The temperature standards for mining transformers are primarily determined based on the thermal resistance class of the insulating materials and the cooling method of the transformer. Below is a detailed explanation:

　　Thermal Resistance Class and Allowable Temperature of Insulating Materials

　　Class A Insulating Materials: Mining transformers typically use Class A insulating materials, such as impregnated organic materials (paper, wood, cotton yarn, etc.). The maximum allowable operating temperature for Class A insulating materials is 105°C.

　　Relationship Between Temperature and Insulating Performance: Higher temperatures degrade the insulating performance of materials, accelerating aging and potentially leading to a loss of insulation, which can result in electrical breakdown and failures.

　　Relationship Between Transformer Temperature and Oil Temperature

　　Oil Temperature Reflects Winding and Core Temperature: In oil-immersed transformers, the heat generated by the windings and core is conducted through the oil circulation to the tank and then dissipated into the surrounding air. The oil temperature reflects the temperature of the windings and core, and measuring the oil temperature is more convenient than measuring the winding temperature.

　　Allowable Upper Oil Temperature Values:

　　For transformers with natural oil circulation self-cooling or forced-air cooling, the upper oil temperature should not exceed 95°C. To prevent rapid deterioration of the transformer oil, the upper oil temperature should not frequently exceed 85°C.

　　For transformers with forced-oil circulation guided forced-air cooling, the upper oil temperature should not exceed 80°C.

　　For transformers with forced-oil circulation water cooling, the upper oil temperature should not exceed 75°C.

　　Temperature Rise Standards

　　Definition of Temperature Rise: The difference between the transformer temperature and the surrounding air temperature is called the temperature rise of the transformer.

　　Temperature Rise Standards for Class A Insulated Transformers: When the maximum surrounding temperature is 40°C, national standards stipulate that the winding temperature rise should be 65°C, and the allowable temperature rise of the upper oil should be 55°C. As long as the upper oil temperature and its temperature rise do not exceed the specified values, the transformer can operate safely within its specified service life.

　　Impact of Temperature on Transformer Lifespan

　　Relationship Between Insulation Aging and Temperature: Insulating materials age over time when exposed to heat, and the aging process accelerates at higher temperatures. When the insulation ages to a certain extent, it becomes prone to cracking under operational vibrations and electrodynamic forces, leading to electrical breakdown and failures.

　　Relationship Between Temperature and Service Life: If the operating temperature of the insulation exceeds the allowable value, the aging process of the insulation accelerates, shortening its service life. For example, when the operating temperature of the insulation is 95°C, the service life is 20 years