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Chapter 1 of 12 тАв Page 1 of 248ЁЯФТ Protected PDF тАв Watermarked
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Air gap between stator and rotor
10 mm
mm
mm
100 mm
mm
The air gap between the stator and rotor in an induction motor is kept minimal to reduce the reluctance of the magnetic path. A smaller air gap significantly decreases the magnetizing current required to produce the necessary flux, thereby improving the power factor and overall efficiency of the machine.
The air gap between the stator and rotor in an induction motor is kept minimal to reduce the reluctance of the magnetic path. A smaller air gap significantly decreases the magnetizing current required to produce the necessary flux, thereby improving the power factor and overall efficiency of the machine.
S=╬╝0тАЛ╬╝rтАЛAlgтАЛтАЛ тАФ Reluctance of the air gap where lgтАЛ is the gap length
ImтАЛтИЭN╬жтЛЕSтАЛ тАФ Magnetizing current dependence on reluctance
The stator winding produces a rotating magnetic field which must cross the air gap to induce current in the rotor conductors. Since air has a very high reluctance (low permeability), a larger air gap requires a much higher magnetizing current (ImтАЛ) to maintain the air gap flux (Phi). By keeping this gap as small as mechanical tolerances allow, the reactive power consumption is minimized.
The air gap in small induction motors is typically 0.2 mm to 0.5 mm.
A larger air gap increases the magnetizing current and lowers the power factor.
Mechanical clearance limitations prevent the gap from being zero.
Eccentricity due to bearing wear can cause mechanical vibration if the gap is too small.
Improved power factor
Higher efficiency due to reduced magnetizing current
Increased risk of mechanical collision between stator and rotor
Requires tighter manufacturing tolerances
Induction motors
Synchronous machines
DC machines
In large machines, the air gap might be slightly larger to facilitate cooling and mechanical stability, but it remains a fraction of a millimeter or a few millimeters.
Option B (mm) is contextually correct in technical literature as it refers to a small value (typically sub-millimeter or low-millimeter range).
B is correct тАФ The air gap is kept in the range of millimeters (typically 0.2mm to 1mm) to minimize reluctance and improve the magnetic coupling between the stator and rotor.
Always remember: Reluctance of air is thousands of times higher than that of iron. Therefore, the air gap dictates the design of the magnetizing circuit in electrical machines.