中文摘要：

换流变压器油纸绝缘材料的电导率受电场强度与温度的影响呈非线性变化。为研究材料非线性对换流变压器极性反转电场分布的影响，对油纸绝缘电导率的非线性变化规律进行了数值拟合，利用RC等效电路进行了计算与分析，并运用ElecNet有限元软件对一台±400kV换流变压器网侧和阀侧绕组端部电场进行了仿真。计算与仿真结果表明非线性材料极性反转完成时油中最大电场强度为线性材料的78％，但稳态时油中电场强度是线性情况下的36倍。电导率的电场强度非线性会均化由温度梯度带来的电场梯度。最后根据计算与仿真结果提出绝缘的改进方向。

英文摘要：

Converter transformer oil-board insulating material＇s conductivity changes nonlinearly with electric field intensity and temperature. This nonlinear change rule is data-fitted in order to study the influences of material＇s nonlinearity to the distribution of converter transformer polarity reversal electric field. Calculation and analysis were carried out using RC equivalent circuit. The upper part of line and valve side windings＇ electric field of one ± 400 kV converter transformer were simulated by using the finite element software ElecNet. The results show that while the polarity reversal finishes, the maximum field strength of nonlinear material is of 78% compared with linear material. While at steady state, the field strength in the nonlinear oil is 36 times of linear oil. The conductivity change caused by electric field would homogenize the the electric field gradient caused by the temperature gradient. Finally, a few improvement measures are offered according to calculation and simulation results.