Temperature rise standard of electric motor The motor starts running at normal temperature (the temperature of each part of it is the same as the ambient temperature), and the temperature continues to rise. When it is higher than the ambient temperature, it continues to absorb heat and slowly heat up. On the other hand, it begins to radiate heat to the surroundings. When the motor is in a thermal balance state and the temperature no longer rises, the difference between the motor temperature and the ambient temperature is called the motor temperature rise. That is: Temperature rise = motor temperature - ambient temperature in K. The maximum allowable temperature of the motor is the maximum temperature that the winding can withstand. When used for a long time at this temperature, the physical, mechanical, chemical and electrical properties of the insulating material will not undergo significant malignant changes. If this temperature is exceeded, the properties of the insulating material will undergo qualitative changes or cause rapid aging. Therefore, the maximum allowable operating temperature of the insulation material is determined based on its economic service life. The maximum allowable temperature of the motor is determined, and the temperature rise limit at this time depends on the temperature of the cooling medium. Generally, the cooling medium in motors is air, and its temperature varies with regions and seasons. In order to manufacture motors that can be applied throughout the country throughout the year and to clarify unified inspection standards, the national standard stipulates: the temperature of the cooling air is set to 40℃. When the motor is running, the greater the output power, the greater the current and loss, and the higher the temperature, but the maximum temperature must not exceed the maximum allowable temperature of the insulation. Therefore, the allowable long-term maximum output power of the motor (that is, the capacity or rated power of the motor) is limited by the maximum allowable temperature of the insulation, or the capacity is determined by the maximum allowable temperature of the insulation. The rated power indicated on the motor nameplate refers to the maximum output power when the temperature does not exceed the maximum allowable temperature of the insulation under the standard ambient temperature (40°C in my country) and the specified working mode. The temperature rise limit basically depends on the grade of the insulating material, but it is also related to the temperature measurement method, the heat transfer and heat dissipation conditions of the measured part, and depends on the maximum allowable operating temperature of the insulating material. When the maximum temperature of the surrounding cooling medium (such as air) is determined, the temperature rise limit of the motor components can be specified based on the maximum allowable operating temperature of the insulating material. The allowable temperature rise refers to the allowable limit for the temperature rise of the motor compared with the ambient temperature, also called the winding temperature rise limit. During the operation of the motor, the temperature rise of each part of the motor winding and core is not completely equal, but has a small amount of difference. This is mainly determined by process factors and ventilation conditions. (In order to avoid permanent damage to the motor due to differences caused by this factor, a 5°C margin is generally left in the measurement. Then there is the measurement error. In temperature measurement, the more accurate method is the resistance method, which requires the resistance value of the winding to be measured quickly and accurately after the motor is stopped, and then converted into temperature. With this method, there should also be room for 5°C. The second is the embedded temperature measuring element method. The error of this measurement method can be smaller. However, the embedded element is not necessarily the highest point of temperature, so there is also an error. Generally, a margin of 5℃ must be left. The allowable temperature rise of the motor is determined by the insulation level of the motor. Different insulation levels have different allowable temperature rises. The insulation grade of a motor refers to the heat resistance grade of the insulation material used, which is divided into grades A, E, B, F, and H. Temperature class of insulation Class A Class E Class B Class F Class H Maximum allowable temperature (℃) 105 120 130 155 180 Winding temperature rise limit (K) 60 75 80 100 125 Performance reference temperature (℃) 80 95 100 120 145 For example: the ambient temperature is 30℃ and the motor temperature is 80℃, the temperature rise is 50K. The temperature rise on the motor nameplate refers to the allowable temperature rise of the winding under the specified ambient temperature (generally set at 35°C). Another example: the temperature rise on the nameplate is 60K, which means that when the ambient temperature is 35°C, the temperature rise of the winding shall not exceed 60K, which means the temperature of the winding shall not exceed 95°C.
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