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An uneven air gap in the stator and the rotor of a squirrel cage induction motor will lead to _________ during operation.
increased vibrations
increased current
increased torque
increased speed
increased vibrations
An uneven air gap in an induction motor creates non-uniform reluctance in the magnetic circuit. This causes an unbalanced magnetic pull (UMP) between the rotor and the stator, leading to significant mechanical vibrations and noise during operation.
IS 1231:1974 (Dimensions of three-phase induction motors)
An uneven air gap in an induction motor creates non-uniform reluctance in the magnetic circuit. This causes an unbalanced magnetic pull (UMP) between the rotor and the stator, leading to significant mechanical vibrations and noise during operation.
FUMPтАЛтИЭg21тАЛ тАФ where FUMPтАЛ is the unbalanced magnetic pull and g is the air gap length
In a balanced machine, the radial magnetic forces acting on the rotor cancel each other out. With an uneven air gap, the flux density is higher where the gap is smaller, resulting in an unbalanced radial force. This force pulls the rotor towards the stator, causing eccentricity that persists and exacerbates as the motor rotates, manifesting as mechanical vibration.
Uneven air gap leads to Unbalanced Magnetic Pull (UMP).
Persistent UMP causes increased mechanical stress on bearings and shaft.
Eccentricity is a common cause of high-frequency vibration in induction machines.
High bearing wear and tear
Increased acoustic noise level
Risk of stator-rotor rubbing (contact)
Option B (increased current) is incorrect because while local flux variations occur, the net magnetizing current does not increase significantly due to air gap geometry unless saturation is heavily impacted.
Option C (increased torque) is incorrect as torque is ideally independent of air gap eccentricity, provided flux remains constant.
Option D (increased speed) is incorrect as motor speed is determined by supply frequency and load, not air gap uniformity.
A is correct тАФ An uneven air gap creates an unbalanced magnetic pull that manifests as mechanical vibrations in the induction motor.
Always remember that in electrical machines, any geometric asymmetry (like air gap eccentricity) leads to parasitic radial forces that degrade mechanical components before affecting electrical parameters significantly.
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