🔍 Key Concepts

• Reverse power flow in AC generators and what it means for direction of power between generator and bus • Conditions that cause a synchronous alternator to start behaving like a motor instead of a generator • Protective relays on a ship’s service switchboard and what each is designed to detect (overcurrent, overspeed, reverse power, etc.)

💭 Think About

• Ask yourself: in what situation would power start flowing from the bus into the alternator instead of from the alternator to the bus? • Which of the listed problems (overload, high transfer, overspeed, motorization) would cause the alternator to draw power rather than supply it? • Think about what could happen to a prime mover (diesel engine or turbine) if the alternator begins to act like a motor and is driven by the electrical system.

✅ Before You Answer

• Be clear on the difference between current/power flowing out of the generator versus into the generator. • Match the relay name: reverse power relay must protect against a condition where the direction of power is abnormal, not just its magnitude. • Eliminate the options that are normally protected by other specific devices (e.g., overcurrent relays, overspeed trips), leaving the one that matches reverse power protection.