Numerical and Experimental Investigations on Influence of Internal Defect Parameters on Partial Discharge Induced UHF Signals in Gas Insulated Switchgear

A detailed study of the influence of internal defect parameters on partial discharge (PD) induced ultrahigh frequency (UHF) signals propagated through an L section of metal encapsulated gas insulated switchgear (GIS) is presented. The study is carried out using PD defect model with varying rise time, defect size, location, and orientation, an ultrawideband UHF internal sensor, and 3 m long L-GIS with dielectric spacers, shorting plates, hand holes and bus bar with disconnector. Presence of higher order modes, multipath propagation, losses, and dispersion inside L-GIS were observed to influence the time and frequency domain characteristics of PD signals induced in the internal UHF sensor with 0.5 to 6.8 GHz operating bandwidth and directional radiation pattern. The rise time of PD signals significantly influenced UHF signal characteristics in time and frequency domains while PD defect size, location and angular orientation primarily affected the signal amplitude. UHF sensor measurements confirmed the complex behavior of PD induced electromagnetic wave propagation inside L-GIS for varying defect parameters in agreement with the simulations. Despite the complex behavior, it is concluded that PD sensing in GIS is possible using ultrawideband internal UHF sensor.