristics. A single luminous pulse could appear at LI wave front, but under the FOI, the continuous and periodic luminous signal was found. With a spacer contaminated by a metallic particle, the luminous amplitude appeared at wave crest was different from those at wave trough. So the space charge would accumulate on the spacer surface in favor of the leader formation leading to low flashover voltages. It also found that the SF6 gas pressure had different effects on initial predischarge voltages depending on the voltage shapes and polarities.