USCG Exam PracticeAC circuits and theory
A shipboard alternator has 4 poles and must produce 60 Hz output. At what speed must the prime mover turn the rotor?
- A. 900 rpm
- B. 1200 rpm
- ✓ 1800 rpmCorrect
- D. 3600 rpm
Why C is correct
Using f = (poles × rpm) / 120 from NEETS Mod. 5 §3-1: rpm = (60 × 120) / 4 = 1800 rpm. A 2-pole machine would require 3600 rpm; an 8-pole machine would require 900 rpm for 60 Hz.
Cited:NEETS Mod. 5 §3-1