The valve-side bushing is a core component of DC transmission systems

and its safe and stable operation is crucial for channel security. To evaluate the influence of ambient temperature variation on the charge at the surface

this paper computes the thermal field distribution from −20 ℃ to 60 ℃. By measuring the conductivity of the epoxy-impregnated paper material of the valve-side bushing core

the relationship between bulk conductivity and surface conductivity with temperature is established. The surface charge and bulk charge distributions on the core under different ambient temperatures are calculated. The results show that a decrease in ambient temperature increases the radial electric field of the core and the normal electric field on the core surface. Low temperature leads to an increase in deep trap density of the epoxy-impregnated paper material

making it difficult for carriers to detrap

thereby increasing the amplitude of surface charge density and bulk charge density. When the ambient temperature drops from 20 ℃ to −20 ℃

the maximum bulk charge density on the air-side core increases by 47.5%

the maximum radial electric field intensity increases by 21.1%

and the air-side normal electric field increases by 10.7%. The reduction in ambient temperature distorts the internal electric field distribution of the bushing to some extent

increasing the risk of insulation failure.