I am working in 6FA machine with Mark V system. Now Machine running with base load (Temperature Control). In S core DWATT signal lost due to transducer failure and others working fine.

What will be the consequence if DWATT signal loss more than one?

 

VIJAY,

If the unit DLN (Dry low NOx) combustors and three, redundant lad transducer inputs, it will likely trip because of the loss of two of the three inputs. DWATT is a very important component of DLN control schemes, and the designers deemed it possibly destructive to the hot gas path components to operate with only a single (out of three) input.

 

Are you checked Electrical measuring transducer "TRIAD"? Usually installed in Exciter panel, and each controller have own transducer.

 

Checked and found problem in S core MW transducer in Exciter panel,
it is showing -52MW. Remaining core transducers working fine and DWATT showing real what we generating.

My question is: In this situation what will the consequence if failure of one more transducer which is installed in Exciter panel?

Failed transducer showing -52MW. Transducer failure alarm compactor constant value is below -75MW. At present DWATT voting mismatch alarm persisting.

 

This is a great post. But I have other issue around DWATT. DWATT, DWATT1, DWATT2 - I have 2 units Fr6B. Unit 2 showing different value on DWATT and Unit 3 showing same value. May I know how important is DWATT value in Mark 6 and turbine load control?

 

@norshamorigin,

In general, DWATT is usually the higher of the two values DWATT1 and DWATT2. DWATT1 and DWATT2 are usually two redundant load sensors, and the Mark* usually compares the two and selects the higher of the two and that selection is given the signal name DWATT. (Why, you ask, is the higher of the two signals chosen? Because the usual failure mode of these types of sensors is to fail with a zero output (which can sometimes actually be negative MW (MegaWatts) depending on how the sensor is configured and scaled.)

DWATT is then used as "the" load signal in the program/sequencing/application code running in the Mark* for control, protection and monitoring of the machine.

Load sensing may be very important for some machines/applications, and not so important for others. If the site uses Pre-Selected Load Control it is required to operate properly when Pre-Selected Load Control is enabled and active. Machines with DLN (Dry Low NOx) combustion systems usually use DWATT for help in stabilizing fuel flow-rates during combustion mode transfers. Having multiple redundant load sensors (two, and in some cases three) helps with machine reliability and availability--and GE is pretty committed to reliability and availability (which is also greatly affected by on-site machine maintenance and care--including Alarm Management, which means quickly troubleshooting and resolving alarms to prevent knock-on effects when and how possible).

Usually when one of the two redundant load sensors (DWATT1 or DWATT2) goes low (zero output) there is usually an alarm to alert a conscious operator and technician of a problem with the respective sensor. The machine will still operate BUT the problem should be investigated and resolved quickly so that machine reliability and availability are not affected.

The above description is typical of many--but NOT all--Mark* systems. There are and have been several methods of sensing load used over the decades of the Mark* turbine control system, and there are often changes applied for specific reasons depending on the requirements of the equipment.

LASTLY, many Mark* turbine control systems will have all three DWATT signals (DWATT1, DWATT2 and DWATT) but only use one of them. Good programming practice would dictate that unused signals are not allowed to be viewed on the control system, but, good programming practice is most often in the eye of the beholder--not the programmer who is charged with getting the equipment out the door as quickly and inexpensively as possible so cleaning up the control signal database to eliminate common unused signals isn't required to happen and therefore usually doesn't. The ONLY way to tell for certain how your machine's turbine control system is configured to examine the materials which document the configuration and programming of the turbine control system controlling and protecting and monitoring the machine(s) in question.

