The color judgement of transformer insulation oil is mainly based on the observation of naked eyes to determine the depth of oil color. The color of oil depends on the content of bitumen, resin and other dyeing compounds. If the asphalt in the original distillate, the less the resin, the higher the light fraction. Generally speaking, the color of the oil becomes lighter and more transparent. The color of oil is also related to the temperature and refining degree of cut fractions. For example, domestic No. 45 transformer oil, because of its low temperature of cut distillate, and the process of overrefining and adding antioxidants, it is light in appearance. It is almost colorless. In the storage and operation of oil, the color of the oil will also gradually deepen under the influence of environmental pollution and resin generated by its own oxidation. Therefore, the oil contact environment, such as temperature, light air (mainly oxygen), electric field, current and so on, can promote the aging of oil and make the color of oil deeper.

Application field of transformer insulation oil: insulation oil and other liquid insulating medium need to test the dielectric loss angle and volume resistivity, such as the use of MS101Y insulating oil dielectric loss tester.
1. extinguishing arc. The arc in the middle of the contact will soon be extinguished.
2. insulation. Each pole of the switch is insulated with each other, while the conductive part of the switch is insulated from the oil tank.
3. anticorrosion. Prevent contact between switch contacts and air to avoid contact oxidation.
4. heat dissipation. The heat emitted by the contact part absorbs the oil and rapidly dissipates heat by convection in the tank. Less oil circuit breakers, because of the small amount of oil, the oil only plays an arc extinguishing function. Its outer casing is usually electrified, and it must not be touched.