USCG Exam PracticeMotors and generators
A self-excited DC shunt generator fails to build up voltage after being brought up to speed. Which of the following is the MOST likely cause?
- A. The armature windings have developed a short circuit to ground
- B. The commutator segments are excessively worn
- C. The field rheostat is set to minimum resistance
- ✓ The field poles have lost their residual magnetismCorrect
Why D is correct
NEETS Mod. 5 §1-3 identifies loss of residual magnetism in the field poles as a primary cause of failure to build up voltage in a self-excited generator. The text also notes that residual magnetism can be restored by briefly flashing the field from a separate DC source.
Cited:NEETS Mod. 5 §1-3