Starting Logic of Auxiliary Motors of Gas Turbine

Hello everyone,

I am working in a captive power plant having GE make gas turbine @19.6 MW capacity (frame-V) with Mark-VIe control system.

Kindly help me understanding the logic of starting of auxiliary motors like (i) Aux Lube oil pump motor, (ii) emergency lube oil pump motor, (iii) turbine and load gear vent fan motor, (iv) diesel starter motor.

With best regards

This is a pretty big question. And, for your machine at your site you should be consulting the programming in the turbine control system for exact details.

The Aux. L.O. Pump and motor is used during:

--Cooldown (Hydraulic Ratchet; or, Turning Gear)

--Starting and Acceleration to approximately 95% of rated speed

--Low Main L.O. Pump Pressure during normal operation

--Operation below approximately 94.5% of rated speed during shutdown or trip from load

The Main (Accessory Gear-driven) L.O. Pump should be providing L.O. pressure and flow any time the unit is above 95% of rated speed, and down to approximately 94.5% of rated speed during shutdown or trip from load.

The Emergency L.O. Pump and motor should be run as a test during starting, and then only when the bearing L.O. pressure drops to a low-low pressure condition. This can happen, usually when the plant loses A.C. power to operate the Aux. L.O. Pump and motor.

Now, since your unit (as described) had a diesel starting means, it could also be capable of black starting--meaning when there is no AC available in the plant for running auxiliary motors (such as the Aux. L.O. Pump motor) the Emergency L.O. Pump motor will be used to provide control oil pressure and Lube Oil pressure and flow during initial starting. If the permissives are met for a black start and an operator initiates a START, the Emer. L.O. Pump will be started to provide L.O. pressure and flow to get the unit broken away from zero speed so that the main L.O. Pump can then provide the necessary L.O. Pressure and flow. Usually, the Emer. L.O. Pump is NOT run all the way up to 95% of rated speed during a black start (to save the battery), but is shut don at approximately 50% of rated speed.

The programming and sequencing (starting/stopping) of the turbine and load gear vent fans has changed a lot over the several decades the Frame 5 has been produced. Sometimes the turbine vent fan starts when flame is detected; sometimes it's started based on a speed level. Sometimes it's stopped when the unit drops below 94.5% speed, or below 50% speed, and sometimes it's run all the way down to zero speed. Sometimes, it's run until the temperature in the compartment drops below a certain temperature. There's no single set of conditions for all Frame 5s.

Same goes for the load compartment vent fan. There's no single set of conditions for all load compartment vent fans.

The diesel starting means is started and run when the unit is being accelerated from zero speed during a START, and it usually runs to help accelerate the unit even after flame detection, up to approximately 50-60% of rated turbine speed.

That should be helpful, but to be certain the best way to know when motors are to be started and stopped is to review the application code in the Mark VIe for your turbine. That's the BEST and ONLY way to be sure exactly how the motors on the unit at your site operate.
Hello CSA..

Thank you so much for elaborate write up. As advised I will also try to get some input from instrumentation.

Thanks and regards



Since we are discussing the Start of Motor, I have one question.

Why do we named the lube oil pump as Pre and Post ( pre-post)? Is there any significant reason of such naming.

>Why do we named the lube oil pump as Pre and Post
>(pre-post)? Is there any significant reason of such naming.

Can you be more specific? (Frame size (3; 5; 6B: 6FA; 7B; 7E; 7EA; 9E; 9FA; etc.); packager (GE USA; GE Firenze; GE Belfort: or BHEL, or John Brown, etc.); turbine control system (Mark IV, Mark V, Mark, VI, Mark VIe)?

The <i>Auxiliary</i> L.O. Pump runs prior (Pre) to FSNL during a start-up and after (Post) FSNL during a shutdown, perhaps? The <i>Auxiliary</i> L.O. Pump should NOT be running during normal full speed, loaded operation. That's about the only thing I can think of?