Single filament partial discharge: Surface charge accumulation

In our experiments the single DC discharges propagate in the “needle - air gap - dielectric barrier - plane” system under atmospheric pressure. Polypropylene (12 μm) and polyethylene terephthalate (100 μm) films were used as barriers. Interelectrode air gap varied in the range of 100-2000 μm, breakdown voltages - in the range of 1200-3800 V. The positive breakdown voltage exceeds the negative one for the same gap. The current discharge pulses (with amplitude of 10-150 mA) were measured in a nanosecond time scale. Surface charge distribution was detected by a rotating capacitive probe. Spatial distribution of surface charge could be approximated by Gauss law. The maximum charge density varies within limits 6-220 nC/cm². In case of different gaps but equal breakdown voltages regardless of polarity the maximum charge density remains constant while the amount of accumulated charge for the positive needle polarity is less than for the negative one.