The Effect of Different Geometry on the AC Breakdown Performance for Transformer Insulation Fluid

Too, Lik Sem (2026) The Effect of Different Geometry on the AC Breakdown Performance for Transformer Insulation Fluid. Final Year Project (Bachelor), Tunku Abdul Rahman University of Management and Technology.

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Abstract

Transformer insulation fluids play a critical role in maintaining both electrical and thermal stability in power transformers, yet the influence of electrode geometry on their AC breakdown performance remains insufficiently studied, particularly when comparing mineral and vegetable oils. This research addresses this gap by examining how spherical, disk, and VDE electrodes affect breakdown voltage across different gap distances, with the aim of improving insulation design. The study combined Ansys Maxwell simulations, which modeled electric field distributions in vacuum and calculated breakdown voltages using relative permittivity and dielectric strength, with experimental testing on a BAUR DPA 75 C oil tester using VDE electrodes at 1 mm, 2 mm, and 2.5 mm gaps for corn, soybean, sunflower, and mineral oils. The simulation results confirmed that disk electrodes achieved the highest breakdown voltages, followed by VDE and spherical, while mineral oil consistently outperformed vegetable oils. Among the alternatives, sunflower oil showed the best dielectric performance in experiment. Simulations underestimated breakdown voltages of VDE electrodes by 18.72% to 43.49% for vegetable oils across oils and gaps and 3.53% to 32.12% for mineral oil. The simulation and experimental breakdown voltages for vegetable oils using VDE electrodes were also lower by 9.17% to 51.86% than the minimum values recommended by IEEE C57.147 for new natural ester fluids, emphasizing the importance of refined preparation techniques. Predictive formulas of the form Vbd = Adn were developed for each fluid, with vegetable oils exhibiting near-linear scaling with gap distance and fitting experimental data within 0.52 to 4.43% differences, reflecting strong agreement with the BAUR DPA 75 C tester measurements. These findings emphasize the advantage of uniform electrode geometries in strengthening dielectric performance and the need for refined preparation techniques, as inadequate sample processing contributed to these gaps, offering insights for optimizing sustainable insulation systems in transformer design