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Control Temperature Mode
Gas turbine MS5002B (with Mark VIe control) frequently works in control temperature mode.

Greetings

Our Gas turbine MS5002B (with Mark VIe control) trips a lot, and it works in control temperature mode a lot. knowing ambient temperature about 40 degree my deep worries are:

why this mode persist? is it abnormal operation? what the really reasons and sources? if is it what could we do for solving this problem?

thank you for the benefit of your experiences and knowledge. It's always much appreciated!

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

I think you need to do some reading on how Speedtronic works. If you don't understand Temperature Control (and tripping), send me an Email to bbobjohnston@gmail.com and I'll send you a beginners document.

By mohamed31 on 18 July, 2017 - 3:00 am

yes of course I will be so thankful sending me some valuable documents MS5002B And MARK6e control

my email: bossmed91@gmail.com

thanks million.

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

Do you mean Temperature Control mode?

Typically the displays used to indicate "Exhaust Temperature Control"--which could mean either Part Load Exhaust Temperature Control ("combined cycle mode, where the exhaust is directed to a HRSG (Heat Recovery Steam Generator--a waste heart recovery "boiler") and the IGVs are used to maximize exhaust heat to help produce more steam), OR Base Load Exhaust Temperature Control--which is maximum available gas turbine power output for the present turbine conditions and ambient conditions.

What Process- and Diagnostic Alarms are active when the turbine is running?

And, more importantly, What Process- and Diagnostic Alarms are annunciated just prior to the trips? And just after the trips?

GE used to have a standard that EVERY trip condition had a Process Alarm message associated with it, and that SHOULD still be true, but sometimes isn't if proper programming and configuration practices are not followed.

BUT, someone at the plant SHOULD have some idea why the unit is tripping so much. I find that one many two-shaft compressor-drive applications there are MANY interlocks, start-check permissive, load runbacks and trips--some added in the field WITHOUT Process Alarm messages per the "standard."

AND, also, often on compressor-drive applications the plant control system has only one or two discrete outputs that Trip the turbine--but those one or two discrete outputs can be actuated by SEVERAL different conditions, which aren't obvious to the operators sometimes.

Both of the temperature control modes above are normal-/not abnormal. If you actually mean 'control temperature' then it might be Process related (two-shaft GTs usually drive mechanical compressors and 'control temperature' might refer to the temperature of the gas being compressed, not the turbine exhaust temperature. It wouldn't be uncommon for a process temperature to be VERY close to the process temperature trip setpoint and causing nuisance turbine trips.

But, we would need to know a lot more about the plant and the turbine to be of more help. And, the Alarm Log and Trip History functions of the HMI should be able to tell you why the turbine trips--EVERY time it trips. And it is possible to look back, usually 30 days, to see what is initiating the trips. It's ABSOLUTELY NOT NORMAL for a GE-design heavy duty gas turbine to be tripping frequently. Either there are are Diagostic Alarms and/or Process Alarms which are being ignored, or the compressor or plant control system interface is not properly configured or not properly tuned, because other plants with good programming and configuration, proper attention to alarms and decent process tuning DO NOT have these problems.

Hope this helps.

By mohamed31 on 17 July, 2017 - 9:46 am
1 out of 1 members thought this post was helpful...

thanks for this clarification .

first of all THE trips are generally customer trip (process). in fact the mainly reason is compressor surge for lack of flow (not enough), and its another problem in the plant. but MY posting about our turbine for getting more ample information about FSR which displays, as you know, in the bargraph of temperature, means the turbine is in control temperature. Honestly I am beginner and I need your helps to understand more and any valuable information or your orientation (documents if possible to understand).

thank you a lot.

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

mohamed31,

Best to send your email to glenmorangie to get his materials to get you started reading on how GE-design heavy duty gas turbines typically operate (the standard GE control philosophy).

Have you looked in the Operations and Service Manuals provided with the turbine? There is usually a section for each of the systems of the turbine, and a section that discusses basics of GE heavy duty gas turbine control philosophy. There are mostly generic write-ups, but they should help you get started in your journey of learning and understanding.

We're here to help answer questions, and we use a modified American version of The Queen's English, hence my unfamiliarity with the term 'control temperature.' Funny thing about technical terms, two words can be used to mean one thing, and then when they get reversed they can mean something entirely different. GE typically calls it 'temperature control' when speaking about the function in English (written and verbally). I don't know how the HMI was configured at your site, but some HMIs have some unusual "translations" of technical words and terms.

If you're referring to the bargraph display of FSR, that's trying to tell you that there are several FSR calculations going on ALL the time while the unit is starting and running, and the lowest of all the values will be the one that actually controls the amount of fuel going to the turbine. In other words, there is a minimum selector in the turbine control system that looks at all of the different FSR calculations chooses the lowest value (the minimum value) to actually control the amount of fuel.

As the turbine is started and loaded and unloaded and shut down, the control can shift from FSRSU (FSR Start-up) to FSRACC (FSR Acceleration Control), to FSRN (FSR Speed Control, to FSRT (FSR Temperature Control), to FSRSD (FSR Shutdown Control). There's even a "manual" FSR control (which can ONLY be used to limit the amount of fuel--not to increase it!).

