Spatial charge transport model driven by Kerr optic-electric measurement in transformer oil under switching overvoltage conditions

Abstract The accumulation of space charge in transformer oil under switching overvoltage considerably influenced its insulation performance, representing a critical factor in transformer insulation design. This study examined the electric field and space charge distribution in transformer oil under varying switching overvoltages, utilizing a Kerr effect electro-optical measurement platform integrated with a novel optical path multiplier device. The results indicated that the maximum electric field distortion rate consistently occurred within the 250–500 μ s range for different voltage levels. Moreover, increasing the applied voltage led to a corresponding rise in electric field distortion within the oil gap, with the maximum distortion rate exceeding 90%. Under switching overvoltage conditions, the space charge in transformer oil displayed a bipolar homogeneous charge distribution, characterized by notable charge injection. With increasing voltage, both the electrode’s charge injection capacity and the average charge mobility were enhanced. Based on the observed space charge distribution patterns and key physical parameters, a bipolar charge transport model was developed, shedding light on the mechanisms of space charge accumulation in transformer oil. Overall, this study provided valuable experimental data and theoretical insights for the insulation design of transformers.