The statistical scatter of breakdown voltages of transformer oil – Part V: An integrated analysis of flow and interfacial tension effects
The fifth part of the column presents an integrated analysis of how breakdown voltage (BDV) values in transformer oil are affected by dynamic conditions, including flow, stirring, and fluid type.
by V. Gurin, M. Grisaru
The fifth part of the column presents an integrated analysis of how breakdown voltage (BDV) values in transformer oil are affected by dynamic conditions, including flow, stirring, and fluid type. Drawing from multiple experimental studies, the analysis highlights the significance of oil movement in both laboratory testing and actual transformer service. A central theme is the critical role of interfacial tension (IFT), which governs the stability of bubbles and contaminants under electrical and mechanical stress. Particular emphasis is placed on the behavior of low-IFT fluids, such as ester-based or aged oils, which tend to form and retain microbubbles under agitation, leading to significant BDV depression. The statistical nature of dielectric breakdown is also addressed, showing how flow conditions alter the distribution type and variability of test results. In the context of modern transformer design, where directed oil flow and compact insulation geometries prevail, understanding these dependencies is essential. The study concludes with diagnostic and design recommendations, emphasizing that the selection of stirred or static BDV testing must be context-specific—tailored to the insulating liquid, its IFT, moisture content, aging level, and operational regime. It advocates for more nuanced testing protocols and calls for industry standards to evolve accordingly.
#BDV#breakdown voltage#dynamic conditions#transformer oil
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