Abstract
Recently, diagnosis of gas insulated switchgears (GIS) is important because number of aged GIS is increasing and maintenance method of GIS is changing from TBM (Time Based Maintenance) to CBM (Condition Based Maintenance). In this paper, the mechanism of electromagnetic wave propagation in a GIS tank is investigated for understanding of fundamental characteristics for partial discharge detection using UHF method. In this paper, the output characteristics of UHF sensor in non-reflection coaxial waveguide are obtained under the various parameters of installation and shape of UHF sensor. The mechanism of electromagnetic wave propagation is investigated with comparison of the experimental result and EMTP (Electro-Magnetic Transients Program) analysis of equivalent circuit. In consequence, it is found that the mechanism of electromagnetic wave propagation can be treated as an equivalent electric circuit in the frequency region below cutoff frequency of TE11 mode, and another mechanism of electromagnetic wave with higher mode dominantly propagates.
