Polarity Reversal of Surface Charges at SiC/Epoxy Coating due to Increase of Voltage Amplitude

In this paper, the surface charge accumulation and dissipation experiments of SiC-coated epoxy composites were carried out under different voltage polarities and amplitudes. The surface charge distributions of coating with 0, 5wt% and 10wt% SiC ingredient were obtained under different levels of voltage. When the voltage was −10 kV, most surface charges were positive, while few were negative. The positive charges distributed near the high-voltage electrode, and the negative distributed near the grounded electrode. After the voltage increased to −20 kV, negative charges accumulated near the high-voltage electrode, and positive charges accumulated near the grounded electrode. As for the charge density and distributed area, the negative was much larger than the positive. Voltage increase leads to the polarity reversal of surface charges. It was inferred that the gas conduction contributed to the surface charge accumulation at −10 kV, while it was dominated by electrode injection at −20 kV. In addition, the surface charge amount was reduced when the content of SiC became higher. This change trend was attributed to the increase of conductivity and shallow traps.