Effect of Temperature on Charge Mobility in Oil-Paper Insulation

Oil-paper insulation serves as the primary insulation material for converter transformers. In the converter transformer, intricate electrical stresses and complex temperature distribution coexist. To achieve accurate calculation of the electric field distribution of insulation structures under various conditions, it is crucial to comprehend the effect of temperature on the charge transport. In this work, the charge mobility in oil-immersed paper at different temperatures is measured using a newly proposed method based on pulsed electro-acoustic (PEA) method. Utilizing epoxy as the blocking material, a double-layer structure with one blocking layer is constructed to establish a unipolar injection condition. The mobility of negative and positive charges in oil-immersed paper is calculated based on the charge distributions of the double-layer sample under various applied voltages. For the oil-immersed samples composed of mineral insulating oil and cellulose insulating paper used in our work, the charge mobility increases with increasing electric field and increasing temperature. The relationship between charge mobility and temperature conforms to the Arrhenius equation, and the mobility activation energy of negative charge is higher than that of positive charge, indicating that the negative charge mobility is more dependent on temperature.