The insulation structure of oil-immersed transformers is mainly oil-paper insulation, which is a combination of transformer oil and insulation paper. The paper insulation part inside the transformer is shown in the figure below, and the transformer oil fills all gaps.

For oil-immersed transformers, temperature is a very important operating control parameter. Because high temperature has a clear and obvious acceleration effect on the aging of transformer oil and insulating paper.

1. The reference environment for oil-immersed transformer design is 20 degrees Celsius. When the external cooling air is 20 degrees Celsius, the transformer is operated at the rated current, and the insulation material of a certain temperature level is damaged due to thermal aging, the life of the transformer is generally 20 years.

2. For oil-immersed power transformers that meet the design, the relative thermal aging rate is 1 when the winding hot spot temperature is 98 degrees Celsius. That is to say, when the hot spot temperature is 98 degrees Celsius, the thermal aging of the transformer meets the requirements of the above specified life.

98 degrees Celsius is for non-thermally modified insulating paper. For thermally modified insulating paper, the relative thermal aging rate of 1 is 110 degrees Celsius.

Three, the principle of six degrees. That is, every time the hot spot temperature decreases by six degrees, the aging speed of the insulating paper will be reduced by half, and the insulation life of the corresponding transformer will be doubled. Therefore, it is of great significance for us to control the operating temperature of the transformer.

Fourth, the hot spot temperature of the transformer should not exceed 140 degrees Celsius. Although the hot spot temperature of the transformer is allowed to exceed 98 degrees Celsius under normal periodic load and long-term emergency load conditions, it is best not to exceed 140 degrees Celsius. Because it exceeds 140 degrees Celsius, the insulating paper may generate bubbles. The higher the moisture content of the insulating paper, the lower the temperature required to generate the bubbles. The generated bubbles may affect the insulation of the transformer and even cause accidents.