Transformer losses and temperature rise

When the transformer is running, the magnetic flux passing through the iron core will be lost in the iron core, and the current passing through the winding will also be lost in the winding. In addition, the leakage flux caused by winding current and the leakage flux outside the iron core during overexcitation can cause additional losses in various layouts, such as coils, iron core layout parts, iron core plates, and oil tanks, as well as losses in the oil pumps and fans of cooling equipment.

Various losses are transformed into heat, with some of this heat used to increase the temperature of various components, while the other part dissipates heat towards the cooling medium adjacent to each component.

The insulation materials used in transformers have a certain thermal life. For example, the heat resistance level of oil immersed transformers is Class A, and the long-term working temperature of Class A insulation materials is 105 ℃.

According to the thermal aging rules of transformer insulation in accordance with GB/T 15164-1994 "Load Guidelines for Oil Immersed Electronic Transformers", transformer insulation is based on the popular temperature of 90 ℃, and the aging rate is doubled for every 6 ℃ increase in temperature; On the contrary, if the temperature drops by 6 ℃, the aging rate will be reduced by 1/2. This is based on GB 1094 "Power Transformers", which corresponds to "operating at an ambient temperature of 20 ℃ and a popular temperature rise of 78K". This is considering that during the operation of the transformer, the ambient temperature changes for a year. When the ambient temperature is higher than 20 ℃, the popular temperature will exceed 98 ℃; When the ambient temperature is below 20 ℃, the popular temperature will be less than 98 ℃.