Thank you very much Mr. Markvguy, for clarifying me the meanings of sinking relays (PTRS AND ETRS). I would like to know more about that. My doubts are as follows.

1. The relays that are present in the TCRA card (all total 60 relays in 2 TCRA cards for Q processors), they have also coils that are energized by 24 V DC or any other voltage source? Are they all sinking relays?

2. If we se the signal flow diagrams then the contact output no 16 (DTBC screw no 61, 62, 63, 64) 17 (DTBC screw no 65, 66, 67, 68) and 18, they require special short circuit protection. Why they need this, because of big size or what? Are these corresponds to solenoid 20CB, 20FD and 20CF, or any other solenoids?

3. This is regarding the air to fuel ratio of gas turbine, is it same at all times (50:1), means during starting, at different loads, etc.?

4. While starting the gas turbine, why the speed of the gas turbine come down after purging cycle? It is to get a stable flame, or any other reason behind that?

Please clarify my doubts.

 

I would be a li'l surprised to know that the speed of the turbine "falls" after purging or firing!! (Q.4) All I knew, so far, was that after 14HM permissive the turbine vent timer starts... During this time the turbine speed increases from 975 RPM to around 1250 RPM, still driven by Diesel Engine... (But never drops!!).. This rate of rise is quite slow (and boring too!!)... After this five minutes delay, the firing takes place... (There is a step change in FSR to a value called as "Firing FSR" and spark plugs ignite for 60 secs)... After flame establishes the FSR reduces exponentially (a first order fall) to a "warm-up FSR" value marking the begining of a 60 Sec warm up time... This is, perhaps, to avoid thermal stresses on the system... Even at this stage, the speed doesn't fall!! It just rises at a lesser rate because of the exponential fall in FSR Value... After the end of this time the FSR rises linearly ("Acceleration FSR") and accelerates the turbine till FSNL...

No where in this sequence, I've noticed a fall in speed of GT at our site... Should there be any??

au revoir
Rahul

 

Be surprised, Rahul. Be very surprised. (Couldn't resist that one!)

Frame 6s, Frame 7s, Frame 9s almost ALL purge at a speed higher than firing, decelerate to just below firing speed, fire, then accelerate to FSNL.

That's not a Mk II or a Mk IV or a Mk V or a Mk VI thing--it's a turbine thing. The control systems are programmed to work as required for the type of turbine being controlled.

So, at your site the units purge and fire at basically the same speed--the starting means system doesn't have the capability to purge at a higher speed then decelerate and fire at a lower speed. It's quite common for Frame 5s; not all turbines are operated like Frame 5s.

markvguy

 

Mr Rahul,

I agree with what Mr Satyanarayan is saying regarding drop in speed during the purge cycle or rather immediately before the firing takes place.

I am talking about Frame 9 machine with Mark 5 control, started up with a 6.6kv motor and a torque convertor, not a diesel engine. This machine does have a HRSG in the exhaust. So i was always under the impression that this is a normal GE mode of operation, i mean about the drop in speed. Now that this point has been raised i would also like to know, whether it is normal? But i must admit that i havent gone thru the CSP to find out if this is normal.
I must also add that in our frame 5 and 6 machines which operate in open cycle, i agree with what Mr Rahul says, i havent seen any drop in speed. And yes these machines are started by Diesel Engines and controlled by Mark 2 control.

So maybe in case of machines with HRSG, the machine is brought upto purge speed, and allowed to spin so that sufficient air is delivered to purge the downstream side and during this perod maybe there is no additional power output from torque convertor resulting in little slowing of the rotor.

Saju

 

We have GE Frame-9E machines, and we have a starting motor (cranking motor) for startup. Yes it is true that after 10% speed there is 1 minute vent timer. At the end of the vent timer speed increases to around 22% speed (660 RPM), but after that speed decreases to around 9.5% and again increases when sped is greater than 10% at which L14HM picks up and stop valve closes (in case liquid fuel). In gas fuel also same sequence occurs.

I think you have Frame 5 or Frame 6 M/C so you have diesel engine. But for firing speed decreases after the end of 1 minute vent timer.

The firing timer is 1 minute timer during this 1 minute spark plug continuously gives spark and at the start of the firing timer FSRSU (FSR Start Up) is around 22% and within this 1 minute itself when 2 out of 4 flames are detected, FSRSU sets up to FSEWU around 14% for 1 minute, then FSRACC comes till FSNL.

