The existing DC flashover models still have some deficiencies

and cannot integrally explain some DC flashover phenomena. In this paper

the phenomenon of charge accumulation inside and on the surface of solid insulation under temperature gradient is studied by electrical-thermal multi-physical field simulation. The results show that

under the DC electric field

the surface potential near a high-voltage electrode can be increased by charge injection at the high-voltage electrode. When the temperature of the high-voltage electrode increases

the area with high potential will gradually extend to the grounded electrode with the charge injection from the body and the surface. This effect can be regarded as the extension of the high-voltage electrode to the grounded electrode

which reduces the effective insulation distance along the surface

and thus reduces the effective insulation distance along the surface. These results validate the concept of "analogous ineffective region". The concept of "analogous ineffective region" verified in this paper can be used to explain the unidentified cause of surface flashover under DC. The results can provide a certain reference for the future design of HVDC insulation equipment.