Partial Discharge Detection Techniques under the Condition of Metallic Particle Adhering to Solid Spacer in SF6

Among the insulation defects in GIS under the operating condition, metallic particles adhered to the solid spacer would be the most critical situation against the surge voltage applications. Nevertheless, because of the complicated partial discharge (PD) mechanisms, PD detection can be recognized very difficult in GIS diagnostic techniques. In this paper, we have successfully simulated the condition of particle adhering on the spacer surface by an experiment applying an ac sudden step voltage. We firstly measured the time dependent PD characteristics, from immediately after the attachment of the particle, by using PD-CPWA (Partial Discharge Current Pulse Waveform Analysis) technique. The PD activities at the particle tip have different characteristics depending on the particle length and the diameter, as well as the gas pressure. Next, we have discussed that depending on the particle conditions, the PD characteristics can be changed with time and with ac half cycle of the polarity and have different sensitivity. Therefore, we need to identify the assessment criteria of GIS, based on the above mentioned phenomena and the facts. Finally, from analyses of PD mechanisms, we proposed the optimum PD detection techniques for adhering particles on solid spacer in GIS.