Insulation oil detection is a series of advanced detection methods that analyze the internal quality and physicochemical properties of transformer oil based on its quality indicators and performance, evaluate the quality of transformer oil, and regularly track and monitor the condition of transformer oil in equipment. It can detect the deterioration tendency and pollution reasons of transformer oil in a timely manner, and develop reasonable lubrication methods and oil change cycles for equipment. The insulation oil testing items include: kinematic viscosity 40 ℃, density 20 ℃, pour point, solidification point, closed flash point, acid value, moisture (trace), corrosive sulfur, water-soluble acid or alkali, breakdown voltage, dielectric loss factor 90 ℃, and interface tension. Insulation oil performance requirements (1) The density should be as small as possible to facilitate the precipitation of moisture and impurities in the oil. (2) The viscosity should be moderate, as too much can affect convective heat dissipation, while too little can lower the flash point. (3) The flash point should be as high as possible, generally not lower than 136 ℃. (4) The freezing point should be as low as possible. (5) The lower the content of impurities such as acid, alkali, sulfur, and ash, the better to avoid their corrosion on insulation materials, wires, fuel tanks, etc. as much as possible. (6) The degree of oxidation should not be too high. The degree of oxidation is usually expressed in terms of acid value, which refers to the amount of potassium hydroxide required to absorb 1 gram of free acid in oil in milligrams. (7) The stability should not be too low. The stability is usually expressed by the sediment of the acid value test, which represents the anti-aging ability of the oil