Interfacial Moisture Accumulation Characteristics in Oil-Paper Insulation: Modeling and Experimental Investigation

Moisture exchange in oil-paper insulation under temperature-varying conditions exhibits significant complexity, particularly with interfacial moisture accumulation readily occurring during cooling-a phenomenon that critically compromises transformer insulation integrity, yet consensus remains elusive regarding key parameters and formation mechanisms of such accumulation under thermal cycling. To address this, a computational model for moisture diffusion and exchange in oil-paper insulation is developed. Through experimental measurements of spatiotemporal moisture distribution in oil-impregnated pressboard and oil moisture content evolution, temperature-dependent relationships for the diffusion coefficientDand interfacial moisture exchange coefficient α are established. Subsequent temperature-varying experiments reveal interfacial exchange hysteresis relative to temperature changes, with hysteresis loop areas expanding with increasing temperature variation rates, temperature ranges, and initial moisture content. Integrated model-experimental analysis demonstrates that interfacial moisture exchange exhibits higher activation energy than the diffusion process, establishing it as the rate-limiting step. Furthermore, moisture accumulation fundamentally stems from coupled interfacial kinetic hysteresis induced by high activation and abrupt solubility changes, where sluggish interfacial exchange during cooling fails to match rapidly escalating oil supersaturation levels. These findings provide theoretical foundations for dynamic moisture prediction in transformer insulation systems and operational load management strategies.