Frame 3 starting systems 1

[mectarek]

Hi,

we have a gas turbine GE Frame 3 that is started by a diesel engine and we want to study the possibility of changing the system to a pneumatic starter.

what I don't understand is why does the diesel engine has a torque converter even though its torque is usually higher than an air starter.

when I calculated the starting torque of the existing diesel engine (with the torque converter multiplication taken in considiration). I found it about 1330 lb-ft. But all the pneumatic starters that I have seen have a max starting toque of around 520 lb-ft.

so how can pneumatic starters breakaway the gas turbine and is there any device between the starter and the turbine that encreases the torque.

 

[ccfowler]

I expect that the main reason is that a diesel needs to be operating at some minimal speed to be able to operate and produce sufficient torque. The torque converter provides the necessary slip for initial diesel engine operation, plus the torque converter provides enhanced torque to accelerate the turbine more rapidly through the lower speed range until the turbine itself can assist effectively in the acceleration process. Once the turbine passes its self-sustaining speed, the added torque provided by the starting system quickly becomes insignificant, and acceleration to operating speed is accomplished by the turine system itself. The torque converter provides a very convenient and orderly acceleration process while the starting diesel is permitted to operate within its suitable operating speed range.

Since you have an apparently good and serviceable diesel engine starting system, why mess around with changing to something else? Unless there is some compelling reason that you have not mentioned, I doubt that there will be any sufficient economic or operating reason to implement such a change.

Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.

 

[NCTHAI]

The purpose of torque converter is to provide variable speed. Remember that Diesel engine rotates at constant speed. It is the torque converter which varies the speed and assist during the start up. For breaking up torque, machine will have either ratcheting mechanism or cranking motor.

 

[huntr52]

We developed an electrical start application on FR3 to specifically replace gas expanders. In some cases a torque converter was requested due to exactly the situation described to provide for speed considerations and slip. Today we are using variable speed drive developed for this application which allows for the slip issues, torque and speed variations.