What is the temperature rise range of the transformer

We all know that electrical appliances generate heat when they work. The longer the use time, the higher the temperature. When a certain period of use is reached, the rise of the electrical appliance reaches a certain critical value, it will not increase, and such a temperature increase The value is called the temperature rise value.

The same is true for transformers. During operation, when the temperature reaches a certain value, it will not increase. The temperature rise in this process is called the temperature rise of the transformer. The transformer, like other electrical equipment, does not rise when it reaches a certain temperature. This rising range is the temperature rise range of the transformer.

1. What is the temperature rise of a transformer

The temperature rise of the transformer refers to the difference between the temperature of the transformer and the temperature of the surrounding air. Among the many factors that affect the service life of a transformer, temperature will cause insulation aging, which is the factor that has the greatest impact on the service life of the transformer.

The heat transmission inside the transformer is not uniform, so the temperature of each part of the transformer is very different, and the temperature rise of each part of the transformer is stipulated when the transformer is at the rated load. This is the allowable temperature rise of the transformer. 

2. The temperature rise range of the transformer:

Generally, oil-immersed transformers use Class A insulation, and the maximum allowable temperature is 105°C. The allowable temperature rise of each part is: the allowable temperature rise of the coil is 65°C. Based on A-class insulation 105℃, when the ambient temperature is 40℃, 105℃-40℃=65℃. Since the temperature of the transformer is generally 10°C lower than that of the winding, the allowable temperature rise of the transformer oil is 55°C.

To prevent oil aging, the temperature rise of the upper oil surface should not exceed 45°C. No matter how the surrounding air changes, as long as the temperature rise does not exceed the allowable value, the safe operation of the transformer within the specified service life can be guaranteed. Generally, the main insulation of the transformer is Class A insulation, and the maximum operating temperature is specified as 105 degrees. The temperature of the windings of the transformer during operation is 10-15 degrees higher than the upper oil temperature. If the upper oil temperature of the transformer in operation is always around 80-90 degrees, that is, the windings are often around 95-105 degrees.

Long-term operation of the transformer under high temperature conditions will shorten the life of the internal insulating paperboard, making the insulating paperboard brittle, prone to cracking, losing its due insulation effect, and causing accidents such as breakdown. When the transformer winding insulation is seriously aging, it will accelerate the deterioration of the insulating oil and affect the service life of the transformer. Therefore, it is necessary to prevent the transformer from operating at high temperatures, especially not operating at high temperatures for a long time.

Insulation grade refers to the heat resistance grade of the insulating material used. According to the insulation grade classification of dry-type transformers, it can be divided into: (A, E, B, F, H, N, C) seven grades, the size of the temperature rise limit Reflects the heat resistance of insulating materials, such as: A-105°C, which means that the temperature of the transformer itself and the ambient temperature of the day when the transformer is working does not exceed 105°C; other grades can be deduced by analogy.

The national standard "Dry-type Transformer" GB6450-1986 clearly stipulates the temperature rise limit of dry-type transformers.