Nonlinear characteristics of the oil-paper insulation system during the polarization and depolarization process.

• At steady-state excitation, the transient electric field distribution in typical multi layer oil-paper insulation at different aging stages was obtained. • The equivalent model of polarization conductivity was proposed, which characterized the nonlinear phenomena at different polarization voltages. • Based on the charge escape trap model, the mechanism of the nonlinear phenomenon of response current in the process of dielectric polarization was revealed. The oil-immersed transformer plays a pivotal role in the power network. Its insulation stability is essential. At present, the application of time-domain dielectric response technology in insulation detection of oil-immersed equipment is relatively mature. However, there is a contradiction between increasing the test excitation amplitude to improve the test accuracy and the nonlinear response characteristics of the test dielectric at high-voltage excitation. The assessment theories all depend on the laboratory test results, and inaccurate test results will affect the assessment results. Therefore, this paper prepared several groups of insulation-scaled aging models in the laboratory and studied the effects of temperature and test excitation amplitude on the polarization and depolarization characteristics of the models. During the polarization process, the electric intensity variation was calculated. Meanwhile, at the time-varying electric field, the influence mechanism of electric intensity on the response current caused by the charge escaping from the trap during the polarization process was obtained. This paper quantified the relationship between the aging state and the height of the interfacial polarization barrier. The study of nonlinear dielectric response in the time domain will help to improve the accuracy of test results when diagnosing the insulation performance of oil-immersed transformers. [ABSTRACT FROM AUTHOR]