Hi to all,

I have few questions about 6fa which Follows,

1.At what RPM of the turbine, starting Mean disengage from the turbine shaft. (we use electric mean starting system with voith coupling and Natural gas used as fuel)?

2.At what rpm purge done?

3.At what rpm firing done?

4.At what RPM Warmup done? and warmup estimate time?

5.at what Rpm acceleration starts?

6.if flame establish fail while startup, is the turbine reduced its speed to cranking speed?

7.on what basis fuel stroke reference for all the gas valves is set while starting the turbine or FSR is CONSTANT?

at last 8. why 100.3% speed at fsnl????????

Great minded peoples, Please do reply as easy...bliss to see.....

thanks and Regards....

 

Dear Jameelrahman,

the Frame 6 machine is not the GE heavy design turbine that I have the most experience with. But I will attempt to answer to the best of my abilities.

1.At what RPM of the turbine, starting Mean disengage from the turbine shaft. (we use electric mean starting system
with voith coupling and Natural gas used as fuel)?

Typically the starting means when they are electric or diesel will disengage at either 50% or 60% of the normal operating speed of the machine. The machines that use a static starter that turns the generator into a motor to crank the machine will typically assist the acceleration of the machine until it is near FSNL. I am pretty sure for your machine the speed is 50% when the torque converter is drained, and no longer transmits torque. The starting motor will usually run for a period of time after the converter is drained to allow the motor to cool.

2.At what rpm purge done?

Purge speed is usually something slightly more than 20% speed but we would need to see your application code to confirm. For most units using the Voith torque converter there are speed switches that set the angle of the vanes in the torque converter and those settings will determine the speed of the unit during the purge cycle. Purge is usually satisfied by the turbine speed being above the speed level detect of 14HM1 for a period of time defined by the purge delay time K2TV.

3.At what rpm firing done?

Typical firing speed on gas is usually 10% speed.

4.At what RPM Warm-up done? and warmup estimate time?

Warm-up is usually not done at a specific speed but a period of time after the unit fires. Typically fuel is admitted to the unit at a "firing" FSR rate. Once flame is established fuel is reduced to the "warm-up" FSR rate to reduce stresses on the turbine mechanical parts. Warm-up time is defined in the application code for your unit, possibly the constant K2W.

5.at what Rpm acceleration starts?

Acceleration should begin once the warm-up timer has completed. Speed will depend on how the torque converter has been accelerating the unit while the warm-up timer was running.

6.if flame establish fail while startup, is the turbine
reduced its speed to cranking speed?

If the unit fails to establish flame during the start sequence and the "firing timer" expires the unit will be tripped. The firing timer (K2F) is usually between 30 and 60 seconds.

7.on what basis fuel stroke reference for all the gas valves
is set while starting the turbine or FSR is CONSTANT?

Firing FSR, warm-up FSR, minimum FSR, and shutdown FSR numbers are constants. Most other operating situations are some sort of closed loop control. Acceleration, temperature, speed etc.

8. why 100.3% speed at fsnl????????

100.3% speed defines a speed where the during synchronization the machine has a positive slip as compared to the grid frequency. The 100.3% speed reference also sets a positive megawatt output of the machine, also known as "spinning reserve".

I hope this information is helpful to you, other contributers may answer your questions in more detail.

 

Hi,

I'll answer two of the questions:

> 7.on what basis fuel stroke reference for all the gas valves
> is set while starting the turbine or FSR is CONSTANT?

Well, FSR is the total amount of fuel to be flowing to the machine, and when there are multiple fuel nozzles operating in a staged system the control system is programmed to split FSR into the various nozzles based on a fixed calculation of the percentage of fuel to flow to each set of nozzles based on the combustion mode the unit is currently operating in. For example, if FSR was 25%, and the combustion mode required 25% of FSR to flow into one set of nozzles and the remainder (75%) to flow through another set of nozzles, the control system would position the appropriate valves to have 6.25% FSR flow to one set of nozzles and 18.75% FSR to the other set of nozzles.

The FSR during firing and warm-up is derived from the two Control Constants (FSKSU_FI & FSKSU_WU) that are modified by a speed- and axial compressor inlet temperature bias (TNHCOR) to help reduce temperature stresses during stating. When th ambient temperature is colder, the machine requires a little more fuel for firing and warm up, and when the ambient is warmer it requires a little less fuel to fire and warm up, but the difference is really only a few tenths of a percent FSR.

> 8. why 100.3% speed at fsnl????????

When synchronizing a heavy duty gas turbine its customary for the generator frequency to be slightly higher than grid frequency. The control system designers decided to standardize on 100.3% as the point at which the unit would be accelerated to during a START in order to be synchronized more quickly. (Having the prime mover running at a speed slightly higher than grid frequency means that when the generator breaker closes and the unit speed decreases to 100%, the extra energy that was keeping the unit just slightly above rated speed will result in a positive power output from the generator, thereby preventing a reverse power condition. And for a machine rated at 80 MW with 4% Droop that means the unit would be producing (((4/0.3)/100) * 80 MW)=+10.33 MW when the generator breaker closes.)

Its just a umber, and for some machines it's a big number and for others it's a smaller number (for a 25 MW machine it's (((4/0.3)/100) * 25 MW)=+3.33 MW; for a 150 MW machine it's (((4/0.3)/100) * 150 MW)=+20 MW). It's not cast in stone--meaning it can be reduced slightly, but it should only be done so with consultation and agreement of the OEM or equipment packager.

Hope this helps!

 

At first, Thanks for your time Brother....And Loads of Thanks for your reply....And one more thing i need to know that fuel Mode changes from one to another (like From primary to Lean Lean mode) based on RPM of the turbine or based on Exhaust temperature.

