Objective This study aims to reveal the influence of temperature gradient on the electric field distribution characteristics of the ±800 kV converter transformer valve-side bushing under high current operation, thereby improving the scientific basis and reliability of insulation design in ultra-high-voltage direct current (UHVDC) transmission projects.

Method Most existing studies on converter transformer bushings focus on thermal or electric field characteristics, typically using 2D or 3D models to analyze steady-state temperature rise or constant-temperature electric field distributions. However, the nonlinear temperature dependence of dielectric properties and electrothermal coupling effects are often overlooked. To address this, a 2D finite element model is established to simulate a ±800 kV valve-side bushing, incorporating literature-based conductivity data for resin-impregnated paper (RIP). Using a multiphysics platform, the temperature field under load is calculated, followed by electrothermal coupling analysis to quantify the impact of temperature gradients on electric field distribution.

Result Simulation results show that under a 6736 A DC current, the maximum temperature of the bushing reaches 130.7 ℃, mainly concentrated in the lower part of the conductor and flange region, with a radial temperature gradient of up to 37.7 ℃ at the capacitor core near the flange. The temperature gradient leads to significant changes in the spatial distribution of material conductivity, causing the radial electric field strength in the capacitor core to shift from 6.8–7.6 kV/mm to 2.8–12.4 kV/mm. The maximum field strength increases by 63.2%, and the electric field distribution changes from a “weak-middle and strong-ends” pattern to an “inner-weak and outer-strong” pattern.

Conclusion The temperature gradient significantly affects the spatial distribution of conductivity in the capacitor core material, resulting in electric field distortion. The two-dimensional electrothermal coupled simulation quantitatively reveals the interaction mechanism between the temperature field and the electric field. The findings provide theoretical support and technical reference for the insulation design optimization and performance verification of ±800 kV converter transformer valve-side bushings.