Study on Surface Charge Distribution of Scaled-down Gas-Insulated Bushings under High-Voltage Direct Current

The capacitor core-SF<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> composite insulation sleeve is widely used in ultra-high voltage engineering, and the interface between the capacitor core and SF<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> is prone to surface charge accumulation in the strong normal component of the DC electric field. The uneven surface charges accumulated in the insulation layer and core of the casing will distort the nearby electric field, becoming a trigger for flashover accidents and threatening the safe and reliable operation of the casing. This article discusses the direct current voltage applied to gas reduction sleeves under different voltages and polarization times. The results indicate that the core of the reduced ratio bushing capacitor is mainly composed of positive polarity charges, and the gas side current is the main source of charge accumulation. As the absolute value of the applied voltage increases, the positive polarity charge gradually increases on the inner wall of the shrink fit sleeve sheath, and the solid body current gradually increases. It is speculated that the formation of charge spots is caused by tiny metal particles adsorbed on the surface. The accumulation of surface charges in both the inner core of the casing and the Fr4 shell may be due to uneven material distribution in practice. The positive charge at the end of the core and the negative charge of the sheath will increase the gas insulation pressure, resulting in radial electric field distortion. This article provides experimental evidence and theoretical basis for the potential safety hazards that may exist during the operation of actual real casing.