Why is silicone oil used in some transformers instead of mineral oil?

Silicone insulating liquids are used where fire safety and high temperature performance are priorities. Silicone fluids can be classified as less flammable and can reduce fire propagation risk compared with standard mineral oil, which helps in dense urban substations, indoor installations, tunnels, and critical facilities. Tradeoffs can include higher fluid cost, different material compatibility requirements, and different moisture behavior versus mineral and ester fluids, so the choice is usually driven by risk and lifecycle constraints.