How fuel is controlled in GE gas turbine? my question is fuel valve characteristic functions adjusted in control system? if trim needs replacement how to proceed and what adjustments need to have correct functioning - controlling of fuel?

 

Fuel valve characteristics are not adjusted in control system. The Service Manuals provided with the turbine and auxiliaries should list the proper part numbers for any replaceable trim or valve internals. If there is any question, you could always contact GE, one of their licensed parts suppliers, or one of many firms claiming to be proficient in the repair and/or refurbishment of fuel control valves provided with GE-design heavy duty gas turbines.

As for the first question:

> How fuel is controlled in GE gas turbine?

It's way too vague to be properly answered in this kind of forum. The Instruction Manuals provided with GE-design heavy duty gas turbines can provide a lot of information (albeit generic and sometimes lacking--but a good place to start, nonetheless) about fuel control.

If you need more information, you need to be more specific.

 

Worked on siemens gas turbines and valve chara. curve of manufacturer is defined in the system but want to know how GE does? do GE have trimmer for fuel control optimization? by the way new and trying to learn and understand GE system with no documents but getting something form control forum, really valuable.

 

Sandy,

GE-design heavy duty gas turbines can basically be divided into two groups: those with conventional combustors and those with DLN (Dry Low NOx) combustors.

Those with conventional combustors do not typically (almost NEVER, actually) have valve characterization tables in the Speedtronic control system.

Those with DLN combustion systems do typically have gas fuel control valve characterization tables in them. They are used to convert a flow-rate reference into a position reference (since most gas fuel control valves used by GE are not equal percentage trim valves). The linearization is very simple, and is only used for tuning emissions control, not for basic speed control.

One thing to remember about German control systems and equipment: They are almost always needlessly complicated. When a simple linearization curve would suffice, it will be augmented with pressure-compensation or position compensation or flow compensation or some other compensation that requires more inputs and outputs than would really be ideal, increasing the complexity and decreasing the reliability. GE-design systems (with the exception of those engineered in their Belfort, France, facility--which seems to have adopted the German concept of complexification and dereliabilification in the misguided attempt at ever finer and finer control) are usually kept as simple as possible, so simple in fact, that most people marvel at how simple they really are. GE has had (in the past) one guiding principle: Reliability. And in the interest of reliability, they have kept things simple and been doing things the same way for decades.

That's all changing now, of course. It will no longer be possible for anyone at site to troubleshoot and diagnose a Speedtronic turbine control system in the very near future--Model-Based Control (MBC) is being thrust upon us and that means that someone from a remote site will have to "dial in" (connect electronically) to the Speedtronic and use proprietary software and methods to understand and troubleshoot problems. Alarms will become even more obtuse and misleading, and local operators and technicians will be helpless to understand and troubleshoot problems (real or perceived).

But, I digress. (It's that time of year.)

While there may be some similarities between Siemens and GE control schemes, there are probably more differences.

Best of luck!

 

Sandy,

Since I alluded to how "simple" the fuel control valves were in GE Speedtronic control systems, I should probably explain in a little more detail.

In general, each valve receives a position reference signal. The position reference signal is derived from calculations done when a turbine is ordered and being configured by the Engineering department. The position reference corresponds roughly to a flow-rate. So, for example, when a gas control valve is told to go to 40% of stroke (opening), that means that the flow-rate reference is approximately 40% of maximum expected flow-rate through that valve for the expected fuel flow and valve internals. (The valve internals are sized and chosen during the Engineering configuration based on expected fuel characteristics (BTU content, available pressure, etc.).)

So, most--but not all--fuel control valves are positioned based on a position reference. Liquid fuel control valves are usually based directly on a flow-rate reference (on the newer machines anyway), and the feedback comes from speed pick-ups looking at toothed wheels on the liquid fuel flow divider (a device that evenly divides the flow from the valve and high pressure liquid fuel pump into individual flows to each of the combustor fuel nozzles). More flow means more speed, hence a higher frequency feedback from the speed pick-ups.

Now, the position reference is mostly derived under some kind of speed control or exhaust temperature control. Droop speed control, for generator drive units connected to a grid in parallel with other prime movers and their generators, and exhaust temperature control when the Speedtronic has been told to make as much power as possible without regard for speed control (this is called "Base Load", or "Peak Load" on units with this extra power output capability; some units even have "Peak Reserve" capability--but Peak and Peak Reserve are for "emergency" situations only and not for normal operation). In Droop Speed Control (which is any load between zero load and "Base Load"), the fuel stroke reference (FSR) is a function of the difference between the Turbine Speed Reference (TNR) and the actual turbine speed (TNH). Under normal circumstances--just as on the Siemens units--TNH is relatively constant (presuming the grid frequency is relatively constant!). So, by varying the turbine speed reference, the error between the reference and the feedback changes. And the error is used to determine how much fuel is going to be admitted to the turbine. If the frequency changes, that can also change the error between the reference and the actual speed, and that will change the fuel flow, too (just as it should have on the Siemens units if they were using Droop Speed Control).

Start-up and acceleration and shutdown are usually "open-loop" control, with newer units using acceleration control for start-up control after initial firing and warm-up.

Hope this helps.

 

As usual well explained by CSA.

Thank you
G.Rajesh

 

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