# Valve position of GCV and SRV of GE Frame 9EA Gas Turbine

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#### Anonymous

Could anyone help me out by providing approximate position of both valves, GCV & SRV of GE Frame 9EA Gas Turbine at FSNL, 25MW, 50MW, 75MW and base load? What are the criteria for verifying both valve openings are correct?

Thanks,

Anonymous

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#### markvguy

Anonymous,

Both of these topics have been covered in other posts on control.com. The search feature of control.com is very powerful (and fast, too!) and you can search for individual words or groups of words or whatever and usually find what you're looking for.

The position of the SRV (Stop/Ratio Valve) is correct when the actual P2 Pressure (usually signal name FPG2) is equal to the P2 Pressure Reference (usually signal name FPRG). Sometimes, for Mk IV units, these signals are expressed in voltages, but when the actual is equal to the reference the SRV is in the correct position.

The thing that baffles most people about the SRV is that it's not a position control loop--but a pressure control loop with position feedback. The value of the P2 Pressure (the pressure between the SRV and the GCV (Gas Control Valve)) is a function of speed. When the unit is at rated (100%) speed (like it is/should be when at FSNL and when the breaker is closed and the unit is generating power), the P2 Pressure Reference remains constant (because the speed isn't/shouldn't be changing). As the unit is loaded or unloaded and the GCV opens or closes, respectively, if the SRV stayed in the same position the P2 Pressure would decrease or increase, respectively. So, the Speedtronic adjusts the SRV's position in order to maintain P2 Pressure equal to the P2 Pressure reference. So, the position of the SRV will vary with load--even if the gas supply pressure doesn't change. And if the gas supply pressure does change--which would tend to change the P2 Pressure--the Speedtronic will adjust the SRV to maintain P2 Pressure equal to the P2 Pressure Reference.

The GCV (Gas Control Valve) position is a little different. AS A _GENERAL_ RULE (but does NOT apply to ALL units and ALL gas fuels), there is a linear relationship between load and GCV position. AS A GENERAL RULE, GCV position at FSNL is TYPICALLY around 20% of stroke, and GCV position at Base Load is TYPICALLY around 70% of stroke. Taking the difference between 70% and 20%, which is 50%, each 25% of load would be equal to a 12.5% increase in GCV position. So, 25% load would be equal to approximately 32.5% IN THIS EXAMPLE, and 50% of load would be equal to approximately 45.0% IN THIS EXAMPLE, 75% of load would be equal to approximately 57.5% of load IN THIS EXAMPLE, and 100% of load would, of course, be equal to approximately 70.0% IN THIS EXAMPLE.

Now some units will have their FSNL FSR (or, GDV position) equal to 15%, and others will have their's at 22.5%; it varies with fuels and nozzles and compressor cleanliness and ambient temperature and inlet filter cleanliness and exhaust duct back pressure and turbine nozzle condition and turbine bucket condition, to name a few variables. And those same units will have their Base Load FSR (or GCV position) equal to 65% or 73% or 77.3%, again with the affect of the same variables.

So, it's possible to determine if the valves are in approximately the correct positions--but it's impossible to say for sure if they are in the exact correct position without knowing a lot about your site and your turbine's condition and how it's operated.

markvguy

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#### Anonymous

Thanks for clear reply mkvguy. But i could not understand how exhaust back pressure can vary valve opening. And could you tell me too approximate position of LFO bypass valve for FSNL,25MW, 50MW,75MW and base load.

anonymous

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#### markvguy

Exhaust back pressure decreases the air flow through the machine. Decreased air flow reduces the amount of fuel that can be burned at Base Load, reducing the GCV position, and the SRV position.

The Liquid Fuel Bypass Valve (LFBV) is a flow control loop; some LFBVs have position feedback, some don't. The LFBV is in the correct position when the Liq. Fuel Flow-rate Feedback (usually signal name FQL or FQLM or FQLM1 or something similar) is equal to the Liq. Fuel Flow-rate Reference (usually signal name FQR).

If fuels are properly matched, the FSR on Liq. Fuel should be approximately equal to the FSR on Gas Fuel for a given load, usually Base Load, and should be fairly closely matched at most other operating conditions.

markvguy

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#### Mark

Exhaust back pressure reduces air flow or flue gas flow?

Mark

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#### markvguy

If you had to breathe through a cloth and the thickness of that cloth were increased or the weave of the cloth was made "finer" (decreasing the distance between fibers increasing the thickness of the fibers), would the amount of air you breathe decrease and/or would you work harder to breathe the same amount of air? Would your body be able to exert the same amount of energy with the change?

markvguy