Analysis of partial discharge signals in 420 kv gas insulated substation

Gas insulated substation (GIS) reliability has been proven for more than forty years, yet some failures has been reported. Some of the failures are due to the presence of metallic and non metallic particles inside the GIS compartment. The defect can be generated in GIS during production, maintenance, installation and due to ageing of the component. The particle can give rise to field nonuniformities, which can reduce the breakdown strength. Proven technique to assess GIS insulation condition is partial discharge measurement in GIS. Hence for proper assessment of the failure it is necessary to have a good understanding of the partial discharge (PD) patterns. This paper identifies PD patterns for different defect using electrical and UHF method. As insulation failure usually starts with PD activity, this paper investigates the differences in PD characteristics in SF6 gas with different types of defects using electrical and UHF method. A series of tests has been done to establish a correlation between partial discharge as well as the applied voltage for different defects. Experimental results show that correct identification of defects can be achieved based on considered PD characteristics.