Broad band pulse detection studies of partial discharges in presence of solid dielectrics in CF6-N2 mixtures

Experiments were conducted to detect partial-discharge (PD) pulses in the presence of solid dielectrics (PTFE and glass-filled epoxy) as well as breakdown pulses in SF₆, N₂, and SF₆ -N₂ mixtures under uniform field conditions using a broadband detection system. The effects of circuit parameters, overvoltages, gas pressure, and the distance between electrodes on pulse shapes were studied for various proportions of SF₆ in SF₆-N₂ mixtures. The observed PD pulses are similar to breakdown pulses for longer electrode gaps (>0.3 cm). In the case of surface discharges the pulses are oscillatory in nature and inconsistent in shape and magnitude. The effect of saturation on the increase in breakdown voltage of SF₆-N₂ mixtures with increase in percentage of SF₆ (i.e. synergism) is also observed in the presence of the solid dielectric. This synergistic effect is reflected in corresponding observed PD pulse shapes