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Getting a better understanding of gas turbine control
How to get a better understanding of gas turbine control?
3 out of 3 members thought this post was helpful...

I'm a rookie in gas turbine using GE MARK VI control system. I see there were a lot of threads replied by CSA, and i found him very knowledgeable.

I was wondering how can a rookie like me to have a better understanding of gas turbine control.

In one thread, CSA advised to read Control Sequence Programs (CSPs) and Control Specification. what is Control Specification? how can i find it?

Thank you.

4 out of 4 members thought this post was helpful...

Hi

GAS TURBINE CONTROLS ARE ;
1) STARTER CONTROL SYSTEM
2) STARTUP SEQUENCE AND SHUT DOWN CONTROL SYSTEM
3) COMBUSTION CONTROL SYSTEM
4) HP SPEED CONTROL SYSTEM
5) Lp speed control system
6) exhaust temperature control system
7) 2 nd stage Nozzle control system
8) Lube oil and cooling system

Best regards
saradhi

7 out of 7 members thought this post was helpful...

Neo,

Welcome to the business. Mark V turbine control panels employ what's formally known as the CSP--Control Sequence Program. Mark VIs (and Mark VIes) employ what's formally known as "application code." Both are terms for the application-specific sequencing, the "logic", that's gets downloaded to the turbine control to make it particular for a specific application and site.

"Reading" the CSP or application code involves learning a new language--relay ladder diagram language. In the case of the Mark VI and the Mark VIe they use function blocks to perform the same operations that rungs used to do in relay ladder logic, but they still use a similar graphical representation to relay ladder diagram logic.

The Mark V CSP can be printed, and so can the Mark VI/VIe application code--but printed application code looks almost nothing like what one sees in Toolbox/ToolboxST and it consumes reams of paper and is usually considered a waste of time and natural resources to print it. Myself, I use MS-Windows screen printing capability to capture bits of code I need to make notes on and study to a MS-Word or MS-Wordpad document, and then print them.

I would be very happy to work through the single most important rung in the GE-design heavy duty gas turbine world: L4. If you have some patience, we can cover everything from what trips your turbine, to all of the start-check permissives required to get L4 to pick up. It's a great way to learn how GE SHOULD name signals and how to look at signals and quickly determine when the logic signal is a logic "1" or "0", and even if it's a timer or an inverse timer or associated with a physical input or output.

The Control Specification is a document that is provided with the Speedtronic turbine control panel. A Control Specification is specific to every turbine (or group of turbines installed and commissioned at the same time on a site). In the old days, GE used to provide the Control Specification, and the Piping Schematics (everyone else in the world calls them P&IDs) in Vol. III of the Service Manuals provided with the turbine and auxiliaries. But, they couldn't leave well enough alone, and it's changes several times over the last decade-and-a-half (which volume of the manual they provide it in). It's a very good document for most things, but I've seen some glaring errors in the Control Specification, such as Control Spec.'s which say the turbine has a diesel starting motor when it has an electric starting motor, and vice versa. So, read it for "intent", not "content"--meaning the description of the starting sequence, in this case, should talk about purging, firing, warm-up, and acceleration. That has to be done regardless of the type of starting means.

Also, many people find the Control Specification years after the unit was commissioned and think the Control Constant values listed in the Control Specification are GOSPEL and start changing the as-running values to match the Control Specification, and that' when the real "fun" begins. If the turbine's been running fine for months or even years, the Control Constant values in the Mark VI are probably just fine, though some could probably use a little "tuning." Just as with hardware ("Berg") jumpers, the positions you find them in on a card which has been working but is suspect are most likely the correct ones--not what some piece of paper says.

So, if you want to work on L4 in this forum, just let me know. It won't be the quickest thing we've every done, but it will be a good and valuable learning experience--I promise.

And, don't neglect the P&IDs--the Piping Schematic drawings. Those are about the single most important group of drawing a technician or operator can have. Every technician, and every operator, should have their own copy, with their own notes and markings.

Finally, one thing I'm coming to understand about newbies is that they don't have a good grasp of how field devices and instruments work. RTDs, in particular, but even thermocouples and pressure switches and temperature switches and limit switches and pressure transmitters--not to mention electro-hydraulic servo-valves and LVDTs. RTDs and T/Cs (thermocouples) have been covered in some detail on control.com. And none of them are particularly difficult to understand--but wiring them to any control system can require some basic knowledge which most people don't have and seem to believe isn't really important. So, if you have any questions about field devices and instruments, open a new thread and we can talk about them, if necessary--after you've researched the control.com archives (past threads, using the 'Search' feature) and if you have any questions.

Looking forward to working with you, Neo.

5 out of 5 members thought this post was helpful...

CSA,

thanks for your detailed reply.

It would be great if i have an opportunity to work with you.

As i am confused about how to start, i think working on L4 is a good choice. And i am interested in of gas turbine control.

But what should i do exactly?

Can you give me guidance and told me what specific i should do.

I am willing to spend several hours a day working on it.

8 out of 8 members thought this post was helpful...

Neo,

Okay! Let's get started. First, some "back-room" stuff. In order to post rungs so that they're legible on control.com we have to use HTML tags, specifically, the 'pre' and '/pre' tags (enclosed by the < and > characters). The 'pre' HTML tag needs to be added to the reply Text immediately before the rung, and then the '/pre' HTML tag needs to be added immediately after the rung--this is necessary to put the forum software into fixed-pitch font mode. (You can usually see the HTML tags in the body of replies.)

So, by putting a 'pre' (with the < and > characters--which won't show in this reply properly on the main pages of control.com--before the L4 rung and then following it with the '/pre' (with the < and > characters) we can display the L4 rung:


L4S L94T L4T L4
-----| |-----------|/|----------|/|------------( )
|
|
L4 |
-----| |------

Also, at least in the web browser that I use one can grab the lower right corner of the control.com Text box and drag it to the right (and down) to get more horizontal (and vertical) space when replying. This will be useful when logic signal names are long, and when there are as many as eight horizontal elements in a rung. You can always use the 'Preview' and 'Edit' buttons to see how your post appears before submitting it.

Also, let's talk about how GE is supposed to write and choose logic signal names (per their own standard--realize that every company has its own standard, and we're just talking about GE here). In the early days of digital Speedtronic turbine control systems it was decided to make the signal name describe when the logic was a "1", or when it was "True." In general, this has been followed over the years, but it's not always followed and that's a real shame, because it's very useful when it is.

Next, we need to be sure everyone (you, Neo, and me) is clear about what normally open and normally closed means. A normally open contact associated with a logic signal will be OPEN when the associated logic is "0" and will be CLOSED when the associated logic is "1". A normally closed contact associated with a logic signal will be CLOSED when the associated logic is "0" and will be OPEN when the associated logic is "1".

To get a logic signal to be a logic "1" it's necessary for power to flow through a series-parallel string to the "coil" of the logic signal, so that means that the logic signals of normally open contacts must be a logic "1" and the logic signals of normally closed contacts must be a logic "0". As an example, let's "read" the L4 rung (because it is, in fact, a sentence).

"When L4S IS a logic "1" OR when L4 IS a logic "1", AND when L94T IS NOT a logic "1" AND when L4T IS NOT a logic "1", then L4 will be a logic "1"."

So, when L4S is a logic "1" its associated normally open contacts will be CLOSED, and when L4 is a logic "1" its associated normally open contacts will be CLOSED, and when L94T is NOT a logic "1" (that is, when it IS a logic "0") its associated normally closed contacts will be CLOSED, and when L4T IS NOT a logic "1" (that is, when it IS a logic "0") its associated normally closed contacts will be CLOSED. And when either L4 or L4S is a logic "1", and when both L94T and L4T are NOT logic "1"s, then L4 will be a logic "1".

I find it easiest to "read" rungs in this fashion--"imagining" what state the associated logic signals of normally open and normally closed contacts have to be in in order for power to flow through the normally open or normally closed contacts to "energize" the logic signal coil(s) at the right end of the rung. Others like to read them in different fashions--possibly like this: When L4S is TRUE OR when L4 is TRUE, AND when L94T is FALSE AND L4T is FALSE then L4 will be TRUE. But, it's the same thing--TRUE and FALSE are another way of describing when logic signals are "1" or "0" and which state the logic signals need to be in in order for power to flow through them to energize the rung's logic signal coil. There are lots of ways to read and interpret rungs--lets' just stick with this one for this discussion, and hopefully it will become clearer why this way works best for GE logic (application code in the Mark VI).

So, from the longname descriptions of signal names in Toolbox, we can see that L4S stands for "L4 Set" (or sometimes called "L4 Start"). It will be a logic "1" (True) when all of the start-check permissives are met and when all of the other final start-checks are completed when a START is initiated. (Don't worry; we'll go over all of them in due time--presuming you have the patience.)

Now, let's continue with the descriptions of the other names of elements of the L4 rung. L94T will be a logic "1" when a normal shutdown is in progress and the fuel is to be shut off in two of the three control processors, <R>, <S> and <T> for a TMR control panel--or just in <R> for a SIMPLEX control panel. L4T will be a logic "1" when any condition which trips the turbine in two of the threee control processors, <R>, <S> and <T> for a TMR control panel--or just in <R> for a SIMPLEX control panel. (There are MANY sub-rungs for L4T, and we'll go over all of them.)

So, what does this tell us about L4? In order to get L4 to go to a logic "1" (to "pick up"), L4S needs to be a logic "1" and L94T and L4T both need to be logic "0"s, and then L4 will also go to logic "1" which will close the normally open contact in parallel with L4S and "latch" or "seal-in" the rung--so that if EITHER L94T goes to a logic "1" OR L4T goes to a logic "1" L4 will "drop out", or go to a logic "0". It should also be clear that it's necessary for L4S to go to a logic "1" to get L4 to also go to a logic "1", but that once L4 is a logic "1" that L4S does NOT need to remain a logic "1" for L4 to remain a logic "1"--as long as both L94T and L4T both remain logic "0".

That's it. Once L4 is a logic "1" there are only two conditions which can "drop out" L4 (make it go to a logic "0")--L94T going to a logic "1" or L4T going to a logic "1". And in order to start, run and shutdown (normal shutdown) the turbine, L4 MUST be a logic "1", and if L4 transitions from logic "1" to logic "0" while the turbine is starting or running or shutting down then the fuel stop valve(s) will be commanded to close and the turbine will be tripped. (Fuel stop valves are not open during purging and prior to firing, but L4 is required to be a logic "1" in order to open fuel stop valves when necessary, and for them to remain open.)

And--presuming that both L94T and L4T are BOTH logic "0"s, which they must be in order to initiate a START--there is only one condition that will allow L4 to pick up (go to a logic "1")and that is when L4S goes to a logic "1". (That's because prior to a START, when a READY to START is indicated to the operator, L4 is a logic "0". This can be seen in the 'Start Check Permissive' display.)

Hopefully you can begin to see how the signal name being chosen to describe when the signal is a logic "1" can be helpful. And hopefully you can also begin to see how knowing how to read signal names (most of them--unfortunately not all, because standards aren't always adhered to) can be very beneficial to quickly reading and interpreting rungs and logic (application code in the Mark VI). There are some little "tricks"--which aren't documented anywhere, not even in GE (sad, but true)--which we will discover on this journey.

So, your assignment, Neo, is to post the L4S rung to this thread (using the HTML tags). And, then, please "read" (write the sentence) that describes when L4S will be a logic "1".

Also, please post the longnames for each of the logic signals in the rung. Here's an example:

L4 = Master Protective ("1" to Run)
L4S = L4 Set
L4T = Master Protective Trip ("1" to Trip)
L94T = Normal Shutdown Trip

(I believe that if you hover the cursor over a signal name in Toolbox the longname description will appear at the lower left corner of the Toolbox window.The longnames I wrote were exact quotes from a Mark VI site; they are not the same for every job. Just post what it says in your application code from Toolbox. Sometimes, there is no longname; and worse, criminally, the longname is wrong. That's life, though. We learn to deal with it.)

We will go through each element of the L4S rung (which has several "sub-rungs", and the L4T rung, which has MANY sub-rungs) so you will get very proficient at using the HTML tags--and "reading" signal names. We'll go over the L94T rung, too. And, we will discuss the various other types of proper (and possibly improper) GE signal names, as well as understand the conditions and permissives.

You're going to have to look up Control Constant values, and various device settings (from the Device Summary document provided with every GE-design heavy duty gas turbine). So, you will need to find the Device Summary document (it also used be in Vol. III, but who knows where "they" put it now...).

If you have any questions or comments on the above, let's deal with those first. If I introduce words or terms you're unfamiliar with, ask for clarification. If you're having some trouble with normally open vs. normally closed contacts, just be patient with yourself. It will begin to become clearer soon. Best not to get caught up in that discussion because it does get very clear after a while--it just takes longer for some people than others, but be patient.

This is going to be a joint effort, but to be of the most benefit to you we are going to use the exact rungs and signals in your Mark VI application code so that it's specific to your turbine and auxiliaries. Your job is to provide requested information--rungs, Control Constant values, pressure switch or temperature switch settings, etc.--and the rest we will sort out as we continue on this journey of discovery.

Remember, relay ladder logic is just another "language"--and it has "sentences" with verbs and predicates and subjects just like any other language. And it's nothing more than logic, sequencing. By learning how to "anticipate" when a logic signal will be a logic "1" (and by inference, when it won't be a logic "1"--that is, when it will be a logic "0") one can more easily read the rungs and begin to understand what is to be happening so that one can understand GE-design heavy duty gas turbine control and GE-design heavy duty gas turbine control philosophy.

Finally, L4 is just one way the turbine can be tripped--from the application code running in the control processors. There is also tripping which can be done through the <P> core and associated inputs to the <P> core--and we'll get to that to as we finish this discussion. Because it's important to understand this isn't the only way a turbine can be tripped--GE has several. Be patient, and we'll cover them all, and in the process learn more about the Mark VI.

I'm looking forward to this journey! Let's keep moving and we're going to "see" some amazing things. "Learning is finding out what you already knew," is one of my favourite quotes. When presented correctly, it's exactly what happens--one says to himself (or herself), "I knew that!" It's just that you hadn't thought it about it that way before. And with a few little hints, tips and tricks it can be very easy--and intuitive, which means, well, you already knew that!

By the way, I'm going to apologize in advance for making a few mistakes along the way. I'm not a good person to proofread my own writing (most people aren't good at proofreading their own writing), and I'm doing this in my spare time, and so I do--and will--make mistakes. Just hopefully, not too many of them. Please be patient with me.

5 out of 5 members thought this post was helpful...

CSA,

Thank you for your reply.I am excited too, feeling i'm on a mysterious trip with you.

This time my assignment is L4S right?

If there are some mistakes and drawbacks or you have advice just let me know,and i'll try to do better next time. I hope to have a long and exciting journey with you.

Here comes the L4S:


L4SX L14HR L14Y L4s
-----||-----------||----------||------------()

where:
L4SX = Master protective set auxiliary logic(confusing)
L14HR = HP zero speed signal
L14Y = time delay loss of master protective(not sure if it is needed)

So, if L4SX, L14HR and L14Y are 1, then L4s is 1, otherwise L14 remains 0.

Should i make further classification? But it is hard for me.

I think L14SX is relatively important, so i dig deeper.
Here comes the L14SX;


L3RS L1X L33cse L63QT L4SX
-----||----------||----------||----------|/|----------()

L3RS = Start up check present(not sure)
L1X = startup check stop master control-startup permiss(confusing)
L33cse = starting means cluth engaged
L63QT = lube oil gen low pressure voted

So, if L3RS, L1X, and L33cse are 1, and L63QT is 0, then the L4SX is 1.

Is it enough for this time? It seems that the logic is endless if i go deeper.

I have questions, and some of them are foolish to you.

1) I think L means the type of variables is logic, and do the number,like 4,14 means something?

2) I am a little confused L4, can you give me some specigication.

3) How is my assignment? I am not sure whether i do it in the way you ask.

Best regards,Neo.

5 out of 5 members thought this post was helpful...

Neo,

This is a good start. Please do be careful when "copying" signal names; if the signal names is in all capital letters in Toolbox, you should use all capitals in your post. If the signal name is in lower-case letters, you should use lower-case letters in your post. And, please double-check to make sure you are typing the proper signal names (see below).

Yes. "L" means the signal is a logic--usually; GE violates that standard occasionally, too, but not very often, fortunately.

And, the numbers--they are VERY important. They correspond to GE's interpretation of the ANSI Device Numbering standard, and GE's interpretation is very close to the ANSI standard. For example, a "4" device is a 'master protective' or 'master control' element/device. A "14" is a speed level element/device. A "33" is a limit switch element/device. A "63" is a pressure sensing element/device (a pressure switch). A "94" is a shutdown (normal shutdown--not emergency shutdown, trip) element/device. A "5" is an emergency shutdown element/device (like an emergency stop pushbutton). It's VERY helpful to commit the ANSI device number standard to memory--or at least have a copy available when you are reading application code. It's critical, actually, and as you get more familiar with the device numbers you will begin to recognize certain functions/signals. You can find lots of ANSI lists on the world wide web with your preferred Internet search engine.

Please be very careful when copying information from Toolbox:

>Here comes the L4S:


> L4SX L14HR L14Y L4s
>-----||-----------||----------||------------( )

>where:
>L4SX = Master protective set auxiliary
>logic(confusing)
>L14HR = HP zero speed signal
>L14Y = time delay loss of master
>protective(not sure if it is needed)

It should be:


L4SX L14HR L4Y L4S
-----||-----------||----------||------------( )

where:
L4SX = Master protective set auxiliary logic
L14HR = HP zero speed signal
L4Y = time delay loss of master protective

Let's deal with the L14HR signal. "14" means it's a speed level signal, "H" means it's related to the HP shaft (and since your turbine is a single-shaft, I presume) the shaft is the HP shaft, and "R" means the shaft is 'at rest' or, 'at zero speed.' So, L14HR is a logic "1" when the turbine-generator shaft is at rest, or at zero speed.

L4SX, as you rightly noted, is important. In this case the "X" means it's a 'permissive' or 'auxiliary' to L4S. In earlier versions of GE digital Speedtronic turbine control systems, there was a limit of eight "elements" horizontal string in a rung. That means there could be no more than seven contacts (normally open and/or normally closed) and one coil--for a total of eight. So, if there were more than seven contacts necessary it was required to split the rung into multiple rungs, and name the "permissive" rungs by applying an "X" suffix to the main logic signal name. Since most of the application code was copied from earlier control systems, this was continued. And on some turbines, there may be additional contacts in either or both of the L4SX and L4S rungs.

So, in your mind you could envision the following:


L3RS L1X L33CSE L63QT L14HR L4Y L4
---| |---| |----| |------|/|-----| |----| |-----( )

because it's exactly the same as the combination of L4SX and L4S.

Let's tackle L4Y. When you see a "Y" suffix on a signal name it almost always means an "inverse time delay" to its namesake, in this case L4. If you look up L4Y in Toolbox, it will look like this:


L4 L4Y
-----|/|-------------------------(T)
1.0 sec

By "inverse time delay" you can see that 1.0 second after L4 transitions from a logic "1" to a logic "0" (which is the inverse of a logic "1") that L4Y will be a logic "1". Or:

"1.0 second after L4 is NOT a logic "1", L4Y will be a logic "1"."

[If you look up L4Z, it will look like this:


L4 L4Z
-----| |-------------------------(T)
1.0 sec

A "Z" suffix almost always means a "time delay" to its namesake, in this case L4.

L4Z is read:

"1.0 second AFTER L4 IS a logic "1", L4Z will be a logic "1"."]

