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Operation of ST Admission/Extraction Valve at Low Load
Looking for information on the operation of a ST admission/extraction valve during low loading

Back for another question. This forum seems to be the only source of reliable information on the MK-V that I have found. Tech manuals are severely lacking.

I am trying to better understand the operation of our ST admission/extraction valve during a period of low loading. A little back information:

Plant info:
Cogeneration Plant
7EA GE Gas Turbine (DLN1+)
MKV GE Control System
GE Steam Turbine

When lowering MW to our dispatched rate, we are placing the ST in IPC and then placing the GT in preselect load and lowering to the desired MW output. Tonight for instance, we are dispatched to 71 MW. That puts us at about 45MW on the GT in preselect load, and 30MW on the ST in Plant MW control.

My question is this. During our descent to 71MW, while lowering MW on the GT, our ST reaches V3 uncontrolled extraction pressure, which if I understand correctly just means that the ST is no longer able to maintain the desired LP extraction setpoint. This isn't really a big problem for us, as we can utilize an IP-LP reducer to maintain the LP pressure as long as the IP extraction pressure isn't compromised. I am trying to understand the process the MK-V uses to determine when to shed LP, IP, or MW load to maintain the inlet steam pressure. Also, I am curious what the V3 valve bias does? Operators have noted that when the valve bias reaches 100%, things start going south. If you know what I mean. Sorry to put it that way, but I can't really describe it better than that.

Hopefully, someone out there (paging CSA...lol) will have a link to a training course on the ST controls of a MK-V, because as I stated, the tech manuals I have access to are extremely lacking...

2 out of 3 members thought this post was helpful...

ChristensonWJ,

I am NOT any kind of steam turbine expert. That's partially by "design" (I have tried to avoid them as much as possible, preferring to work on gas turbines--for many reasons), and partially because up until a couple of decades ago they literally broke the mold every time they made a steam turbine. By that I mean that every steam turbine was just a little bit different--and when it comes to extraction and admission many were a lot different. And, that made understanding steam turbine very difficult--at least for me. I have no answers for your specific questions--without being able to look at the CSP in the Mark V at your site, and even then it would take me some time to figure out what was happening and I would probably have to make a phone call or two to some other people who know very little about gas turbines and a very lot about steam turbines and steam turbine control. You're NOT going to find anything about steam turbine operation and control in any Mark V manual--nothing like what you're asking about. If anywhere, you might find it in the Operation & Service Manual that was provided with the steam turbine, in a document called the "Line-up Instructions." And, with my (desired) lack of steam turbine knowledge I can't offer anything for this issue. So, if you're not interested in a little history and a business model discussion, you can stop reading this reply right now.

As for documentation from GE about their turbines and turbine controls.... The divisions of GE that designed and produced the gas- and steam turbines historically bought the control systems for those turbines from other divisions of GE. Those other divisions of GE were essentially good at designing and building electrical and electronic control systems (and mechanical systems in the early days of control systems), and the turbine divisions didn't want to do that--it wasn't their "core competency" (before that was even a buzzword/term). The control divisions helped implement the turbine divisions' control and protection philosophies into the control systems, and in some cases they even did the programming for the turbine divisions (again; programming and configuring control systems isn't the core competency of the turbine divisions).

And this is where everything went "off the rails" when it came to documentation. The control system divisions produced the control systems, which were programmable and configurable for various kinds of turbines and turbine operations. They wrote manuals that described their control systems--but NOT how turbines were to be operated and controlled. The turbine divisions believed that the control system divisions should be documenting how the turbines were being controlled and operated using their (the control system division's) control systems. And, in the end, nobody did a proper job of documenting how the turbines should be controlled and operated.

I liken it to the early days of personal computers and DOS (disk-based operating systems). Remember the early DOS manuals? You wanted to move a file from one location to another. In the early days of DOS, there was not a MOVE command. You had to know that if the location you wanted to move the file to didn't exist, you had to create it (using MKDIR or MakeDirectory) on the drive where you wanted to move the file. Then you had to use COPY to copy the file to the drive/directory where you wanted it to be moved to. Then you had to delete the file from the original location (DEL or DELETE). The DOS manual didn't have instructions for this process--just for the commands for the various operations (MKDIR, COPY, DEL) which had to be executed to complete the process. (That's how the 'DOS for Dummies' people made all their money--documenting the individual commands required to complete an operation).

Current GE turbine control systems are produced by a division of GE that isn't responsible for designing and building turbines and deciding how the control system does what it needs to do. Believe me when I tell you that as a field engineer there were MANY times when it was necessary to re-write the programming and configuration that came from the control system factory to make it work the way the turbine division wanted it to work or the way the auxiliaries needed it to work. Because there was NO written description of how the turbine should work it was difficult for anyone--programmer, field engineer, Customer--to know how the turbine is supposed to operate so that one could determine if it is operating correctly or not. And this is a SHAME.

