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Mechanically air gaps in induction motor are kept very low to avoid
lower power factor
lagging nature
magnetizing current
all of the mentioned
all of the mentioned
In an induction motor, the air gap is the physical space between the stator and the rotor. Since the permeability of air is very low compared to magnetic materials, a large air gap requires a significantly high magnetizing current to establish the necessary rotating magnetic field, which in turn leads to a poor power factor and lagging characteristics.
In an induction motor, the air gap is the physical space between the stator and the rotor. Since the permeability of air is very low compared to magnetic materials, a large air gap requires a significantly high magnetizing current to establish the necessary rotating magnetic field, which in turn leads to a poor power factor and lagging characteristics.
ImтАЛ=N╬жтЛЕRgтАЛтАЛ тАФ Relationship between magnetizing current, flux, reluctance, and turns
RgтАЛ=╬╝0тАЛAlgтАЛтАЛ тАФ Magnetic reluctance of the air gap
The magnetizing current (ImтАЛ) is directly proportional to the air gap length (lgтАЛ) because the magnetic reluctance (RgтАЛ=╬╝0тАЛAlgтАЛтАЛ) is primarily determined by the air gap. A larger air gap increases reluctance, necessitating a higher magnetizing current from the supply to maintain the flux. This increased reactive power demand results in a more lagging phase angle between voltage and current, thus degrading the power factor.
The air gap acts as high reluctance in the magnetic circuit.
Higher magnetizing current leads to increased reactive power consumption (Q=VтЛЕImтАЛ).
Power factor is defined as cos(╧Х)=VтЛЕIPтАЛ, where high ImтАЛ reduces cos(╧Х).
Induction motors are 'lagging' loads because they consume reactive power to magnetize the core.
Lower magnetizing current improves system efficiency.
Higher power factor reduces line losses and improves voltage regulation.
Extremely small air gaps increase mechanical risk of rotor-stator rubbing (bearing wear).
Very small gaps increase harmonics and slot noise (cogging).
Industrial induction motors
Electric vehicle traction motors
The air gap is kept as small as possible (typically 0.3mm to 2mm depending on motor size) to ensure an efficient magnetic coupling.
Options A, B, and C are all consequences of high magnetizing current caused by a large air gap, hence 'all of the mentioned' is the correct choice.
D is correct тАФ A low air gap is essential to minimize reluctance, which keeps the magnetizing current low and ensures a higher, more stable power factor for the motor.
Always remember that in electrical machines, the air gap is the 'bottleneck' for flux; minimizing it is critical for minimizing the reactive power demand of induction machinery.