Propagation properties of PD-induced electromagnetic wave through L-shaped structure in model GIS measured with UHF sensors

The authors have studied insulation diagnostic technique of gas-insulated switchgear (GIS) by UHF method. It is known that PD-induced electromagnetic wave is affected by a discontinuity part of impedance such as L-shaped structure, spacers and so on. In this paper, we experimentally investigated influence of L-shaped structure on propagation properties of PD-induced electromagnetic wave measured with UHF sensors in a 66 kV model GIS. Focusing on reflecting properties of TE mode at the L-shaped structure, we discussed the effects of the L-shaped structure on the peak to peak amplitude V_pp of propagating electromagnetic wave by comparing the experimental results obtained under straight type GIS. As a result, it was found that TE mode component could be reflected at the L-shaped branch, which can result in increasing V_pp due to the superimpose of the reflected TE mode to TEM mode component depending on the distance between sensor position and L-shaped branch.