- 2067 Mangsir (old course) · 8 marks
Suitability of DC motors for applications
Short answer
DC series motors provide very high starting torque and speed falling with load, suited for traction and vacuum cleaners. Shunt motors offer nearly constant speed, ideal for paper making. Cumulative compound motors combine high starting torque with safe no-load speed, making them suitable for shearing and punching.
Explain with reason, the suitability of DC series, DC shunt and DC compound motors. Identify suitable DC motor for the following application: i) Electric traction ii) Vacuum cleaner iii) Paper making iv) Shearing and punching
DC series motor
Characteristics: very high starting torque (), speed falls as load rises (automatic power adjustment), dangerous at no load.
Suitable for: loads that need high starting torque and can be directly coupled: traction, cranes, hoists, trolleys, vacuum cleaners and similar.
DC shunt motor
Characteristics: almost constant speed from no load to full load, moderate starting torque, easy speed control by field rheostat.
Suitable for: constant-speed loads that start with light load: lathes, drilling machines, fans, blowers, pumps and paper machines.
DC compound motor
Characteristics (cumulative): good starting torque (better than shunt) with a safe no-load speed, and a drooping speed with load.
Suitable for: loads with sudden changes and heavy starting torque: shears, presses, punches, rolling mills, elevators and conveyors (flywheel loads).
Application selection
| Application | Suitable motor | Reason |
|---|---|---|
| i) Electric traction | DC series | Very high starting torque; speed falls automatically on a gradient, torque rises with load |
| ii) Vacuum cleaner | DC series (universal) | High speed at light load; runs on AC or DC; compact |
| iii) Paper making | DC shunt (or separately excited) | Constant, accurately controllable speed |
| iv) Shearing and punching | Cumulative compound | Sudden heavy load; the flywheel supplies the energy and the motor slows, then recovers; high starting torque and safe at no load |
✓ Answer checked by Claude Opus 5.5 (high effort)
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