 

Dear WTF,

Thank you for the insightful response.
My application is GTG Fr6B conventional combustion with HRSG. I am not a control engineer. I am a mechanical guy. Our site has been suffering with 2 issues at unit 2; 1st one is high exhaust spread and one is synchronising issue. Both still not well understood. Currently tackling high exhaust spread issue by replacing the suspected faulty thermocouples based on thermocouples reading showing lowest value around the combustion zone. Sometimes I recommended to reduce the load by changing from baseload mode to pre-selected load and high exhaust spread 1 improved and let the GTG stay online like this until I have SD window to replace thermocouples. 2nd one is difficulty to synchronise the generator at every start up and currently tackling it by changing a Constant (at the time I am writing this I forgot what the constant name) but it worked every-time during synchronisation which I don’t understand and cannot explain this. After synched that constant is changed back to original value. Okay….back to DWATT, DWATT1 and DWATT2….I have checked today DWATT description is Max Selected. DWATT1 is megawatt transducer 1 and DWATT2 is megawatt transducer 2. Strangely I checked today, DWATT value is 22MW. DWATT1 is 29MW and DWATT2 is 40 MW. By right DWATT value should follow DWATT due to Max Selected. Unfortunately DWATT value although configured Max-Select; it has its on value not 40 MW. With these 2 issues I have(repeatedly high exhaust spread and difficulty in synchronization at every startup) made me to look for what is actually controlling the turbine firing temperature. I am trying guessing DWATT is the culprit of both issues. So this is where I stand right now - I am recommending to replace both DWATT1 and DWATT2 because Mark 6 never selected the highest one at all. Mark 6 shows DWATT 22MW. Cut story short, I have repeatedly high exhaust spread issue, I have repeatedly generator synchronising issue at start up unless our technician changed the ‘constant’. I am actually speculating this since we have never missed CI, HGPI and MI and I see no evidence of fuel nozzles anomalies and I see our fuel gas is good quality sales gas. The only doubt here is the DWATT since they are not tally and I compared unit 3, DWATT, DWATT1 and DWATT3 are identical and has no the 2 issues we are facing in unit 2. Unit 1 is been long out of service awaiting MI.

 

@norshamorigin,

I know you're new to Control.com, but it's been said MANY times before over 20+ years--the longname descriptions of signal names CANNOT be trusted 100% of the time. They are correct many times, most times in fact, but there are times when they are wrong. It's sad--but true. One MUST go to the Toolbox application code display and search and discover the actual meaning/use of specific signals to be 100% certain of their function and derivation. I'm sorry; it's just the truth.

SOME Mark* turbine control systems--but not all, not even in the same "family" (Mark* V, or Mark* VI or Mark* VIe)--use two DWATTn signals wired to each of the three control processors and each control processor then does the selection of the highest value to be DWATT. As was written--there are a number of ways the selection can be done. And what you are describing doesn't seem to be possible, BUT we can't examine/review the application code running in the Mark* VI to see how it's configured and operating. We don't know where you are getting the three signal values from. I presume it's from somewhere in Toolbox, but where? Are you actually looking at the block that compares DWATT1 and DWATT2 to derive DWATT?

Let's shift for a moment to the exhaust temperature spread issue. We don't know what fuel(s) the machine burns so that's one unknown. We don't know what kind of combustion system the machine has (DLN, conventional (including multi-nozzle quiet combustors)--another unknown. BUT, I can tell you this with a very high degree of certainty: Most exhaust temperature spread problems are DEFINITELY the result of some kind of fuel nozzle or combustion hardware issue. This statement presumes the exhaust thermocouples are properly inserted in the radiation shield tubes and the tips are not touching metal. I'm also presuming the wiring interconnecting the exhaust thermocouples to the Mark* has bee done correctly (this subject has also been covered MANY times before on Control.com--thermocouple wiring is somewhat unique and must be done properly.) People just don't want to believe the problems can be mechanical in nature--because that Mark* thing has SO many wires and LEDs and it just must be the source of the problem. The fact that the spread value changes when load is reduced historically points to a mechanical problem (blocked fuel nozzle orifice; enlarged fuel nozzle orifice; cracked combustion liner or transition piece; etc.). There are MANY possibilities--if the machine uses water injection for emissions reductions it could be one or more of the water injection spray nozzles is plugged. If the machine burns liquid fuel (diesel; naphtha; crude oil) there could be carbonization build-up on the fuel nozzle orifices. The actual list is long--and I'm just suggesting possible issues because there's a lot we don't know about the machine.

