This paper presents an approach for calibration of ultra-high-frequency (UHF) partial discharge (PD) signals in high voltage direct current (HVDC) transformer. A linear relationship between the amplitude of the UHF PD signal and PD apparent charge was obtained through the theoretical analysis. The finite-difference time-domain (FDTD) model of the simulated converter transformer showed that the UHF PD electromagnetic waves in converter transformer can propagate outside by the transformer bushing. The UHF PD signals propagated from the transformer bushing were obtained by the FDTD calculation. The simulation results showed that the amplitudes of the UHF PD signals were related to the transformer bushing and the detection position. Artificial cavity insulation model were designed to generate UHF PD signals, which were detected by a Peano fractal antenna in a series of experiments. The experimental results show that the antenna can detect the UHF PD signals inside of the transformer from the bushing and the PD apparent charge can be calibrated by the proposed approximate equations.
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