Let's read the combined L4SX/L4 rung:

"When L3RS is a logic "1" AND L1X is a logic "1" AND L33CSE is a logic "1" AND L63QT is NOT a logic "1" AND L14HR is a logic "1" AND L4Y is a logic "1", then L4S will be a logic "1"."

L3RS = Ready to Start
L1X = Auxiliary to START command
l33cse = Clutch-Starting Engaged (driven by a discrete (contact) input
L63QT = Low L.O. Pressure TRIP
L14HR = HP Shaft at Rest
L4Y = L4 Inverse Time Delay

I think (I hope!) that the signal you wrote as L33CSE was actually l33cse (all lower-case alpha characters), because that's GE's "standard" for signals that associated with inputs and outputs--to express the signal names in lower-case characters. It's not required--but it's intended to be helpful to people reading the application code to let them know those particular signal names with lower-case alpha characters are associated with physical inputs or outputs. (Again, GE doesn't always follow their own standards. But we learn to live with it.)

So, now, let's re-read the combined L4SX/L4S rung:

"1.0 seconds after L4 goes to a logic "0" AND the 'Ready to Start' signal is a logic "1" AND the START command auxiliary is a logic "1" and the Starting Clutch is engaged AND there is NOT a Low L.O. Pressure Trip and the shaft is at zero speed, then L4S will be a logic "1"."

In order to be able to start a GE-design heavy duty gas turbine, the operator interface must display a "READY TO START" indication. Most HMIs have a "Start-Check Permissive Display which can be used to determine why a Ready to Start indication is not being displayed. (We are going to go through all of that--just be patient.) Part of the 'Ready to Start' indication is that there are no turbine trips (L4T is a logic "0")--remember L4T from the L4 rung. (A "3" is a complete sequence element/device. In this case, the ready to start sequence is complete.) L3RS will be a logic "1" when the start-check ("Ready to Start) sequence is complete.

When the "READY TO START" indication is seen AND when the operator selects START and executes the command then L1X will pick up (a "1" is a starting element/device per ANSI & GE). When L1X picks up, that starts several auxiliaries, including the Aux. L.O. Pump, which pressurizes the L.O. system after a few seconds (if the Aux. L.O. Pump is not already running). L1X is an auxiliary signal that is a logic "1" when a turbine START is active.

Also, L1X usually starts the Hydraulic Ratchet pump to engage the starting clutch, which should cause actuate limit switch 33CS-1 after the clutch halves are engaged to make l33cse go to a logic "1". The signal name tells you when it's going to be a logic "1"--when the starting clutch (the jaw clutch on most machines; a SSS clutch on some units) is Engaged.

When the low L.O. pressure switches at the collector end of the generator (the furthest point away from the L.O. pumps) are actuated--meaning they have sensed minimal L.O. pressure--then logic signal L63QT will go to a logic "0". A 63 is a pressure sensing element/device, mostly a pressure switch per GE's interpretation. When you see a "Q" in a logic signal name it means oil, or flow. In this case it means L.O., and the "T" means 'Trip.' L63QT will be a logic "1" when the L.O. bearing header pressure--as sensed by the switches at the collector end of the generator--is below the minimum pressure required to protect the bearings. Again, the signal name tells you when it's going to be a logic "1"--when the L.O. Bearing Header pressure is low enough to initiate a turbine trip. In this case, we want it to be a logic "0" (because we need the normally closed contact to be closed to get power flow through the contact) so we want L63QT to be NOT a logic "1"--which is the same as saying when the L.O. pressure is NOT low enough to initiate a turbine trip. And, again, that will happen several seconds after the Aux. L.O. pump starts and pressurizes the bearing header and the pressure switches at the collector end of the generator are all actuated.

L14HR is a logic "1" when the HP shaft is at Rest.

L4Y is a logic "1" 1.0 seconds after L4 is NOT a logic "1".

And that's L4S (and L4SX).

Regarding your confusion about L4, it's the signal that says "It's okay to run the turbine" when it's a logic "1". And when it's NOT a logic "1" (when it's a logic "0"), then the turbine is to be tripped. If you look at how many places in the application code L4 is used, you will--it's a LOT! Probably the most used signal, because it's the permissive to start run a lot of auxiliaries, to energize a lot of solenoids, to permit fuel to flow, and on and on. L4 must be a logic "1" to burn fuel in the turbine, and if it changes from logic "1" to logic "0" the fuel flow-rate will be stopped--tripping the turbine.

This logic signal, L4, should >>>NEVER<<< be forced to a logic "1". Never. Ever. NEVER. Not even when the turbine is at zero speed. If this signal is forced to a logic "1" when the turbine is not running, a lot of auxiliaries may start and run, and a LOT of alarms will be annunciated, and in the worst case, fuel might be accidentally admitted to the combustors. It's just not ever permissible to force L4. Even if some GE document tells you to do so--it's wrong. And, it should absolutely NEVER be forced to a logic "1" when the turbine is running--because if L4T is picked up (by, say, low L.O. pressure, or high vibration, or loss of flame, or exhaust overtemperature, etc.) the turbine will NOT trip. So, to anyone reading this: Never force L4 to a logic "1"--whether the turbine is running or not.

I hope it's becoming clearer how to "read" logic signal names. In general, the signal name tells you when the logic is going to be "1". And, armed with this information, it should be easier to read application code.

Don't try to think that you have to learn everything right now. You have this information, you can print it, and you can review it any time you wish. And, it's always available on control.com.

Dear CSA,

I am a mechanical engineer by qualification, trying to understand GE 9FA control system. I have a question on L4 & L4Y commands. How both of them can be a logical state "1" simultaneously? As you mentioned L4 needs to be "1" for getting start permissive and apparently L4Y too needs to be "1" in L4S loop. This is a bit confusing. Sorry in advance if it's a stupid question.

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

Batman,

Good on you for expanding your knowledge; it's very helpful for mechanical engineers to understand how turbines operate, too, not just to know how to turn a wrench or orient an orifice plate.

I believe you found a typographical error in my post (something I had just chided Neo for making... and then I made a serious one!). The rungs in questions are:


L3RS L1X L33CSE L63QT L4SX
-----| |-----| |-----| |-----|/|------------( )

L4SX L14HR L4Y L4S
-----| |---------| |---------| |------------( )


The first, L4SX, is an "auxiliary" to L4S, made necessary because a sequence editor can't have more than eight (8) elements, so it was broken into two rungs by making the first an "auxiliary" and then including the auxiliary in the "actual" rung.

The resulting rung (which I mistyped) would look like this:


L3RS L1X L33CSE L63QT L14HR L4Y L4S
---| |---| |----| |------|/|-----| |----| |-----( )

Hopefully this part was clear:

>L4Y is a logic "1" 1.0 seconds after L4 is NOT a logic "1".

So, the rung which I mistakenly put L4 over the coil, should have been L4S, and this should help clear your doubt.

The rung for L4 is always:


L4S L4T L94T L4
----| |--------|/|-------|/|----------( )
|
L4 |
----| |-----

Does this help? Sorry for any confusion--and there is no such thing as a stupid question when one is trying to learn something new. Just dumb answers.

Thank you CSA for the quick reply in spite of your busy schedule. I'll summarize what I understand (about L4Y), then I'll ask you a question.

1) L4 is a master protective signal, which is normally "1", when everything is fine.

2) But, just before start up, it is "0", so that L4Y which is used in STCK2 is "1" which makes L4S "1" if all other conditions are met.

3)Once after L4S is "1", L4 changes its state from "0" to "1" if L94T & L4T are "0", and it remains "1" until L94T or L4T change their state.

Now I have a question (Assuming my comprehension is correct so far)

Why time delay for L4Y is only one sec, if it's used to block an immediate start attempt followed by a trip/shutdown? One second seems to be little impractical. I guess it's main purpose is to avoid a start attempt when L4 is "1", but not convinced with the time delay. Please correct me if I miss something here.

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

Batman,

L4Y is used in other rungs, not just L4S. The reason there is a timer at all is to prevent what's called a "relay race" during very "busy" times when L4 is changing state from "1" to "0". I honestly don't know why it's set for 1.0 seconds, but I know it works.

And I know that changing things like this without understanding all the knock-on effects (in all the other rungs that L4Y is used in) can have very bad effects.

A lot of the application code in Speedtronic turbine control panels are artifacts from the days of electro-mechanical relays. That's one of the things that makes Speedtronic panels unique--every time a new Speedtronic panel comes out GE doesn't reinvent the way it controls the turbine. And, for sites/Customers that buy new turbines with Speedtronic turbine control panels, or technicians with experience and knowledge from older versions of Speedtronic turbine control panels, it's very easy to troubleshoot and understand the way the turbine is being controlled.

There was one exception to this--Mark II Speedtronic--when GE went away from relay ladder logic and diagrams to a "logic gate" type of depiction. A lot of people really didn't like that format, even though it was "modern" and functionally exactly like Mark I (the turbine operated in virtually the same way). A LOT of Mark II-equipped turbines were sold around the world (and a LOT of Mark IIs were still in service), but a lot of Customers with older Speedtronic turbine control panels complained, and when GE developed the Mark IV it went back to relay ladder logic/diagrams.

The upshot of all this is: a time delay may not be necessary for today's digital control systems. But, why fix something that isn't broken? It may not seem that L4S needs a time delay, but other rungs/functions probably do.

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

> I honestly don't know why it's set for 1.0 seconds, but I know it works.

Engineering inertia is the reason the time delay on L4Y is set to 1.0 second. Back in the days of Mark I, 4Y was a time delay dropout relay (electromechanical), and I believe 1 second was about the minimum setting on the device. Basically, it's always been that way, it works, why change it?

otised,

I'm going to use 'Engineering Inertia' in the future, probably many times.

You're so PC (Politically Correct)!

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

Batman,

I likely didn't address your explanation of what's happening--but it's basically correct.

1) L4 must go to a logic "1" in order to start the turbine, and it must remain a logic "1" in order to keep fuel flowing to the turbine once flame is established.

2) When the unit is at rest or when it's on Cooldown (ratchet; turning gear; etc.) L4 is a logic "0". And it doesn't go to a logic "1" until an operator puts the unit into some mode other than OFF and initiates a START (and all the other permissives are met).

3) Yes; L4 remains "1" until L4T or L94T changes state. L4T goes to "1" when the control processors detect a condition that requires an immediate shut-off of fuel (and emergency trip). L94T goes to a logic "1" (during normal operation) when flame is lost during deceleration, or the unit drops "blow-out" speed for a specified period of time, or when the unit hasn't reached "blow-out" speed within a certain period of time after a STOP was initiated.

So, with a few qualifications, your comprehension is correct.

Thank you CSA. your explanation made me understand L4Y better, will start focusing on rest of the control signals.

Batman,

You're very welcome. Thanks for the feedback!

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Neo,

I don't believe you've told us what turbine you are working on at your site.... And what fuel(s) it burns.... And what kind of starting means it has....

Your next assignment is to examine L3RS. Post the rung, and the logic signal names from Toolbox, and write your sentence of how the rung works.

One of the contacts should be L3STCK, and the L3STCK rung should have several contacts like L3STCK0, L3STCK1, L3STCK2, etc. Please post the L3STCK rung from your Toolbox file.

CSA,

Should i wait for you comment and guidance or just continue to examine the signal L3RS?

Best regards.

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

Neo,

I am working on my response; L3STCK0 is a fairly extensive rung.

Please check the "sense" of L45FP_STCK (normally closed or normally open). It is confusing me.

It might be a good idea to put the rung in your reply.

Please take your time and be certain of the case of signal names and the sense of contacts.

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

CSA,

Thank you sincerely for your detailed reply. Your comment makes it easier for me to read application code.

Firstly, i should make some clarifications:
1) The gas turbine is MS6001B,burning syngas.
2) The signal name of l33cse is in lower case letter.

This time my assignment is to examine L3RS, and i find it a little complicated.
Here comes the L3RS:


L3RS1 L3RS2 L5VPRO_LATCH L3RS
----------||----------||----------|/|-----------()

Where:
L3RS1 = Start check stop ready to start logic1;
L3RS2 = Start check stop ready to start logic2;
L5VPRO_LATCH = Protective VPRO card trip_latch(Never heard it before)

SO,when Ready To Start 1 signal(L3RS1)and Ready To Start 2 signal (L3RS2) are logic 1,and
L5VPRO_LATCH is 0, the L3RS will be logic 1.

It will be necessary to examine L3RS1 and L3RS2, and this time i'll examine L3RS1.


L3STCK L3RS1
------------||------------()

Where:
L3STCK = Startup check stop stop start check permissive.

And the signal L3STCK:

L3STCK0 L3STCK1 L3STCK2 L3STCK3
----------||----------||----------||-----------||----------()


L3STCK0 = Startup check stop start check logic 0;
L3STCK1 = Startup check stop start check logic 1;
L3STCK2 = Startup check stop start check logic 2;
L3STCK3 = Startup check stop start check logic 3;

In conclusion, the L3RS is divided in L3RS1 and L3RS2, and L3RS1 is devided in L3STCK0, L3STCK1 ,L3STCK2 and L3STCK3.

I was wondering what kind of signal will be grouped in L3STCK0, L3STCK1, L3STCK2 and L3STCK3 respectively.

L3STCK0(start check logic 0 for units without third fuel and no HRSG by pass)(?)


L27BN l3cp L86TCI L3IGVFLT L5WSTOP L5ESTOP1 L45FP_STCK L3STCK0
-------||----------||----------|/|----------|/|----------|/|-------|/|-------|/|------------( )
| |
| |
L27BZ | TRUE |
-------||---------||-------

Where:
L27BN = AC BUS normal;
L27BZ = AC BUS undervoltage(confusing);
l3cp = startup check stop customer permissive to start (difference between l3cp and L1X?);
L86TCI = compressor inlet thermocouple disagree (not clear);
L3IGVFLT = IGV valve position servo trouble;
L86MP = startup check stop master prot startup lockout (not sure);
L5ESTOP1 = state of E-STOP 1 (confusing);
L45FP_STCK = Fire protection start permissive (not clear);

SO, if any of L27BN and L27BZ is logic 1, AND l3cp is logic 1, whenL86TCI, L3IGVFLT, L5WSTOP, L5ESTOP1and L45FP_STCK are logic 0, then L3STCK is logic 1.

I'll start with the signal L3IGVFLT. The L3IGVFT :


L3IGVF1 L3IGVFLT
--------||------------( )
|
L3IGVF2 |
--------||---------

The signal L3IGVF1 and L3IGVF are outputs from L86GVTV2 block,and my interpretation is when the csgv is <31 and >35, the L3IGVFLT is logic 1.

It seems that the L3IGVFT signal will function only before gas turbine startup. (am not sure for i cannot figure out the signal L3IGV).

I am poor in electric knowledge, so the other signals are not easy for me. But i did what i can, i looked up the ANSI device numbers;

27: undervoltage relay
86: lockout relay

1. Does that mean signal names with 27/86 are related to the status of certain relay?
And what's the difference between undervoltage relay and lockout relay?

2. Can you explain the word lockout for me ,because it's hard for me to understand.
If the above questions are too easy, just let me know, and i'll try to find answer on my own.

I would like to continue next time,is it ok? Because it is not easy for me :}

And i'll try to do better next time.

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Neo,

Thanks for the information about the turbine at your site. What is the source of the syngas? Does the unit start and stop on syngas, also, or does it use another fuel (natural gas or liquid fuel (distillate) for starting and stopping and you have to transfer to syngas at some speed/load?

As for questions being too easy, sometimes the easiest ones are the hardest ones to answer. I learn a lot from teaching, and I like to say, "There is no such thing as a dumb question--just dumb answers."

A 27 may be related to a protective relay, or it might be related to the presence/absence of voltage in one of the MCCs or the battery charger. Undervoltage is undervoltage; it indicates the loss of or the lack of a minimum level of voltage for some condition.

A lock-out condition is one that requires some manual intervention to reset. The intent is to make certain that someone is aware of the problem and has taken appropriate action to resolve the condition before the alarm condition is unlatched, and many times before the turbine can be re-started.

An 86 device is a lock-out--which may be a relay, or it may be a latched alarm/trip condition as described above. An 86 lock-out relay is a relay that must be manually latched (against spring pressure that would otherwise open the latch). When one of several other relays operates (when a serious condition is detected), it operates an electric coil that unlatches the relay.

There are many different generator/transformer protective relays or relay functions each with its own unique ANSI device number.

So, if 2 of the 3 the VPROs in the <P> core initiate a trip, from the signal name L5VPRO_LATCH I would presume they are latched in the trip condition and L5VPRO_LATCH would go to a logic "1". Once the trip condition is resolved and cleared to reset the alarm and unlatch the trip one probably has to issue a 'Master Reset' from the HMI to make L5VPRO_LATCH to go back to logic "0"--which is the good condition. When L5VPRO_LATCH is a logic "1" the "READY TO START" indication can't be achieved.

Yes; the next logical rung would be L3RS1, which is "driven by" L3STCK, which is driven by the four start-check rungs: L3STCK0, L3STCK1, L3STCK2 and L3STCK3 (for your machine). If there wasn't a limit to the number of horizontal rung elements there would only need to be a single rung--probably L3STCK, but since there are well more than seven start-check permissives there has to be more than one rung, with "auxiliary" rungs used to get all the start-checks to finally pick up L3STCK.

And the next logical step would be to analyze L3STCK0. Though, at one point you listed L3STCK0 as "Startup check stop start check logic 0" and in another place you listed it as "start check logic 0 for units without third fuel and no HRSG by pass". Where did you find the two descriptions? (I guess the second description was from a 'Comment' in the application code.?.?.?)

I think you might have been in a great hurry when typing your response.... I think the L27BN and L27BZ should have been l27bn and l27bz and the contact for L45FP_STCK should have been normally open, not normally closed. This is because both l27bn and l27bz are usually associated with individual discrete (contact) inputs from relays in the generator protection panel.

And, if the signal name L45FP_STCK was chosen correctly, then it should be a logic "1" when the Fire Protection System is capable of detecting a fire, tripping the turbine, and discharging fire extinguishing agent. And we want the Fire Protection system to be capable of all of the above. If L45FP_STCK is a logic "1" when it's "ready" then the normally closed contact you drew would be open, and L3STCK0 would not got to a logic "1"--which is what we need to get a READY TO START.

l27bn = is a logic "1" when the Bus Voltage is Normal
l27bz = is a logic "1" when the Bus Voltage is NOT Normal (the "Z" in this case means 'inverse')
l3cp = logic "1" when the 'Customer Permissive' to START is a logic "1"
TRUE = ??? This is one I'm not familiar with, but I think it's always a logic "1"--ALWAYS
L86TCI = is a logic "1" when the redundant axial compressor inlet thermocouples disagree (have a wide discrepancy) by more than a setpoint
L3IGVFLT = is a logic "1" when an IGV Fault has been detected
L5WSTOP = (you didn't provide a description, and I'm not familiar with this one--at all)
L5SETOP1 = is a logic "1" when one of the E-STOP Push-button inputs to the <P> core is actuated (open)
L45FP_STCK = is (should be) a logic "1" when the Fire Protection Start-check Permissive is satisfied (unless the signal name was chosen incorrectly)

So, let's read the rung:

"If the bus voltage IS normal OR the bus voltage is NOT normal, AND if the Customer Permissive to Start is a logic "1" OR TRUE is a logic "1", AND the compressor inlet thermocouples DO NOT disagree with each other AND there is NOT an IGV fault AND there is NOT an L5WSTOP AND the first E-Stop input to the <P> core is NOT actuated AND the Fire Protection Start-check Permissive is NOT [???] satisfied, then L3STCK0 will be a logic "1".

