A Study On The Interface Polarization Of Double Composite Structure Containing Nonlinear Dielectrics

The interface polarization occurring in the interface between two linear dielectrics with different dielectric properties is well known as Maxwell –Wagner polarization. The transient and steady state characteristics of Maxwell –Wagner polarization can be understood through theoretical derivation. The application of nonlinear dielectrics as electric-stress grading material in high voltage insulation presents new complex interface problems in linear/nonlinear or nonlinear/nonlinear dielectrics. Deep understanding of the interface polarization characteristics of nonlinear dielectrics provides the important basis for reasonable application of nonlinear dielectrics in engineering. Due to the complexity of nonlinear problems, it is rather difficult to describe the interface polarization characteristics for the interface in linear/nonlinear or nonlinear/nonlinear dielectrics through the theoretical derivation.Based on the above reasons, the double-layer dielectrics and the simplified physical model are taken as the research objects to explore the interface polarization mechanism under the panel three-electrode structure. The simulation is carried out using MATLAB/Simulink and the experiments are conducted mainly by the megger of Kethly6517 B.The simulation results show that the interface polarization with nonlinear dielectrics is obviously affected by the excitation voltage, different from the condition of double linear dielectrics. Under step voltage, the polarization process is affected by the applied electric field and the induced electric field together, whereas the depolarization is affected by the induced electric field only.Thus, finally, the time of depolarization reaching steady state is much longer than that of polarization. Also, the polarization gets faster and the depolarization gets slower with the increase of the voltage amplitudes. For the condition of the timeconstants of two layers intersect, the polarity of interface charges will reverse as the average electric field gets higher. It's caused by the relationship of the conductivity changing with the applied voltage. The maximum value of the transient interface charges and electric fields and currents under the polarity reversal DC voltage are significantly higher than the maximum transient value under the step voltage. The reason is that the dissipation of the interfacial charges can't keep up with the changing of the applied electric field at the instant of the voltage polarity reversal, the initial value of the two layers are greatly increased by the two electric fields function together. The experimental results present that the species and amount of the filler in nonlinear dielectric and the temperature have a great influence on the polarization and depolarization of the double layer composite structure containing nonlinear dielectrics. That is because the microstructure and macroscopic property of the fillers, the amount of fillers, and the temperature affect the conductance property and dielectric property of the nonlinear dielectrics. Moreover, the time constant and the conductance currents will be affected. In conclusion, the experimental results further verify the effect of voltage amplitudes and polarity reversal voltage on the interface polarization of double composite structure containing nonlinear dielectrics. The simulation results and the measured results have achieved good consistency with each other.