The temperature rise of transformer refers to the difference between the temperature of transformer and ambient air temperature.
Among the factors that affect the service life of transformer, temperature will cause insulation aging, which is the most important factor affecting the service life of transformer.
The internal heat transmission of transformer is not uniform, so the temperature difference of each part of transformer is very big. When the transformer is under rated load, the temperature rise of each part is regulated, which is the allowable temperature rise of transformer.
Temperature rise range of transformer
General oil immersed transformer adopts A-class insulation, and the maximum allowable temperature is 105 ℃.
The allowable temperature rise of each part is as follows:
The allowable temperature rise of coil is 65 ℃. Based on class a insulation 105 ℃, when the ambient temperature is 40 ℃, 105 ℃ - 40 ℃ = 65 ℃. Since the temperature of transformer is generally 10 ℃ lower than that of winding, the allowable temperature rise of transformer oil is 55 ℃.
In order to prevent oil aging, the temperature rise of upper oil surface shall not exceed 45 ℃. No matter how the ambient air changes, only if the temperature rise does not exceed the allowable value, the safe operation of the transformer can be ensured within the specified service life.
The main insulation of general transformer is A-class insulation, the maximum service temperature is 105 degrees, and the temperature of winding in operation of transformer is 10-15 degrees higher than that of upper oil.
If the upper oil temperature of the transformer in operation is always around 80-90 degrees, that is, the winding is often around 95-105 degrees.
If the transformer operates at high temperature for a long time, it will shorten the service life of the internal insulation paperboard, make the insulation board brittle, easy to break, lose its insulation function, and cause breakdown and other accidents.
When the insulation of transformer winding is seriously aged, the deterioration of insulating oil will be accelerated and the service life of transformer will be affected.
Therefore, it is necessary to avoid the transformer operating at high temperature, especially not to operate at high temperature for a long time.
Insulation grade refers to the heat resistance grade of insulating materials used. Dry type transformer can be divided into seven grades according to insulation grade: (a, e, B, F, h, N, c),
The temperature rise limit value reflects the heat resistance performance of insulation materials, such as: a-105 ℃. It means that the temperature of the transformer itself and the ambient temperature of the day are not more than 105 ℃; other grades are similar.