Regards,

Satyanarayan Pradhan

 

You certainly have a lot of doubts.... Most dictionaries define doubt as "skeptical; disbelieving; distrustful; lacking certainty." Another poster has referred to the information being provided in response to his queries as being specious. Please be specific about your "concerns", or just state that you have questions. We happily answer questions here; but if the responses are deemed dubious, then, the desire to respond is quickly diminished. (Responses deemed specious... well, they don't get any further comment. Period.)

1. (NOTE: This question is related to Mark 5 Control Systems.) As was previously stated, nearly every relay in a Mark V turbine control panel (and ALL the relays on the TCRA cards) are "sinked" relays. Look at the Signal Flow Diagrams for the relay outputs--you can see that 24 V is applied to one side of all the coils continually from the TCDA card, and the signals coming from the TCDA card(s) must therefore act somehow to cause current to flow through the coil--by "sinking" the other side of the relay coil to COM.

2. (NOTE: This question is related to Mark 5 Control Systems.) Later revisions of the Mark V Application Manual had some extra explanations of those three relay outputs--which are intended for SPECIFIC applications (transient high current draws for Compressor Bleed Valve Solenoids and Liquid Fuel Forwarding Stop Valve Solenoids; voltage-reducing resistors for Electric Fuel Pump Clutches). The K17 and K18 relay outputs of the TCRA in Loc. 5 (i.e., CO47 and CO48) are intended expressly for ignition transformers (or, high energy ignitor excitors).

3. (NOTE: This question is unspecific to Mark V control systems.) No. Amazing as it may seem, air-to-fuel ratios are NOT controlled in any manner--that is, they are not measured or monitored or a part of the control scheme for GE-design heavy-duty gas turbines. The air-to-fuel ratio varies with compressor speed (during starting and acceleration) and Inlet Guide Vane angle (particulary for machines with modulated IGVs--i.e., most units built since the mid-1980s). The air flow which enters the combustor around the fuel nozzle (we're speaking of conventional combustor-equipped machines) is used for combustion and is only a small portion of the total air flow entering the combustor (the remainder of which is used for cooling and dilution of the combustion gases before then enter the first stage turbine nozzles). The combustion liner openings are all fixed, but since air flow varies with compressor inlet temperature, compressor speed, and IGV angle the amount of air entering the combustor varies as well. This author is not familiar with any specific air-to-fuel ratio, though it would seem logical that there would be a desirable range which the unit should be operated in for optimum combustion and efficiency. Gas turbines do operate with quite a bit of "excess air" as opposed to other fossil-fueled equipments.

4. (NOTE: This question is also unspecifc to Mark V control systems.) First, not all units behave this way. There are many units which just accelerate to one speed, purge at that speed for a fixed period of time, then admit fuel and energize the ignitors/spark plugs. For those units which accelerate to one speed (usually higher) for purging, then declerate to a lower speed for "firing" (ignition), it's done to shorten the purge time (higher air flow at higher compressor speeds), and the deceleration to a lower speed is done to keep the fuel admitted during firing to a minimum to reduce the thermal stresses on the machine and to ensure a more reliable ignition at a lower air flow. The starting means (diesel or electric motor or expander turbine) is used to accelerate the unit up to about 50-60% of rated speed as the power available from low-speed firing is insufficient to accelerate the machine. (F-class machines operate slightly differently.)

markvguy

 

Ours is a Frame V turbine, which doesnt evince this behaviour... May be I should be more circumspect in generalising my experiences and even "surprises"...

au revoir
Rahul

 

Seems there has been a mistake in my choice of words... The posting, where the word "specious" was used didnt mean to cast a doubt over mkvguy's responses... (None of us in this forum are equipped with sufficient information to raise a reasonable doubt over mkvguy's responses...!!) I searched that posting where the word specious was used... I read and re-read it over again...

http://www.control.com/1026221106/index_html

And by no means it was an insinuation to any of mkvguys' responses... (Infact, in that posting I had expressed doubt over my own rationale (referring to my own rationale as being "specious") to a certain query...)

Dictionaries convey only meanings not the "feeling" of a word... So on one hand if "I doubt" seems innocuous, "I am distrustful" sounds more harsh... English is not my mothertongue so am prone to making such errors... and I admit them... But, nonetheless, none of my remarks or words were "designed" to offend someone who, we all acknowledge, is doing a good job by sharing his knowhow...

au revoir
Rahul

 

It's not a matter of whether or not the unit has a heat-recovery steam generator (HRSG--fancy name for a "boiler"), it's just how the designers decided to use the starting means to start the units. The starting means has to be capable of purging at one speed and firing at another; the variable torque adjustor mechanisms on the torque converters allowed this fairly easily. (Of course, setting up the limit switches on the torque adjustor mechanism has caused many people much grief over the years--sure wish some of those designers actually had to use their "instructions" to actually perform the tasks!)

