Abstract
The authors have studied diagnostic technique of gas insulated switchgear (GIS) using partial discharge (PD) induced electromagnetic wave measured by UHF sensors. So far, we have proposed to discriminate discharge type by introducing amplitude ratio Rp: the positive peak value Vp+ to the negative one Vp- of the first wave of incoming electromagnetic wave measured with UHF sensors. In this paper, we discuss electromagnetic wave radiated from simulated pulse and PD measured with disk-type UHF sensors and built-in sensors consisting of a metal ring embedded in epoxy spacer of GIS. The shape of electromagnetic wave measured by the built-in sensor was distorted and high frequency components attenuated through a spacer in comparison with signal measured with the UHF sensor. It was suggested that the spacer may play the role of a low pass filter. Moreover, we proposed to discriminate discharge type based on the first wave of electromagnetic wave measured with the built-in sensors. We also investigated frequency spectrum of propagating UHF signals in GIS with different tank size by finite difference time domain (FD-TD) method with focusing on the influence of higher-order modes.
