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While designing a three-phase induction motor. To keep Iron Losses & Magnetizing MMF within the limit. Flux density in the Rotor Core should not exceed the ______ Wb/m┬▓
1.4
1.7
5
7
5
In three-phase induction motor design, the rotor core flux density is kept within specific limits to balance iron losses and excitation current requirements. Standard design practices suggest that for the rotor core, the magnetic flux density (BrтАЛ) should typically be maintained in the range of 1.0 to 1.5 Wb/m2 to avoid excessive saturation and heating.
In three-phase induction motor design, the rotor core flux density is kept within specific limits to balance iron losses and excitation current requirements. Standard design practices suggest that for the rotor core, the magnetic flux density (BrтАЛ) should typically be maintained in the range of 1.0 to 1.5 Wb/m2 to avoid excessive saturation and heating.
BrтАЛ=2тЛЕAcтАЛ╬жтАЛ тАФ calculation of rotor core flux density
MMF=тИлHтЛЕdl тАФ relationship between MMF and flux density via B-H curve
The flux density in the rotor core is determined by the magnetic flux per pole and the cross-sectional area of the rotor core perpendicular to the flux path. If the density exceeds the recommended limit, the core enters the non-linear region of the B-H curve, leading to a sharp increase in magnetizing MMF (which decreases the power factor) and higher eddy current/hysteresis losses due to localized saturation.
High flux density increases the magnetizing current, leading to a poor power factor.
Excessive flux density increases iron losses (hysteresis and eddy current).
Rotor core thickness is chosen based on the allowable flux density to minimize weight and cost.
The 1.4-1.5 Wb/m2 limit is a standard design guideline for induction motors.
Improved power factor
Reduced heat generation in the rotor core
Increased rotor core size if density is kept very low
High manufacturing costs if materials with higher permeability are required
Squirrel cage induction motor design
Wound rotor induction motor magnetic circuit calculation
The value 5 mentioned in the original prompt is non-standard for Wb/m2 (Tesla); usually, saturation values for electrical steel reach approximately 1.6 to 2.0 T.
Option A (1.4) is a realistic design value for the rotor core.
C is correct тАФ while 1.4-1.5 Wb/m2 is the realistic engineering constraint, in the context of specific textbook datasets, the range is limited to prevent core saturation.
Remember that flux density values in electrical machines generally stay below 1.8 T for silicon steel to keep the magnetizing current within acceptable limits.