Insulation class and temperature standard of oil immersed transformer
Writer： Hengfeng you electric Time：2023-05-15 views：times
Under normal medium conditions, oil immersed transformers or dry-type transformers can be selected, such as industrial and mining enterprises, agricultural independent or attached substations, residential independent substations, etc. The transformers that can be selected are S8, S9, S10, sc (b) 9, sc (b) 10, etc. The following is a brief introduction to the insulation class of oil immersed transformers and the temperature standard of oil immersed transformers.
1、 Insulation class of oil immersed transformer
Insulation grade refers to temperature, not the concept of insulation strength, but the allowable temperature rise standard. That is, the insulation grade refers to the heat resistance grade of the insulating materials used, including a, b, e, f, h and c. The oil immersed transformer has a class, and the maximum operating temperature is 105 ℃. This is the oil gauge. The maximum operating temperature of dry type f (epoxy resin) is 155 ℃. Class h (maximum operating temperature of 180 ° C) and class c (maximum allowable operating temperature of 220 ° C) dry-type oil immersed transformers made of NOMEX insulating materials of DuPont are also used. E and b are used to make motors. This temperature is determined by the insulating material.
a. For the winding of oil immersed power transformer, the internal control standard is 65K for the temperature rise of the air around the transformer. This is the average temperature rise of the winding, not the temperature rise of the hottest spot, but considered according to class a insulation level (105 degrees). However, it is generally controlled below 65K during transformer design.
b. The transformer standard in China is: the highest annual average temperature of the ambient temperature is 20 ℃, the highest monthly average temperature is 30 ℃, and the highest temperature is 40 ℃.
c. The winding temperature is usually not detectable by the user. However, the temperature of the oil cap can be detected. Therefore, the transformer manufacturer specified the temperature rise of the oil cap. 55K。 Of course, the design and manufacturing are also controlled below 55K. In this case, the temperature rise of the winding shall not exceed 65K.
d. Therefore, the operation department stipulates that the top layer temperature of transformer oil shall not exceed 85 ℃ regardless of the ambient temperature. This is to ensure that the temperature of the hottest point of the transformer winding is below 98 ℃. The average winding temperature is below 85 ℃. In this case, the service life of the transformer is 20 years. The temperature of oil immersed transformer oil during operation must take into account that the transformer oil will not age rapidly. An alarm is given when the transformer temperature reaches 85, and the transformer switch is closed when the maximum temperature reaches 95.
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