The l27bn/l27bz parallel combination is a way to be sure the bus PTs are both sensing voltage or both NOT sensing voltage. (The "bus" is the voltage on the other side of the generator breaker--the grid voltage, the "running" voltage as it's often called.) The two logic signals should each be driven by separate discrete inputs (which is why I put the signals names in lower-case letters) from a bus under-voltage relay that is picked up when both PTs sense bus voltage, or when both PTs DO NOT sense bus voltage. If there is a problem sensing bus voltage there should be a Process Alarm to alert the operator to the condition.

Note that a complete lack of bus voltage does not prevent a start; many times for testing there is no bus voltage when a turbine is started, or some turbines have the ability to close on to a dead bus. So the lack of bus voltage does not prevent a start; but when there is no bus voltage (a complete lack of bus voltage) there is a process alarm for that to alert the operator to the condition, but, again it does not prevent a start. A recent thread on control.com indicated some turbines start with a dead bus, and then close on the bus with a "dead" generator, and then apply excitation and slowly increase generator terminal voltage to "charge the line" (the "bus" line).

And, this is a good time to mention that every start-check permissive should be accompanied by a Process Alarm to alert the operator why a 'READY TO START' is not being displayed--EXCEPT one signal. And we'll get to that one soon enough.

The l3cp/TRUE parallel combination is a way to bypass a 'Customer Permissive to Start' discrete input which usually exists in most all Speedtronic systems. It might be from the DCS saying the HRSG drums are full and heat can be applied to the HRSG from the gas turbine exhaust, or it just might an operator selection from the DCS saying they are prepared for a gas turbine start. (This signal does not trip the turbine when the turbine is running if it goes to a logic "0"; it just must be a logic "1" to start the turbine. If it's not, there should be a Process Alarm to alert the operator there is no Customer Permissive to Start.) The TRUE is the software "bypass" to l3cp; if there is no discrete input connected to the Speedtronic it will never change state, so the software TRUE (which is ALWAYS a logic "1") is used to bypass l3cp when there is no signal from the "Customer." In the "old" days, we used to just put a hardwire jumper on the l3cp discrete input terminals to permanently make l3cp a logic "1"; this is just a software equivalent of that. The signal could have been just deleted from the rung; TRUE completely baffles some people since it's not explained in any GE documentation--anywhere.)

L86TCI a logic signal that warns the operator of a problem with the axial compressor inlet thermocouples, usually signal CTIF-1, CTIF-2 and sometimes CTIF-3 (Compressor Temperature-Inlet, Flange 1, -2 or -3). There is some logic in the application code that checks to make sure the three signals are within an allowable range of each other; if not, then a gas turbine start is not permitted. This is because axial compressor inlet temperature is used for biasing HP shaft speed for some very important functions (the resultant signal is TNHCOR, Turbine Speed-HP Shaft, Corrected). So, if the temperature measurements are not reasonably close to each other then there is a good possibility that TNHCOR can be adversely impacted which could affect turbine operation.

The "86" in the signal name is an indication that the condition requires a Master Reset to unlatch the alarm once the condition has been corrected. Signals with "86" in the name are generally called "lock-out" signals. Most do require a Master Reset; some do not (unfortunately; another occasion when GE doesn't adhere to its own standard).

L3IGVFLT is a logic signal that we can spend more time on if you wish. As you noted, it's checking to make sure the IGVs are within reasonable limits of where they should be prior to starting. The minimum mechanical stop on the IGV ring is set for approximately 32 DGA, so the lower limit should be something slightly less than that--and 31 DGA is a reasonable number. The minimum operating angle during starting is 34 DGA and the IGVs shouldn't be much more open that prior to a start, so 35 DGA is also a reasonable number. This is just a check to make sure the IGVs are in a reasonable position prior to starting (presuming the LVDT feedback is properly calibrated). The IGVs are one method to limit axial compressor surge/stall during starting by keeping them "closed" (34 DGA or so is considered closed). (Axial compressors are very unusual and have some very unique requirements.)

The description you provided, probably from Toolbox, can be misleading. A servo problem might be the cause of this logic signal being "1", but, it might just be that the IGVs were left in some position other than what they should be after a maintenance outage, or the IGV LVDT calibration is inaccurate (this happens a LOT, unfortunately)--which is NOT a servo-valve problem, it's a human problem. Sometimes, the IGV minimum mechanical stop is also not set correctly after a maintenance outage when the IGVs have been worked on, resulting in the IGVs going to 30.9 or 30.8 DGA--which is not horrible, but is approaching the limits of acceptability. When a START signal is initiated, the IGV Trip Solenoid, 20TV-1 will be energize and hydraulic pressure will move the IGVs to the minimum operating condition (34 DGA). So, if personnel are CERTAIN the IGV LVDTs are properly calibrated AND that the mechanical stop has not be properly set it's sometimes permissible to change the limit to prevent the alarm. But, any value less than approximately 30.5 DGA means the minimum mechanical stop should be repositioned (it was moved) or the IGV LVDTs have not been properly calibrated--which, again, is NOT a servo-valve problem; it's a measurement and calibration procedure problem which should be corrected before starting.

Also, I would be interested to know if the application code for your turbine requires a Master Reset to unlatch L3IGVF1 and L3IGVF2 once the condition has been resolved. If so, this would be an example of a lockout that doesn't have "86" in the name. (Isn't this fun?)

I would like to see the rung for L5WSTOP, as it's not something I'm familiar with. So, if you would, please, post it to your next reply.

L5SETOP1 is a logic signal that comes from the <P> core when one of E-Stop P/B (Pushbutton) circuits is NOT closed. (E-Stop P/B circuits are normally closed, and when the circuit opens (by pressing the the E-Stop P/B) the turbine is tripped. There are a couple, if I recall correctly, E-Stop P/B inputs so it's easier to identify which E-Stop P/B has been actuated (or possibly a wire in the circuit has come loose--it does happen!). Note again--this comes from <P> core. It is a hardware trip, as opposed to a software trip. It's meant to be a "positive" means of tripping the turbine (by opening the circuit) without having to go through software to trip the turbine. (There are also software trips, but I believe many insurance companies and some technical regulations and standards require a hardware method of tripping the turbine.) Hopefully, we will remember to cover this when we get to the L4T rungs, and other ways to trip the turbine.

L45FP_STCK; this one I believe is either an incorrectly chosen signal name, a typo, or the contact sense (normally open vs. normally closed) is typed wrong. The signal name indicates this signal will be a logic "1" when the fire protection circuit is "ready" to detect a fire, trip the turbine and discharge fire extinguishing agent (CO2 or water sprays). If the signal name is correct--the logic is "1" when it's active and in a "ready" condition then the contact sense as shown is wrong. If the contact sense is correct (from the application code), then this is an example of someone not choosing a signal name correctly....

Let's work on L3STCK1 next, but, also please post the L5WSTOP rung, and if the sense of the L45FP_STCK contact is correct as you have typed it, please post the L45FP_STCK rung, also. And, please check on the case of signals l27bn and l27bz; if they are indeed all capitals, then please check to see if they are driven by discrete inputs; this could also be another example of GE not adhering to their own standards.... (What's the purpose of having standards, eh?)

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

CSA,

Glad to continue this finding journey, and thank you angain for your detailed reply.

First i have to apologize to you for several unnecessary mistakes i made. So, i'll start with some clarification:

1)The sense of L45FP_STCK is normally open.

2)There is no signal named L5WSTOP,it should be L86MP.(weird mistake,sorry again)

But the signal L27BN and L27BZ do in capital letter.

SO the L3STCK0 rung should be:


L27BN l3cp L86TCI L3IGVFLT L86MP L5ESTOP1 L45FP_STCK L3STCK0
-------||----------||----------|/|----------|/|----------|/|-------|/|-------||------------()
| |
| |
L27BZ | TRUE |
-------||---------||-------

Where:
L27BN = AC BUS normal;
L27BZ = AC BUS undervoltage;
l3cp = startup check stop customer permissive to start ;
L86TCI = compressor inlet thermocouple disagree ;
L3IGVFLT = IGV valve position servo trouble;
L86MP = startup check stop master prot startup lockout(confusing) ;
L5ESTOP1 = state of E-STOP 1;
L45FP_STCK = Fire protection start permissive ;

I Checked the source of signal


true true
l27bn1---------||---------L27BN; l27bz1---------||---------L27BZ;

In your reply, you mentioned if the signal is driven by a discrete(contact) input it should be in lower case letter.
I am confused about the meaning of the word 'discrete'.

Do you mean that if one signal is directed from sensors it's name should be in lower case letter?

I am still a little confused about relay, as my understanding, a relay functions like a switch,when DO is logic 1, then it closed and the circuit is powered with electricity.

The (undervoltage) relay and (lockout) relay confuse me. Take signal L27BN as an example, how does a undervoltage relay related to L27BN?

Yeah, the application code in my turbine requires a Master Reset to unlock L32IGVF1 and L3IGVF2.

Last thing to clarify the second description of LSTCK0 do comes from Toolbox,and i find it misleading.
-------------------------------------------------------------------------------------------------------
Here comes the LSTCK1:


l26qn L28FDSCK L430 L14HR L86HD l12hblt L3STCK1
-----------||---------||--------|/|---------||------------|/|---------|\|------()

Where:
l26qn=Lube oil tank temperature low low;
L28FDSCK=Flame detector trouble;
L430=Off modo selected;
L14HR=HP zero speed signal;
L86HD=Hydraulic protective trouble;
l12hblt=overspeed bolt trip;

If the 'lube oil tank temperature is lower than setpoint' AND 'any one of the flame detector detect no signal of flame before start AND 'off MODE' is not selected'AND'the HP-shaft' is at rest AND 'Hydraulic protective is not logic 1 'ANd'overspeed bolt trip is not logic 1', then L3STCK will be logic 1.

As to signal l26qn, does it from a temperature switch which outputs 1 when the temperature is lower than setpoint? I think the temperature of lube oil affect its performance.

It seems the signal is related to the fuel servo system ,and i think it is important. Should i examine it next time?

I am confused about L430 signal, does it an input from HMI? And just to normally shutdown gas turbine?

Up to now, i was confronted a lot of signals and i find it hard to sort it out? What should i focus on through this journey?

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

CSA,

I will give a brief introduction of gas turbine on my site some time later. I will prepare it.

Best regards.
Neo

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

CSA,

I reread the your response below.

"The l27bn/l27bz parallel combination is a way to be sure the bus PTs are both sensing voltage or both NOT sensing voltage. (The "bus" is the voltage on the other side of the generator breaker--the grid voltage, the "running" voltage as it's often called.) The two logic signals should each be driven by separate discrete inputs (which is why I put the signals names in lower-case letters) from a bus under-voltage relay that is picked up when both PTs sense bus voltage, or when both PTs DO NOT sense bus voltage. If there is a problem sensing bus voltage there should be a Process Alarm to alert the operator to the condition."

I think there are two PTs measuring the bus voltage,both of them output its logic signal through the status of a relay. The relay outputs signal l27bn is closed when the bus voltage is normal and the other relay that outputs signal l27bz is closed when the bus voltage is below setpoint.

So it is the hardware way of judging the status of bus voltage.
It can also be done in software way by implementing the compare block.

Is it right?

Best regards
Neo

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

Neo,

Whoa, there. Let's not get too far ahead of ourselves.

You had asked about relays and discrete inputs (and by extension, discrete outputs) and you're talking about relays here like you have a good understanding of them.

A discrete input (or output) to a programmable control system (and the Mark VI is a purpose-built programmable control system--built, primarily, for the purpose of controlling GE-design heavy duty gas turbines) is one that is either "on" or "off", "1" or "0", "true" or "false", "energized" or "de-energized", "picked up" or "dropped out", "close" or "open", and so on. It has only one of two possible states.

A relay is simply a device for conveying information via contacts, that are either open or closed, when the relay is energized or de-energized. Relays usually have more than one set of contacts. The contacts can be electrically separate (have no common electrical circuits), or they can have electrically common contacts (so-called "c-form" contacts that have a normally open and normally closed terminal and share a COMmon terminal). In the case of an undervoltage relay, it is sending a discrete signal to the Speedtronic about the presence, or absence, of voltage. Additional contacts of the undervoltage relay may be used in other circuits for the same purpose (to indicate the presence or absence of voltage). Relays are pretty simple devices, however, they require a power source (110/220 VAC; 24 VAC; 24 VDC; 125 VDC; and many others depending on the manufacturer and application). They are electromechanical devices, and as such, they can fail when the electric coil fails, or when the contacts weld closed or the spring fails.

Now to your present question about L27BN and L27BZ. GE and it's packagers typically use two PTs to sense bus voltage, and two PTs to sense generator terminal voltage--both arranged in what's called an open-delta configuration. If any phase voltage is lost, or if there is a failure of any single PT then, in this case (the bus voltage) l27bn1 (I believe you said it was at your site, that drives L27BN) will not pick up. Conversely, both PTs have to indicate there is NO bus voltage before l27bz (which I believe you said drives L27BZ at your site) will indicate a complete loss of bus voltage. There really is no point in starting a gas turbine that drives a generator if there is a problem with the bus voltage because it is very likely that the gas turbine will have to be stopped to sort the problem.

As for whether or not the checks could be done with a COMPare block, well, yes. But then one would need to have additional AC voltage input circuits (at additional cost and complexity) when simple relays will do the job more than adequately by providing discrete inputs.

Discrete inputs have historically been much cheaper to implement than analog inputs (voltages; currents). Unfortunately, sometimes discrete inputs don't have as much "information" available (such as the actual voltage levels, versus a minimum or zero voltage level, or even a maximum voltage level in some cases).

Also, historically it was much easier to predict the failure mode of most types of discrete input devices (pressure switches; temperature switches; etc.). And GE is all about reliability and in the past transmitters weren't so reliable and could fail full on as well as full off.

Also, historically providing power (24 VDC or 110/220 VAC) for transmitters was expensive, as were transmitters, themselves. As was the cost and complexity of analog input circuits. For reliability, it would be necessary to have redundant analog inputs which would also increase cost and complexity. So, mostly discrete inputs were used--and very successfully, too. Older Speedtronic panels (pre-digital versions) only had limited analog inputs and outputs: speed (frequency, and prior to that voltage); temperature (thermocouples--more reliable than RTDs and don't require additional power supplies, though they did require cold junction compensation circuits (be VERY thankful we don't have to do THAT any more!); one or two pressure transmitters (fuel gas intervalve (P2) pressure and axial compressor discharge pressure (CPD: Compressor-Pressure, Discharge); LVDTs; servo-valve outputs. Almost every other signal was a discrete input or -output.

And this brings me to say things need to slow down just a little, well, maybe a little more than that. I have just been given a rush assignment at work and I need to devote time to that (since I get paid at work, and I don't get paid for this endeavour). Also, you have asked several questions about terms and words and we haven't had a chance to cover them in any detail yet. We need to keep some focus here so that we don't get ahead of ourselves. We need to be sure that all questions get answered before we jump to another topic or rung.

Control systems have gotten more and more sophisticated over the last few decades. And they have gotten both cheaper--and more expensive. I can recall when USD140,000.00 for a Mark IV Speedtronic turbine control panel was a LOT of money--and it wasn't all that capable as a programmable control system. Now, Mark VIes are nearly two- to three times as much, but they do have a LOT more capability, and they are much more expandable (inputs or outputs can be "easily" added to the control system (easily is a relative term--much easier than the Mark IV!).

But, one has to remember that as the control systems changed and improved over the decades, GE-design heavy duty gas turbines basically remained the same. The turbine designers and packagers were loathe to change inputs and outputs (lots of changes to layout drawings, and schematics, and manufacturing practices and sourcing and warehousing and parts lists and manuals). It can become VERY expensive to change inputs and outputs just because the control system capability has improved.

And, it's one of the things that have made GE-design heavy duty gas turbines so reliable and so desirable: They don't change very much. They are pretty constant things in a very fast-changing world. They are RELIABLE--when they are operated and maintained properly by people who are properly trained and have access to quality parts and services. The control philosophies GE has employed over the years have proven to be very robust and very scalable (meaning that as GE-design heavy duty gas turbines have gotten larger and more powerful the control systems were able to be expanded to maintain similar operation and protection philosophies and methods). So, when you ask, "Couldn't this be done with a COMPare block?" one has to think back to how things have evolved to the present condition when someone can ask a question like that.

Imagine how many wires would be have to be used to interconnect all these devices to a single control system. Imagine how complicated and large such a control system would have to be. I don't know about you, but I LOATHE European-style, high-density terminal boards--even when appropriate sized wires are used on them. I prefer to have terminal boards that have to use a voltmeter easily and without fear of shorting or grounding, and where I can see terminations visually and where I can handle wires for troubleshooting and repair purposes. And, you're proposing even more wires and more terminal boards and more printed circuit cards and more complexity.

Anyway, I'm enjoying our time and this journey, but I have to limit my time for the next couple of weeks. As I said before--don't try to ingest all of this right now, immediately. That's the great thing about this forum: it will be here for a long time. And the things that are written here will be here for a long time. And you can refer to them as your understanding grows. And you should be reading and re-reading them over time as your knowledge and experience grows. It's a LOT of information to try to take in all at once--we haven't even touched on inversion masking! And we haven't finished the start-check permissives. And we haven't started the trips!

So, let's dial it back a little bit, and let me get caught back up at my day job, and finish one rung before we start another. There's always time for more questions.

5 out of 5 members thought this post was helpful...

Neo,

As for that second description of L3STCK0, GE is trying to use the same sequencing with slight modifications for all heavy duty gas turbines. Makes sense, right? If it works, why change it? And it works. Has for decades. Again, it's one of the things that make GE units so desirable and so reliable--the operation and control philosophies have not changed much over the years and it's very reliable.

That Comment from the application code is supposed to be for the requisition engineers who put the application code together in the factory. Sometimes (often) those engineers don't really have any field experience at all, and they make silly Comments. That's a silly Comment.

As for L3STCK1. You made a pretty huge mistake on the first signal, l26qn. Why would you want to start a turbine if: "the lube oil tank temperature is lower than setpoint" (your words from the sentence for L3STCK1)?

l26qn is a logic "1" when the L.O. Tank temperature is normal. It's driven by a discrete input from a temperature switch, 26QN-1. The switch contacts are closed when the tank temperature is "normal" (whatever the switch setpoint is from the Device Summary drawing, usually above approximately 60 deg F). And when the switch contacts are closed, l26qn will be a logic "1". This discrete input is NOT inverted. (We'll get to inversion masks shortly, but I want to get you started thinking about and anticipating the concept.) There will be a Process Alarm to indicate the L.O. Tank Temperature is Low.

L28FDSCK is a signal that is a logic "1" when none of the flame detectors is indicating flame when the unit is not running. And, one doesn't want to start a turbine when one or more of the flame detectors indicates flame when fuel isn't flowing.... There will be a Process Alarm to say the flame detectors are not in a ready-to-start condition.

L43O. The contact is normally closed, and L43O is a logic "1" when OFF mode is selected, so to have power flow through the normally closed contact L43O would have to a logic "0", or when OFF mode is NOT selected. Here's the ONLY start-check permissive that doesn't have a Process Alarm to alert the operator. Why? Because one doesn't need a READY TO START indication if the unit is in OFF mode. In other words, to get a READY TO START indication the operator has to select CRANK, FIRE, AUTO or one of the other available modes, but when OFF is selected the unit can't be started anyway. It's not a alarm condition when OFF mode is selected. So, operators just have to know: When they want or need a READY TO START they have to be in some mode other than OFF.

