Transformer oil is a kind of mineral oil obtained from distillation and refining of natural petroleum, which is a mixture of liquid natural hydrocarbons with pure and stable, low viscosity, good insulation and cooling property obtained from lubricating oil distillate through acid and alkali refining treatment.Commonly known as square shed oil, light yellow transparent liquid, relative density 0.895.The freezing point is <-45 ℃, and the specific heat capacity is about 0.5 (calorie/g * degree). It is mainly composed of three kinds of hydrocarbons, mainly naphthenes (about 80%), and the others are aromatic and alkane.In our country, transformer oil has paraffin base oil, naphthenic base oil.
Good transformer oil shall be a clean and transparent liquid free of deposits, mechanical suspensions and cotton-like substances.If it is contaminated and oxidized, and resin and sediment are produced, the oil will deteriorate and gradually change color to a light red, until it becomes a dark brown liquid.In general, transformer oil is not suitable for use when it is light brown.In addition, transformer oil can be shown as turbidity emulsion, oil color black, dark.Transformer oil is milky, indicating that the oil contains water.Dark oil color indicates aging insulation of transformer oil.Oil – colored black, even coke smell, indicating that the transformer internal fault.
Generally, the insulation of oil-immersed transformer is mostly a-class insulation material, and its oil-resistant temperature is 105℃.It is stipulated that the highest temperature of winding in normal operation is 98℃, and the average temperature is 98-13=85℃, the highest temperature of transformer oil is 95℃, and the average temperature of transformer oil is 95/1.2=80℃.The average annual temperature is 20℃, so the windings’ temperature rise to the air is allowed to be 85-20=65k, the oil’s average temperature rise to the air is 80-40=40k, and the winding’s average temperature rise to the oil is 65-40=25k.
