Two mechanically coupled alternators deliver power at 50 Hz and 60 Hz respectively. What is the highest speed of the alternators?
- A. 3600 rpm
- B. 3000 rpm
- C. 600 rpm
- D. 500 rpm
Answer: C. 600 rpm
Explanation: Since N = 120·f1/P1 = 120·f2/P2, P1/P2 = 50/60 = 5/6. Minimum even pole numbers are P1 = 10 and P2 = 12, giving highest shaft speed N = 120 × 50 / 10 = 600 rpm.