Research on the moisture distribution of oil-paper insulating bushing based on polarity reversal PDC

Moisture is one of the most critical factors contributing to the inability of oil-paper insulating bushings to operate safely and stably, primarily originating from the internal capacitive core and the end screen area. This paper investigates a rough estimation method for moisture distribution in oil-paper insulated bushings based on the Polarization and Depolarization Current testing technique. First, simulation models of internal and external moisture ingress in the bushing were constructed using COMSOL, verifying the differences in moisture distribution under the two moisture ingress conditions. Subsequently, a Debye model of macroscopic charge polarization was derived, and the impact of the proton conduction migration mechanism of hydrolyzed H⁺ ions on the difference in positive and negative ion mobility was analyzed. Combined with experimental results from non-uniformly moistened samples, it was demonstrated that the current difference observed during polarization (depolarization) under polarity reversal originates from the disparity in macroscopic charge polarization intensities due to the differing migration strengths of the ions. Finally, a rough identification method for moisture distribution in bushings was proposed, and its effectiveness was validated through experiments using a scaled-down bushing model.