Transformer oil they use a mineral insulating oil, oil products as a sub-distillation, the main components are alkanes, cycloalkanes family of saturated hydrocarbons, aromatic compounds such as unsaturated hydrocarbons.
       Good transformer oil should be clean and transparent liquid, without sediment, mechanical impurities suspended solids and cotton wool material. If its contamination and oxidation, and produces resins and sediment, transformers oily quality will be degraded, the color will gradually become light red, until the liquid becomes dark brown. When the transformer failure, it will change the color of the oil under normal circumstances, transformer oil was light brown when it should not be used again. In addition, the transformer oil can be expressed as turbid emulsion, oil color black, hair dark. Transformer oil emulsion turbidity, indicating that the oil contains water. Oil color dark, indicating that aging transformer oil insulation. Oil color black, and even coke smell, indicating that internal transformer fault.