同轴电极结构中非线性介质空间电荷极化与退极化暂态过程仿真研究

Simulation on Space Charge during Polarization and Depolarization of Non-Linear Dielectric in Coaxial Electrode Structure

非线性介质是指其电导率和（或）介电常数随电场强度变化而变化的电介质。非均匀电场中非线性介质由于介质的介电性能参数在空间呈梯度变化，在电场作用下将发生空间电荷极化，而极化形成的空间电荷又影响电场的分布，探明这种空间电荷极化的动态过程有助于高压直流绝缘结构的设计和故障分析。为此，利用COMSOL Multiphysics有限元软件中的瞬态求解器仿真研究了同轴电极结构下具有场致增强型和温度增强型电导的非线性电介质在阶跃电压下的极化和退极化过程。研究结果发现：极化建立过程中，内电极附近空间电荷密度随时间变化会出现“过冲”现象；退极化过程中，内电极附近空间电荷会出现“反极性过冲”现象；“过冲”现象与“反极性过冲”现象相互呼应，均源自动态松弛时间的时空分布；温度梯度与场强对空间电荷“过冲”行为的影响规律不同。

The nonlinear dielectric is a sort of dielectrics that their conductivity and （or） permittivity will change with the electric field. Under inhomogeneous field. The nonlinear dielectric will polarize for its conductivity and （or） permittivity that have strong dependence on temperature and electric field. The space charge accumulated in polarization process will affect the electric field pattern. To ascertain the characteristics of this space charge polarization is of a great significance to help to design the insulation structure and to diagnose the insulation breakdown. In this paper, a coaxial model of high voltage direct current （HVDC） cable insulation was built and the finite-element analysis software （COMSOL Multi-physics） was employed to simulate space charge dynamic process caused by the nonlinear conductivity of insulation with different temperature gradients and step voltage amplitudes. The results show that a space charge density overshoot phenomenon occurs during polarization and an opposite polarity charge density overshoot occurs during depolarization near the inner electrode. The polarity charge density overshoot and opposite polarity charge density overshoot are both induced by the distribution of dynamic relaxation time in dielectrics. The phenomenon of overshoot during polarization and depolariza-tion echoes each other. The temperature gradient and the electric field have different influence on space charge overshoot phenomenon.