L43O doesn't come from the HMI. The HMI sends a command to the Speedtronic to switch to OFF mode, and if all of the permissives are satisfied to allow OFF mode to be selected then logic signal L43O is set to a logic "1". The HMI doesn't do any control or protection--it just sends commands to the Speedtronic, and monitors the operation of the unit (via signals from the Speedtronic), and, of course--it displays alarms from the Speedtronic. LOTS of alarms. Too many alarms, most would say--but that's because of poor configuration and/or poor maintenance or lack of understanding or just lack of response to alarms. Most operators, and their supervisors/managers, just don't pay any attention to any alarms as long as the turbine runs and doesn't trip. They think the Speedtronic will protect the turbine and trip it if it's necessary--and for the most part, it will. But there are some conditions that require operator action, and most operators (and technicians--and operations supervisors/managers) don't know when an alarm is indicative of a possibly larger problem. And, that's just poor training--and lack of personal motivation--both of which are permitted in too many plants.

L14HR is a logic "1" when the unit is at rest, or when it's at zero speed. MANY people look at the logic that drives L14HR and they see that it doesn't actually change state at 0.000 percent speed, but something slightly higher, and they think that's wrong (??!!!??!) and so they change it to 0.000% and then the Speedtronic doesn't work. Passive speed pick-ups aren't very good at very low RPMs and that's why the speed level isn't set at exactly 0.000% (0 RPM). I think it's set for something like 3 RPM, which is just fine for this purpose--which is to protect the jaw clutch from being damaged if it's engaged when the turbine shaft is spinning. That's (probably) why your unit has to wait to get down to "zero" speed to start--because it has a jaw clutch which shouldn't be engaged when the turbine shaft is still spinning (and 3 RPM isn't very fast!).

L86HD. This is a condition and Process Alarm that confuses many people--because of the alarm message text: Hydraulic Protective Trouble. For present-day GE-design heavy duty gas turbines this alarm has NOTHING to do with the Hydraulic System. It is related to the Trip Oil system, and the presence of Trip Oil pressure in the system when there should NOT be pressure. It is a lock-out--signified by the "86" in the signal name, which means that when the Trip Oil pressure condition is resolved a Master Reset is required to unlatch the alarm, and permit a READY TO START.

l12hblt is driven by a discrete input (the signal name is all in lower-case letters), and it's a logic "1" when the mechanical overspeed bolt is actuated. This input IS inverted, which means it is a logic "1" when the contacts of the overspeed bolt are open. As explained, the contacts of the L.O. Tank temperature switch, 26QN-1, are closed when the tank temperature is normal, and l26qn is a logic "1". It is NOT an inverted input. In this case, when the contacts of 12HBLT are open l12hblt is a logic "1"--which is the opposite (inverted) of what one would expect would happen.

Why does GE use inverted logic? It's a poor-man's method of something called "contact supervision." What's contact supervision? It's a method whereby the control system monitors discrete input circuits to ensure a wire in the circuit has not come loose, or has not been cut/damaged. Most contact supervision circuits use "end-of-line" resistors placed across the physical switch contact terminals and the control system is always checking to see if there is current flowing in the circuit--whether or not the switch contacts are open or closed. More current flows when the switch contacts are closed, and only a small amount of current flows when the switch contacts are open, and when no current is flowing the control system alarms to alert the operator to a bad circuit/wiring.

GE decided decades ago to standardize on circuits that were closed under normal operating circumstances, and opened to alarm or trip the turbine. To detect a closed contact, the circuit has to be intact (the wiring has to be good; the terminations have to be good) in order for current to flow--that's how the control system detects closed contacts. Open contacts result in no current flow.

Let's say the overspeed bolt limit switch contacts were configured to close when the overspeed bolt actuated (because of a turbine overspeed). And, let's say that one of the wires of that circuit had come loose from its crimp and had fallen away from the terminal. If the turbine oversped and the bolt limit switch contacts closed the control system would never detect the contact had closed--because of the disconnected wire. No current would flow in the circuit when the overspeed bolt contacts closed, so the control system would never know the contacts had closed. NOT good.

Now, let's say the overspeed bolt limit switch contacts were configured to open when the overspeed bolt actuated. Under normal circumstances, when the overspeed bolt limit switch contacts were closed current is always flowing in the circuit and the turbine thinks everything is just fine. And, let's say the turbine is running just fine at 73.4% of rated load, and suddenly one of the wires in that circuit vibrated loose from its crimp and became disconnected (it doesn't have to be a sudden disconnection--it just sounds better to say "suddenly"...). Even though the overspeed bolt limit switch contacts are still closed (there was no overspeed), because the circuit is now open there is no current flowing--just like if the switch contacts had opened. If the control system interprets no current flow as bad then it can take appropriate action, alarm and/or trip. In this way, the operator, and the technician, are aware of a bad circuit--could be a failed switch, just as easily as a loose wire, but the circuit is not intact and that's not a good condition under any circumstances.

So, GE's answer to ensuring that circuits are in good condition (before there was even contact supervision available in any programmable control system) was to "invert" the input. In this way, the signal goes to a logic "1" when the external circuit is open (no current flowing). The signal names are generally chosen to indicate when there is a problem (alarm or trip), and this matches the inversion philosophy--a logic "1" when the external circuit is open.

This is big one: inversion masking. Lots of people--myself included for years--used to say it was done to be "fail-safe." That's one way to think of it (not a good way in my opinion, because it doesn't really describe how or why--it's just a quick answer that sounds good).

Now, some people will say, "Well--if the turbine alarms or trips every time a wire comes loose, that's not very reliable!" And, they would be right. Wires should not come loose, but they do. Switches should not fail, but they do. So, GE's answer to that was to use redundant switches. It's not likely that two wires will come loose at the same time, or two switches will fail at the same time. But, if either did happen, then that's certainly a condition that should be resolved. But, if a wire comes loose or a switch contact fails in one of two redundant circuits and the logic (application code) requires two open circuits to alarm or trip the turbine on a serious fault then the turbine won't trip. GE also wrote logic to alert the operator/technician to a "disagreement" between redundant discrete inputs so the problem could be investigated and resolved.

So, it's about reliability. Making sure that circuits and switch contacts are serviceable and can and will alarm or trip on serious trouble. Inversion masking is something that generally takes some time to "absorb" and comprehend, but once one internalizes the concept and the practice its something that helps understand and improve lots of other aspects of control and automation. And, can help explain a lot of nuisance alarms and trips on other systems where a standard wasn't adopted and followed (and it happens a LOT in many control systems!).

Re-stating the sentence for L3STCK1:

"When the L.O. Tank Temperature IS normal AND when the flame detectors ARE in a ready-to-start condition AND when OFF mode is NOT selected AND when the turbine shaft IS at zero speed (at rest) AND when there is NOT a Trip Oil pressure problem AND when the mechanical overspeed bolt limit switch is NOT de-actuated THEN L3STCK1 will be a logic "1"."

That should take care of L3STCK1.

One more comment about l2hblt--it doesn't trip the turbine. This logic signal does NOT (and SHOULD NOT) trip the turbine. It's simply a limit switch that indicates when the mechanical overspeed bolt has been actuated (which de-actuates the limit switch). The mechanical overspeed bolt will "dump" Trip Oil pressure--which is what trips the turbine. The limit switch just says, "The mechanical overspeed bolt is NOT actuated," or, "The mechanical overspeed bolt is in the RESET position, ready to indicate when the bolt has been actuated." Which is the position the mechanical overspeed bolt needs to be in to start the turbine.

Why shouldn't this limit switch be used to trip the turbine in the Speedtronic turbine control panel? Because, it's a single limit switch--there's no redundancy. If it fails, vibrates loose, or a wire is disconnected, then if this input is used to trip the turbine--it will trip the turbine. It's extremely rare that a single discrete input will be used to trip the turbine--extremely rare. It reduces reliability (using a single switch). The only purpose of this switch is to indicate the overspeed bolt has been actuated--or, that is has not, as it's being used in the L3STCK1 rung.

Now, have we satisfied all your queries about relays and lock-outs and such?

Do you want to spend any more time on L3STCK1 before proceeding to L3STCK2? If not, let's continue.

Do you have any questions about inversion masking? (You can have questions about it later, too. But if you have them now, let's try to answer them now. It's a very important concept, and it's key to troubleshooting and understanding GE turbine control systems--at least the digital ones.)

Let me know if you're okay with what we're doing here. Is there a way to make it easier? Or better?

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

CSA,

Very glad to receive your response. I appreciate your patient and detailed reply.

I have been enjoying this journey with you as your comment is always enlightening and helpful.
You are a very patient and excellent teacher indeed.

You asked me whether i am okay with what we are doing, and my answer is yes,certainly.

And you asked me if there is a way to make things to make things easier. I think i should do some adjustments to make this journey easier for you.

1) I think i should focus on the main line,like present i should focus on L4S. I should set some questions that are not important at present aside, as we will have opportunity to discuss those questions latter (I wish:))

2) If your comment wanna to cover every side of a signal ,it will take a lot of time and effort of you, and i think it will disturb your day work. In order to avoid this situation, i think it will be better if you just comment the important information i should know at this present.

3) We could keep in touch every day, but just examine no more than one rung. And i will split my response my reply in several section, and if you are busy, you can just reply one of them,and continue next time.

In general, I think this journey is vary exciting, but it is difficult to start, but i think it will be easier if we continue.

And thanks again for what you have done as i and this forum don't pay :)
-----------------------------------------------------------------------------------------------------
1) As to L3STCK1,I made a pretty mistake about l26qn.
I thought that the toolbox description refers to the logic 1 situation.

l26qn=Lube oil tank temperature low.
l26qn L3STCK1
-------||--------......------()

So i think when lube oil temperature is lower than set point ,it will be logic 1.

2) I do have questions about inversion masking, like when we should use inversion masking.Why l26qn is not inversed when l12hblt has to be inverted??? Does it related to the type of relay,NC or NO.How it helps us to read application code.

I think take examples would make things easier to understand.

----------------------------------------------------------------------------------------------------
I think we should keep on moving, and i'll just write down the rung and examine it next time.
L86CB L4Y L3BHSTCK L30CC_STCK l33cl1 l45fp1 l27f
--------|/|-------||---------||---------|/|------|/|-------|/|-----|/|--------()
| |
| |
--------------------
true

L86CB = Surge protection trouble startup lockout;
L3BHSTCK = Comp operating limit BH start check perm logic;
L30CC_STCK = Fire protection trouble-GT start inhibited;
l33cl1 = Fire protection aux/turb/laod compt CO2 locked;
l45fp1 = Fire protection aux/turb/laod compt fire pre-detec;
l27f = Fire protection trip relay undervoltage;
----------------------------------------------------------------------------------------------------

Best regards
Neo

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

Neo,

>1) I think i should focus on the main
>line,like present i should focus on L4S.
>I should set some questions that are not
>important at present aside, as we will
>have opportunity to discuss those
>questions latter (I wish:))

If you have questions, let's try to answer them. If we need to come back to them later, we can. I do believe, though, that the more we continue the more things will become clearer--but, if the questions are preventing you from understanding something let's try to answer them.

>2) If your comment wanna to cover every
>side of a signal ,it will take a lot of
>time and effort of you, and i think it
>will disturb your day work. In order to
>avoid this situation, i think it will be
>better if you just comment the important
>information i should know at this
>present.

I think the important thing to get out of this exercise is how to "read" signal names and logic (rungs). DO NOT trust the longname description from Toolbox--just as with l26qn. When you wrote the sentence for the rung, it doesn't make sense to start the turbine with low lube oil tank temperature. You're saying, "If I can't trust the longname description in Toolbox, what can I trust?" Well, you have to analyze the information in front of you, and use any other resources you have to make sense of the situation.

For example, if you went to the VCRC input where 26QN-1 is connected, you would see the input is NOT inverted (it's "Normal"). And, if you went to the Device Summary document, which lists the setpoints for most of the devices provided with the turbine and auxiliaries (but, unfortunately, not all of them....) you would see the switch is (likely) set for 60 deg F (approx 16 deg C) INCreasing, and the NO (Normally Open) contacts of the device are to be used for the indication. This means that as the L.O. Tank Temperature increases above approximately 60 deg F the NO contacts will close. (The Device Summary should also list the DECreasing setpoint, something around 50 deg F, for a deadband on the switch of approx. 10 deg F. This means that once the L.O. Tank temperature had risen above 60 deg F, closing the NO contacts, that the L.O. Tank temperature would have to drop below approx. 50 deg F to cause the NO contacts to open, or "reset" as many people like to say--meaning go back to the "un-actuated" state.)

So, knowing that the input is NOT inverted, and that the switch contacts are closed above approximately 60 deg F, one can deduce that the longname description of the signal is wrong--that is, it does NOT describe when the signal name is going to be a logic "1".

You asked why this input is not inverted, but l12hblt is inverted. The input could have been inverted, and it would work just fine. Of course, the signal name would be exactly opposite of what it should be because it would be a logic "1" when the L.O. Tank temperature was less than normal. Sometimes these things, even though they could go one way or the other (with a signal name change to make it easier) are just continued for decades--and this is one of them.

I believe if you will post the L26QN_ALM rung (I'm guessing at the alarm signal name; it will likely be different--unless I am very lucky today) you will see it looks something like this:

     l26qn         L26QN_ALM
-----|/|-------------( )

This rung, if it matches your application code, is a violation of another one of GE's control philosophies: That the logic that drives an alarm should be a logic "1" to make the alarm active. Do two wrongs make a right? In this case, it seems to. ;-) We learn to live with it.

A former colleague of mine used to say, "This ain't rocket science." And, it's not. Does it have to be exact? No. Should it be exact? It would certainly help. Is it critical to proper operation of the unit? No. Would it take much to fix it? No--but, at GE there is no one who really understands all of stuff and is in charge or reviewing it to be sure it's accurate and consistent and so long-standing mistakes like this just keep getting repeated, decade after decade. Even if someone realizes it should be changed, that person likely is afraid to do so--because most of the people writing the application code have little or no hands-on, field experience.

And yet, someone has changed the longname signal description--because for decades it was always "Lube Tank Temperature Normal", and in the application code at your site it's "Lube oil tank temperature low" (which is the alarmed condition of the input--the one that will prevent a READY TO START....). Again, the people who really do understand this stuff at GE realize--it's not critical. It's always been that way. Should it be changed? Probably. But, "If it ain't broke, don't fix it." The circuit has worked for decades even if it's not exactly as per philosophy, so it just gets neglected.

Anyway, I can't read the next rung as you wrote it--you clicked on 'Submit Post' with a mistake in the html tags (you used /pre BEFORE and after the text; it needs to be pre before, and /pre after). Please correct the text and re-submit. You also forgot to put L4Y's longname description in the list of signals in the rung.

One of the reasons I'm spending a little more time on signal descriptions is that a lot of other people read these posts, and it might help them to understand GE-design heavy duty gas turbine operation and control philosophy if there is a little more detail. So, please be patient with me.

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

CSA,

You said "I think the important thing to get out of this exercise is how to "read" signal names and
logic (rungs)."

Ok, i will keep this in my mind.
------------------------------------------------------------------------------------------------------
I'm still confused about the concept of inversion masking.
You said "So, GE's answer to ensuring that circuits are in good condition (before there was even
contact supervision available in any programmable control system) was to "invert" the input."

Just take the signal l26qn for example, the temperature switch contact is closed(logic 1) under normal operating circumstances,and when the circuit fails, l26qn will turn to logic 0. So, it has
the function of circuit supervision.

So why inversion masking.

As the same to signal l12hblt,if the circuit fails,it will become logic 0.

Again why should the l12hblt be inverted.

"GE decided decades ago to standardize on circuits that were closed under normal operating
circumstances, and opened to alarm or trip the turbine."

Does that mean logic 1 refers to normal operating circumstance, and logic 0 to alarm or trip the turbine.

"For example, if you went to the VCRC input where 26QN-1 is connected, you would see the input is NOT inverted (it's "Normal").

How is one signal inverted,in hardware way or software way. If it is in software one, a signal can be inverted like this:


prestate poststate
( )---------|/|-------( )

------------------------------------------------------------------------------------------------------
"You asked why this input is not inverted, but l12hblt is inverted. The input could have been inverted, and it would work just fine. Of course, the "signal name" would be exactly opposite of what it should be because it would be a logic "1" when the L.O. Tank temperature was less than normal. Sometimes these things,even though they could go one way or the other (with a signal name change to make it easier) are just continued for decades--and this is one of them."

I am confused about "sigal name",the name of signal? If does mean name of signal, i think whether or not the signal is inverted, is has no effect on signal name,just a name.

So, this confuses me .
------------------------------------------------------------------------------------------------------
In one reply, i typed one rung below:

 
L45FP_STCK L3STCK
---.....------|/|---------()

The contact sense of L45FP_STCK is typed wrong,Which should be:

L45FP_STCK L3STCK
---.....------||---------()

You found that mistake,and deduced that either an incorrectly chosen name or the contact sense is typed wrong.

How did deduce it?

And you said the signal name indicates this signal will be a logic "1" when the fire protection circuit is ready to detect a fire.

How did you know it is a logic "1" not a logic "0" when the fire protection circuit is ready to detect a fire?

Those are the questions bother me a lot, and maybe it is good to deal those questions right now.And i hope it will not bother you too much as some of them are silly.
------------------------------------------------------------------------------------------------------


L86CB L4Y L3BHSTCK L30CC_STCK l33cl1 l45fp1 l27f L2STCK2
--------|/|-------||---------||---------|/|------|/|-------|/|-----|/|--------( )
| |
| true |
--------------------

L86CB = Surge protection trouble startup lockout;
L3BHSTCK = Comp operating limit BH start check perm logic;
L30CC_STCK = Fire protection trouble-GT start inhibited;
l33cl1 = Fire protection aux/turb/laod compt CO2 locked;
l45fp1 = Fire protection aux/turb/laod compt fire pre-detec;
l27f = Fire protection trip relay undervoltage;
I will examine this rung next time.

Best regards
Neo

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

Neo,

It would seem after you most recent post that inversion masking is becoming clearer to you. Yes; the exact purpose of inversion masking is to make the logic signal associated with a discrete input (DI) a logic "1" when the contact--or the circuit--is open. And, if the signal name is chosen correctly it will describe the condition when the contact is open.

And, yes, you are correct--l26qn is a violation of that philosophy and could have been configured to be inverted IF the signal name had been chosen to be something like 'l26ql' (except, that signal name is used on many older turbines.... so it would have had to be something similar, but different). And then the L3STCK1 rung could have been written:


l26ql L3STCK1
------|/|------ - - - ----( )
and the Low L.O. Tank Temp Low alarm rung could have been written:

l26ql L26QN_ALM
------| |-----------------( )

I presume you used 'View | Reports... | I/O Report' to find the information you posted with the inversion mask and the description.?.?.? (Though I don't know where that description came from in Toolbox.... it's very odd, indeed. But, stranger things have been coming out of Belfort and Hyderabad--much stranger things.)

For the Mark VI and Mark VIe, that report works fine because it actually looks at every I/O point and correctly reports the configuration (inversion mask; signal scaling; etc.). But--it does NOT work for the Mark V. The I/O Report is >>>NOT<<< only looks at the actual I/O Configuration when the report is first created--and after that, if any changes are made to I/O Configuration or location a conscientious person has to manually edit TC2KREPT.TXT to make the appropriate changes. While the Mark V I/O Report is probably 97.9% correct, it always seem like when it's late on a Saturday night and someone is relying on it for proper information--it's usually not right for the I/O point being worked on. (Sorry; I needed to do that for the people with Mark Vs reading this.)

It should also be noted that an input is NOT configured to be inverted or normal via this report. It is done at the I/O card level (usually a VCRC for a Mark VI).

But, you do seem to be getting the correct idea here. When you find what you believe to be a violation of GE's control philosophy, should you make the appropriate modifications to make it comply with GE's control philosophy? No. NO. NO. Emphatically, NO! You use GE's fall-back control philosophy: "If it's not broken, don't break it."

