Study on the Effect of Aging on the Space Charge Characteristics of Transformer Insulating Paper Using an Improved Charge Transport Model

The accumulation of space charges distorts the electric field distribution of the transformer insulating paper and eventually leads to its failure. In this article, a bipolar charge transport (BCT) model is simulated, and certain modifications are proposed to get a more physically reliable and realistic model that helps to understand the micromechanism of space charge accumulation. Three cases are studied; first, the outcome of the presence of impurities developed with insulation aging on the charge accumulation process is analyzed. The presence of impurities causes more trap sites to be developed, resulting in enhanced distortion of the electric field. Second, a hopping-based mobility model is developed using an electric field and temperature-dependent mobility equation, including the probability of charged ions escaping the traps along with trap depth. Third, the effect of heterocharges on the charge accumulation is also analyzed using hopping-based mobility of the second case, indicating that these charges distort the electric field with aging the most as less recombination and trapping of ions occur, and more ions migrate and get accumulated on the charged electrode surface. The research results show the best coincidence with the established experimental results and, thus, will be helpful in designing the transformer insulating system and maintaining and optimizing the insulation performance.