Epoxy-based model insulators were manufactured and fluorinated under a F2/N2 mixture (12.5% F2) at 50 °C and 0.1 MPa for 15 min and 60 min. Surface charge accumulation and decay behavior were studied with and without dc voltage application. The effect of direct fluorination on surface charge migration as well as on flashover voltage was verified. The obtained results show that the charge decay of epoxy-based insulators is a slow process, but the decay rate increases when an outer dc electric field is applied. The surface charge distribution is changed when a streamer is triggered on the insulator surface. The existence of heteropolarity surface charges can decrease the dc surface flashover voltage to some extent, while the surface flashover voltage is almost unchanged when charges of the same polarity accumulate on the insulator surface. The short time fluorinated insulator can modify the surface resistivity, and the rate of surface charge dissipation is greatly increased under a dc electric field.

Spacers are key components that are used to support high voltage conductors in gas-insulated substations or gas-insulated lines. The analysis of the surface charge patterns on spacers remains a difficult task, which requires a comprehensive understanding of the physical mechanism of the gas-solid interface charging phenomenon. In this letter, we reported a field dependent property of surface charge accumulation patterns on spacers under DC stress. We verified this finding through experiment, and further, we put forward a field-dependent charging model based on dominant charge transport behavior under different electric fields. It was found that the charging characteristics of the spacer are dominated by the Ohmic conduction from the volume below an electric field of 2.5 kV/mm. When the electric field stress is higher than 2.5 kV/mm, the charging property of spacers is dominated by the enhanced gas ionization according to Townsend's law. The correctness of this model was verified by surface charge measurement results in literature studies, and a method for determining the dominant mechanism of charge accumulation under different electric fields was proposed.

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This report intends to reveal the role of electron migration and its effects in triggering direct current (DC) surface flashover under temperature gradient conditions when using epoxy-based insulating composites. The surface potential and the surface flashover voltage are both measured using insulators that are bridged between two thermo-regulated electrodes. The space charge injection and migration properties under different temperature are detected. The results show that the surface potential rises significantly because of electron migration near the high voltage (HV) electrode under high temperature conditions, thus creating an “analogous ineffective region”. The expansion of this “analogous ineffective region” results in most of the voltage drop occurring near the ground electrode, which serves as an important factor triggering positive streamers across the insulation surface. This work is helpful in understanding of DC surface flashover mechanism from a new perspective and also has important significance in design of a suitable DC insulator to avoid surface flashover problem.