I'm still confused by the 'true' "element" in parallel with l33cl1 and l45fp1. Is it a normally open contact that is in parallel with the two DIs? If so, it's a really SAD and shameful method of "deleting" the two contacts from the start-check rung. Perhaps it was done temporarily (I'm trying to give the commissioning engineer the benefit of the doubt here), but it's still very, very sad. I wonder what the alarm rungs for those DIs look like??? Are there normally open 'false's in those rungs, or normally-closed 'true's? Do the rungs even exist?

Anyway, you didn't write your sentence for the rung....

As for how I deduced (makes it sound very sleuth-like!) the errors in signal naming or contact sense, it is really just experience--and lucky guessing. A very well-respected person who retired from GE many years ago said at his retirement dinner in response to questions about how he'd been so successful, "The harder I worked, the luckier I was. And, I'd rather be lucky than good." That's kind of how I feel--one can be good and unlucky, and that can be fatal. I'd rather be lucky, and be thought good--and the way to be luckier is to work hard, study hard, reflection, and constant review and reflection (kind of like continual process improvement in many manufacturing/quality programs. I think reflection is one of the most often overlooked qualities of success--in the olde days, people used to keep journals. If you've ever read the journals of famous people (who were considered successful and pre-eminent in their field) those journals describe lots of mistakes, reflection, successes, and reflection, and ponderment, and reflection. A quiet place to reflect, to consider what was and what could have been and what could be is really inspiring, invigorating and critical to getting lucky (improvement and "goodness").

So, again, as I've suggested in the past: Continue to look at this post, and others, and continue to develop your understanding based on your experience working with the equipment. Your understanding will grow, exponentially at first (though it seems difficult), and the respect of your peers and supervisors will also grow. The mistake that happens in a lot of places is that when someone gets technically good in their job they get promoted--and they don't mentor people who are coming up behind them to pass along the benefit of their knowledge. Too many people think, "Why should I make it easy for them; I had to struggle to get to where I was--no one made it easy for me. I made a lot of mistakes along the way, and I learned from those mistakes. Let others do the same."

I'm paying back what I was fortunate to have been the beneficiary of decades ago. Please do the same, Neo. Maybe not this particular field, but pay it back.

It really is a good feeling.

So, write your sentence and ask your questions. We've still got quite a distance to cover here.

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

CSA,

"The mistake that happens in a lot of places is that when someone gets technically good in their job they get promoted--and they don't mentor people who are coming up behind them to pass along the benefit of their knowledge. Too many people think, "Why should I make it easy for them; I had to struggle to get to where I was--no one made it easy for me. I made a lot of mistakes along the way, and I learned from those mistakes. Let others do the same."

I appreciate what you said above,and you are a good teacher not only technically.

From this point, i am lucky :)

Last time i didn't write the rung, because i am afraid it will disturb your day work if too much things you have to deal with.

I'll try to write sentence in several hours, and be patient with me. :)

Best regards.
Neo

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

CSA,

Here comses the L3STCK2:


L86CB L4Y L3BHSTCK L30CC_STCK l33cl1 l45fp1 l27f L3STCK2
--------|/|-------||---------||---------|/|------|/|-------|/|-----|/|--------( )
| |
| true |
--------------------

L86CB = Surge protection trouble startup lockout;
L3BHSTCK = Comp operating limit BH start check perm logic;
L30CC_STCK = Fire protection trouble-GT start inhibited;
l33cl1 = Fire protection aux/turb/laod compt CO2 locked;
l45fp1 = Fire protection aux/turb/laod compt fire pre-detec;
l27f = Fire protection trip relay undervoltage;

--------------------------------------------------------------------------------------------

L86CB is a logic signal that warns the operator a problem with the surge protection system:
1.IGV 2.Compressor Bleed Valve


L86CBA L86CB
--------||----------|------( )
|
L86TV |
--------||----------|
|
L30CBC_AL |
--------||----------|

L4 L14HS L520ONLINE L20CBX L20CBZ
-------||---------||---------||------------( )---------------(T)


l33cblO L86CBZ L20CBA
--------||--------|------||-------( )
l33cb2O |
--------||--------|


L20CBZ is a logic 1 when the gas turbine is under normal condition(TNH>97% rated speed),and i think it is a command to close compressor bleed valve when it is logic 1.And if the valve is still open when L20CBZ is logic 1, then L20CBA is logic 1.

The same to L86CBC_AL. When the compressor bleed valve is required to open(L20CBZ is logic 0), but it is still closed , then L86CBC_ALM is logic 1.

I deduce it from the knowledge that the compressor bleed suction works when the gas turbine is under part load to prevent the compressor from surge.

If i knew nothing about surge protection, how can i know what does it mean when l33cb1o is logic 1,whether it refers the valve is open or closed? Or when L86CB is logic 1, it is a command to close the valve or open the valve?

From signal name and description form toolbox(but sometimes it is misleading)?

As to L86TV, it is a little weird.


L3IGVF2 L14HA L83BW L86TV
-------||--------||---------|/|---------( )

It means when the TNH >50% rated speed, csgv>35deg , and L83BW is logic 0,then L86TV is logic 1.

I am confused about L86TV,what deos it mean when it is logic 1.And is it related to surge protection. Besides, we had checked L3IGVF2 in L3IGVFLT in L2STCK0.

-------------------------------------------------------------------------------------------------

L3BHSTCK is a logic 1 when IBH system is in trouble.


L3BHF1 L3BHF3 L3BHSTCK
----------|/|-----------|/|-----------( )

L3BHF1(bleed heat feedback trouble alarm) is not difficult to understand,for it is just like command not following.
L3BHF3 is a little complicated.


L3CPRAH L3BHF3
--------------||----------------|------( )
|
L3BHF1 L3BHF2 L14HS |
--------||-------||--------||---|
|
LCPRERR |
--------------||----------------|

The lockout logic is left out.

L3CPRAH = Ambient pressure indication high logic.
LCPRERR = Compressor operating limit control falut.

So when the inlet pressure is higher than the set point OR L3BHF1 and L3BHF2 is logic i when THN>97% rated speed OR CPR is reaching its max limit, then the L3BHF3 is logic 1.

Can you explain The L3BHF3 for me, am confused about it? How are L3CPRAH and LCPERR are related to IBH?

------------------------------------------------------------------------------------------------
L30CC_STCK is logic 1 when there is a problem in fire protection system.

l27f is a logic 1 when its voltage is low.

-----------------------------I-------------------------------------------------------------------

In conclusion,when surge protection system is normal, AND IBH system is normal,AND fire protecion
trip relay is not undervoltage,And fire protection system is normal,then the L3STCK2 will be a logic 1.

Best regards.
Neo

Neo,

I think there are some errors in the rungs and the explanations. Please review them and let us know what you find.

I'll get back when I can devote the required amount of time and the errors have been corrected.

Thanks!

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

>CSA,
>
>Here comes the L3STCK2:


> L86CB L4Y L3BHSTCK L30CC_STCK l33cl1 l45fp1 l27f L3STCK2
>--------|/|-------||---------||---------|/|------|/|-------|/|-----|/|--------( )
> | |
> | true |
> --------------------

>L86CB = Surge protection trouble startup lockout;
>L3BHSTCK = Comp operating limit BH start check perm logic;
>L30CC_STCK = Fire protection trouble-GT start inhibited;
>l33cl1 = Fire protection aux/turb/load compt CO2 locked;
>l45fp1 = Fire protection aux/turb/load compt fire pre-detec;
>l27f = Fire protection trip relay undervoltage;
>--------------------------------------------------------------------------------------------
>
>L86CB is a logic signal that warns the operator there is a problem with the surge protection system:
>1.IGV 2.Compressor Bleed Valve

> L86CBA L86CB
>--------||----------|------( )
> |
> L86TV |
>--------||----------|
> |
> L30CBC_AL |
>--------||----------|

L86CBA = Cool seal air comp bleed/valve pos trouble close (what is cool seal air)
L86TV = Inlet guide control troubles
L30CBC_AL=Comp bld valves failure to open

> L4 L14HS L520ONLINE L20CBX L20CBZ
>-------||---------||---------||------------()---------------(T)
(PS:I made some simplifications.)

L520ONLINE = Unit online (confusing)
L20CBX = Cool seal air Air comp bleed 3 way valve ctrl signal

l33cblo L86CBZ L20CBA
--------||-------- |------||-------( )
l33cb2o |
--------||---------|

l33cb1o = cool seal air comp bleed valve#1 pos switch open
l33cb2o = cool seal air comp bleed valve#2 pos switch open

L20CBZ is a logic 1 when the gas turbine is under normal condition (TNH>97% rated speed), and i think it is a command to close compressor bleed valve when it is logic 1. And if the valve is still open when L20CBZ is logic 1, then L20CBA is logic 1. When the compressor bleed valve is required to open(L20CBZ is logic 0) while it is still closed, then L86CBC_ALM is logic 1.

I deduce it from the knowledge that the compressor bleed suction works when the gas turbine is under part load. And it is one means to prevent the compressor from surge.If i knew nothing about surge protection, how can i know what does it mean when l33cb1o is logic 1,whether it refers to the valve is open or closed? As to L86TV, it is a little weird.


> L3IGVF2 L14HA L83BW L86TV
>-------||--------||---------|/|---------( )

L3IGVF2 = IGV-Vanes open alarm
L83BW = water wash offline washing start check
L14HA = HP accelerating speed signal

It means when TNH is above 50% rated speed,csgv>35deg , and L83BW is logic 0,then L86TV is logic 1. I am confused about L86TV,what oes it mean when it is logic 1.And how is it related to surge protection. Besides, we had checked L3IGVF2 in L3IGVFLT in L2STCK0.
>-------------------------------------------------------------------------------------------------
>L3BHSTCK is a logic 1 when IBH system is in trouble.


> L3BHF1 L3BHF3 L3BHSTCK
>----------|/|-----------|/|-----------( )

L3BHF1 (bleed heat feedback trouble alarm) is not difficult to understand,for it is just like command not following.
L3BHF3 is a little complicated.

> L3CPRAH L3BHF3
>--------------||----------------|------()
> |
> L3BHF1 L3BHF2 L14HS |
>--------||-------||--------||---|
> |
> LCPRERR |
>--------------||----------------|

>The lockout logic is left out.
>L3CPRAH = Ambient pressure indication high logic.
>LCPRERR = Compressor operating limit control at max error.
>So when the inlet pressure is higher than the set point OR L3BHF1
>and L3BHF2 is logic 1 when THN>97% rated speed OR CPR is reaching
>its max limit, then the L3BHF3 is logic 1.Can you explain L3BHF3 for
>me, I am confused about it? How are L3CPRAH and LCPERR related to IBH?
>------------------------------------------------------------------------------------------------
>L30CC_STCK is logic 1 when there is a problem in fire protection system.
>l27f is a logic 1 when its voltage is low.
>-----------------------------I-------------------------------------------------------------------
>In conclusion,when surge protection system is normal, AND IBH system is normal,AND fire protection
>trip relay is not undervoltage,And fire protection system is normal,then the L3STCK2 will be a logic 1.

Best regards.
Neo

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

Neo,

I don't see much in the way of correction; the 'ltrue' still doesn't seem to have a contact (NO or NC). L4Y is not listed.

The axial compressor bleed valves MUST be open prior to a start of the gas turbine, otherwise it's likely the unit will suffer extremely high vibrations as a result of compressor problems during starting which could even result in damage to axial compressor blading (stationary and rotating). The condition that can occur during starting--and shutdown--of the axial compressor is commonly referred to as surge and/or stall and occurs when the air flow through the compressor doesn't move as it should--as if it's blocked. This is true of most axial compressors, not just those of GE-design heavy duty gas turbines.

The limit switches on the bleed valves are designed to be actuated when the bleed valves is fully open. When the bleed valves are commanded to open there is a timer (usually 11 seconds) that starts, and if both bleed valves are not fully open by the end of the timer then the turbine is tripped and a start is prevented until the condition is corrected and a Master Reset is initiated. (The same is true of closing the compressor bleed valves--there is a timer that starts when they are commanded to close and if neither of them moves from the open position then there is an alarm, and on most DLN combustor-equipped units there is also a trip (which requires a Master Reset to clear once the condition has been resolved). Some newer units (especially the F-class turbines) have limit switches for BOTH the open and the closed positions.

I was going to write that the signal name descriptions are getting very strange, but then I remembered this unit is a Frame 6B which means the Belfort Bunch has their brand all over the "logic."'Cool seal air' probably refers to 'Cooling and Sealing Air' which is the P&ID that the axial compressor bleed valves are shown on. But, the axial compressor bleed valves have little (if anything) to do with the cooling and sealing air system. Once again, instead of clarifying things, Belfort is actively making them less clear and more confusing--needlessly. "If it's not broke, break it," seems to be their driving philosophy. Or, probably, more truly, "If it's clear, de-clarify it; if it's simple, complicate it."

L4Y is a timer that is a logic "1" one second AFTER L4 is NOT a logic "1" (an "inverse" timer). It's used here just to provide at least 1 second after a trip during starting before another start might be initiated--and it also prevents a start if L4 is already a logic "1".

The L3BHSTCK logic is also something which seems to have been "improved" by the Belfort Bunch. An excellent example of this is confusion created by the L3BHF3 rung you are experiencing. I don't believe the 96AP-n transmitters are used for IBH (I believe they are used to trigger the L3CPRAH logic), and L3CPRERR used to be used to detect a problem with the CPR calculation--which isn't directly related to IBH, either--just to the calculation of the axial compressor pressure ratio which is used to determine exhaust temperature control limit and protection. Inlet Bleed Heat (IBH) is a very poor name for the function it provides--compressor protection when the IGVs are operating at reduced angles so the turbine can operate in Premix Steady-state combustion mode at lower loads than would otherwise be possible. So, without being able to see the logic driving both signals (L3CPRAH and L3CPRERR) it's not possible to say for sure exactly what is being attempted with those two conditions driving L3BHF3. The other parallel string, L3BHF1 and L3BHF2 are blocked from actuating L3BHF3 below 95% speed by the L14HS logic, so, it just adds to the complication and muddling of the rung and it's use in the L3BHSTCK rung. It's understandable that the turbine should not be started if the ambient pressure transmitters are not working properly (the L3CPRAH function, I believe), but previously the L3CPRERR was also not enabled below 14HS (may still be), but the whole thing is just a mess to decipher and make sense of and try to explain. Sorry; I wish it weren't so, but this is a perfect example of Belfort thinking and logic.

L30CC_STCK is almost another Belfort kludge, except that a 30 device is the ANSI device number for an alarm relay or device so it almost makes sense that if this signal is a logic "1" the start-check should be blocked. The bad part about this signal name is the STCK at the end--which conflicts with the whole L3STCKn naming convention--but, this is the Belfort way: complicate and confuse whenever possible. The concept here is that the turbine should not be started if the fire protection system (usually a CO2 system--hence the "CC" part of the signal name) isn't capable of detecting or extinguishing a fire.

The next two signals, l33cl1 and l45fp1, appear to be coming from locking devices on compartment fire protection systems--which would be a logic "1" if either of them were prevented from being operated, which should be a start-check permissive. But, someone has seemingly (because it's not clear from your "drawing" of the rung) put a ltrue (NO) around them which effectively disables this part of the fire protection system logic. If there are no physical wires connected to the discrete inputs driving l33cl1 and l45cp1 then these signals should have just been removed from the application code (freeing-up a couple of discrete inputs for possible usage at some other time) and uncomplicating the start-check "logic." But, again, this is not per the Belfort way--so, complicate and confuse drives the mess.

Why l27f couldn't be incorporated into the L30CC_STCK logic is just, yet AGAIN, stupefying. 'Nuff said.

Finally, the L52ONLINE logic is a DLN relic. It usually goes to a logic "1" sometime after the generator breaker closes AND the unit is above some "minimum" load, sometimes 5 MW, AND the axial compressor bleed valves are closed. It's kind of unnecessary if the turbine trips of the axial compressor bleed valves aren't closed when the unit is above 14HS, but it seems to have a life of its own (part of the "if it's not broke, don't break it"--because it's not understood, not because it needs complication or confusion).

Wow! This rung was difficult; sorry. This is why it's really necessary to have paper copies of rungs with hand-written notes on them to help remember what these things are when one has to try to understand them--and if one has to go back to them in future years. Trying to figure this stuff out months or years later can be just as difficult as the figuring it out the first time--so notes are really helpful, now and in the future.

PLEASE make sure you are drawing the rungs properly and completely as we progress. We haven't even finished the start-check stuff, and we still have all of the tripping stuff to go through. So, clarity and accuracy is crucial to keeping on track.

CSA:

Thank you for your detailed reply.

1)We have dealt with L4Y before, that's why i didn't list its definition.

2)If is 'True',it is always a NO contact.

I have been occupied with work these days ,and i will reply to you as soon as possible.I hope you can comment on my understanding and answer my questions if it means something.In this way, i will get more interested in this journey.

And my next assignment is L3STCK3?

Best regards.
Neo

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

Neo,

Yes; I'm busy at this time, too, so I'm not devoting as much time to this as I'd like.

Yes; you're next assignment is L3STCK3.

2) I've seen some usages of 'ltrue' that were NC, not only NO. It can be either. If it's NO, then the contacts will be closed (because 'ltrue' is always a logic "1"); if it's NC then the contacts will be open.

There's also an 'lfalse', that's always a logic "0", and can be NO or NC.

To your questions:

a) Cooling and Sealing Air is air that's extracted from a couple of points from the axial compressor that's mostly used to cool various spaces, like wheelspaces. It's also used to pressurize other areas, such as bearing seals, in an effort to keep lube oil from leaking out of the bearings along the shaft. For more information, please refer to the Cooling & Sealing Air P&ID, as well as the System Description for the Cooling & Sealing Air system in the Service Manuals provided with the turbine and auxiliaries.

For some reason, the compressor bleed valves appear on the Cooling & Sealing Air P&ID, probably because there's not really anywhere else to put them.?.?.?

b) l33cb1o & l33cb2o are logic signals, driven by limit switches on the compressor bleed valves, and they are a logic "1" when the compressor bleed valves are fully open (the "o" at the end of the signal name stands for "open").

There is another very useful document provided with most GE-design heavy duty gas turbines called the Device Summary. It lists most (but not all) of the field devices and instruments provided on the turbine and auxiliaries by the packager. It typically does NOT list the devices provided with the generator (except for the low and low-low L.O. pressure switches) and exciter and generator controls, and quite often these days does not list some devices provided on skids supplied by subcontractors. But, it does have good information which can be very helpful and useful. It's most useful aspect is that it lists the settings for the majority of the pressure- and temperature- and limit switches on the unit.

c) L86TV is weird in the context shown, and it violates the concept of a lock-out device since it has no seal-in and doesn't use a Master Reset to unlatch the signal. L83BW is a logic signal that's a logic "1" when a water wash is being performed--usually an off-line water wash, but has been used for on-line water wash indication as well. Again, there are some messy logic signals in many Speedtronic control panels, and this appears to be another one. (I had no idea we were going to encounter so many on this journey! But, it's probably just as well since it's a journey of discovery and one discovers good things and bad things on most journeys, right?)

I think that covers most of the questions, or are there others I've missed?

CSA,

I am back :)

I will do my assignment as soon as possible.

Neo.

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

CSA,

Sorry for be absent for more than a week.

In the last rung, you explained that: LCPRERR used to be used to detect a problem with the CPR calculation--which isn't directly related to IBH, either--just to the calculation of the axial
compressor pressure ratio which is used to determine exhaust temperature control limit and protection.

