GE Frame 5 starter 1

[Meshry]

Our GE Frame 5 gas turbine; the starting system consists of fixed speed induction motor with hydraulic torque converter (twin disc make/ single stage).
How the machine is accelerating from firing speed (20%) to self sustain speed(60%)?? The starter motor is fixed speed and the torque converter does not have any link to the control system (MARK V). Also there is no manual throttle valve in the torque converter.
I under stand, the turbine cannot accelerate to the self sustaining speed without the starting device help.

Thanks

 

[ScottyUK]

Once the engine lights off the power turbine starts to develop torque. Initially it's only a little additional torque but it's enough for the machine to accelerate.

As the machine accelerates the compressor starts to become more efficient and starts to actually compress air rather than act as a not-particularly-good fan. The increasing airflow from the compressor allows more fuel to be burned, and so the power turbine has greater gas flow available with which to develop torque. This in turn drives the compressor faster, resulting in a positive feedback loop.

The engine continues to accelerate under the combined torque of the starter gear and the power turbine until it reaches a speed at which the power turbine is able to develop sufficient torque to drive the compressor without the assistance from the torque convertor and the engine becomes self-sustaining. Above this speed the starter gear shuts down.