Some early Frame 7s did NOT have the capability to reduce speed for firing and sometimes they would ignite--sometimes they would not; and sometimes, there would be a very loud, low rumble when they finally did fire at the very end of the firing timer and all the fuel in the turbine and exhaust ignited. If anyone ever witnessed this after dark, it was pretty spectacular--scary but spectacular!

markvguy

 

Granted, English is not your native language. This author has observed that many people for whom English is a second language speak a more "formal" English than that used/spoken by the Americans--which can be a bit too informal. The issue here is that this topic has been covered several times and this author is unable to find the words necessary to convince you that while it SEEMS that the power output would increase because the CPD-biased turbine exhaust temperature limit increases when CPD decreases, that power output goes DOWN even though the exhaust temperature limit goes up. Counterintuitive, yes; but "them's the facts."

The frustration stems from the fact that rather than using the methods previously suggested to prove (or disprove) the validity of the responses given, that intuition is being used instead of facts to prolong the same discussion. The specious remark was interpreted to be in reference to the counterintuitive nature of CPD-biased exhaust temperature control--that because the actual operation is in opposition to intuition that the responses have been "plausible but false" (to quote one definition of specious).

It shouldn't bee too hard to see how the interpretation was made, given the nature of the discussions of this topic. Having only encountered the word once or twice in 48 years of speaking English, it was necessary to refer to a 12 year-old, tattered and worn copy of Oxford's English Dictionary purchased in Melaka, Malaysia, on this author's first international assignment when it was realized very quickly that the English being spoken by the Japanese architect/engineer and the Malaysian owner's representatives was much more formal than accustomed to. (Repeated use of the word "polemic" forced that purchase; nobody in the USA uses that word, except talking-head expatriates expounding on some political topic on television!)

The simplest way to prove to yourself that this conterintuitve business is true (or not) is to use the Realtime Plotting feature of the Mark V <I>(s) you have access to and plot CPD, TTRX, TTXM, FQG (for gas fuel flow), DW (or DWATT, depending on which signal is used on your unit), and CTIM, and monitor these values for several days, making printouts two, three or four times a day (depending on the time frame used on the display) every day at the same time and comparing the values. (Sound familiar? http://www.control.com/1026218083/index_html) [This is presuming the unit is operating at Base Load, CPD-biased exhaust temperature control--AND that the unit is actually operating on the CPD curve and NOT the back-up (FSR or DW/DWATT) curve!]

[This author has seen many <I>s which were not properly configured to use all the features of Realtime Plotting; if you feel your <I>(s) aren't, then that can be easily resolved--just let us know. Specifically, if you are not able to configure a Realtime Plot display to gather this data, and then return to the display using the same parameters quickly and easily, this can be simply and easily changed.]

When you do so, you WILL find that when the unit is operating at Base Load on the CPD-biased exhaust temperature control curve, as CPD decreases so will fuel flow AND power output; and that as CPD increases so will fuel flow and power output. You WILL also find that as CPD and fuel flow and power output decrease, the CPD-biased exhaust temperature control limit (TTRX) will INCREASE and the actual exhaust temperature (TTXM) will increase, also!

This is the part which is so frustrating: The means and the ability and the instructions to answer your own questions using the turbine control panel, operator interface, and test equipment (frequency meter, VOM) have been provided, but intuition drives your thinking even though the responses to your queries have told you that the operation is COUNTERintuitive.

Granted, the bean-counters, ...er, uh, the Production Department, can be difficult to work with when attempting to gather data, but for THIS particular question there is ABOLUTELY NO CHANCE of interrupting turbine operation by gathering data with the <I>.

markvguy (diligently working to eliminate specious responses)

P.S. This author wishes to encourage people to contribute their experience and knowledge to control.com. It's extremely encouraging to see more and more people contributing as time goes by, and we all benefit from the questions and responses posted by everyone.

The one feature which really makes control.com a valuable forum is feedback. In particular, when troubleshooting a problem, if something works--or doesn't, as the case may be--if feedback is posted indicating what worked and what didn't, we all benefit the most. The search function here at control.com is very quick and powerful, and when people search for previous posts to see if their question has already been asked and answered, if the thread includes feedback, they find immediate validation of the procedures/suggestions. Not only that, but the responders learn what works and what doesn't, also. Many thanks to those who do provide feedback!

 

dear mr markvguy
u have posted here that u were on an international assgnment in melaka, malaysia long time back. was it at the melaka power plant in tanjung kling, melaka? im asking this because actually im working at this plant now

thx n tc
sridaran
([email protected])