Characteristic Parameters Extraction of Oil-paper Insulation Aging Based on Davidson-Cole model

In order to further explore the quantitative relationship between the parameters of the dielectric response model and the actual aging state of transformer, this paper mainly base on the principle of dielectric response, simultaneously, frequency domain dielectric spectroscopy method is carried out for transformer oil-paper insulating in the conditions of different temperature and different aging time. Then the nonlinear least squares fitting method is used to extract the three characteristic parameters beta, tau and Delta epsilon of Davidson-Cole model, and the relationship between the characteristic parameters of the aging model and the aging state of the transformer oil-paper will be established. The results show that the three model parameters extracted from the experimental data are all related to the degree of polymerization of the oil-paper. With the extension of aging time, the value of the shape parameter beta and the relaxation time parameter tau will all decrease with the reduction of the degree of polymerization, but the former presents an exponential relationship, the latter is a linear relationship. Besides, the Delta epsilon will increase with the decrease of the degree of polymerization, and it is not related to the temperature in a certain range.