When the temperature of dry-type transformer reaches 95 ℃, it is already high, and the load can not be increased any more.
Low voltage equipment generally requires that the temperature rise should not exceed 60 degrees (i.e. ambient temperature + 60 degrees). Too high temperature will accelerate the aging of equipment insulation and shorten the service life.
200KVA three phase dry type transformer (protective type)
The most direct way is: when you touch the device, you can hold on for more than 10 seconds. If you can't stick to it, even if the temperature is high, it depends on the heat resistance grade of your transformer. At present, according to the insulation grade of dry-type transformers in China, there are (a) (E) (b) (f) (H) (c). According to the heat-resistant grade, transformers can be divided into seven heat-resistant grades: A, e, B, F, h and C. different kinds of insulating materials have different heat-resistant ability. Generally, the insulation grade of oil immersed transformers belongs to Grade A.
Maximum allowable temperature (℃) 105 120 130 155 180,
Winding temperature rise limit (k) 60 75 80 100 125
Performance reference temperature (℃) 80 95 100 120 145
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 resistance grade of the insulation material used, which is divided into a, e, B, F and H grades. The specific allowable temperature rise standard of each insulation grade is as follows:
The allowable temperature of class a insulation material (insulation paint of cotton yarn, silk and common enameled wire after insulation impregnation treatment) is 105 ℃, the rated operating temperature is 95 ℃, and the maximum allowable value is 140 ℃. The allowable temperature of class E insulation materials (epoxy resin, triacetic acid fiber film, polyester film, high-strength enameled wire insulation paint) is 120 ℃, the rated operating temperature is 110 ℃, and the maximum allowable value is 155 ℃ (beyond this temperature rise, the insulation damage rate will exceed the allowable range).
The allowable temperature of class B insulation (mica, glass fiber, asbestos and other inorganic materials bonded or impregnated with organic materials) is 130 ℃, the rated operating temperature is 120 ℃, and the maximum allowable value is 165 ℃.
Class F insulation (mica, glass fiber, asbestos and other inorganic materials are bonded or impregnated with special organic materials, such as synthetic resin paint modified by silicon organic compound as adhesive) the allowable temperature of the material is 155 ℃, the rated operating temperature is 145 ℃, and the maximum allowable value is 190 ℃ (if the temperature rise exceeds this, the damage rate of the insulation will exceed the allowable range).
Class H insulation (mica, glass fiber, asbestos and other inorganic materials are bonded or impregnated with special organic materials, such as silicone organic paint, silicone organic rubber and inorganic filler). The allowable temperature of the material is 180 ℃, the rated operating temperature is 175 ℃, and the maximum allowable value is 220 ℃ (beyond this temperature rise, the damage rate of the insulation will exceed the allowable range).
The allowable temperature of class C insulation (special paper, laminate, etc., such as aramid polymer) material is 220 ℃, the rated operating temperature is 210 ℃, and the maximum allowable value is 250 ℃.
According to gb1094.11, the rated operating conditions of dry-type transformer are as follows: the altitude is not more than 100 meters, the average temperature of the hottest month is 30 ℃, the maximum annual average temperature is 20 ℃, the minimum temperature of outdoor dry-type transformer is - 25 ℃, and the minimum temperature of indoor dry-type transformer is - 5 ℃. Under this standard condition, the allowable temperature rise of dry-type transformer varies with different insulation levels. The average temperature rise limit of class a insulation under rated current is 60K, class E insulation is 75K, class B insulation is 80K, class F insulation is 100k, and class H insulation is 125k. If the operating conditions are not the specified standard conditions, the temperature rise limit shall be determined by both parties through negotiation. The higher the temperature is, the higher the resistance of dry transformer winding is, the higher the heating will be, and the lower the efficiency will be. This is a positive feedback problem. If it is a class F insulation system, it is more appropriate to control the normal operation at 50 ~ 60 ℃.
In addition, according to the characteristics of the dry-type transformer, if the winding works at a relatively high temperature for a long time, although it is allowed, it will also accelerate the insulation aging and shorten the service life of the dry-type transformer, which is different from that of the oil immersed transformer. Therefore, the load rate of the dry-type transformer should be considered to leave sufficient surplus, and the operating temperature of the dry-type transformer should not be too high. For class C transformer, the allowable temperature is higher. If the temperature of dry-type transformer reaches 95 ℃, it is already higher. No more load. Low voltage equipment generally requires that the temperature rise should not exceed 60 degrees (i.e. ambient temperature + 60 degrees). Too high temperature will accelerate the aging of equipment insulation and shorten the service life. The limit of 125k is class H insulation.
The national standard "dry type transformer" gb6450-1986 specifies the temperature rise limit of dry type transformer. 1. For the coil of dry-type transformer, when class a insulating material is used, the maximum temperature rise should be less than 60K when the limiting working temperature is 105 ℃; when class E insulating material is used, the maximum temperature rise should be less than 75K when the limiting working temperature is 120 ℃; when class B insulating material is used, the maximum temperature rise should be less than 80K when the limiting working temperature is 130 ℃; when class F insulating material is used, the maximum temperature rise should be less than 80K when the limiting working temperature is 120 ℃, When the limit working temperature is 155 ℃, the maximum temperature rise should be less than 100k; when the H-class insulating material is used, the maximum temperature rise should be less than 125k when the limit working temperature is 180 ℃; when the C-class insulating material is used, the maximum temperature rise should be less than 150k when the limit working temperature is 220 ℃. At present, most dry-type transformers are made of H-class insulating materials, so generally speaking, the temperature of dry-type transformer should be below 180 ℃.
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