Identification of extended Debye model parameters for oil-paper insulation based on voltage response characteristic

Due to the difficulty in setting the extended Debye relaxation time constant, which can reflect the insulation state, the application of the voltage response (VR) method in the diagnosis of oil-paper insulation state is limited. In this paper, based on the extended voltage response (EVR) method of single-polarization multiple measurements, the relaxation time constant was determined according to the first and last initial slopes that, respectively, reflect the rapid polarization and slow polarization of the medium, so that by measuring the initial slopes of return voltages (S-r) after different discharging times, various time constant polarization can be investigated. The insulation resistance is directly determined by the initial slope of the decay voltage (S-d) which is directly proportional to the conductivity of the insulation. Based on the characteristic parameters of the dielectric response of moisture and aging samples, the coincidence degree between the simulation results and the measured values is higher than 91% and 98%, respectively. The state of insulation was analyzed with the identified parameters. With the increase of moisture and aging degree of insulation, the time constant tau(pi) decreases gradually, and the polarizability alpha(pi) increases gradually. The method presented in this paper provides a reference for the application of the EVR method in the diagnosis of transformer oil-paper insulation state.