Comparative compatibility study of silicone oil and mineral oil with materials in power transformer

The long-term reliability of power transformers is fundamental to the security and stability of the power system, and this reliability depends critically on the compatibility of the insulating liquid with all internal materials. The growing demand for enhanced fire safety has prompted increasing interest in silicone oil as an alternative to mineral oil in power transformers. However, its compatibility with the full range of internal materials has not been systematically evaluated. In this study, a comparative compatibility evaluation of silicone oil and mineral oil with representative transformer materials was conducted through accelerated thermal aging experiments at 100 °C for up to 328 h, during which the temporal evolution of both compositional and functional properties was systematically monitored. Results show that silicone oil maintains stable molecular structure and generates substantially fewer acidic and polar degradation products than mineral oil. In terms of functional properties, silicone oil shows only marginal changes in kinematic viscosity, flash point, and fire point, while its dielectric dissipation factor remains over 80% lower and power frequency breakdown voltage approximately 50% higher than those of mineral oil after aging. However, its initial advantage in negative polarity lightning impulse breakdown voltage was partially compromised after aging. These findings provide both a compatibility assessment and practical guidance for the application of silicone oil in power transformers.