It seems that LCPRERR is more related to tell whether the CPR is approaching the Cprlim.
--------------------------------------------------------------------------------------------------------------
Here comes the L3STCK3:


L4T L39VD3 L3TFLT LAUXGAS_PT L30IPFLT2 L3IPSTCK L3STCK3
------|/|------|/|---------|/|---------|/|----------|/|--------|/|---------( )

L4T = Master protective trip;
L39VD3 = Vibration start inhibit;
L3TFLT = Compressor discharge pressure fault alarm;
LAUXGAS_PT = Auxgas Press or Temp Detected at Meter Tube;
L30IPFLT2 = IP fault no flow detected-during transfer off aux;
L3IPSTCK=Inert purge system system start check;

I think L4T is an important signal name, but i have little knowledge about it. All i know is that if L4T is logic 1, then the gas turbine trips.

So i think all signals that will trip a gas turbine will finally go to L4T.And i think there is a connection between L4 and L4T.


L14HS L4 L14HSX
---------||--------------||-----( )
|
L14HSX L94X |
------||------|/|----

L94X = Startup check stop GT normal shutdown;
L14HS = HP operating speed signal;

A>B----|
| L14HSX L3TFLT
---------| |---------||-----------( )

A = CAKCPD(35psi)
B = CPD
L14HSX = Auxiliary signal to L14HS

If CPD is less than 35psi when gas turbine is under normal operation (L14HS is logic 1), then L3TFLT is logic 1 (indicates the pressure transducer is in fault?)

I was wondering the function of the L14HSX signal, and can L14HSX in the L3TFLT rung be replaced by L14HS?
I am confused with the signal L94X. In the toolbox, its description is: Startup check stop GT normal shutdown (startup or shutdown?). And i found 94 is related to tripping or trip-free relay in ANSI device number.


L39VD3_GT L39VD3
--------||------------( )
|
L39VD3_GEN |
--------||-----
|
L39VD3_LG |
--------||-----

According to the above rung,there are three groups of vibration sensors in this unit: one for gas turbine, one for generator and the last one for load gear. And if anyone of the sensor groups is faulty or disabled (qty of sensors in group faulty or disabled > = 1; > = (#sensors+1)/2; both sensors in any pair faulty or disabled.), then L39VD3 is logic 1. I referred to the L39VV7 block, and was confused about the difference with faulty and disabled. Whether a vibration sensor is fault or not is decided by HLTHn, while disabled or not is decided by ENABLEn.

LAUXGAS_PT

 
LFPAG0LL LAUXGAS_PT
-------|/|------------------( )
|
LFPAG0 |
-------||-----------
|
LFTAGI false |
-------||------||---
|
CA43P2 false |
-------||------||---

LFPAG0LL = auxgas supply pressure low low;
LFPAG0 = auxgas supply pressure detected;
LFTAGI = auxgas supply temperture detected;
CA43P2 = initiate P2 cavity blocking;

If the LAUXGAS_PT is logic 1, then there is a problem in the auxgas supply system. According the above rung, if the pressure is lower or higher than the setpoint, then it is presumed that the auxgas supply system has a problem. I think auxgas refers to the gas fuel, right? And FPAG in the signal name stands for something?

L30IPFLT2 and L3IPSTCK are related to purge system. As to my understanding, there is a need to purge before start a gas turbine in order to clear away the residual gas fuel in combustor.

In conclusion, if L4T is logic 0, and the vibration sensors works well, and CPD is more than 35 pisg when under normal operation, and there is no problem in auxgas supply system and inert purge system, then L3STCK3 is logic 1.

CSA,

I am waiting for your reply:)

Best regards!

Neo,

Sorry, I missed your post.

I also believe that the unit you are operating may be burning more than one gas fuel, based on some of the logic signals in the post (_IP--Inert Purge, for one). You didn't tell us about that.

Give me some more time to review your post.

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

Neo,

You are reading the Longname description for LCRPERR very literally--and that can be a mistake sometimes. As we've learned. If that logic signal has a rung, can you post it?

Your sentence for L3STCK3 is correct.

And you are also right: L4T is VERY important (we're headed there soon!). But, you are NOT correct in that every trip is not run to/through L4T--because there can be trips connected to <P> and from <P> (remember the overspeed/rate of speed change trips that is <P>'s primary function!). L4T is all of the turbine trips that come from <Q> (<R>, <S> and <T>)) and the application code running in <Q> and the trip inputs connected to <Q>.

The "connection" between L4 and L4T is:


L4S L4T L94T L4
---| |-----|/|------|/|----------( )
|
L4 |
---| |---

Remember? That's where we started: L4. We're now working on how L4S gets to be a logic "1" and when L4T is NOT a logic "1" and L94T is NOT a logic "1" then L4 will be a logic "1" (when L4S goes to a logic "1"--which it does for a few seconds at most).

Again, the whole FPAG (Fuel Pressure - Aux Gas) seems to be related to a second gas fuel, perhaps an "off-gas" from some process nearby that has some heat content that can be burned in the gas turbine--but the turbine can't be started on the aux gas, and the aux gas piping needs purging.?.?.?

I wouldn't be too shocked to find this is "max-case" logic meant for machines with dual gas fuel capability--and your unit doesn't have it, or maybe it was supplied with the intent of having it some day.?.?.? But, this is where I'm coming up with the aux gas stuff--these signals seem to be indicating that you didn't tell us about a second gas fuel capability, OR (perhaps more likely) it doesn't exist and was (sadly and almost criminally) left in the application code.

Hope this helps!

If you're questions about L3STCK3 have been answered, we can move on. Otherwise, let's get them answered to your satisfaction before we do (move on).

And if you have other questions (related) that have come up recently, let's deal with those here, too, and now.

I don't understand why you posted L14HSX, and then didn't discuss it all....

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

CSA,
Thank you for your reply,and you reply is always enlightening.
It seems that you know every thing, and most of your guess about this unit is right!

This is a PG6561B-L(MS6001B) gas turbine, and i think L is for low heat content fuel.

When it is under normal operation it burns BFG(Blast Furnace Gas) and COG (coal oven gas), BFG and COG do are "off-gas" from nearby steel plant. And BFG and COG are premixed(syngas). And this unit starts on light diesel oil.We can choose fuel in HMI from "syngas,distillate fuel and gas/distillate fuel mix".

And there is a IGCC module in toolbox,and i think it is related to the gas fuel system.

I have several questions:

How did you deduce these information from siganl names? What is IP stands for in L30IPFLT2?

Why this unit have to start on liquid fuel,low heat content? If we chosen syngas on gas turbine start by mistake, what will happen?

You said "but the turbine can't be started on the aux gas, and the aux gas piping needs purging". What does the purging
system for? I found this unit is equipped gas fuel and liquid fuel purging system.

I think the auxgas in application code is sygas,right? And it is weird, where is the primary gas?

Sorry for bothering you with so many questions,but it really haunts me.
Thank you.

Best regards!
Neo.

CSA,

I find it is not convenient to print CSP.

CSP will be split by page marker and the page is not fit into A4.

Best regards!

Neo

CSA ,
It seems that you do not respond as soon as before :(

What's wrong?

If you do not wanna go on this journey, you can just let me know. That't ok.

Neo
Best regards.

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

Neo,

I've been having computer hardware issues with my old and trusted desktop--which is the computer I use for writing the long missives for this thread. (It's too difficult to respond to this thread using a tablet--I don't have a keyboard for the tablet.)

I'm still keen to continue--and complete the journey--but I do, also, have a paying job that I must devote attention to. In this business one can never anticipate when something will break or someone will decide they want to upgrade their equipment this week--only to decide next week that it's too expensive and they want to keep their current equipment without doing any maintenance.

I don't understand the comment about printing the CSP. The designers of Toolbox never envisioned anyone would want to print the application code (it's CSP for the Mark V; sequencing for the Mark IV; and application code for the Mark VI and Mark VIe--isn't this fun?). So, while they made a half-hearted attempt at a Print function, they didn't do a very good job of it.

As I said, I use the MS-Windows capture hot-key sequences--and with Win7 and Win8.1 there's the 'Snippet' tool--to "grab" what's in Toolbox display and copy it to the Clipboard and then past the contents in a MS-Word or Wordpad document and then print that to make notes on.

There is just so much empty "white space" (wasted space) in the Toolbox and ToolboxST printouts and the way elements are displayed can be extremely confusing (again because of the half-hearted printing routine used in Toolbox and ToolboxST) that it's just not worth the effort unless one has LOTS of time, toner cartridges, and reams of paper.

As for the comments about how did I know the unit burned low-BTU gas fuel, well, from the Longname descriptions you provided which included the Inert Purge term.

Natural gas will always be the "primary gas fuel" even if the unit doesn't burn natural gas. Any other gas fuel--for the time being--will be the "aux" gas, and sometimes referred to as "syngas." I believe that portions of the purging sequence in your machine were likely copied-and-pasted from the IGCC unit control schemes (Integrated, Gasified Combined Cycle--the test units for trying coal gasification) as they use purging quite extensively in the gas fuel system(s).

Generally, the reason most turbines are started on "conventional" fuels is that there simply isn't enough heat content in the secondary fuel(s) ("aux" gas, in your case) to reliably start the unit. It works one day, but not the next--and usually because the heat content of the secondary fuel isn't consistent. So, the decision is made to start on a more consistent (conventional) fuel for reliability.

If the application code is written correctly, if you try to start on "aux" gas, it just won't allow the START to be initiated--most likely. And if it did, again, it might start today but then might not start tomorrow or next week on the "aux" gas.

Gas fuel purging is to remove the "aux" gas from the piping, usually for safety's sake--and ALSO to keep hot combustion gases from the other fuel (liquid fuel in your case) from entering the gas fuel passages and causing problems when running on liquid fuel.

Liquid fuel purging is also done for two reasons--to remove the liquid fuel from the fuel nozzles to prevent coking (carbonization of the liquid fuel by the heat from hot combustion gases when running on the "aux" gas), and also to ensure hot combustion gases don't enter the liquid fuel nozzles or atomizing air passages when running on "aux" gas.

GE is consistently inconsistent with it's use of words and terms--as are most other manufacturers in the world. Frankly, there are just too many people working on various parts of the gas turbine, the control system, and the auxiliaries and there's no one person or group that's making sure consistent words and terms are used throughout the documentation (including comments in the application code, the Control Specification, and System Descriptions, etc.).

The interesting thing to note here is that GE and packagers of its turbines sell a LOT aeroderivative gas turbines to military organizations around the world. And they have to provide documentation that is consistent and explicit. The US government, for example, will insist on seeing the documentation (training manuals; system descriptions; maintenance and parts manuals) BEFORE they will start receiving and inspecting equipment. This is because they want to be sure that operators, technicians and repair personnel have good-to-excellent documentation to work from when servicing this equipment at sea, or while on the ground (for aircraft)--especially in times of conflict. They don't call for a service person to come to fix the equipment; they have trained personnel to do that and they want to make sure the manuals and documentation their personnel have are very, very good.

Too bad the same thing doesn't happen for heavy duty gas turbines.... It's really too bad it doesn't. Their lives (GE field service personnel), the experiences of operators and technicians, and the work of mechanics would all be SO MUCH easier if the heavy duty units had manuals and documentation that's even half as good as the military documentation.

But, I digress.

What rung are you going to document next on our journey? (Realizing we both have jobs and lives, of course.)

CSA,

"As for the comments about how did I know the unit burned low-BTU gas fuel, well, from the Longname descriptions you provided which included the Inert Purge term."

Is the Inert Purge term special for low-BTU system? If one unit burns natural gas,purge system is still needed,right?

I happened to see a test bench application code.

The test bench application does't have IGCC module,and its GAS_LIQ_PURGE module has LIQ_NO_DLN and GAS tasks,while our application has IGCC module,but only LIQ_NO_DLN task in GAS_LIQ_PURGE module.

So i think you deduction "that portions of the purging sequence in your machine were likely copied-and-pasted from the IGCC unit control schemes as they use purging quite extensively in the gas fuel system(s)" is right.

I wondered that if an IGCC unit has an unique purge system?
And for our unit that burns low-BTU gas fuel, should its purge system be different from those that burns natural gas?

Maybe these questions are very boring, but i am still curious.
May it not bother you.

Best regards!
Neo.

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

Neo,
Usually, whenever a GE-design heavy duty gas turbine burns multiple fuels (even two different gaseous fuels) there are fuel purge systems. This primarily to ensure that there is no fuel in the system which is not in service which can accidentally ignite, and also one of the primary purposes of the purge system is to provide a flow of cooling air through the fuel system not in service. Another benefit of this flow of air through the fuel system which is not in service is that it prevents the backflow of hot combustion gases into the fuel system which is not in service and which can cause very serious damage to piping and components (especially fuel nozzles and flexible piping section).

Some fuels are very dangerous if exposed to oxygen, even atmospheric oxygen, so the purge is used to ensure that no unburned fuel is ever present in the piping.

A fuel purge system is a fuel purge system in my opinion. I don't think one fuel or process has a purge system that is that much different than any other--except when some inert gas is required to purge the fuel to avoid coming into contact with oxygen. These systems will be more complicated, necessarily so, because of the additional piping and regulators and valves and solenoids and such. I don't know if the low-BTU fuel at your site qualifies as such, but it could. Gas turbines are burning a lot of different fuels these days as people are looking to prevent flaring off-gases to reduce emissions--and to increase the efficiency of the process by utilizing available energy from hydrocarbons instead of just burning it or venting it.

Hope this helps!

Next rung in the L4 Journey, please?

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

CSA.

Very glad to receive your reply,and thank you sincerely for your engagement.I am not rich,or i am willing to pay you for this interesting journey:)
And if you are busy,just let me know. You know waiting is miserable.
I hate to quit and i wanna to go on this journey and finish it.
Thank you again for your help.
-----------------------------------------------------------------------------------------------------------
You missed this quetion below:



A>B----|
| L14HSX L3TFLT
---------| |---------||-----------( )

A=CAKCPD(35psi)
B=CPD
L14HSX=Auxiliary signal to L14HS

And i tried to find the differece between L14HS and L14HSX.

L14HS L4 L14HSX
---------||--------------||-----( )
|
L14HSX L94X |
------||------|/|----

L94X=Startup check stop GT normal shutdown;
L14HS=HP operating speed signal;


As for L3TFLT,if CPD is less than 35psi when gas turbine is under normal operation,then L3TFLT is logic 1.

I was wondering the function of the L14HSX,and whether can L14HSX in the L3TFLT rung be replaced by L14HS.
I am confused about L94X.In the toolbox, its description is :Startup check stop GT normal shutdown.
----------------------------------------------------------------------------------------------------------

L3RS1 L3RS2 L5VPRO_LATCH L3RS
-------||----------||------------|/|----------( )

L3RS1=Startup check stop ready to start 1;
L3RS2=Startup check stop ready to start 2;
L5VPRO_LATCH=Protective VPRO card trip-latch;

As we just finished L3RS1,i think L3RS2 is my assugnment this time.

L52ONLINE L3COMM_IO L3ACS L3RS2
------|/|---------||-------||------( )
L52ONLINE= Unit online ;
L3COMM_IO=VCMI state changes for <R>,<S>,<T> OK;
L3ACS=Auxiliary check servos;

I find L3ACS is not easy,so i decide to deal this sigal this time.


L3GFLT L3LFLT L62TT2 L3ACS
----|/|-----|/|------|/|--------( )
| |
L84TL | L84TG |
-----||------||----

L3GFLT=Gas fuel control fault;
L3LFL=Liquid fuel control fault;
L84TL=On total liquid fuel;
L84TG=On total gas fuel;
L62TT2=startup check stop mutiple start counter;


let me start with L62TT2:<Pre>

Timer_sec _Counter
L2FZ(log_in) (log_out)L62TT-----------L62TT(INC) (AT_CNT)L63TT2
K62TT(pu_del) K62TT2(MAX_CNT)
L1XY(RESET)

L2FZ=startup check stop multiple starts permissive;
K62TT=startup check stop multiple start time delay(5s);
L62TT=startup check stop multiple start and atuo refire;
K62TT=startup check stop multiple start count(2);
L1XY=startup check stop aux to master contr-stup perm;

When the number of pulse(L62TT signal) is less than 2(K62TT2),than L63TT2 is logic 0.
There are several combinations which will make L3ACS logic 1 when L63TT2 is logic 0:
1.L84TL=1,L3LFLT=0; The gas turbine is on total liquid fuel,and the liquid fuel control is not in fault.
2.L84TG=1,L3GFLT=0; The gas turbine is on total gas fuel,and the gas fuel control is not in fault.
3.L3GFLT=0,L3LFLT=0; The fuel control system is not in fault.

CSA,I am confused about L62TT2,and can you explain it briefly.
According to the above combination,the gas turbine can start up when one of the fuel control systems is fault,and is it reliable?

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

CSA.

Very glad to receive your reply,and thank you sincerely for your engagement.I am not rich,or i am willing to pay you for this interesting journey:)

And if you are busy,just let me know. You know waiting is miserable.
I hate to quit and i wanna to go on this journey and finish it.

Thank you again for your help.

---------------------------------------------------------------------------------------------------------------------------------
You missed this question below:



A>B----|
| L14HSX L3TFLT
---------| |---------||-----------( )

A=CAKCPD(35psi)
B=CPD
L14HSX=Auxiliary signal to L14HS

And i tried to find the differebce between L14HS and L14HSX.

L14HS L4 L14HSX
---------||--------------||-----( )
|
L14HSX L94X |
------||------|/|----

L94X=Startup check stop GT normal shutdown;
L14HS=HP operating speed signal;

As for L3TFLT,if CPD is less than 35psi when gas turbine is under normal operation,then L3TFLT is logic 1.

I was wondering the function of the L14HSX,and whether can L14HSX in the L3TFLT rung be replaced by L14HS.
I am confused about L94X.In the toolbox, its description is :Startup check stop GT normal shutdown.
----------------------------------------------------------------------------------------------------------

L3RS1 L3RS2 L5VPRO_LATCH L3RS
-------||----------||------------|/|----------( )

L3RS1=Startup check stop ready to start 1;
L3RS2=Startup check stop ready to start 2;
L5VPRO_LATCH=Protective VPRO card trip-latch;

As we just finished L3RS1,i think L3RS2 is my assugnment this time.

L52ONLINE L3COMM_IO L3ACS L3RS2
------|/|---------||-------||------( )
L52ONLINE= Unit online ;
L3COMM_IO=VCMI state changes for <R>,<S>,<T> OK;
L3ACS=Auxiliary check servos;


L3GFLT L3LFLT L62TT2 L3ACS
----|/|-----|/|------|/|--------( )
| |
L84TL | L84TG |
-----||------||----


L3GFLT=Gas fuel control fault;
L3LFL=Liquid fuel control fault;
L84TL=On total liquid fuel;
L84TG=On total gas fuel;
L62TT2=startup check stop mutiple start counter;

let me start with L62TT2:

Timer_sec _Counter
L2FZ(log_in) (log_out)L62TT-----------L62TT(INC) (AT_CNT)L63TT2
K62TT(pu_del) K62TT2(MAX_CNT)
L1XY(RESET)

L2FZ=startup check stop multiple starts permissive;
K62TT=startup check stop multiple start time delay(5s);
L62TT=startup check stop multiple start and atuo refire;
K62TT=startup check stop multiple start count(2);
L1XY=startup check stop aux to master contr-stup perm;

When the number of pulse(L62TT signal) is less than 2(K62TT2),than L63TT2 is logic 0.
There are several combinations which will make L3ACS logic 1 when L63TT2 is logic 0:
1.L84TL=1,L3LFLT=0; The gas turbine is on total liquid fuel,and the liquid fuel control is not in fault.
2.L84TG=1,L3GFLT=0; The gas turbine is on total gas fuel,and the gas fuel control is not in fault.
3.L3GFLT=0,L3LFLT=0; The fuel control system is not in fault.

