Evaluation Method of Aging State of Oil-Paper Insulation Based on Time Domain Dielectric Response

Transformer's stable operation is necessary for safety of power network. Although the dielectric response technology can evaluate the aging state of transformer, there is little equivalent model for evaluating. This paper tests the polarization and depolarization current(PDC) of the oil-paper insulation model of the transformer under variable temperature and calculates its isothermal relaxation current curve correspondingly. For the calculation results, it's found that with the raise of test temperature, the relaxation period of the isothermal relaxation current decreases. Also, the dielectric spectrum calculated according to the current curve shows that with the test temperature rises and the aging degree increases. The peak position of time-domain dielectric spectrum curve of the isothermal relaxation current gradually shifts to the right, and the main relaxation peak and relaxation time constant gradually increase. Thus, this paper establishes the calculation equation of main peak relaxation time and cellulose oil-impregnated paperboard cellulose, which can reasonably evaluate the aging degree of the oil-paper insulation system.