Breakdown voltage in high voltage direct current cable insulations considering space charges

During operation of high-voltage direct current (HVDC) power cables heat is generated in the inner conductor and the insulation. As a result, a thermal breakdown may occur if more heat is generated than can be dissipated. The electric field stress due to space charges accumulating in the insulations superimposes the geometric electric field due to the applied voltage in the cable. In this work, the thermal breakdown process is analyzed including the effects of these space charges. The breakdown voltage at different temperatures is computed in numerical simulations coupling the heat conduction equation and Poisson's equation for a suitably extended HVDC cable model. The results show the breakdown voltage depending on the temperature at the outer sheath. The breakdown voltage decreases or increases with increasing temperature and space charges, depending on the influence of the temperature distribution on the material.