Frequency bandwidth dependence of PD current waveforms in transformer oil measured with the SHF_PDPW system

This paper deals with partial discharge (PD) current waveforms in transformer oil measured with the SHF_PDPW (super high frequency wideband PD current pulse waveform measurement) system that enables us to obtain accurately waveforms up to SHF band (3-30GHz). We investigated the PD current pulse waveform, especially on the rise time, the current peak, and the charge quantity obtained by the time integral of the waveform, to focus on the dependences of the applied voltage and the discharge polarity. Also, we investigated the measurement frequency bandwidth f_BW dependence of the waveforms by decreasing the f_BW from the maximum value to the 1GHz. As a result, the rise time of the PD current waveform below 1 nano second was observed, in some case that is a pico to a tens pico seconds order rise time, and the dependences of the applied voltage was also obtained. The distinct differences in the waveforms between positive and negative polarities were also observed in this study. These results could contribute to understand the PD phenomena and to improve the UHF method for the power transformers.