Influence of chemical composition on partial discharge characteristics in hexadecane

Partial discharge (PD) characteristics of hexadecane were studied in a needle-plane electrode geometry under AC field with tungsten needles of 10 and 20 μm tip radii. Initial experiments focused on establishing a relationship between chemical impurities in the dielectric fluid and the PD characteristics through addition of chemicals with known electrochemical properties such as N,N-dimethylaniline (DMA), a low ionization potential compound, and 1,1,1-trichloroethane (TCE), which is highly electronegative. The presence of DMA increases ionization and eases the formation of avalanches relative to pure hexadecane. The addition of TCE at low concentration initially suppresses the overall PD pulse rate for negative discharges and with increasing concentration, the negative streamers tend to become faster and more filamentary; hence, their charge magnitudes become comparable with those of positive streamers.