非线性屏障层对HVDC电缆电场分布的影响

Influence of Nonlinear Barrier on Electric Field Distribution in HVDC Cable

电缆绝缘中的电场分布是决定高压直流电缆输电线路长期可靠运行的主要因素,非线性材料能够在电场不均匀的情况下自行均化电场的分布,对电树枝的生长和空间电荷的产生起到明显的抑制作用。为此,尝试将非线性材料作为屏障层置于电缆屏蔽层与绝缘层之间,并采用多物理场耦合软件建立仿真模型,分别在不同温度梯度下研究屏障层结构对高压直流（HVDC）电缆绝缘中暂态和稳态电场分布、空间电荷的影响。仿真结果发现：与无屏障层相比,添加非线性屏障层的电缆绝缘中稳态及暂态电场强度最大值均有所降低,即屏障层结构能够抑制绝缘中空间电荷的注入,改善电场分布;屏障层越厚,绝缘中空间电荷越少,电场强度最大值越小,但界面电荷会有所增加。从上述结果可以看出：屏障层可均化电缆绝缘中的电场分布,但同时会引起界面电荷的积聚。因此在开发具有非线性屏障层结构的HVDC电缆时,屏障层厚度的选择应综合考虑界面电荷积聚和电场分布,从而达到改善电缆绝缘性能的目的。

Electric field distribution of cable insulation is a main factor affecting the long-term and reliable operation of HVDC cable. Nonlinear materials can not only homogenize the electric field distribution by themself, but also have obvious inhibition effects on electrical trees growth and the formation of space charge. Therefore, we tried to use a nonlinear material as barrier layer and put it between shield and insulation.Moreover, we established a simulation model by the software of COMSOL Multiphysics. Meanwhile we studied the influences of barrier layer structure on the steady and transient electric field distribution and space charge of HVDC cable insulation at different temperature gradients. The simulation results show that, compared with the non-barrier cable, the steady and transient electric field strength maximums of the cable insulation with nonlinear barrier layer are both decreased. That is to say, the injection of space charge into insulation is inhibited and the distribution of electric field is improved by the barrier layer structure. As the barrier layer thickness increases, the space charge in the insulation and the maximum field strength decreases, but the interface charge increases. According to the simulation results, the electric field distribution of cable insulation can be optimized by a barrier layer. However, it also causes the accumulation of interfacial charge. Therefore, when HVDC cable with a nonlinear barrier layer structure is developed, the interface charge accumulation and electric field distribution should be considered for the selection of barrier layer thickness, so as to improve the cable insulation performance.