The air gap is the space between the stator and rotor of the motor. During the operation of the motor, the stator does not rotate, but the rotor needs to rotate relative to the stator. The air gap is necessary for the operation of the motor; the size of the air gap varies depending on the type of motor. Generally speaking, the air gap of an asynchronous motor is small, while the air gap of a synchronous motor is large.
Importance of Motor Air GapThere are many geometric dimensions of the motor, including core size, winding size, overall size, installation size, and the sizes of various other structural components. But which are the main dimensions: the electromagnetic process of the motor is mainly carried out in the air gap, and the conversion of its energy form is carried out through the "main magnetic flux of the air gap".
Therefore, the main dimensions must be closely related to the air gap. Practice has proved that the armature diameter close to the air gap and the effective length of the core are the main dimensions of the motor, and the air gap can be said to be the third dimension. From a geometric point of view, once these dimensions are determined, the other dimensions are roughly determined, and many electromagnetic properties are basically affected by them or slightly changed. The motor air gap is appropriateThe air gap is an important part of the motor magnetic circuit and has a great influence on the motor performance. To manufacture a good asynchronous motor, the air gap should not only be uniform, but also have an appropriate air gap length. The larger the air gap, the greater the excitation current, the more reactive power consumed, and the lower the motor power factor. In order to reduce the excitation current and improve the power factor, the air gap should be as small as possible.
However, if the air gap is too small, it will increase the additional loss of the motor, and even cause the stator and rotor to rub against each other. In order to reduce the additional loss caused by magnetic field pulsation and reduce harmonic leakage, and make manufacturing and assembly easy and reliable, the air gap cannot be too small, so all aspects must be taken into account. The air gap of medium and small asynchronous motors is usually 0.2~1.5mm. Air gap characteristics of permanent magnet synchronous motorThe main dimensions of a permanent magnet synchronous motor can be determined by the required maximum torque and dynamic response index. The dynamic response performance index of a permanent magnet synchronous motor is reflected in the time required for the motor to accelerate from a standstill to a turning speed under the action of the maximum electromagnetic torque. Under the premise of ensuring the motor response characteristic index, the maximum value of the stator inner diameter is determined. This determines the stator core length of the motor.The air gap length of a permanent magnet synchronous motor is generally greater than that of an induction motor of the same specification. The speed-regulating permanent magnet synchronous motor uses high-performance rare earth permanent magnet materials, so a slight increase in the air gap will not cause a change in the motor performance. The selection of the motor air gap is not only related to the rotor magnetic circuit structure adopted, but also to the requirements of the motor's weak magnetic expansion capability. In the speed-regulating permanent magnet synchronous motor with a surface or rotor magnetic circuit structure, the tile-shaped magnets on the rotor core need to be equipped with a magnet protection cover. In order to reduce magnetic leakage, the protective cover is generally made of non-magnetic conductive materials, so the effective air gap of the permanent magnet synchronous motor is larger. For speed-regulating permanent magnet synchronous motors that use an internal rotor magnet structure and require a certain constant power operating speed range, the air gap should not be too large, otherwise the motor's direct axis inductance will be too small, the weak magnetic capability will be insufficient, and the required maximum speed cannot be achieved.When determining the stator outer diameter of a permanent magnet synchronous motor, it is generally based on the premise that the motor has sufficient heat dissipation capacity. In order to improve the efficiency of the permanent magnet synchronous motor, the stator outer diameter is increased, or in order to reduce the manufacturing cost of the motor, the stator outer diameter is reduced, depending on the specific situation.
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