Electric Field Distribution of ± 800kV Valve Side Bushing Capacitor Core Influenced by Temperature Gradient

Electric field distribution is determined for the design and long-term performance of bushing yet gets complicated when coupled with temperature due to the highly temperature dependent conductivity of insulation. In this paper, an electro thermal coupling model is established based on the geometry of a real ± SOO kV converter transformer valve side bushing. The measured temperature-dependent conductivity of RIP material is adopted and fitted according to the Arrhenius formula. The electric field distribution inside a condenser core under the influence of temperature was investigated, and the related mechanism was analyzed by an equivalent circuit model, considering the actual working conditions. The temperature gradient within the condenser core is verified, and the electric field migration is observed. It is indicated that the electric field strength shows a strong dependence on temperature and increases along the radial direction. The maximum field strength appears at the outmost shield layer under the operating voltage and the load current 4500 A, which is higher than that under the DC long-term withstand voltage of 1455 kV without thermal stress. More attention should be paid to the design and operation of converter transformer valve side bushing.