中文摘要：

电场分布是决定电缆绝缘短时耐压能力和长期运行可靠性的关键因素。HVDC电缆稳定运行时，绝缘材料的电导率决定电场分布，在较高温度梯度分布下有可能出现电场分布翻转现象。由于电缆绝缘材料的非线性电导率是温度及电场的函数，在投入运行和电压极性反转时HVDC电缆暂态电场分布更为复杂。为此，采用多物理场耦合软件仿真研究了绝缘材料非线性电导属性对不同温度梯度、不同施压方式下电缆绝缘稳态和暂态电场的影响规律。仿真结果发现：当绝缘材料非线性属性确定，绝缘内温度梯度越高，稳态时电场分布翻转现象越严重；电压反转过程暂态电场最大值与电压极性反转时间密切相关，反转时间越短暂态最大电场越高，且暂态最大电场的位置越靠近导体屏蔽。仿真结果同时表明：降低材料电导活化能和提高材料电导率对电场依赖性有利于在温度梯度下对电缆绝缘稳态和暂态电场分布的控制。根据仿真研究结果，建议在HVDC电缆料研发时应采取有效的调控手段降低材料电导活化能和提高场致增强型电导的场强依赖系数；而在HVDC电缆设计时，要特别关注温度梯度效应和极性反转过程中的暂态电场分布问题。

英文摘要：

Electric field distribution is the key factor determining the short-time voltage withstanding ability and the long-term running reliability of HVDC cable insulation. Under stable operation condition, the electric field distribution of HVDC cables is mainly determined by the conductivity of insulating materials, and the phenomenon of electric field distribution reversion will happen under the higher temperature gradient. The transient electric field distribution in HVDC cable at the moment putting into operation and voltage polarity reversion will be complicated due to the nonlinear conductivity of insulation materials related with temperature and electric field. For this reason, the effect of the nonlinearity of insulating materials on the electric field distribution in HVDC cables under different temperature gradients and different voltage types were analyzed using the software of COMSOL Multiphysics. The simulation results show that： for the determined insulating material with the certain nonlinear properties, the phenomenon of electric field distribution reversion in the cable insulation will be more serious under the higher temperature gradient; the maximum transient electric field during the voltage reversal process is closely related to the voltage polarity inversion time, the maximum transient electric field will increase and the location of the maximum electric field transient will move to the conductor shield as the voltage polarity inversion time decrease. The simulation results also show that the steady-state and the transient electric field in cable insulation under certain temperature gradient can be uniformed though reducing the conductivity activation energy and increasing the electric field dependent coefficient of conductivity of the insulating materials. According to the simulation results, it is recommended that the conductivity activation energy should be reduced and the electric field dependent coefficient of conductivity of the insulating materials should be increased by the effective cont