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

doi:10.11985/2018.11.007

Abstract

Abstract:

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.

Key words: Non-linear dielectrics, temperature gradient, space charge, polarization, depolarization

CLC Number:

TM215

Sun Yunlong,Li Zhonghua,Suo Changyou,Zheng Huan. Simulation on Space Charge during Polarization and Depolarization of Non-Linear Dielectric in Coaxial Electrode Structure[J]. Journal of Electrical Engineering, 2018, 13(11): 52-64.

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	内、外电极(铜)	介质
电导率γ/(S·m^-1)	5.998×10⁷	γ(E, T)
相对介电常数ε_r	108	2.3

边界	温度/K
内电极边界T_in	T_out+ ΔT
外电极边界T_out	313

物理过程	时间段/s	步长/s
极化过程（括号内为退极化过程）	0~1(50 000~50 001)	0.01
	1~10(50 001~50 010)	0.1
	10~100(50 010~50 100)	1
	100~1 000(50 100~51 000)	10
	1 000~10 000(51 000~60 000)	100
	10 000~50 000(60 000~150 000)	1 000