When the unit is trying to produce maximum power, then FSRT should be the minimum value of FSR. All the other values of FSR are higher then exhaust temperature control. When on exhaust temperature control, often called "Base Load," the turbine control system is looking at the operating condition of the turbine, specifically the axial compressor discharge pressure, and there is a "curve" which is programmed into the turbine control system that says for this axial compressor discharge pressure the exhaust temperature should be this value--and it puts as much fuel into the machine as possible trying to maximize the exhaust temperature. The value of exhaust temperature is called the exhaust temperature limit, because the exhaust temperature is never supposed to exceed that amount. If it does exceed the exhaust temperature limit by more than 25 deg F then an alarm is annunciated, and if the exhaust temperature exceeds the maximum allowable amount by more than 40 deg F then the turbine is tripped (the message is EXHAUST OVERTEMPERATURE TRIP).

The exhaust temperature limit curve is flat (constant) during starting and early loading, then it begins to drop as axial compressor discharge pressure increases. So, above a certain axial compressor discharge pressure the exhaust temperature limit value starts to actually decrease. When the actual exhaust temperature for the present axial compressor discharge pressure equals the exhaust temperature limit--the unit is said to be on exhaust temperature control, or "at Base Load" which is the most power it can make for the machine conditions at the time.

Hopefully you will find some examples of the curve and some better explanation.

BUT, one thing to know, if the turbine is experiencing a lot of trips (for whatever reason) while it's operating on exhaust temperature control (FSRT)--then the internal parts of the gas turbine are being stressed by the sudden temperature changes when fuel is shut off very quickly and flame is lost and there is a lot of air flowing through the machine (from the axial compressor discharge). This is NOT good for the turbine--not good at all. GE typically has some complicated charts and formulae for determining how much the stress reduces the internal parts life and how it hastens the next maintenance outage.

Think about it--the internal combustor diffusion flame temperature can be as high as almost 3000 deg F, and then it gets cooled to somewhere around 2100-2200 deg F before it enters the turbine sections. And when it's at Base Load, the turbine control system is putting as much fuel as it can into the turbine to try to make the exhaust temperature equal to the exhaust temperature limit (which is pretty high, possibly around 900 deg F). And, then--all of a sudden, the fuel is shut off (which is what happens during a trip), and now the flame is extinguished. Now, the axial compressor discharge air, which is probably only at approximately 700 deg F or so, is flowing into and through the combustor and the turbine sections. That's a BIG temperature differential--VERY BIG--to happen is a split second. And, the turbine internal parts don't really like that very much. Do it a lot, and those parts aren't going to last as long as they should. Which means the machine is going to have be shut down before originally planned to inspect and replace those parts--because to wait longer just invites some part to break, and that part can then cause a LOT of damage as it goes through the turbine sections and into the exhaust.

So, reducing the number of trips helps to increase the life of the internal parts, which means the turbine can run longer between maintenance outages, which means the production can be higher between maintenance outages, and the amount of labor and parts for a maintenance outage doesn't have to be spent as often. And the likelihood of something breaking and causing severe damage is also reduced.

Many plants have 'trip reduction' programs to try to determine why the number of trips are so high, what is the major cause of the tripping, and then working very hard to solve the underlying problems to prevent the trips. Trips cost real money--in lost production and re-start time and fuel, and also in maintenance cost (increased frequency of maintenance outages and spare parts), and, a LOT of really severe turbine damage can often be traced to a high number of trips, and/or a specific trip which caused a part to fail, which then caused more parts to fail--and greatly increased the cost of the outage to repair the damage and also the lost production.

Hope this helps!

Send me an email address, and I'll send you a document which will answer all your questions.

By mohamed31 on 19 July, 2017 - 2:24 am

yes I am thankful and this is my email;

bossmed91@gmail.com

> Send me an email address, and I'll send you a document
> which will answer all your questions.

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

Some general comments/questions on this thread:

1. If this is a MS5002B with Mark VIe control, I strongly suspect the Mark VIe is a replacement control. The original control was likely a Mark II control or possibly a Mark IV. Is the Mark VIe simplex or triple redundant?

2. The IGV's may be the 2-position variety (full open or full closed rather than modulated).

3. Does this unit have a regenerator on it?

4. The gas turbine should not be tripping on high exhaust temperature - the control should keep it below the trip point. If you are reaching the control limit on exhaust temperature, the unit is at base load - you cannot increase the load above this. The LP turbine will decrease in speed if the process conditions try to increase the load.

5. If the load compressor is operating with the recycle (anti=surge) valve open, and the recycle gas is not cooled, then you will likely exceed the discharge temperature limit of the gas compressor fairly quickly. That will likely trip the gas turbine.

6. What is the control mode for the speed of the LP shaft? Discharge pressure? Maybe with low suction pressure override? Flow control?

By Leandro Carletti on 24 July, 2017 - 9:09 am

working in temperature control for a MS5002 is not abnormal condition. is not a alarm condition is only indication.

Best Regards