When AC generators are paralleled, which component maintains constant frequency? (Abbreviation form)

• A. CSD
• B. GCB
• C. AVR
• D. PSM

Answer: (A)

Frequency in an AC generator is tied to the rotor speed, so when several generators run in parallel you need a means to keep that speed fixed to maintain a steady frequency across the system. The Constant Speed Drive (CSD) is designed to do just that: it keeps the generator operating at a constant speed, so the output frequency remains constant even as the engine speed or load changes. The automatic voltage regulator handles voltage, not frequency; the generator circuit breaker is a protective switch, and the PSM is not responsible for frequency control. So, the device that maintains constant frequency in paralleled operation is the Constant Speed Drive.