High-voltage AC gas-insulated switchgear (GIS) plays a crucial role in ensuring the reliable transmission of electrical power

but it also introduces new challenges to the resilience of power systems against ice-related disasters. Compared to traditional segmented DC ice-melting methods

GIS-connected lines ice-melting method is more efficient when dealing with widespread ice accumulation on power grids. However

when transitioning from DC ice-melting to AC power supply restoration

the basin insulators in GIS systems are vulnerable to surface flashover due to the stress of DC-AC switching electric fields. This study combines experimental and simulation approaches to investigate the charge transport mechanism and flashover characteristics of epoxy resin (EP) under DC-AC switching electric fields. The results show that under DC electric fields

charge accumulation occurs at triple junctions

with charge density positively correlated with both voltage and charging time. Upon switching to AC

the electric field strength sharply increases during the half-period of opposite polarity

combined with dissipation of accumulated charges leading to an 80% higher flashover probability. Compared to negative polarity DC

positive polarity DC results in higher charge density (up to 60%) and more significant field distortion

thereby increasing the risk of flashover. Based on simulations of the 252 kV basin insulator

this study suggests that using a negative polarity DC source is preferable during GIS-connected lines ice-melting operations

providing key theoretical support for engineering insulation design.