How does thermal conductivity of transformer oil affect cooling performance?

Thermal conductivity determines how effectively heat moves from hot windings and core surfaces into the bulk oil. Higher conductivity helps transfer heat to radiators and coolers, reducing hot spot temperature and slowing insulation aging. However cooling performance also depends on viscosity, specific heat, and flow regime. If viscosity is too high, oil circulation weakens and cooling suffers even with decent conductivity. In practice, oil selection and cooling design are optimized together, and operators monitor top oil and winding temperatures to ensure heat removal remains adequate under load.