Partial discharge detection and induced surface current analysis using transient earth voltage method for high voltage equipment

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.