Abstract
The authors have studied insulation diagnostic technique of gas-insulated switchgear (GIS) by UHF method. In this paper, we investigated the effect of spacer type (metal flange type (MT) or bush type (BT)) on the propagation properties of PD-induced EM wave in GIS with UHF method. Low pass filtering process for cut-off 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 reduced superimposition of TE mode and TEM mode. Furthermore, we 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.
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