USCG Exam PracticeMotors and generators
A shipboard DC series motor driving a cargo hoist is accidentally uncoupled from its load while running. What is the immediate danger?
- A. The motor will stall due to excessive counter-EMF with no load to absorb it
- B. The motor will reverse direction because the series field loses its polarity reference
- ✓ The motor will accelerate uncontrollably to a dangerously high speedCorrect
- D. The motor will draw reduced current and overheat the field windings
Why C is correct
NEETS Mod. 5 §2-2 states that a series DC motor must never be run without a mechanical load because unloaded it accelerates uncontrollably. For this reason series motors are belted or geared directly to their loads rather than coupled through a clutch that could release.
Cited:NEETS Mod. 5 §2-2