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Which of the following Performance parameter of the three-phase induction motor is/are disadvantage/s of the large air gap length?
Overload capacity
Pulsation losses, Noise, & Unbalanced Magnetic Pull
Cooling
Power Factor
Power Factor
A large air gap in an induction motor significantly increases the magnetizing current required to establish the rotating magnetic field. Since the power factor of an induction motor depends on the ratio of active current to magnetizing current, a larger air gap leads to a lower power factor.
A large air gap in an induction motor significantly increases the magnetizing current required to establish the rotating magnetic field. Since the power factor of an induction motor depends on the ratio of active current to magnetizing current, a larger air gap leads to a lower power factor.
RgтАЛ=╬╝0тАЛAlgтАЛтАЛ тАФ Reluctance of the air gap proportional to length lgтАЛ
cos╧Х=Ip2тАЛ+Im2тАЛтАЛIpтАЛтАЛ тАФ Power factor as a function of active (IpтАЛ) and magnetizing (ImтАЛ) current
The air gap acts as a high-reluctance path in the magnetic circuit. According to Ohm's law for magnetic circuits, ╬ж=RgтАЛFтАЛ, where RgтАЛ is the reluctance of the air gap. Since RgтАЛ=╬╝0тАЛAlgтАЛтАЛ, increasing the length lgтАЛ increases the reluctance, requiring a higher MMF (magnetizing current) to maintain the flux, which ultimately degrades the power factor.
The air gap of an induction motor is kept as small as possible to minimize magnetizing current.
A small air gap improves efficiency and power factor.
Excessive air gap increases excitation current, leading to a higher reactive power demand.
Reduced power factor
Increased magnetizing current
Increased iron losses
Option B relates to physical/mechanical design constraints rather than electrical performance parameters like power factor.
Small air gaps are limited by mechanical clearance and manufacturing tolerances.
D is correct тАФ The magnetizing current of an induction motor is directly proportional to the air gap length; therefore, a larger air gap increases the reactive power demand, which lowers the overall power factor.
Always remember that in electrical machines, any increase in the reluctance of the main magnetic path directly increases the no-load (magnetizing) current.