Effect of Interface Charge on Partial Discharge Characteristics of Oil-pressboard Insulation in Non-uniform AC/DC Combined Electric Field Under Different Temperatures

The investigation of partial discharge characteristics within oil-pressboard insulation systems is pivotal for the operational integrity of converter transformers. This research scrutinizes the substantial influence of thermal conditions on partial discharge (PD) attributes, with a focus on delineating the temperature-dependent variations in PD behaviors of oil-pressboard insulation under asymmetric AC/DC electrostatic fields. Additionally, this study delves into the intricate role of interface charge accumulation and its consequential impact on PD dynamics. Empirical observations underscore that an ambient temperature escalation from 20℃ to 80℃ precipitates a notable decrease in the Partial Discharge Inception Voltage (PDIV) and surface flashover thresholds by 72.7% and 9.94%, respectively. This thermal elevation also catalyzes an augmentation in key PD parameters, encompassing discharge recurrence frequency and aggregate discharge intensities. Significantly, the study identifies an ‘attenuation effect’ induced by interface charges on PD traits. Elevated thermal conditions attenuate both the superficial and volumetric resistivity of oil-pressboard insulation, thereby diminishing its dielectric robustness and curtailing interface charge build-up. This scenario aggravates PD progression. The synergistic interplay between interface charge dynamics and the resistivity attributes of the oil-pressboard matrix elucidates the thermal sensitivity of PD phenomena. These findings contributes to a deeper understanding of the thermal modulation of PD in oil-pressboard systems, offering critical insights for the refinement of insulation design and the optimization of electrical strength testing methodologies pertinent to such insulation matrices.