What are the roles of air gap/air gap flux in an electric motor?

Air gap is a most important considerations when designing any kind of electric motor.Efficient functioning of electronic devices requires the circuit’s magnetic components contain substances (such such as iron) with a an extremely low resistance to the movement in magnetic flux. This minimizes the amount electric energy required to create an electromagnetic field.

However, the gaps within the circuit’s magnetic field are usually not a problem. They are filled with air. Because it provides a high magnetization resistance these gaps can cause unwanted increases in the current of magnetization and consequent electrical loss.

This is especially true of generators and motors. The air gap required to keep the rotor in a separate place from the stator needs to be as small as is possible to decrease the power required for magnetizing and yet big enough to avoid contact between them despite the manufacturing tolerances for their dimensions or the movement that results from mechanical deflection or looseness in the bearings supporting them.

There aren’t many design guidelines to follow when choosing the size of air gap that is most suitable for any rotating machine. In the case of induction motors, with the range of power ratings ranging from 3/4 to 750 kilowatts, real ranges of 0.2 to 5 millimeters are normal; the greater motor speed and the greater the gap. An esoteric calculation that is common involves the speed of the rotor’s peripheral, the stack length and diameter of the rotor. While expanding the air gap can increase the magnetizing current but it also tends to reduce stray load loss.

In any case the gap has to be sufficiently large to ensure that the rotor’s eccentricity relative to the stator won’t cause the stiffness of the shaft to be overpowered by an magnetic pull that is unbalanced which may allow the rotor’s shaft to hit the stator.

Whichever gap is utilized the gap must be homogeneous. An uniform gap can cause increased vibration and noise. The variation is typically restricted to a maximum of 10% of the average value.

In both synchronous and d-c machines, two distinct fields are interacting within the gap between air and. The a-c-field created through an”armature reaction” (stationary for the synchronous machines, and rotating within the machine that is d-c) alters the field created by the d-c field, decreasing its efficiency and affecting the machine’s performance. A larger air gap reduces the effects of the “armature response.” Therefore, these machines have air gaps that are several times bigger than those of the induction motors.

 

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