Effect of Surface Charges on the Surface-breakdown Characteristics of Polytetrafluoroethylene

Abstract

Under the DC electric field, surface charge accumulates on the surface of PTFE and increases the risk of surface insulation failure. On the basis of self-built surface potential measurement system, the DC voltage of $2. 5\mathrm {k}\mathrm {V}\sim 4\mathrm {k}\mathrm {V}$ was applied to the needle electrode for non-contact charge injection on the surface of PTFE, a Kelvin probe was used to measure the surface potential of PTFE. The relationship between the surface charge distribution and the applied voltage were obtained. Then the effect of surface charges on the flashover voltage was studied. Experimental results showed that the surface charge of PTFE was concentrically circularly distributed. The surface charge density increased with the increase in applied voltage. When the surface charge was injected on the discharge channel, the positive charge enhanced the electric field near the cathode so as to reduce the negative streamer inception voltage. Similarly, the negative charges also reduced the electric field near the anode and decreased positive streamer inception voltage. Therefore, when the average surface charge density of the accumulating charges was $16.7 \mathrm {p}\mathrm {C}/\mathrm {m}\mathrm {m}^{2}$, the flashover voltage decreased by 5.9%. When the average surface charge density is $-17.2\mathrm {p}\mathrm {C}/\mathrm {m}\mathrm {m}^{2}$, the flashover voltage decreased by 6.8%.