Various temperature protection settings of transformer
Writer： Hengfeng you electric Time：2023-04-03 views：times
The specified ambient temperature of the transformer is the maximum temperature of 40 ℃, the minimum temperature of outdoor transformer is - 25 ℃, and the minimum temperature of indoor transformer is - 5 ℃.
The insulation grade of transformer is not the concept of insulation strength, but the standard of allowable temperature rise, that is, the insulation grade refers to the heat-resistant grade of the insulating material used, which is divided into Grade A E B F h. The specific allowable temperature rise standards of each insulation grade are as follows:
Insulation grade A E B F H maximum allowable temperature (℃) 105 120 130 155 180, winding temperature rise limit (℃) 60 75 80 100 125, performance reference temperature (℃) 80 95 100 120 145
The difference between the temperature of the transformer and the ambient air temperature is called the temperature rise of the transformer.
The "rated temperature rise" in the transformer nameplate refers to the temperature higher than the "standard ambient temperature" generated by heating during transformer operation. For oil immersed transformer, its value is equal to the upper oil temperature of the transformer minus the "standard ambient temperature". For dry-type transformer, its value is equal to the temperature of transformer winding minus the "standard ambient temperature".
The so-called "standard ambient temperature" is set at 40 ℃ in China. The standard ambient temperature is set to distinguish a unified reference standard when using transformers in different places and seasons.
The startup, shutdown and overtemperature alarm values of the temperature controller of the dry-type transformer shall be set according to the insulation grade of the transformer, and the principle is not to exceed the maximum allowable temperature.
Take the most common class F and class h for example: Class F can set 95 ℃ fan, 75 ℃ fan stop, 110 ℃ ultra-high temperature alarm and 130 ℃ over temperature trip. Class h can set 105 ℃ fan, 85 ℃ fan shutdown, 130 ℃ overtemperature alarm and 150 ℃ overtemperature trip. Of course, this setting value can be adjusted according to the actual situation.
Reasons for low temperature setting of oil immersed transformer:
Because most oil immersed transformers are class a insulation, the maximum heat-resistant temperature is allowed to be 105 ℃, and the winding temperature during transformer operation is 10-15 ℃ higher than the average temperature of the upper oil, that is, when the upper oil temperature reaches 85-95 ℃, the winding has actually reached about 105 ℃. If it operates at this limit temperature for a long time, the winding insulation will be seriously aged, It also accelerates the deterioration of insulating oil and affects the service life. Therefore, the upper oil temperature can be set as 65 ℃ fan, 55 ℃ fan shutdown, 80 ℃ overtemperature alarm and 90 ℃ overtemperature trip.
The number of transformer oil refers to the freezing point of transformer. The freezing point of No. 10 transformer oil is not higher than 10 ℃, the freezing point of No. 25 transformer oil is not higher than - 25 ℃, and the freezing point of No. 45 transformer oil is not higher than - 45 ℃.
