Question

Stator of three-phase induction motor is made by

• A. Cast iron frame
• B. Soft iron frame
• C. Steel frame
• D. Aluminium frame

Hint:

Always distinguish between the Stator Frame (the outer mechanical body, typically made of Cast Iron) and the Stator Core (the internal magnetic path, made of laminated Silicon Steel sheets).

Answer 1

The Correct Option is A

Step 1: Analyzing Motor Frame Requirements:
The outer frame of a three-phase induction motor must hold the stator core laminations securely, protect the internal windings, and dissipate operational heat. It also needs high mechanical rigidity to minimize vibrations during operation.

Step 2: Material Properties and Selection:

• Cast Iron Frame: Cast iron is highly rigid, mechanically durable, and has excellent vibration damping properties. This makes it the standard choice for manufacturing stator frames in medium-to-large industrial motors.
• Soft Iron Silicon Steel: Used specifically for the stator core laminations (to minimize hysteresis and eddy current losses), rather than the outer supporting frame.
• Aluminium: Sometimes used for small, low-power fractional horsepower motors to reduce weight, but is not standard for larger industrial three-phase induction motors.

Step 3: Conclusion:
Therefore, the outer stator frame is typically constructed from a Cast iron frame, corresponding to option (A).