CSA,I am confused about L62TT2,and can you explain it briefly.
According to the above combination,the gas turbine can start up when one of the fuel control systems is fault,and is it reliable?

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

Neo,

I'm not quite sure what the question is, but let's try this. The comparator is checking to make sure the median value of CPD is greater than 35 psig; if it's not then when the unit is above 14HS and running (we'll get to that in a minute) then L3TFLT is a logic "1" and usually, these days, that means a turbine trip--especially for machines with DLN combustors (because CPD is very important for exhaust temperature control--VERY important).

L14HSX is a unique L14HS in that, as you can seem from the rung once the unit is running (L4 is a logic "1") and the unit gets above 14HS (usually 95% TNH), then L14HSX latches in (through the L94X/L14HSX parallel part of the rung). L94X is a very important signal--a 94 device is a shutdown device, not a TRIP, but a normal, orderly shutdown. As, in an operator selects STOP and the unit starts unloading, the breaker opens, and the unit goes into a fired shutdown until is reaches Cooldown.

Some other operating conditions can also initiate an "automatic" shutdown (sometimes high-high inlet air filter differential pressure, or similar) can do the same thing--through L94AX which drives L94X (have a look at the application code in your machine).

So, if the turbine trips, L4 goes to a logic "0" and at whatever speed it's at then L14HSX will go to a logic "0". BUT, if the unit goes below 14HS (usually 94.5% speed) when it's operating (that means the grid frequency is more than 5.5% below normal!!!) then L14HSX will remain a logic "1", and in the case of L3TFLT the rung can still activate if CPD drops below 35 psig. Kind of confusing, but not really. (I hope!)

L3RS2 would be the next logical progression; yes.

And the important logic signal in L3RS2 is L3ACS--another signal which should be relatively straightforward but which has become somewhat perverted over the years.

L62TT2 stands for "Turbine Tried Twice to Start". It's a "relic" (old) bit of logic that causes a LOT of problems. It was put into GE logic way back when a lot of GE-design heavy duty gas turbines were being used for peaker units (during times of high electrical demand) and natural gas compressor drive, and a lot of these sites were unmanned. So, if a START was initiated from a remote location (say 250 km away) and something not too critical interrupted the START sequence, a second START would automatically be initiated by the Speedtronic panel without any operator intervention. (This was long before the days of SCADA and Ethernet and HMIs, so alarms were grouped into critical and non-critical bunches and the only alarm the remote operator would get would be a "Group1" or "Critical" alarm, so it wasn't much help.)

If the turbine still failed to start and accelerate to FSNL on the second, automatic attempt L62TT2 would go to a logic "1" and then someone would have to go to site to check on the unit. Sometimes, the remote operator could just initiate another START if it failed the second automatic start, but usually, once L62TT2 picked up starting was prevented until someone went to site and initiated a MASTER RESET--which was the mechanism for requiring a human to reset the Speedtronic in the event of a critical problem before the turbine could be re-started. So, that's a little history of the signal.

It has, unfortunately, remained in the logic even for combined cycle power plants--even though it has caused a lot of problems. For example, if a START is unsuccessful for some minor reason and a FAILURE to START alarm is annunciated, while the operators are scratching their heads about what went wrong the Speedtronic will automatically--without operator intervention--initiate another START sequence, at which point everyone is shocked and surprised. And this is because of L62TT2 being left in the control scheme even for combined cycle power plants--which are almost NEVER unmanned.

Another problem that occurs is when the turbine is STOPped before the generator breaker synchronizes (which is usually Complete Sequence these days), which increments L62TT2 once, and when the unit gets back down to zero or minimum firing speed (depending on the machine) it will automatically START again--which also causes quite a lot of surprise and consternation.

I wish GE would stop shipping application code with that logic to manned sites, and only add it if the site is converted to unmanned, or block it with a NO 'false' or something like that, because it really causes a lot of grief and can be very scary. But, since most of the engineers at GE don't understand how the signal came to be and aren't capable of critical thinking they just leave the signal in--and, it usually results in at least one problem during commissioning, and again afterwards--when no one is expecting the unit to automatically re-start, but it does.

So, except for certain unfortunate circumstances you can presume that L62TT2 is always a logic "0". And, unfortunately, without being able to see all of the application code in the machine at your plant it's impossible to say precisely what those certain unfortunate circumstances are.... Thank you, Belfort, yet again. AAARRRGGGHHH!!!

The L3COMM_IO is one of the ways that the Speedtronic checks to make sure that all three control processors (<R>, <S> and <T>) are healthy and communicating with each other. I have, unfortunately, heard of people being able to force this logic to be able to TRY to start the machine when there is a problem with one of the VCMI cards and then when the unit won't start they are furious, to say the least. Because of the way the Mark VI (and VIe) are configured, it might be possible for a start to actually be successful--but it shouldn't, and I believe that most Mark VI firmware has been "fixed" to stop this from being even an unlikely possibility.

So, write the sentence for L3RS2--and for L3ACS, Neo.

Yes; if the unit is not on Total Gas (L84TG is NOT a logic "1") and there is a fault with the gas fuel system the unit can still be started. Will it be "reliable"? What's your definition of "reliable"?

CSA,

Thank you for your detailed and enlightening comment on L14HSX, L62TT2 and L30COMM_IO.

When the selected fuel control system is not in fault(L84TL=1,L3LFLT=0 or L84TG=1,L3GFLT=0) and L62TT2 is logic 0, then L3ACS will go to logic 1.

When the unit is not online(L52GX=0),all three control processors are healthy and communicating with each other,and L3ACS is logic 1,then L3RS 2will goes to logic 1.
-----------------------------------------------------------------------------------------------------------


L4S L94T L4T L4
-----| |-----------|/|----------|/|------------( )
|
|
L4 |
-----| |------

It seems that we have just finished L4S,so what is my next assignment,L94T or L4T?
-----------------------------------------------------------------------------------------------------------
Before moving on, i have several questions to ask about L62TT2.
1)

Timer_sec _Counter
L2FZ(log_in) (log_out)L62TT-----------L62TT(INC) (AT_CNT)L62TT2
K62TT(pu_del) K62TT2(MAX_CNT)
L1XY(RESET)

As we can seen from the above rung,if L62TT2 is logic 1 after a second startup failure ,it will reset to zero when L1XY picks up, then means L1X goes to logic 0.

TO my understanding, if the unit stops,L1X goes to logic 0(Is it right?),then L62TT2 goes to logic 0.But you said: "Once L62TT2 picked up starting was prevented until someone went to site and initiated a MASTER RESET."

Should i post L2FZ rung and L1X rung? Maybe it helps.

2) You said if the turbine fail to start for some minor reasons,the unit will start up automatically,and if it
fail again then starting was prevented until someone went to site.

My question is how can i deduce this from application code,which part of application code should i read to confirm this?
-----------------------------------------------------------------------------------------------------------
As we can see from L2ACS rung,if the unit is not on Total Gas (L84TG is NOT a logic "1") and there is a fault with the gas fuel system the unit can still be started.

In my last reply i doubted its reliability.I just wondered if we changed to gas fuel during operation,and gas fuel system is in fault,that will be a problem. Why not make sure both of the fuel control system is OK?

CSA,

Thank you so much for your comment on fuel purge system.You are always patient to answer all kinds of questions.

I think you missed another reply of mine.:)
--------------------------------------------------------------------------------------------------------
This time i will examine L94T,and i think it is very important too.
Here comes L94T:


L94XZ L94T
------||---------|----()
|
L28FD L83RB |
-----|/|-----||---
|
L2CANT |
------||---------

L94XZ=Startup check stop fired shutdown
L28FD=Flame detected
L83RB=startup check stop ramp to blowout selected
L2CANT=Trip on can flameout timed out

I confronted withmany signal name descriptions that start with "startup check stop",while i think these signals has nothing to do startup check,just like L94XZ.

As we can see from above rung,there are three kinds of conditions that will lead L94T to logic 1.
And i will start with L28FD and L83RB.
----------------------------------------------------------------------------------------------------------


L28FD L83RB L94T
-----|/|-----||-----------( )


L60RB L94SD L83RB
---------|/|--------||----------( )


L60RB=startup check stop above ramp to blowout speed
L94SD=startup check stop shutdown with breaker open

I am a little confused about the term "blowout speed",and i think "ramp to" can be "increase to" or "decrease to",right?


(TNH>K60RB)----
| L28FDY L60RB
------------| |-----|/|--------( )

According to the above rung,when TNH is less than 30% rated speed or Flame is not detected,then L60RB is logic 0.And while L94SD is logic 1,then L83RB is logic 1.When l83RB is logic 1 and Flame is not detected,then L94T is logic 1.

It seems that whether TNH is less than 30% rated speed or not doesn't matter,for when flame is not detected no matter what value of THN is the L94T will be logic 1(with l94SD=1).
------------------------------------------------------------------------------------------------------------

     L94XZ                   L94T
-----------||---------------------( )
L52GY L94X L94XZ
-----------||--------||----------(T)
8min

If STOP command was sent for more than 8min and the breaker is open,then L94T is logic 1.
------------------------------------------------------------------------------------------------------------


L28CAN1 L28CAN L2CANT
-------||--------------(T)----------(T)
| 1s 5s
L28CAN2 |
-------||------
|
L28CAN3 |
-------||------
|
L28CAN4 |
-------||------

L28CAN=Any can flameout
L2CANT=Trip on falmeout timed out

Take L28CAN1 for example:
L28FDF1 L28FDA L28CAN1
------||-------|/|----------()
L28FDF1=Flame Detector 1 Funtional
L28FDA=Flame Detector Channel #1

L28FDA L94SD L4 L28FDF1
------||-----||------||------()
|
L28FDF1 |
------||-----

L94SD=Startup check stop shutdown with breaker open

When STOP command sent and the breaker is open,if any one of the Flame Detector doesn't detect flame, L2CANT
is logic 1.
------------------------------------------------------------------------------------------------------------
I wondered why there are three kinds of condition that will lead L94T to be logic 1.
If STOP command is sent by operator,it will go though which rung?
And the gas turbine fail to start after ignite,it will go through which rung to stop?
------------------------------------------------------------------------------------------------------------
CSA,you should respond when you are not busy.
May not disturb you to make money:.
Just a joke:)

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

Neo,

Yes; L94T is very important. L4 will drop out (goes to a logic "0") when either L4T or L94T picks up (goes to a logic "1"). L4T is from the application code trip detection (Low-low L.O. Pressure; High-high L.O. Temperature; High-high vibration; etc.--we'll cover them all!). But these trips are only the ones detected by the application code running in <R>, <S> and <T>--not <P>.

L94T is the way fuel is shut off during a normal shutdown--either an operator-initiated STOP or an automatically-initiated STOP. A '94' device is a normal shutdown device. This is not to be confused with a trip--an emergency shutdown.

During a normal shutdown from load, the unit load is ramped down at some uniform rate until the generator breaker opens on reverse power, at that point the Speedtronic goes into what's called 'fired shutdown' mode, where the fuel is reduced in steps to decelerate the unit until it reaches (ramps down to--you are correct in that a ramp, in this case, is a decrease in speed) and then after a certain time below that speed (K60RB) the L4 will drop out and fuel will be shut off, and the unit will continue to decelerate to Cooldown.

Before the advent of digital control systems, shortly after the generator breaker opened fuel was cut off. This represents a large thermal stress to the hot gas path components, and so when the control systems became more capable it was decided to reduce the fuel slowly while the turbine was decelerating until such time as it was felt the fuel could be shut off without introducing too much thermal stress to the turbine.

Somebody thought a good name for this speed level would be "blow-out" speed--who knows why; it's not a very good or appropriate name. It is intended to mean that if fuel were to be further reduced the air flowing through the machine would be insufficient to maintain flame (the fuel-air mixture would be too lean) and the flame would be blown-out.

There is also logic that says if the unit doesn't reach that blow-out speed before flame is lost in any combustor with a flame detector for a second or so that fuel would be shut off at that point. The thinking here is that if the air flow is so high for the fuel flow at that point that one or more combustors lose flame that this would result in a high exhaust temperature spread condition which is also very damaging to hot gas path components.

So, fuel is just cut off if flame is lost for a brief time during shutdown--and the alarm 'CHAMBER FLAMED OUT DURING SHUTDOWN' is annunciated, and the unit continues to decelerate to Cooldown.

This alarm simply means that flame was lost "prematurely"--before the unit reached "blow-out" speed (again, that poor name). It means that if the condition continues on subsequent shutdowns that someone should be investigating changes to the shutdown FSR to keep flame on longer to help reduce the thermal stresses. This is especially true if the condition happens at speeds above, say 70% or 80%--and even more critical if it happens when shutting down on natural gas fuel.

It is VERY important to note that it is VERY difficult to maintain flame while shutting down when liquid fuel is being burned to speeds below approximately 50% without having lots of white smoke in the gas turbine exhaust. This is because of the lack of atomizing air (usually the Booster Atomizing Air Compressor is NOT running during a fired shutdown, and only the main AA compressor is running), resulting in poor, incomplete combustion which is the cause of white smoke in a gas turbine's exhaust when running on liquid fuel.

So, it's very common for there to be two "blow-out" speeds for units that can burn natural gas and liquid fuel--one for natural gas (around 20%, usually; sometimes as high as 30%), and one for liquid fuel (usually somewhere around 50-60%, sometimes even higher, because white exhaust smoke can be very bad during shutdown while burning liquid fuel because of the lack of atomizing air).

Finally, there is logic that says if the unit doesn't reach "blow-out" speed within a certain time after a normal STOP is initiated without losing flame in any combustor that fuel will just be shut off. Why? Sometimes, the fuel is excessive during a fired shutdown and the unit doesn't decelerate past a certain point and just kind of "stalls" at some speed. No point in continuing to pump fuel into the machine if it's not going to decelerate.

Again, if this happens someone should be looking at adjusting the shutdown FSR constants to maintain deceleration all the way down to "blow-out" speed. Some units, newer units, have some alarm to "alert" a conscious operator to the excessive time on fired shutdown. I don't recall the Process Alarm text message, and I've seen at least two different text messages for the same condition, so it seems there is no "standard" for the alarm text.

So, them's all the conditions for L94T.

Yes; some of signal names can be very misleading, VERY. Again, it's best not to just inherently trust every signal name, but, rather to analyze and form one's own opinion and definition. But, the one thing it does do (besides making things difficult for many) is it forces one to use their critical thinking skills and to investigate and analyze. That's why I like to make hand-written notes on printed copies of application code--especially as I'm working to understand what a particular signal's function is.

I have also objected to the use of the word "trip" in shutdown logic over three decades, but it just fell on deaf ears. Makes it really hard to get people to properly call a trip a trip and stop a shutdown when the longname descriptions are misleading. But, I'm only one person, and while I never gave up hope that someone might listen and understand and make the changes, I'm also a pragmatist. Just not a defeatist. I'm still trying--just in a slightly different way.

;-)

Hope this helps!

So, what's your sentence for L94T?

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CSA

I have to say your comment on L94T is great, great, great!
It must not easy to get where you are now.

So during a normal shutdown, when the generator breaker is open, if the speed of the HP ramped down to K60RB, or any one of the flame detector detects no flame, or it has been more than 8min since the generator breaker was open, L94T will go to logic 1,and that means fuel will be cut off?

Just a few questions:

1) "During a normal shutdown from load, the unit load is ramped down at some uniform rate until the generator breaker opens on reverse power, at that point the Speedtronic goes into what's called 'fired shutdown' mode, where the fuel is reduced in steps to decelerate the unit until it reaches (ramps down to--you are correct in that a ramp, in this case, is a decrease in speed) and then after a certain time below that speed (K60RB) the L4 will drop out and fuel will be shut off, and the unit will continue to decelerate to Cooldown."

I think your above comment refers to the rung below.

            
L28FD=Flame detected
L83RB=startup check stop ramp to blowout selected

L60RB L94SD L28FD L94T
---------|/|--------||--------|/|------( )
L60RB=startup check stop above ramp to blowout speed
L94SD=startup check stop shutdown with breaker open

(TNH>K60RB)----
| L28FDY L60RB
------------| |-----|/|--------( )


According to the above rung,during a normal shutdown,if TNH ramps down to blowout speed while flame is detected(L28FD=1),the fuel will not cut off. That seems unreasonable.

If i were the programmer of application code, i would like to replace the above with that below:


(TNH>K60RB)----
| L60RB
------------| |------( )

L60RB L94SD L94T
---------|/|--------||------------( )


Is it Ok?

2) There are four flame detectors while there are 18 can combustors. so if one of the can that not installed with flame detector blows out during a normal shutdown, fuel will not cut off, and this hot gas path component will suffer high thermal stress, right?

Best regards
Neo

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

Neo,

Thank you for the kind words.

Yes; I agree with your sentence describing the L94T rung.

1) Yes; my comment refers to the L60RB. Remember, the comparator says if TNH is greater than than K60RB, then L600RB will be a logic "1". And, remember, we said that sometimes signal names are not chosen properly. L60RB is a logic "1" when the turbine speed is above K60RB AND flame has not been lost for some period of time during shutdown, and L60RB is a logic "0" when either TNH<K60RB OR flame is lost before TNH<K60RB. It would have made more sense if L60RB were a logic "1" when TNH<K60RB OR flame was lost for more than a couple of seconds during shutdown--but nobody consulted me.

Why would you eliminate the L94SD?

2) Yes, there will be increased thermal stress if flame is lost in any combustor which doesn't have a flame detector during shutdown because fuel will not be shut off. But, there are tradeoffs--do you want to pay for 18 flame detectors? And maintain 18 flame detectors? And remove and replace 18 flame detectors during maintenance outages? With all the wiring and tubing (I'm presuming the flame detectors are water-cooled at your site)? But, in general, this "low cycle fatigue" logic works very well because it keeps fuel on much longer during deceleration that was previously possible (remember--flame was shut off at 95% speed during every shutdown).

Can we start on L4T now, please?

CSA,
Here comes the L4T!

L4T(1)


L4PST
-----||-------
|
L4PRET |
-----||-------
|
L4POST |
-----||-------
|
L3SMT |
-----||-------
|
L4IGVT |
-----||-------
|
LFPAUXG2LLX |
-----||-------

L4PST = Protective status trip logic 1
L4PRET = Pre-ignition trip
LPOST = Post-ignition trip
L3SMT = Starting means device trip
L4IGVT = Inlet guide vane control trouble trip
LFPAUXG2LLX = Auxgas P2 pressure low low delayed

According to the above rung, the trip signals are classified into six categories,and i will start with L4PST.


L4PSTX1
-----|/|-------
|
L4PSTX2 |
-----|/|-------
|
L4PSTX3 |
-----|/|-------
|
L4PSTX4 |
-----|/|-------

L4PSTX1 = Protective status trip logic 1
L4PSTX2 = Protective status trip logic 2
L4PSTX3 = Protective status trip logic 3
L4PSTX4 = Protective status trip logic 4


L63QTX L45FTX L5ESTOP1_FZA L86GT L63ETH L63CSHH L4PSTX1
------|/|------|/|------|/|-------|/|-------|/|-------|/|-----( )

L63QTX = Lube Oil Gen Prssure Low Low Trip
L45FTX = Fire Indication Trip
L5ESTOP1_FZA = VPRO E-STOP PB Circuit Open
L86GT = Generator Protective Trip
L63ETH = Exhaust Duct Pressure High Trip
L63CSHH = Flow Inlet Duct Diff Pressure GT Trip

1)L63QTX
L63QTX is related to L63QT(Low L.O. Pressure TRIP). So when te L.O. pressure is too low to protect the bearings, L63QT will be logic 1.

