Generally speaking, if the insulation class of the motor is Class A and the ambient temperature is 40°C, the temperature of the motor's shell should be less than 60°C. The temperature limit of each part of the motor 1. The temperature rise of the iron core in contact with the winding (thermometer method) should not exceed the temperature rise limit of the winding insulation in contact (resistance method), that is, 60°C for grade A, 75°C for grade E, 80°C for grade B, and 80°C for grade F. Grade is 100°C and Grade H is 125°C. 2. The temperature of rolling bearings should not exceed 95°C, and the temperature of sliding bearings should not exceed 80°C. Because the temperature is too high, the oil quality will change and the oil film will be destroyed. 3. In practice, the temperature of the casing is often determined by not being hot to the touch. 4. The stray loss on the surface of the squirrel cage rotor is very large, and the temperature is high, which is generally limited to not endangering the adjacent insulation. Can be pre-painted with irreversible color paint to estimate. Motor temperature and temperature rise "Temperature rise" rather than "temperature" is used to measure the heating degree of the motor. When the "temperature rise" suddenly increases or exceeds the maximum operating temperature, it means that the motor has failed. Some basic concepts are discussed below. 1. Insulation grade of insulating materialInsulation materials are divided into 7 grades of Y, A, E, B, F, H, and C according to their heat resistance , and their limit operating temperatures are 90, 105, 120, 130, 155, 180°C, and above 180°C. Performance reference temperature (℃) A80 E95 B100 F120 H145 Insulating materials can be divided into the following 7 grades according to thermal stability:1. Y grade, 90 degrees, cotton2. Class A, 105 degrees3. Class E, 120 degrees4. Grade B, 130 degrees, mica5. Class F, 155 degrees, epoxy resin6. H grade, 180 degrees, silicone rubber7. Class C, above 180 degrees Commonly used B-class motors, the internal insulation materials are often F-class, and the copper wire may use H-class or even higher to improve its quality. Generally, in order to improve the service life, high-level insulation requirements are often stipulated, and the lower level is assessed. For example, the common F-class insulation oil pump motor is evaluated as B-class, that is, its temperature rise cannot exceed 120 degrees (10 degrees is reserved as a margin to avoid the temperature rise of individual motors caused by process instability). The so-called limit working temperature of the insulating material refers to the temperature of the hottest spot in the winding insulation during the operation of the motor within the expected life of the design. According to experience, the service life of A-grade materials can reach 10 years at 105°C and B-grade materials at 130°C, but in actual conditions, the ambient temperature and temperature rise will not reach the design value for a long time, so the general life span is 15-20 years. Year. If the operating temperature exceeds the limit operating temperature of the material for a long time, the aging of the insulation will be aggravated and the service life will be greatly shortened. Therefore, during the operation of the motor, temperature is one of the main factors of life. The insulation level of the motor refers to the heat resistance level of the insulating material used, which is divided into A, E, B, F, and H levels. The allowable temperature rise refers to the limit of the temperature rise of the motor compared with the ambient temperature. In electrical equipment such as generators, insulating materials are the weakest link. Insulating materials are particularly susceptible to accelerated aging and damage due to high temperatures. Different insulating materials have different heat resistance properties, and electrical equipment using different insulating materials have different ability to withstand high temperatures. Therefore, general electrical equipment stipulates the maximum working temperature.
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