Surface Charge Accumulation of Cylindrical Insulator in Atmospheric Pressure Air After Positive and Negative Impulse Flashover

Atmospheric or compressed air exhibits adequate insulating properties for electrical insulation applications, making it a eco-friendly alternative to global warming <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{SF}_{6}$</tex> gas. However, surface insulation remains the weakest link in air-insulated electrical equipment, especially when the insulator endures transient impulse voltages and undertakes residual surface charges caused by impulse flashover. Investigating the charge characteristics at gas-solid interfaces and the evolution of discharges in air is crucial for improving the design of environmentally friendly, high voltage electrical apparatus. In this study, a cylindrical insulator was designed to study the surface charge accumulation after positive or negative lightening impulses. A charge measurement platform for gas-polymer surface discharge was constructed to measure charge density distribution. The results indicate under positive impulse voltage, the boundary between leader and streamer discharges is located approximately 20 mm from the high-voltage electrode. Under negative impulse voltage, this boundary gradually moves toward the ground electrode as the voltage increases. In the impulse voltage range of 12.5 kV to 16 kV, the separation threshold of charge density between leader and streamer discharges is between 350 and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$680 \text{pC} / \text{mm}^{2}$</tex>, with the transverse potential boundary around 9 kV and the longitudinal potential boundary between 6 kV and 8 kV. In the negative impulse voltage range of −9.5 kV to 17.5 kV, the threshold of charge density is between 500 and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$600 \text{pC} / \text{mm}^{2}$</tex>, the average field strength in the streamer region is between <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1.0 \text{kV} / \text{mm}$</tex> and 1.6 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{kV} / \text{mm}$</tex>, and the field strength in the leader channel is between <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.15 \text{kV} / \text{mm}$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.20 \text{kV} / \text{mm}$</tex>. This study can provide some references to the development of high voltage, air insulated power switchgears, especially for applications under DC voltage.