What are the limits on the operating temperature of dry-type transformers?

As an important device in the power system, the operating temperature of dry-type transformers has a significant impact on performance and life. Understanding the operating temperature limits of dry-type transformers is critical to ensuring their safe and efficient operation.

What are the limits on the operating temperature of dry-type transformers?

‌The operating temperature of dry-type transformers is limited by many factors, including the heat resistance level of the insulation material, ambient temperature and load conditions, temperature monitoring and heat dissipation, etc.

1. Limitation of heat resistance grade of insulation materials

The operating temperature of dry-type transformers is first limited by the heat resistance grade of their insulation materials. The heat resistance grade of insulation materials determines the maximum temperature that the transformer can withstand. According to different insulation materials, the heat resistance grade can be divided into Class A, Class E, Class B, Class F, Class H and Class C. Among them, Class F and Class H insulation materials are more common in dry-type transformers.

Class F insulation material: The maximum operating temperature is 155℃ and the allowable temperature rise is 100K. This means that when the dry-type transformer adopts Class F insulation material, its operating temperature shall not exceed 155℃.

Class H insulation material: The maximum operating temperature is 180℃ and the allowable temperature rise is 125K. Therefore, when the transformer adopts Class H insulation material, the upper limit of its operating temperature is 180℃.

2. Ambient temperature and load conditions

The operating temperature of dry-type transformers is also affected by ambient temperature and load conditions. Changes in ambient temperature will cause the absolute temperature of the transformer to be different in summer and winter, so it is necessary to pay attention to whether the maximum absolute temperature value of the winding exceeds the standard. In addition, the load condition will also affect the temperature of the transformer. Overload operation will cause the temperature to rise, which may cause risks such as insulation aging, short circuit and even fire.

3. Temperature monitoring and heat dissipation

Since excessive temperature will accelerate the aging of the insulation parts inside the transformer and even cause faults such as short circuits and fires, the operating temperature of the dry-type transformer must be strictly monitored. Usually, the transformer is equipped with a temperature sensor and a heat dissipation system to ensure that heat dissipation measures can be started in time when the temperature exceeds the safe range, such as automatically starting the fan for cooling. At the same time, regular inspection and maintenance are also essential to ensure that the heat dissipation system of the transformer is always in good working condition.

Risks of exceeding temperature limits

When a dry-type transformer exceeds its temperature limit during operation, a series of risks will arise. First, excessively high temperatures will accelerate the aging of the insulation materials inside the transformer, thereby shortening the service life of the transformer. Second, high temperatures may also cause pyrolysis of transformer oil, producing harmful gases that pose a threat to the environment and human health. Finally, continued high-temperature operation may cause transformer failures and even safety accidents such as fires.