Electromagnetic (EM) wave characteristics in GIS and measuring the EM wave leakage at the spacer aperture for partial discharge diagnosis

For the insulation diagnosis of gas-insulated switchgears, the UHF method, which detects electromagnetic wave (EM-wave) in the UHF band (300 MHz to several GHz) with little noise influence, has rapidly developed in recent years. The study in this paper has proposed the evaluation of the location of adhering metallic particles based on the theory of EM-wave propagation by only using the time-waveform information of the EM-wave emitted due to partial discharge, and also analyzed and studied the validity using the FD-TD method. As a result, the duration of the time-waveform differed with respect to the location of the adhering metallic particle, and this difference was caused by the difference in the relative electric field intensity at the tip of the metallic particle among EM-wave modes and the difference was more when the tank diameter was larger. Based on this result, the method for evaluating the location of metallic particle according the time-waveform was studied. In addition, the characteristics of the leakage EM-wave at the spacer aperture were analyzed, and based on the result obtained, two types of antennas, patch and waveguide slot antennas, achieving compactness and a high sensitivity were proposed