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While designing a three-phase induction motor. What is the permissible limit of core flux density?
5
1 to 1.7
1 to 1.8
2 to 1.4
2 to 1.4
In three-phase induction motors, the core flux density is restricted to the range of 1.2 to 1.4 Tesla to maintain the magnetic material within the linear region of the B-H curve. Higher densities lead to excessive core losses due to hysteresis and eddy currents, as well as increased magnetizing current requirements.
In three-phase induction motors, the core flux density is restricted to the range of 1.2 to 1.4 Tesla to maintain the magnetic material within the linear region of the B-H curve. Higher densities lead to excessive core losses due to hysteresis and eddy currents, as well as increased magnetizing current requirements.
B=A╬жтАЛ тАФ Relation between flux and cross-sectional area
V=4.44fN╧ХmaxтАЛ тАФ EMF equation relating flux to supply parameters
The flux density B is directly related to the applied voltage V and the frequency f by the relation VтЙИ4.44fN╬жmтАЛ, where ╬жmтАЛ=BmтАЛA. To prevent magnetic saturation of the stator and rotor iron, the design must ensure that the peak flux density BmтАЛ does not exceed the saturation point of the silicon steel lamination, typically limited to 1.4 Tesla to keep iron losses within economic limits.
Typical flux density in induction motors ranges from 1.2 T to 1.4 T.
Higher flux density results in increased core losses (hysteresis and eddy current).
Saturation leads to higher magnetizing current and poor power factor.
Silicon steel is used to minimize hysteresis loss at these densities.
Reduction in core losses
Improved power factor by limiting magnetizing current
Higher flux density leads to increased iron losses
Excessive heating of the stator core
Industrial induction motor design
Transformer core magnetic circuit sizing
The range of 1.2 to 1.4 Tesla is standard for 50Hz induction motors.
Option B (1 to 1.7) is technically outside the typical economic design range for standard machines.
Flux density values higher than 1.5 T in induction motors lead to significant non-linearity and magnetizing current distortion.
D is correct тАФ The standard permissible flux density for the core of a three-phase induction motor is typically maintained between 1.2 T and 1.4 T to optimize efficiency and material usage.
Always relate flux density limitations to the magnetizing current; as saturation begins, the B-H curve flattens, requiring a sharp increase in current to maintain the flux, which degrades the motor's power factor.