Super High Frequency Wideband Measurement of Partial Discharge Current Waveform in Mineral Oil

—Difference in PD Phenomena Depending on Degassing Treatment and Polarity Effect—

Abstract

Liquid insulators have excellent cooling and insulation performance, but impurities and contaminants in the liquid or dissolved gases and moisture are known to have a significant influence on insulation performance. In this paper, using the Super High Frequency-wideband Partial Discharge (PD) current Pulse Waveform measurement system, “SHF_PDPW system”, that the authors have developed and applied to PD measurement in SF₆ gas so far, PD current waveforms in mineral oil were investigated in detail. Differences in PD current waveforms due to degassing treatment condition of the mineral oil and polarity effect of applied voltage could be clearly clarified. These differences cannot be observed by ordinary oscilloscopes with analog bandwidths around 1GHz, and are important findings to understand PD phenomena, which were first observed by the super-wideband measurements.