SUMMARYWe have investigated the propagation properties of Lamb waves and motion characteristic of free moving metallic particle in a gas-insulated switchgear (GIS) tank to diagnose the insulation performance of GIS. We have proposed a new identification technique for defect location in GIS based on the time-frequency analysis of the Lamb waves using the Wavelet Transform. In this paper, we measured the acoustic signals excited by a metallic particle colliding with the tank sheath. Furthermore, we measured the moving particles under a high electric field in GIS using a high-speed video camera. As a result, we examined the relationship between maximum lifting height and the flight time during subsequent impacts of a moving particle. Moreover, we estimated particle size based on the propagation properties of Lamb waves.
MemberThe 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 V p+ to the negative one V p− 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 builtin 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.
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