Abstract
This study deals with advancement of insulation diagnosis technology by partial discharge (PD) detection with transient earth voltage (TEV) signal in high voltage equipment such as oil-filled transformer. TEV detection method allows to detect signals by attaching TEV sensors to the outer wall of the existing facilities. Experiment and analysis of TEV signal propagation using finite-difference time-domain (FDTD) method are carried out for an iron box model which simulates a tank of an actual transformer. Results revealed that TEV signal caused by PD dominantly consists of two kinds of frequency components; i.e. high-frequency component of 500 MHz and low-frequency one of 30 MHz. Namely, the high frequency component of TEV signal propagates from the aperture of the bushing, while the low-frequency component flows through the ground line. Furthermore, it was found that the high-frequency component contained in the TEV signal is attributed to the resonant frequency determined by the size of the metal tank. As a result, if the magnitude and the frequency band of detected TEV signal are known, it is possible to determine where the discharge source is located inside or outside of the metal tank.
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