Dry-type transformers reach a temperature of up to 95°C during normal operation and should not be overloaded. The temperature rise of low-voltage equipment generally does not exceed 60°C (i.e., ambient temperature + 60°C). Excessive temperatures accelerate insulation degradation and shorten the lifespan of the equipment. A direct method is to touch the device and hold for at least 10 seconds.
What are the temperature ratings of dry-type transformers? Currently, dry-type transformers in my country are classified according to insulation level: (A), (E), (B), (F), and (H). Dry-type transformers are classified according to heat resistance level: A, E, B, F, and H. Maximum Allowable Temperature (°C): 105, 120, 130, 155, 180
Wire Temperature Rise Limit (K): 60, 75, 80, 125
Performance Reference Temperature (°C): 80, 95, 100, 120, 145
The rated operating conditions for dry-type transformers are an altitude not exceeding 100 meters, an average temperature of 30°C in the hottest month, and an annual average temperature of 20°C. The minimum operating temperature for outdoor dry-type transformers is -25°C, and the minimum operating temperature for indoor dry-type transformers is -5°C. Under these standard conditions, the allowable temperature of dry-type transformers varies depending on the insulation level. The average temperature rise at rated current for Class A insulation is 60°C, for Class E insulation is 75°C, for Class B insulation is 80°C, for Class F insulation is 100°C, and for Class H insulation is 125°C. If operating conditions do not meet the specified standard conditions, the temperature rise value shall be determined by negotiation between the buyer and seller.
Furthermore, due to the characteristics of dry-type transformers, while prolonged operation at relatively high temperatures is acceptable, insulation degradation is accelerated, shortening the lifespan of the dry-type transformer. This differs from oil-immersed transformers. Therefore, the operating temperature of dry-type transformers should be kept within a reasonable range, ensuring sufficient margin for load factor.