2)


l45ftx1
-----||------
|
l45ftx2 |
-----||------|
|
l94f1b false|
----||---||--

l45ftx1 = fire protection aux/turb/load compt fire detection
l45ftx2 = fire protection exciter compt fire detection
l94f1b=fire protection exciter compt CO2 release

If fire is detected in specified space,l45ftx1 or l45ftx2 will be logic 1.

I will continue next time, and i need to time to refer to background information.
------------------------------------------------------------------------------------------------
I would like to know why there should be such a trip (like L63QTX), and what will happen if the there were not such trip signal (when L63QTX is logic, the unit doesn't trip). And what does the signal name stands for (l63QTX, 63 for pressure switch, Q for oil, T for??, X for Aux?).

It seems that L4T is much more complicated than those signals we confronted with before, do you have any suggestion for how should i examine L4T. i need your guidance.

Best regards!
Neo

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Neo,

Let's back up just a minute, please, and explain why you wanted to remove L94SD from the L60RB rung.

As for L4T--yes; it's much more involved as it has most of the critical protection for the turbine and auxiliaries in it, so it's going to take a while. That should be okay, though, because there's a lot to learn here--a LOT.

As for the question about L63QTX and the need for a low-low L.O. pressure trip, it's very important to protect the machine (turbine, reduction gear, generator) bearings from being "wiped" (destroyed) because of lack of lube oil pressure and flow. And, I would have thought you would have been all over this one--because, when the turbine is being started from zero speed when it's off Cooldown (and the Aux. L.O. Pump is not running) the turbine should be tripped! But, to get a ready to start the turbine has to be NOT tripped, and to get L4 to pick the turbine has to be NOT tripped. So, let's put up the L63QTX rung and see how it works so we can explain how the turbine is not tripped when there is no L.O. Pressure during starting when the Aux. L.O. Pump is not running. It's pretty important, wouldn't you say?

As we go through L63QTX you will see why there is a "auxiliary" signal to low-low L.O. pressure (a '63' device is a pressure switch; 'Q' generally stands for Oil, but sometimes stands for 'Flow', and the 'T' stands for Trip, and yes--the 'X' stands for auXiliary.

Also, we are gonna have some fun (NOT!) with that LFPAUXG2LLX logic signal, too!

Yes; L4T is (or at least it's supposed to be) divided up into several categories--namely:

Protective Status Trips - If any of these trips are detected at any time (turbine running or not) then a trip will be initiated. The purpose is to protect the turbine and auxiliaries, running or not, from potential catastrophic damage.

Pre-Ignition Trips - As the name implies, these are conditions which, if detected before flame is detected ("ignition") will result in a trip of the unit.

Post-Ignition Trips - As the name implies, these are conditions which, if detected after flame has been detected will result in a trip of the unit.

Starting Means Trip - This is (was) intended to be the way the turbine was tripped by the starting means if a problem with the starting means was detected.

IGV Trips - This is (was) intended to be the way the turbine was tripped if a problem was detected with control of the IGVs.

Interesting Named Trips - Yes; this is another poorly implemented trip (probably should have been in Post-Ignition Trips) as well as an extremely good example of an extremely poor choice of a signal name. We're gonna have a good time with this one.

It's, again, critical to remember that these trips ARE NOT all of the possible trip conditions. There are trips connected to the TREG (<P>), as well as the overspeed trips and the dreaded "Composite Trip" that are generated in the PPRO IO Packs, AND the Emergency Stop ("E-Stop") pushbutton circuit.

One of the most important things any technician (and operator) can do to learn how the turbine at their plant operates is to develop a list of "Runbacks, Shutdowns, and Trips". We are going to be working on the trips that are detected by the control processors (<R>, <S> and <T>) as we work through L4T.

We might be able to open another thread (when we complete this one) that can investigate the other trips everyone should know and understand--the ones connected to and generated by <P>.

And, if you're really interested we might be able to open still another thread (when we complete the other two) about Runbacks--conditions that result in a load reduction to some setpoint or to FSNL (with the generator breaker open) to protect the unit. (At that point, it's up to the operator to understand the condition--which should have a Process Alarm to indicate the cause of the Runback--and take appropriate action, either to resolve the problem and re-load the unit, or to shut the unit down until such time as the problem can be corrected and the unit re-started and re-loaded.)

Traveling can be such fun!

CSA

Thank you again for this exciting journey,and i am willing to continue this journey until the end of doomsday.

I was wondering how i should examine L4T,as there are so many signals involved.Should i examine those signals one by one? And what should i foucs on?

And this thread is getting very long. I think I'm going to make this part the beginning of a new thread next time with the same name called part 2. I will put a note in the beginning of the threads stating that it comes in two parts along with the URL of other part.

Have seen this thread yet: http://www.control.com/thread/1403944262
I would like to know your opinion.

I am a little exhausted today, and i will try to reply to your previous respond tomorrow.

BTW, it seems that there are more than one CSA in this forum :)
It will confuse me whether i am talking to "the CSA".

Best regards
Neo

Neo,

I think it will be best if we examine most every trip condition--not all of them--but probably most of them. They are very useful in understanding what conditions lead to a turbine trip from the controllers (<R>, <S> and <T>).

You are avoiding answering the question about why you think L94SD is unnecessary....

And, yes, poster H.A.R. has decided to use 'CSA' as his moniker. He only has a single star next to his CSA, so that would be your first clue as to who was responding to you. ;-)

And, good idea about starting a 'Part Deux' for this thread. The first post should be about L63QTX.

Question Regarding Inversion Masking
______________________________________________________________________

Dear CSA,

I've been following this thread (I read this whenever I get time) and I appreciate the time and energy you devote to the community. Please continue this thread. As your last two posts are not appearing when I open this thread, I'll be good if this discussion is continued in other thread (part II as Neo said).


L86CB L4Y l27qel L3CP l63fdl
---|/|-------||--------|/|-------||-----|/|--------( ) L3STCK2
| |
| L43FTG |
|----||----|


L3STCK2: Start check 2
L86CB : Compressor bleed valve or IGV position lockout
L4Y : Loss of master protective
l27qel : Emergency lube oil pump under-voltage
L3CP : Customer permissive to start
l63fdl : Distillate fuel supply pressure switch
L43FTG : Transfer to Gas

As already said I'm also on this journey with you and Neo. I've learned to read the Rungs and interpret how it'll work. I've managed to get some of the Application Code running in our Speedtronic Mark VI, and I've a question regarding inversion masking.

let me read the Rung:

when L86CB is logic "0" AND L4Y is logic "1" AND l27qel is logic "0" AND L3CP is logic "1" AND l63fdl is logic "0" OR L43FTG is logic "1" L3STCK2 will be logic "1".

now interpreting it:

When there is NO compressor bleed valve or IGV position lockout AND loss of master protective timer is complete AND Emergency lube oil pump is NOT undervoltage AND Customer permissive to start is selected AND Distillate fuel supply pressure is NOT low OR transfer to gas is selected, start check 2 is completed.

Coming to my question, I think the signal l27qel and l63fdl are inverted.

For l27qel: When EOP is not under-voltage, the NC contacts will remain closed and thus it will allow L3STCK2 to pickup. When EOP is under-voltage the NC contacts will open and will prevent L3STCK2 to pickup. Thus when the contacts are closed then only L3STCK2 coil is allowed to pick up. This ensure when the contacts are closed EOP is not under-voltage and the switch is also in healthy condition, thus doing the work of supervision too. Instead, had GE had chose the contacts to close when EOP is under-voltage, we wouldn't have known even if the circuit is intact or not.

For l63fdl, When the distillate supply pressure is not low the NC contacts will remain closed thus alowing L3STCK2 to pickup. When the distillate fuel supply pressure is low, the NC contacts will open, thus preventing L3STCK2 from picking up. Thus here also the contacts must be close, which ensures that the distillate supply pressure is normal and the switch circuit is intact.

Am I right? I've tried hard to understand the concept of inversion masking by reading (and re-reading) your explanations in this thread. Please correct me if I'm wrong.
______________________________________________________________________

As you asked about the machine at our site in http://control.com/thread/1403711658#1404062279. It is a PG5361. It is having conventional combustors. The machine is duel fuel capable. It can be operated on Natural Gas or Naptha, but it is operated on NG only since last 10 years. out of two machines, one was installed in 1988 and the other in 1996. Both the machines can be operated in Droop and Isochronous mode. Our plant generally (not all the time though) remains separated from the grid. Both the machines exhausts in HRSG. This arrangement is having a By-Pass stack.

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SB,

Inversion masking. Okay. I have to make this short as I've just been given a last-minute opportunity for a holiday in the South Pacific Ocean that one dreams about, and I'm going to take advantage of it. So, I'm leaving tomorrow and have just a few minutes. I'll check this thread on my return in about a week-and-a-half.

HOPEFULLY the contacts of the 27QE relay are NORMALLY OPEN, and close when there is voltage to the starter and open when there is no voltage to the starter. (When there IS voltage to the starter, 27QE should energize, and that will close a NO contact connected to the l27qel input of the Speedtronic. Now, if the input were NOT inverted, that would mean that l27qel would be a logic "1", but that's in 'violation' of proper signal naming conventions because l27qel is supposed to be a logic "1" when the Emergency L.O. Pump voltage is Low (the L (or l) at the end of the signal name means the signal name is a logic "1" when the voltage is Low). So, the signal is inverted by software on the discrete input card BEFORE it drives the contacts in the associated with the input signal in the sequencing (or application code).

Let me try to draw it here by attempting to show the physical contact from the undervoltage relay of the Emer. L.O. Pump motor starter connected to the Speedtronic's input screw for the Emer. L.O. Pump Motor Undervoltage input, and show the software coil driven by the contact input, because that's what EVERY discrete (contact) input does: it drives a coil in software, and contacts associated with that software coil are used in the sequencing (application code). In the case of inverted inputs, the coil status is the opposite (the inverse) of what one would normally expect it to be when the contacts are closed or open.


Physical | Software
Contact |
27QE Input Screw l27qel
---| |----------o------------------(I)---

The "I" in the software coil for l27qel means the input signal is inverted, which means that when the normally open contact of 27QE that's connected to the Speedtronic input screw is closed l27qel WILL NOT be a logic "1"; instead, it WILL be a logic "0"--which is the inverse (opposite) of what one would think it should be when the contact was closed.

If the normally open contact of 27QE were connected to real physical electromechanical relay and it was closed (when there WAS voltage to the Emer. L.O. Pump motor starter) the electromechanical relay coil would be ENERGIZED, it would be "1". Without some additional electronic devices there can be no "inversion" of a hard-wired contact driving an electromechanical relay coil. But, using software a closed input will NOT cause the software coil it drives to be a logic "1"--it will cause it to be a logic "0" (the inverse of what one would expect). And when the contacts are open, an inverted software coil will NOT be a logic "0", but it will be a logic "1" (the inverse of what one would expect).

Now, after the inversion, in software normally open and normally closed work exactly as one would expect when the associated coil driving them is a logic "1" or a logic "0". When l27qel is a logic "0", normally open contacts associated with l27qel will be open, and when l27qel is a logic "1" then normally open contacts will be closed. Normally closed contacts of l27qel will be closed when l27qel is a logic "0", and normally closed contacts of l27qel will be open when l27qel is a logic "1".

So, when the contact of 27QE (in this case, it should be a normally open contact, that is open where there is an undervoltage, and closed when there is NO undervoltage) is CLOSED, then l27qel will be a logic "0" (NOT a logic "1" as would be expected) and normally closed contacts of l27qel would be CLOSED--because the Emer. L.O. Pump motor voltage is NOT low.

Just apply the same logic (thinking) to l63fdl. A normally open contact of the pressure switch will be open when the liquid fuel supply pressure is LOW, and closed with the liquid fuel supply pressure is NOT low (when the supply pressure is normal). l63fdl will be a logic "1" when the liquid fuel supply pressure is Low, and because that input is inverted that means that the contact will be OPEN when the supply pressure is low--which will be the case when there is low pressure (or no pressure) and the input is wired to a normally open contact of the pressure switch. The normally closed contact in the rung will be closed when the liquid fuel supply pressure is NOT low (when l63fdl is a logic "0", which will be when the contact of 63FD is closed, and a normally open contact of 63FD will be closed when the pressure is above the setpoint of the switch).

Finally, think about it this way. If a normally closed contact of 63FD were wired to the Speedtronic, then when there WAS pressure to the switch the normally closed contact would be open. If that contact was wired to a non-inverted input called l63fdl then l63fdl would be a logic "0" when there was pressure (which is all well and good!).

However, if a wire falls off one of the terminals of that normally closed contact of 63FD AND at some point after that the liquid fuel supply pressure drops below the switch setpoint and the normally closed contact closes the Speedtronic will NEVER know that the liquid fuel supply pressure dropped. So, GE uses contacts that are to be CLOSED when the condition is NORMAL, and OPEN to alarm or trip (when the condition is NOT normal). Better to get a false alarm when a wire comes loose or a switch fails but the condition is normal, than not to get an alarm when there is a real problem.

WHEW!!! I gotta finish packing, kick the wife and kiss the dogs--er, ..., uh, ..., I mean kiss the wife and kick the dogs. Er, ..., uh, ..., I gotta go! Please read this, and re-read it and re-read it. It's a LOT to digest in even three readings, but at some point it should start to make sense.

ALOHA!!!

CSA,
First of all happy journey!
Hope you'll enjoy a lot and come back even with more energy!

Thanks for taking the time to respond. Your replies are valuable to me (and many more like me).

Yes,
It has started to make sense as you said. I'm gonna read it many more times till you come back.

Dear CSA,

It seems that further discussion on L4T rung is not continued in this thread. I would like to know if the discussion was continued on any other thread. Also, I am very new to gas turbine control. I am hoping to learn a lot from you.

Thanks in advance!!!

party,

If you click on a Member's name it will show all of the posts which the Member has made. I clicked on 'Neo' and I found all of the posts which he has made. And, there are several which you might benefit from.

Can you tell us a little about your position, the equipment you work with, and your work experience?

Dear CSA,

Presently, I am working with 3 nos. GE frame 5 gas turbine, co-gen cycle, Naptha fuel while running & HSD for start up. I am an electrical engineer with 6 month of experience in this field. I am working as a Power Plant operation engineer. Right now, I have gone through the GT support system manual and have read Part-I of this topic & there is still so much to grasp. Let me complete all the parts of this topic and I will let you know if I will come across any problem in understanding the same.

Thank You!!

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

Neo,

This thread is getting pretty large/long and I'm not sure I'm seeing all of the replies in a timely manner. So, if I miss a message/questions just let me know.

L62TT2, is, again, kind of an "artifact" of code that GE just refuses to remove from manned sites. L1X is not usually "cancelled" until the operator selects STOP or the unit synchronizes (I think that's the final permissive in the automatic drop-out of L1X these days; it used to be just complete sequence, L3, but it's been modified over the years. No use in starting a generator-drive turbine unless the generator breaker closes, right? (Except for testing purposes.))

L62TT2 was put in place so that if the unit did not fire/accelerate to FSNL when a "remote" start was initiated that it would automatically attempt a second firing attempt provided the reason for a failed start was not critical--which would have set the Master Protective Lock-out, which would have required a Master Reset to be initiated ON SITE (Master Resets were not allowed to be initiated from a remote location). Typical reasons for not starting were air in the liquid fuel supply piping, air in the gas fuel supply piping, borderline start-up parameters, etc. So, it was felt that--unless the turbine tripped--a second automatically-initiated start attempt was warranted on remotely started and -operated machines.

Again, since people making these decisions about application code today weren't around then, and since there isn't really any documentation in GE that explains some of the older sequencing these people just are loathe to make any changes because they don't understand if there will be any knock-on effects--and worse, they can't work through the application code to see what the signals do and if there will be any knock-on effects and how to mitigate them if there will be.

Without being able to see all of the application code at your site I can't say for sure how it has been "modified" and what it does today. Back in the day, yes; when L62TT2 picked up, it was latched in by a Master Reset. Someone had to go to site to observe the start and resolve the issue, rather than just continuing to pump fuel into a turbine (or not as the case may be). A lot of the older peaking units were liquid fuel-only machines, and there can be lots of issues with liquid fuel machines that aren't operated regularly and frequently on liquid fuel.

You just have to look at the L1X, L1XX, L1XY and L62TT2 rungs and contact usage and determine what, if anything, will happen at your site if the unit doesn't fire on the first START. If the turbine trips on a START, then L62TT2 doesn't come into effect (usually). It's only if there's a failure to fire--which is NOT USUALLY a trip (though Belfort seems to think differently about that, and on occasion; they are as consistently inconsistent as other divisions of GE can be).

So, let's say there was too much air in the liquid fuel supply piping and the turbine failed to fire on a START attempt. The Mark VIe should annunciate a "FAIL TO IGNITE" alarm, and the unit should continue to crank. Under the old L62TT2 logic, it would re-initiate the purge timer and the unit would go through another purge and then re-try another firing attempt. If the second attempt failed, the unit would just go back to cooldown (ratchet) after annunciating a second FAIL TO IGNITE, and the operator would have to take appropriate action. That would be typical of the L62TT2 action of the past. Again, without being able to see all of the application code in your Mark VIe, it's very difficult to say what function L62TT2 actually serves--if any.

As for the reason for allowing a start on one fuel if the other fuel is "locked-out", you may need to start and run the machine for some reason while the other fuel system is "unavailable." Your machine might not have that capability, but many multi-fuel machines do. The liquid fuel might be very expensive--but if someone needs the power, they might be willing to pay that if the turbine can't run on the other fuel for some reason.

Again, GE is all about trying to make the machines as reliable as possible, under the widest set of circumstances possible. Try to imagine other sites and circumstances when working through logic, remembering that the same application code is used for LOTS of machines (modified as necessary for the different types of auxiliaries) so while it may not seem logical for your machine, it may be for others. And, leaving it so probably doesn't hamper operation of your machine (though it may; a careful analysis is best when you find something like this).

Hope this helps.

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

CSA,

I find out how to see whether a DI is inverted or not.


name value description
l12hblt invert inversion makes signal true if contact is open.
l12qn normal inversion makes signal true if contact is open.

So it is defined in I/O definitions.

I think inversion masking is a way to meet a standard that when the discrete signal is logic 1,
it means the alarm is actuated.

And l12hblt follows that standard while l12qn violates.

Is it right?

Best regards.
Neo

CSA,

I am following this interesting discussion few days ago. I would like to join it and ask you about GE philosophy in arranging start check parameters into groups and go deeper asking if each parameter related to the others in each group or just random arrangement.

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Shimy,

Good question, and welcome to the discussion. In the beginning, it was intended that the groups be of like conditions, but over the years that has ceased to be the case. And, in some cases, some conditions would not fit into a group with any other condition. Which would mean a lot more "auxiliary" start-check rungs. Really, a start-check is a start-check is a start-check, and the only reason they are broken up in digital control systems is, again, because of the limitation of the sequencing editors to no more than eight elements (seven contact in a horizontal series string, plus the rung coil--for a total of eight elements). In the days of hard-wired electromechanical relays there was no limit to the number of contacts in a series string (which made troubleshooting rather difficult at times).

So, while the GE-design heavy duty gas turbine control philosophy was originally intended to group start-check conditions, that has stopped being the case in the last 20 years or so, particularly as more and more start-check permissives have been added to the unit as they become more and more sophisticated.

Hope this helps!

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Neo

Another favorite document of mine to understand the Mark V controls is the A010 drawing- Constants and Diagnostics 377a3378.

I am not familiar with the Mark V1 but is should have something similiar.

Bill