Gas Turbine Starting System (Diesel Engine) Reliability Check


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We have SSS 64T clutch installed on starting system of our Fr6B gas turbine. The starting system comprises of diesel engine and torque converter &sss clutch.

We intend to start the diesel engine occasionally while the gas turbine is in service to ensure reliability of starting system (especially diesel engine).

Advice on below queries is requested:

- If we can operate the diesel engine while the gas turbine is service at its normal operating speed?

- Is there any harm suspected to SSS clutch internals?

- What additional checks/parameters on clutch can be monitored during such exercise to prevent from any damage to the clutch?

Presuming you have a Mark* Speedtronic turbine control system provided by the packager of the turbine-generator, it's very common for there to be a manual push-button somewhere near the diesel engine starting means assembly (in the Accessory Compartment) for testing the diesel engine while the unit is running. This was done in the past with both jaw clutch assemblies and SSS clutch assemblies.

This pushbutton (43DE/TEST it was usually called, I believe) was only capable of starting the diesel engine and allowing it to idle. It didn't accelerate the diesel--just started it and allowed it to idle as long as the pushbutton was held in (manually--by a human). If I recall correctly, it was usually mounted very near the manual Hydraulic Ratchet Jog (43HR/JOG) pushbutton in the Accessory Compartment, which was usually on the right side of the Compartment, near the Accessory Gear. (There were two manual pushbuttons, sometimes (often) mounted in the same electrical box.)

Now, some sites/local regulations don't allow people in the compartments when the turbine is running, and perhaps this pushbutton has been moved to a location where it's accessible from outside the Accessory Compartment, or possibly deleted altogether for this reason or as a cost-savings. It may also be that a "target" for this purpose appears on some HMI screen....

The design of SSS (Synchronizing, Self-Shifting) clutches is such that when the output shaft speed is greater than the input shaft speed the clutch disengages. And, the design of a SSS clutch is also such that the clutch engages when the input shaft speed is greater than the output shaft speed, and since that's not true when the turbine shaft is at rated speed this design should also prevent SSS clutch engagement.

So, even if the diesel were to be accelerated while the unit was running at rated speed, it should not engage (because the input shaft speed is much less than the output shaft speed). And, during normal starting the turbine shaft side (output side) of the SSS clutch over-runs the input shaft speed (from the diesel engine/torque converter) at about 50-60% of rated turbine speed. So, the output shaft of the torque converter doesn't spin at turbine rated shaft speed, so this is another reason the SSS clutch should not engage if the diesel engine were started/running when the turbine is running at rated speed. (I would NOT recommend manually increasing the diesel engine speed from idle when the turbine was running!)

Usually, there was a limit switch (a proximity switch, actually) used to monitor the engagement of the SSS clutch). And, the switch is "closed" when the clutch is engaged (usually signal L33CSE in a digital Speedtronic turbine control system).

I believe the manual Diesel Engine TEST pushbutton is usually shown on the Starting Means P&ID, as well, if it's provided.

Hope this helps!