High-Temperature Resistance Oil-Paper Insulation With Polyimide: A Study on Dielectric Properties

The increasing attention toward natural ester (NE) as a feasible substitute for mineral insulating oils is attributed to its exceptional biodegradability and high heat resistance. However, the limited temperature tolerance of NE-paper insulation, stemming from the low-temperature resistance of cellulose paper, poses a hindrance to its application. In contrast, polyimide (PI) insulation paper exhibits superior heat resistance and holds the potential for effectively replacing cellulose paper when utilized in conjunction with NE, thereby expanding the permissible temperature range. This study entailed the preparation and testing of samples of PI insulation paper impregnated with NE (PI-NE). The dielectric properties of PI-NE were investigated under various temperatures, especially the breakdown strength, dielectric constant, dielectric loss, and volume resistivity. The results indicate that the breakdown strength enhances by 25% at elevated temperatures, in contrast to room temperature circumstances. Meanwhile, the dielectric constant and volume resistivity decline, while the dielectric loss increases. In addition, molecular dynamics simulations are used to clarify how intermolecular forces impact insulation performance under various temperatures. The simulations reveal that PI insulating paper introduces traps, which inhibit space charge accumulation, thereby the composite’s insulation effectiveness is enhanced. As temperature rises, the distance between PI molecules and NE molecules decreases so that interface defects between the insulation paper and insulating oil are reduced. These ensure the new oil-paper insulation structure maintains stable insulation performance under high-temperature conditions.