Influence of insulating spacer type on propagation properties of PD-induced electromagnetic wave in GIS

The authors have studied insulation diagnostic technique of gas-insulated switchgear (GIS) by UHF (ultra high frequency) method. In this paper, the authors investigated the effect of insulating spacer type (metal flange type (MT) or bush type (BT)) on the propagation properties of partial discharge (PD) induced electromagnetic (EM) wave in GIS with UHF method. Low pass filtering process for cutoff frequency of TE11 mode was used to eliminate the higher order mode above TE11 of detected signal. Results revealed that reduction of the magnitude of measured EM waveform by passing through spacers. The reduction was found to be not due to attenuation by the spacer, but mainly due to superimposition of reduced TE mode and TEM mode. Furthermore, the authors investigated relationship between the propagating EM wave in GIS and a leaked EM wave from a BT spacer. This result suggests that insulation diagnosis by a sensor placed outside of GIS could be carried out to detect the leaked EM wave through a BT spacer.