Electric machines (DC suitability): Which motor is NOT suitable for use as a DC machine? Identify the motor type designed for AC induction operation only. Choose the correct option.

Difficulty: Easy

Squirrel-cage induction motor
Universal motor
Permanent-magnet DC motor
Separately excited DC motor

Correct Answer: Squirrel-cage induction motor

Explanation:

Concept
A squirrel-cage induction motor requires a time-varying AC magnetic field for induction and does not operate as a DC machine. Universal motors can run on AC or DC; PM and separately excited types are DC machines.

Final Answer
Squirrel-cage induction motor

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