How does the air gap between stator and rotor affect the motor temperature?
The air gap between stator and rotor of motor is one of the factors to ensure the mechanical rotation of motor, and determines some performance parameters of motor, such as starting current and starting torque. At the same time, the heat emitted by the rotor during the operation of the motor is also conducted in the radial or axial direction through the air gap between the stator and the rotor.
From the physical spatial layout analysis of motor stator and rotor, compared with the stator part, the heat emitted by the rotor is more difficult to dissipate, and has a positive correlation with the stator winding temperature, that is, when the rotor temperature is high, the stator winding temperature and temperature rise of the motor will rise due to the thermal radiation.
(Heat radiation refers to the phenomenon that an object radiates electromagnetic waves due to its temperature, which is one of the ways of heat transfer)
If the temperature rise of the motor is slightly higher, the outer diameter of the rotor can be appropriately reduced, that is, the air gap between the stator and the rotor can be enlarged. At this time, although the no-load current of the motor will increase, it will have a miraculous effect on the temperature rise control of the motor, or the temperature rise problem is solved, and the side effects caused by the increase of no-load current are not obvious. Especially when the power factor of the motor is not very high, it is undoubtedly a simple and effective practical measure to ensure the temperature rise index of the motor by increasing the air gap.
The size of the air gap directly affects the uneven degree of the air gap between the stator and the rotor, and further has a greater impact on the mechanical performance of the motor. The unevenness of air gap between stator and rotor reaches a certain level, and unilateral magnetic pull will appear when the motor is running, which will lead to the problem of bore sweeping between stator and rotor in severe cases. Local friction overheating will seriously affect the reliability of windings, and will also have adverse consequences for the temperature rise of the motor.
In order to avoid the mechanical friction between the stator and the rotor during rotation, the air gap length should be chosen as large as possible under the condition that conditions permit. How to balance the relationship between the air gap and various performance indexes is very important.
Because the air gap between stator and rotor has a great relationship with the performance of motor: the larger the air gap, the larger the magnetic resistance and the larger the excitation current, which is not even a simple linear relationship. The most direct effect of increasing the air gap length is that it will deteriorate the power factor of the motor, and the increase of the required excitation current will indirectly affect the efficiency index. It can be said that the change of air gap length leads to the whole body, which means the orientation of motor design principle.