# Getting a better understanding of gas turbine control

N

#### Neo

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.
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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.

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:<pre>
prestate poststate
( )---------|/|-------( )</pre>
------------------------------------------------------------------------------------------------------
"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 .
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In one reply, i typed one rung below:<pre>
L45FP_STCK L3STCK
---.....------|/|---------() </pre>
The contact sense of L45FP_STCK is typed wrong,Which should be:<pre>
L45FP_STCK L3STCK
---.....------||---------()</pre>
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.
------------------------------------------------------------------------------------------------------
<pre>
L86CB L4Y L3BHSTCK L30CC_STCK l33cl1 l45fp1 l27f L2STCK2
--------|/|-------||---------||---------|/|------|/|-------|/|-----|/|--------( )
| |
| true |
--------------------</pre>
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

N

#### Neo

CSA,

I find out how to see whether a DI is inverted or not.<pre>
name value description
l12hblt invert inversion makes signal true if contact is open.
l12qn normal inversion makes signal true if contact is open.</pre>
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

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 <b>IF</b> 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:<pre>
l26ql L3STCK1
------|/|------ - - - ----( )</pre>and the Low L.O. Tank Temp Low alarm rung could have been written:<pre>
l26ql L26QN_ALM
------| |-----------------( )</pre>
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 <b>does NOT</b> work for the Mark V. The I/O Report is <b>>>>NOT<<<</b> only looks at the actual I/O Configuration when the report is <i>first</i> 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. <b>NO.</b> 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.

N

#### Neo

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

N

#### Neo

CSA,

Here comses the L3STCK2:<pre>
L86CB L4Y L3BHSTCK L30CC_STCK l33cl1 l45fp1 l27f L3STCK2
--------|/|-------||---------||---------|/|------|/|-------|/|-----|/|--------( )
| |
| true |
--------------------</pre>
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<pre>
L86CBA L86CB
--------||----------|------( )
|
L86TV |
--------||----------|
|
L30CBC_AL |
--------||----------|

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

l33cblO L86CBZ L20CBA
--------||--------|------||-------( )
l33cb2O |
--------||--------|</pre>
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.<pre>
L3IGVF2 L14HA L83BW L86TV
-------||--------||---------|/|---------( )</pre>
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.<pre>
L3BHF1 L3BHF3 L3BHSTCK
----------|/|-----------|/|-----------( )</pre>

L3BHF1(bleed heat feedback trouble alarm) is not difficult to understand,for it is just like command not following.
L3BHF3 is a little complicated.<pre>
L3CPRAH L3BHF3
--------------||----------------|------( )
|
L3BHF1 L3BHF2 L14HS |
--------||-------||--------||---|
|
LCPRERR |
--------------||----------------|</pre>
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

#### CSA

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!

N

#### Neo

>CSA,
>
>Here comes the L3STCK2:<pre>
> L86CB L4Y L3BHSTCK L30CC_STCK l33cl1 l45fp1 l27f L3STCK2
>--------|/|-------||---------||---------|/|------|/|-------|/|-----|/|--------( )
> | |
> | true |
> --------------------</pre>
>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<pre>
> L86CBA L86CB
>--------||----------|------( )
> |
> L86TV |
>--------||----------|
> |
> L30CBC_AL |
>--------||----------|</pre>
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<pre>
> L4 L14HS L520ONLINE L20CBX L20CBZ
>-------||---------||---------||------------()---------------(T)
L520ONLINE = Unit online (confusing)
L20CBX = Cool seal air Air comp bleed 3 way valve ctrl signal<pre>

l33cblo L86CBZ L20CBA
--------||-------- |------||-------( )
l33cb2o |
--------||---------|</pre>

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.<pre>
> L3IGVF2 L14HA L83BW L86TV
>-------||--------||---------|/|---------( )</pre>
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.<pre>
> L3BHF1 L3BHF3 L3BHSTCK
>----------|/|-----------|/|-----------( )</pre>
L3BHF1 (bleed heat feedback trouble alarm) is not difficult to understand,for it is just like command not following.
L3BHF3 is a little complicated.<pre>
> L3CPRAH L3BHF3
>--------------||----------------|------()
> |
> L3BHF1 L3BHF2 L14HS |
>--------||-------||--------||---|
> |
> LCPRERR |
>--------------||----------------|</pre>
>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-------------------------------------------------------------------
><b>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.</b>

Best regards.
Neo

#### CSA

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.

N

#### Neo

CSA:

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

#### CSA

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.

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 <b>does NOT</b> 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?

N

#### Neo

CSA,

I am back

I will do my assignment as soon as possible.

Neo.

N

#### Neo

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:<pre>
L4T L39VD3 L3TFLT LAUXGAS_PT L30IPFLT2 L3IPSTCK L3STCK3
------|/|------|/|---------|/|---------|/|----------|/|--------|/|---------( )</pre>

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.<pre>
L14HS L4 L14HSX
---------||--------------||-----( )
|
L14HSX L94X |
------||------|/|---- </pre>
L94X = Startup check stop GT normal shutdown;
L14HS = HP operating speed signal;<pre>
A>B----|
| L14HSX L3TFLT
---------| |---------||-----------( )</pre>
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.<pre>
L39VD3_GT L39VD3
--------||------------( )
|
L39VD3_GEN |
--------||-----
|
L39VD3_LG |
--------||-----</pre>
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 <pre>
LFPAG0LL LAUXGAS_PT
-------|/|------------------( )
|
LFPAG0 |
-------||-----------
|
LFTAGI false |
-------||------||---
|
CA43P2 false |
-------||------||---</pre>
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.

<b>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.</b>

N

CSA,

Best regards!

#### CSA

Neo,

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.

#### CSA

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 <b><i>every</b></i> 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:<pre>
L4S L4T L94T L4
---| |-----|/|------|/|----------( )
|
L4 |
---| |---</pre>
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....

N

#### Neo

CSA,

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.

N

#### 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

N

#### 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.

#### CSA

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.)

N

#### Neo

CSA.

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:
<pre>

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

</pre>

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

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

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

L94X=Startup check stop GT normal shutdown;
L14HS=HP operating speed signal;</pre>

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.
<pre>
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;
</pre>

Timer_sec _Counter
L2FZ(log_in) (log_out)L62TT-----------L62TT(INC) (AT_CNT)L63TT2
K62TT(pu_del) K62TT2(MAX_CNT)</pre>
L1XY(RESET)
</pre>
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?