Mineral oil is widely used, economical, and provides strong dielectric and cooling performance, but has lower fire point and lower biodegradability. Ester oils, natural or synthetic, have higher fire points and are more biodegradable, and can improve paper moisture equilibrium, but they often have higher viscosity and higher cost. Silicone oils offer excellent fire resistance and good dielectric performance and remain stable at high temperatures, but they are usually the most expensive and may require specific handling practices. Each type has different testing limits and maintenance considerations, so fluid choice affects lifecycle strategy.
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