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The effect of oxidative and paper degradation impurities on partial discharge characteristics of hexadecane

Partial discharge (PD) characteristics of hexadecane were studied in a needle-plane electrode geometry under AC field with a tungsten needle of 20 μm tip radius. PD experiments were conducted on samples containing known concentrations of oil/paper degradation compounds. Partial discharge inception voltage (PDIV), streamer repetition rates, and phase resolved PD (PRPD) patterns were acquired. Ionization potentials (IP) and electron affinities (EA) of hexadecane and a selection of additives were calculated with density functional theory (DFT) and correlated to PD characteristics. IP did not have a significant effect on the number of streamers initiated as most additives had higher IP relative to hexadecane. The presence of electronegative oxygen changes substantially the PD characteristics and, for most additives, increases the number of positive and negative streamers initiated. The greatest changes in PD characteristics, a reduced number of negative streamers, was observed for compounds with large electron capture cross section, even those with negative EA.