Comparison of PD Current Waveforms between Aged and New Insulation Oils and Oil Types by Super-Wideband Measurement

Abstract

Liquid insulators such as mineral oil and silicone oil have excellent cooling and insulation performance, but impurities, dissolved gases and/or moisture in the liquid are known to have a significant influence on insulation performance. So far, the authors have shown that partial discharge (PD) current waveforms in mineral oil differ significantly depending on degassing treatment condition and on positive and negative polarity by super high frequency-wideband measurement. In this paper, using aged mineral oil which was used in a distribution transformer over 48 years, difference in PD current waveforms between new and aged mineral oil and between mineral and silicone oils as difference in insulation oil type were investigated by the super high frequency-wideband measurement system, so-called “SHF_PDPW system” with a 33GHz oscilloscope. In addition, PD-emitted electromagnetic (EM) waves in those oils were measured with an antenna with sensitivity in the UHF band, and differences in the polarity and relationship between PD current and PD-emitted EM waves were investigated from the viewpoint of applicability of the UHF method.