For a motor, although it is not a uniform material, the basic characteristics of the heating process are generally applicable to the motor. In order to ensure that the temperature rise of the motor does not exceed a certain value, it is necessary to reduce the losses generated in the motor and increase the heat dissipation capacity of the motor.
With the increasing capacity of a single motor, improving the cooling system and enhancing heat dissipation capacity to limit the temperature rise of the motor has always been one of the main problems in the development and progress of the motor.
When the motor operates normally at a certain capacity, its temperature rise is also constant. Therefore, only by specifying the temperature rise of the motor can the capacity of the motor have a definite meaning. The purpose of temperature rise calculation is generally to calculate whether the temperature rise of several heating components in the motor exceeds the allowable limit value during rated operation, and considering the necessary margin. Ms. will share with you today on the topic of temperature rise.
Principles for determining temperature rise limits
When a motor operates for a long time at its rated state and its temperature reaches a stable level, the allowable limit of temperature rise for each component of the motor is called the temperature rise limit. The temperature rise limit of the motor is specified in national standards, and different heat resistance levels correspond to different temperature rise values.
As far as the winding is concerned, the temperature rise limit basically depends on the maximum temperature allowed by its insulation structure and the temperature of the cooling medium, but it is also related to factors such as the temperature measurement method, the heat transfer and heating conditions of the winding, and the allowable heat flux intensity. The following are the explanations:
The materials used for the insulation structure of the motor winding will gradually deteriorate in mechanical, electrical, physical and other properties under the action of temperature. When the temperature rises to a certain extent, the characteristics of the insulation material will undergo essential changes, and even lose its insulation ability. In electrical technology, insulation structures or systems in motors and appliances are often classified into several heat resistance levels based on their ultimate temperature. The insulation structure or system generally does not undergo any qualitative performance changes when operated for a long time at the corresponding temperature level.
2. The insulation structure can achieve a relatively economical service life at the specified limit temperature. Theoretical derivation and practical proof have shown that the service life of insulation structures is exponentially related to temperature, making them highly sensitive to temperature. If the working temperature exceeds the limit temperature of 8-14 ℃, its service life will be shortened by an average of half. For certain special purpose motors, if their service life is not required to be very long, in order to reduce the size of the motor, the allowable limit temperature of the motor can be increased based on experience or test data.
Although the temperature of the cooling medium varies with the different cooling systems and cooling media used, for the various cooling systems currently used, the temperature of the cooling medium basically depends on the atmospheric temperature and is roughly the same in numerical terms as the atmospheric temperature. But atmospheric temperature varies with different times and locations within a year. According to statistics, the average annual temperature in various regions of China is below 22 ℃, with an average maximum temperature not exceeding 35 ℃. The absolute maximum temperature is generally between 35-40 ℃, and only a few areas are between 40-45 ℃. Currently, countries around the world generally use the absolute highest atmospheric temperature in most regions as the temperature of the cooling medium,