USCG Exam PracticeAC circuits and theory
A shipboard 60 Hz alternator has 4 poles. At what rotor speed must the prime mover maintain the machine to hold the correct output frequency?
- A. 3600 rpm
- B. 1200 rpm
- ✓ 1800 rpmCorrect
- D. 900 rpm
Why C is correct
Using f = (poles × rpm) / 120: 60 = (4 × rpm) / 120, solving gives rpm = 1800. A 2-pole machine would require 3600 rpm; a 6-pole machine 1200 rpm. (NEETS Mod. 5 §3-1)
Cited:NEETS Mod. 5 §3-1