And, I believe it's one of the things that's contributing to GE's problems--people are just sick and tired of the poor documentation that comes with the turbines and generators and auxiliaries. And if the people who program the control systems don't know what's supposed to happen, then people who work on them don't, either--and so the field service people (because they're not engineers any more!) don't either. And, if the field service people can't write a good PAC case, they they won't get a good answer. And, if the PAC people don't understand the question--or how the turbine is supposed to operate--then the whole process is screwed.

And, the people selling, and designing, and commissioning the equipment don't care--they all have their own little sandboxes and Profit & Loss centers, and users and service people and operators will just get what they are given and will be damn happy for what they got, and of course, will pay dearly for it, too.

In the early days of steam turbines the manuals were much better than they are today. There was a document called the Steam Turbine Line-up Instruction which was EXTREMLY useful for understanding how the turbine and auxiliaries operated. And, there were some really good system descriptions in the steam turbine Operations & Service Manuals. But, when the two turbine departments (steam and gas) were merged into one and when steam turbines started using the Mark V, well, things started really going downhill, especially for the steam turbine group; the gas turbine group was already a long ways down the wrong road for documentation and it just got worse with the Mark V (and that took some doing to make it worse, but it got done!). And, along about that time, gas and steam turbine production was really picking and it was all most manufacturers could do to keep up with production much less produce good documentation.

The GE power generation business model should be a Harvard Business Review case study--in how NOT to organize a business. And this is just one part of how the Customer and the product suffers because of a lack of oversight and responsibility and a concentration by each business (P&L--Profit & Loss Center) which just has their blinders on and only concentrates on their part of the product. (Really, the discussion could go on and on and on about how screwed-up that business "model" is and how it's been allowed to be that way for so long. And how it stretches across many other divisions, too!)

1 out of 1 members thought this post was helpful...

CSA,

Thank you for your response. I appreciate you taking the time to type all that out! It seems your knowledge of steam turbines is a bit more than you would like to let on!

I will agree with you about the lack of documentation, and say this. Having come from a military background, where everything had a procedure, and you were required to know it inside and out. Not understanding a piece of equipment or the way it responds to simple inputs is very frustrating. I am considering sending an email to GE and asking them to send us some material on how this thing is supposed to work. Like I said, very frustrating when your machine doesn't come with simple instructions. Like trying to put together a desk from IKEA with no instructions.... Nope...

Thanks again

2 out of 2 members thought this post was helpful...

Yes, if GE used the same documentation procedures for their industrial gas turbines as they do for their military gas turbines everything would be a LOT better for everyone. BUT, the difference is that the governments pay for documentation. In fact I've been told that when the government is accepting bids for this type of equipment they ask to see the documentation first, make comments on it, and when they let the contract it states very clearly that if any changes to the equipment are made before delivery that the documentation be updated first--a contractual requirement. Of course, the cost of this gets factored into the price paid for the equipment, but it certainly does make the equipment a lot easier to service, repair and operate.

Now, for your dilemma. It would help your cause if you would have a look at the CSP for the steam turbine at your site and look for one of two Big Blocks: SAX or DAX (Single Automatic Extraction Control and Double Automatic Extraction Control, respectively). When you write GE you should ask for the Big Block Help for the Block you found in in your CSP. The Block Help will list the various priorities and what gets sacrificed when.

WARNING: It's a VERY brief and terse description, but it's better than nothing.

I think it's still available: GE Control Connect or GE Controls Connect. It's a website that Customer of GE can use to get assistance with their issues. You might use the control.com Search function to look for the website address if you can't find it easily using your preferred World Wide Web search engine.

The thing I don't like about using Control(s) Connect is that it only benefits one person because other people can't see the questions or the answers. That's the beauty of forums like control.com--LOTS of people can see the answer and the questions, and if feedback is provided then readers can see if the information was helpful, or not. (The Thumbs Up/Down icons don't really allow people to see if the information was useful, and if it wasn't, why not. Better than nothing but I'm not sure it's really useful.)

Please write back to let us know what you learn.!

By CuriousOne on 27 May, 2018 - 9:35 pm

By placing the steam turbine in load control and then placing the gas turbine in preselect; the operators have limited the heat output the gas turbine can supply to the steam generator. The MKV is alarming to ensure that operators know that the steam pressure supplied by the steam generator to the steam turbine can no longer be controlled by the admission valve, which has reached 100%.

Depending on ambient temps, The 7EA at 45MW is on the edge on coming out of DLN due to combustion reference temp approaching its lower value. The bleed heat valves are nearly full open and exhaust temps are within specs but BTU from the exhaust is low.

The valve is not at fault. Heat input to the HRSG is the problem. Tuning can allow the MKV to switch modes as needed. But remember AUTO is NOT preselect. Preselect means I have control and I know what needs to happen.