What is the chemical composition of transformer oil?

Transformer oil is primarily composed of refined hydrocarbons derived from petroleum, mainly paraffinic and naphthenic molecules with controlled aromatic content. In inhibited oils, oxidation inhibitors are added to slow degradation. Alternative fluids include natural esters, synthetic esters, and silicone oils with different chemical structures. The composition directly affects dielectric strength, viscosity, oxidation stability, and environmental performance.