Partial discharges and associated mechanisms for micro gap delamination at epoxy spacer in GIS

For accurate detection and diagnosis of Partial Discharges (PDs) in Gas Insulated Switchgears (GISs), there is a need for better understanding of the physical mechanisms for the PD activity. Accordingly, we have been investigating the PD characteristics and associated mechanisms for electrode/epoxy delamination of GIS spacers as one of the severest defects in GIS. The gas pressure inside delamination usually changes from sub-atmospheric pressure, just after delamination initiates, to filled SF6 gas pressure in the GIS tank, after SF₆ gas infiltrates into the delamination area. Therefore, in this paper, the PD activity at different gas pressures, from 0.02 to 0.4 MPa, is acquired. Delamination gap length at the level of 50 μm is considered, simulating possible size of actual delamination in a GIS spacer. The relative PD generation rate is analyzed regarding the phase characteristics at different pressures and then discussed from the viewpoint of PD mechanism in order to assess the possibility of delamination diagnosis in GIS spacers. Experimental results show that, PD parameters and phase characteristics change significantly with infiltrating SF₆ gas from the GIS tank into the delamination. The obtained results give a characterized feature for the delamination defect and can be useful for delamination diagnosis.