A turbine engine is equipped with a starter-generator, and its control circuit includes a cutout relay. What is the primary purpose of this cutout relay?
- ATo regulate generator output voltage once the unit transitions to generator mode
- BTo automatically disconnect the starter circuit from the electrical bus once the engine reaches self-sustaining (generator) speed, protecting the unit from overheating in starter mode
- CTo prevent battery voltage from exceeding a preset limit during engine starting
- DTo control ignition exciter timing relative to fuel introduction during light-off
Show answer & explanationAnswer & explanation
Correct answer: B. To automatically disconnect the starter circuit from the electrical bus once the engine reaches self-sustaining (generator) speed, protecting the unit from overheating in starter mode
The cutout relay senses when the engine reaches a speed at which it becomes self-sustaining, at which point continued operation as a starter (drawing heavy current as a motor) would overheat the unit. The relay automatically opens the starter circuit, allowing the unit to transition to generator mode without operator action, protecting the windings from thermal damage.
Why the other options are wrong
- A. Voltage regulation in generator mode is the job of the voltage regulator, not the cutout relay.
- C. Limiting battery voltage during start is not the cutout relay's function.
- D. Ignition-fuel timing coordination is unrelated to the starter-generator's cutout relay.
Starter-Generator Cutout Relay
A relay that automatically disconnects the starter circuit once the engine reaches self-sustaining speed, preventing the starter-generator from overheating while operating as a motor.
- Prevents continued heavy starter current draw after the engine no longer needs starter assist.
- Allows smooth automatic transition from starter mode to generator mode.
- Protects starter-generator windings from thermal damage.
Memory trick: Cutout relay pulls the plug on the starter before it cooks itself.