Jumping to the synchronization issue--you need to tell us what Control Constant value you are changing, and what you are changing it from and what you change it to--for us to be of any help. There is a Synchronizing Display on the Mark* HMI--and on that display there should be six little squares indicating the status of the synchronizing permissives--when a square is red that means the permissive is not in the state to permit synchronization. When the square is green that means the permissive is in the state to permit synchronization. ALL SIX squares must be green for automatic synchronization to be possible and must REMAIN green as the synchroscope needle passes the 12 o'clock (vertical) position. They can't be green for 2/3 of a revolution of the synch scope needle and then one of them turns red as the needles approaches 12 o'clock; they all have to be green as the needle approaches and passes the 12 o'clock position.

I REALLY wish I could be more help--and I could be if you are patient and will provide the answers to the questions asked above (even if the sentence doesn't end in a question mark--the things we don't know are still questions!) and be patient.

You can take pictures of Toolbox screen and paste them into replies on Control.com. The only thing we ask is that you paste CLEAR photos (not grainy, unfocused photos) so that we can read them. Try to get the entire HMI monitor display in the photo, also. Sometimes there are things elsewhere on the display which can be helpful to solving the problem(s).

I can say with a very high degree of certainty that when the machine is disassembled for maintenance it is very likely some issues will be discovered in the combustion section. Again, this presumes the exhaust thermocouples are properly inserted into the radiation shields AND that the interconnecting wiring conforms to the wiring practices necessary to properly transmit millivolt signals from the exhaust thermocouple tip to the Mark*--for ALL exhaust thermocouples, in every junction box from the exhaust thermocouple to the thermocouple terminal board in the Mark*.

Tell us more about the machines at your site--what fuels they burn (maybe they start on diesel and switch to naphtha for loaded operation and shut down on diesel); maybe they have DLN combustors, or water injection for emissions reduction. There are Mark* VI turbine control systems and there are Mark* VIe turbine control systems--and LOTS of people call Mark* VIe turbine control systems Mark* VI--and that's incorrect and when talking to others it can be misleading. Please confirm if your site uses Mark* VI or Mark* VIe turbine control systems (TMR Mark* VI turbine control systems have four processor racks in the center cabinet (<P>, <R>, <S> & <T>). Mark* VIe turbine control systems don't have recognizable processor racks; instead they use small processor packs for <R>, <S> & <T> and LOTS of unshielded, twisted pair Ethernet cables and networks switches to interconnect all the I/O packs and processors). It's an important distinction--the difference between Mark* VI and Mark* VIe.

One more thing. Most people ignore Diagnostic Alarms--because they've been told that a Diagnostic Alarm cannot cause the turbine trip. And while, technically, that's true--there ARE combinations of Diagnostic Alarms that CAN cause the turbine to trip (there will most likely be some Process Alarms also warning of problems, perhaps even an impending trip)--but Diagnostic Alarms ARE important. And when troubleshooting things like the DWATT issues on your Unit 2 they can be very helpful. Diagnostic Alarms are important and just because the Diagnostic Alarm text messages are cryptic and difficult to understand, they can be "interpreted" by others and be very helpful in resolving some issues. USUALLY, if a Mark* VI I/O card has one or more Diagnostic Alarms associated with it there will be a yellow or red LED either flashing or continuously illuminated on the face of the card. All of the green LEDs of all the cards in a Mark* VI turbine control system should be blinking at the same time and the same rate. If there are any red or yellow LEDs lit or flashing on a card or multiple cards that will help you to determine which cards to look at in Toolbox to read the Diagnostic Alarms (if they aren't displaying on the Alarm Window along with the Process Alarms).

AND, if you can tell us what Process Alarms are active in the Alarm Window (you can take a clear photo of the Alarm Window and attach it to your response) we can probable be of more help, also.

So, lots of information here. And we can't know what you are seeing and what you've done to try to troubleshoot the problems of your Unit 2. Tell us what you're seeing, what you've done. And, provide as much information as possible and I'm certain you will probably be happy with the response(s) you will receive.

Help us to help you.