Characteristics of PD induced electromagnetic wave propagating through T-branch of 154 kV GIS in the presence of epoxy spacer

It is important for reliable diagnosis technique to clarify electromagnetic (EM) wave propagation characteristics at the impedance discontinuity part in gas insulated switchgear (GIS) like spacer, disconnecting part, L branch, and T branch. In this paper the influence of the existence of the insulating spacer on the partial discharge (PD) induced EM wave propagating through T-Branch of 154 kV GIS tank model was examined by the UHF PD measurement. It is observed that PD induced EM wave was attenuated with the distance even in the absence of the spacer. The existence of the spacer decreases the transmission rate of PD induced EM wave. The transmission rate of high frequency component of EM wave (TE mode) was almost the same with the transmission rate of raw EM wave, while the transmission rate of low frequency component of EM wave (TEM mode) was higher than the transmission rate of high frequency component with and without spacer. The transmission rate of PD induced EM wave is influenced mainly by propagation of high frequency component (TE mode) of PD induced EM wave. The existence of the spacer has less influence on the propagation characteristics before and after T branch. The transmission rate through straight direction is higher than the transmission rate through turn direction for the raw wave and the high frequency component of PD induced EM wave.