Time-Domain Dielectric Response Characteristics of Oil-Immersed Paper Bushings Under Radial Nonuniform Moisture

The moisture intrusion of high-voltage oil-immersed paper (OIP) bushing may cause insulation deterioration. Polarization and depolarization current (PDC) technology is an effective and nondestructive method to evaluate the moisture state of OIP bushings’ insulation. However, the current PDC assessment methods are difficult to evaluate the nonuniform moisture status of OIP bushings. To address this issue, this article studies the PDC characteristics of OIP bushings under radial nonuniform moisture distribution. Initially, by combining with the laboratory PDC measurements and finite element method (FEM) simulation, the influence laws of the dampest insulation layer’s moisture content and position on the overall PDC curve of OIP bushings are explored. The results show that the moisture content and position of the dampest insulation layer have a significant influence on the overall polarization current curve. The peak value, steady-state value, and integral value of the polarization current are negatively correlated to the position and positively correlated to the moisture content of the dampest insulation layer. The moistest layer’s position of the radial nonuniformly damped bushing can be determined by polarization current integral difference under positive and negative PDC link-wire ways. This research provides the theoretical basis and technical support for the nonuniform moisture state evaluation of OIP bushing insulation.