________________ motor will be preferred for require high-speed and high starting torque application.

Question

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Option A: Universal Motor

Explanation & Concepts:
A Universal Motor is preferred for applications requiring high speed and high starting torque. It is a AC series motor capable of operating on both direct current (DC) and single-phase alternating current (AC). Due to its high no-load speed and series field characteristics, it generates a high starting torque proportional to the square of the armature current.

Working Principle: When powered by an AC or DC source, current flows through both the armature winding and field winding in series. The current in both windings reverses direction simultaneously during alternate half cycles of AC supply, producing unidirectional torque. Torque is proportional to $I^2$ ($T \propto I^2$), which results in very high starting torque at low speeds.

Key Formulas: $T \propto I^2$ — Electromagnetic torque relation at starting; $N \propto \frac{E_b}{\Phi}$ — Speed relation showing high speed at low field flux/light load

Key Points: Operates at speeds up to 20,000 RPM, much higher than induction motors.; Has a inverse torque-speed characteristic ($T \propto \frac{1}{N^2}$).; Starting torque can be 300% to 450% of full-load torque.

Advantages: Very high starting torque; High operating speed capability; Compact size with high power-to-weight ratio

Disadvantages: Brushes and commutator cause sparking and high wear/maintenance; Produces high noise and electrical interference (EMI)

Applications: Vacuum cleaners; Mixers, grinders, and food processors; Portable hand drilling tools

Additional Info: Capacitor start and capacitor run motors are single-phase induction motors with operating speeds limited by supply frequency ($N_s = \frac{120f}{P}$, max 3000 RPM at 50 Hz).. Shaded pole motors provide very low starting torque and low efficiency, used mainly in small fans.

Answer: A is correct — Universal motors deliver high starting torque and run at high speeds because they have series motor characteristics operating on AC/DC.

Exam Tip: Remember that single-phase induction motors (like capacitor start/run types) cannot exceed 3000 RPM on a 50 Hz supply, so any application requiring >3000 RPM must use a Universal Motor or a variable frequency drive.

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Option B: Capacitor run motor

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Option C: Capacitor start motor

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Option D: Shaded pole motor

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