USCG Exam PracticeAC circuits and theory
When paralleling two alternators onto a common bus, which set of conditions must be satisfied before closing the incoming machine's breaker?
- ✓ Equal voltage, equal frequency, same phase sequence, and correct phase angle at the instant of closingCorrect
- B. Equal voltage, equal power factor, same phase sequence, and equal kVA rating
- C. Equal frequency, equal field current, same governor setting, and equal kW output
- D. Equal voltage, equal frequency, same winding configuration (wye or delta), and equal cable impedance
Why A is correct
NEETS Mod. 5 §3-2 specifies exactly four conditions: equal voltage, equal frequency, the same phase sequence, and correct phase relationship at the instant of closing, verified with a synchroscope and lamps. Paralleling out of synchronism produces a violent current surge that can damage machines and trip breakers. Power factor, kVA rating, and winding configuration are not listed among the four synchronizing conditions.
Cited:NEETS Mod. 5 §3-2