Question

DC shunt motor is used in

• A. Blowers and fans
• B. Vacuum cleaners
• C. Rolling mills
• D. Heavy planners

Hint:

Think of DC motors this way:

• Shunt Motor = Constant speed applications (fans, blowers, lathes, centrifugal pumps).
• Series Motor = High starting torque applications (traction, electric locomotives, cranes, hoists).

Answer 1

The Correct Option is A

Step 1: Understanding DC Shunt Motor Characteristics:
A DC shunt motor is characterized as a constant-speed motor. In a shunt motor, the field winding is connected in parallel (shunt) with the armature winding across a constant voltage supply. As a result, the excitation field flux ($\Phi$) remains practically constant regardless of variations in load current.

Step 2: Analyzing Speed and Torque:
The speed $N$ of a DC motor is given by: $$N \propto \frac{V - I_a R_a}{\Phi}$$ Since flux $\Phi$ is constant and the armature voltage drop $I_a R_a$ is very small at normal operating loads, the speed remains nearly constant from no-load to full-load conditions.

Step 3: Matching Characteristics to Applications:

• Blowers and fans: Require steady, constant-speed operation to supply continuous airflow without fluctuation. Thus, DC shunt motors are highly ideal.
• Vacuum cleaners: Require very high speeds and high starting torque, making AC/DC Universal motors the preferred choice.
• Rolling mills: Experience sudden, extreme load fluctuations and require heavy starting torque, which is best handled by DC Series or Cumulative Compound motors.
• Heavy planners: Require reversible, highly dynamic speed control under variable loads (such as Ward-Leonard systems).

Thus, option (A) is correct.