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Which of the following is not correct with increased in the length of air-gap?
zigzag leakage flux (\u2193)
leakage reactance (\u2193)
the diameter of the circle diagram (\u2191)
Over Load Capacity (\u2191)
zigzag leakage flux (\u2193)
Increasing the air-gap length in a polyphase induction motor increases the reluctance of the magnetic circuit, which leads to a reduction in the leakage flux and magnetizing current. The zigzag leakage flux, which depends on the proximity of stator and rotor slots, actually decreases as the air-gap length increases because the flux path becomes less defined by slot geometry.
Increasing the air-gap length in a polyphase induction motor increases the reluctance of the magnetic circuit, which leads to a reduction in the leakage flux and magnetizing current. The zigzag leakage flux, which depends on the proximity of stator and rotor slots, actually decreases as the air-gap length increases because the flux path becomes less defined by slot geometry.
XlтАЛ=2╧АfLlтАЛ тАФ Leakage reactance, which decreases as air-gap length increases
S=╬╝0тАЛAgтАЛlgтАЛтАЛ тАФ Reluctance of the air-gap, which increases with length lgтАЛ
The air-gap length lgтАЛ acts in series with the main magnetic circuit. As lgтАЛ increases, the effective reluctance S=╬╝0тАЛAgтАЛlgтАЛтАЛ increases. Consequently, the magnetizing current ImтАЛ (required to establish the air-gap flux) increases. Since leakage reactance is proportional to the permeance of the leakage flux paths, and these paths are disrupted by a larger gap, the leakage reactance XlтАЛ decreases, leading to an improvement in the circle diagram diameter and overload capacity.
Increasing the air-gap length reduces the magnetic coupling between stator and rotor.
Higher reluctance necessitates a higher magnetizing current (ImтАЛ).
The circle diagram diameter is inversely proportional to the total leakage reactance of the machine.
Zigzag leakage is specifically associated with the interaction of stator and rotor teeth, which is attenuated by a larger gap.
Improved overload capacity
Increased starting torque capabilities
Reduced harmonic losses due to slotting
Increased magnetizing current leads to lower power factor
Lower efficiency due to higher current requirements
Higher noise level due to larger magnetic gap
High-starting torque induction motors
Motors requiring high peak torque capability
The circle diagram diameter is defined as DтЙИX1тАЛ+X2тА▓тАЛVтАЛ. As XlтАЛ decreases, D increases.
Zigzag leakage is part of the stator/rotor slot leakage flux, which is inversely proportional to the air-gap reluctance path.
A is correct тАФ Zigzag leakage flux decreases, not increases, when the length of the air-gap is increased because the flux path becomes more resistive.
Always remember that in induction motors, the air-gap length is a compromise: smaller is better for power factor, but larger is better for overload capacity and reduced harmonic effects.