An Experimental Study on Oil Impregnation Physics in Transformer Insulation

Transformers are fundamental components of electric power systems, enabling voltage regulation from generation to distribution at various power levels. In high-voltage applications, insulation design and materials play a crucial role in ensuring reliable and efficient operation. Liquid-filled transformers are widely used, where oil and cellulosic pressboard serve as key insulating components. Ensuring complete oil impregnation of pressboard pores is crucial to preventing partial discharges and insulation failures. Current impregnation studies often rely on indirect measurements, such as tracking capillary rise in paper insulation, or on discrete weight measurements that disrupt the process and introduce variability. This work introduces a continuous gravimetric method to track oil absorption in high-density pressboard under vacuum without interrupting the process. By measuring real-time weight gain, impregnation dynamics can be accurately captured, enabling clear identification of when the pressboard approaches full saturation. Experimental results align with existing capillary-driven theories and reveal the influence of oil temperature on the impregnation rate. Overall, the study presents the development of a new experimental test method for measuring the oil impregnation properties of pressboard materials and correlating the results with existing physics.