Thanks in advance.........

 

i blissed with your Reply CSA
Thanks so Much.
i have two more questions,

1.on what basis the gas fuel mode changes,whether it based on RPM of the turbine or the exhaust temperature?

2.what is the IGV angle at various startup sequence?

and one more thing from the reply of MIKEVI, which is the first reply of my post. In that first one , he said the starting mean disengage at 50 or 60 % speed of the turbine rpm.And also he told, the starting mean provide acceleration to turbine upto FSNL(100.3%) of the turbine. how it give acceleration to the turbine while it disengage at 60% or 50% speed of the turbine.

Please do reply ..Eagerly waiting for your answer.

thanks and regards.

 

MARKVI,

Great detail--thanks!

I only have one quibble--and that is what happens when the unit fails to establish flame during starting. In my experience, when the unit fails to fire on the first START attempt the unit just continues to spin ("crank") until an operator takes some action.

Some units have "legacy" sequencing that will automatically try a second firing--with no operator action required, which surprises many people to be discussing the first fails START attempt and to see the unit has established flame and is accelerating "all by itself."

I have heard of machines that do trip on "Failre to Ignite"--but I think they're the exception rather than the rule.

How many turbines do you see, as a percentage of the total machines you work on, trip on "Failure to Ignit"?

 

Dear Jameelrahman,

First I need to answer the question posed by MR CSA. In my experience I have never had a machine trip on failure to ignite. I have seen the legacy code you speak of that is designed to initiate a second attempt to fire if the first attempt fails, but I have never tested the logic to see if it would actually work. I have also seen the code that will trip on the first failed attempt, but never tested that either. I admit that I definitely do not have the field or life experience with the GE heavy duty turbines that you have. But I still attempt to help, and I appreciate you catching me when I might be wrong, or at least questionable in my answers.

For you Jameelrahman here goes a couple more.

1.on what basis the gas fuel mode changes,whether it based
on RPM of the turbine or the exhaust temperature?

Fuel mode changes are most always a function of TTRF1 which is the calculated temperature of the gases entering the 1st stage turbine nozzles. I assume by fuel modes you mean primary-secondary-lean-lean and premix. Or in the DLN2.6 machines the admission of fuel from various nozzles of PM1, PM2, PM3 and quat. I believe that the TTRF calculated number is used since the calculation is the best way to estimate a consistent load and mass flow through the machine that is not affected by ambient conditions and compressor efficiency.

2.what is the IGV angle at various startup sequence?

The IGV's and inlet bleed heat are primarily used to protect the compressor during startup and shutdown of the unit when the compressor is most susceptible to stall. These two systems are also used to control airflow through the compressor and combustion cans to best match the supply of fuel. This is done to control CO and NOX emissions at various loads. So I really can't give you a number of what IGV angle is at various times in the startup sequence. I believe that they are mostly closed during runup from firing speed to prevent compressor stall, and they start to open at around 80% speed because that is the speed at which the compressor starts to become efficient.

and one more thing from the reply of MIKEVI, which is the
first reply of my post. In that first one. he said the
starting mean disengage at 50 or 60 % speed of the turbine
rpm. And also he told, the starting mean provide acceleration
to turbine upto FSNL(100.3%) of the turbine. how it give
acceleration to the turbine while it disengage at 60% or 50%
speed of the turbine.

I did not want to confuse the situation with my answer, but I did anyway so I will try again. With machines using an electric motor as a starting device they may use a torque converter coupled to the accessory gear. The older starting systems used a "jaw type clutch". Do a google search and look for articles about gas turbine jaw clutches, I found a couple from SSS that have good pictures and descriptions. The jaw clutch systems were arranged where the output shaft of the torque converter had a "jaw" attached. The input shaft of the accessory gear also had a "jaw" attached. When a start was initiate pistons would push the two jaw clutch halves together and torque from the motor and torque converter would turn the turbine rotor through the accessory gear. Switches on the jaw clutch would indicate to the control system that the clutch was coupled together. As the unit accelerated past the "self-sustaining speed" the turbine would start to outrun or overspeed the torque converter shaft. This would push the jaw clutches apart, and the control system would see that by a change in status of the clutch switch. At this point the starting means would shut down since it was no longer providing torque to accelerate the unit. Later units used a similar system but replaced the jaw clutch with a SSS clutch. But with these systems there were switches to indicate when the clutch was applied, and would also signal the system when the turbine was accelerating on its own and the starting means was no longer needed. The speed when this occurred was typically between 50-60% speed.
Now in the case of your unit using a Voith torque converter I do not think there is any type of clutch. The output shaft of the torque converter is directly coupled to the input shaft of the accessory gear so it spins all the time the machine is running. In this case there is typically a speed setpoint in the control system that determines when the unit has reached a self sustaining speed and can accelerate on its own without the starting device. This speed is set in logic and for your unit I think should be 50% speed.

Finally I mentioned that the large frame machines, 7FA, 9FA, and the H class machines do not use electric motors for starting. Rather they use a load commutated inverter (LCI) which transforms the generator into a motor to crank the unit. This type of starting system can transmit torque all the way to FSNL.

I hope this clears up my answer.

 

thanks Brother, For give me a clear view of thoughts.....

Best regards....

 

The default design practice when I was directly involved in heavy duty gas turbine controls (Mark I and Mark II time period) was to hold at crank (purge) speed after a failure to fire, and wait for the operator to decide whether to try again (the re-fire was initiated by moving the selector switch from AUTO or FIRE to CRANK and then back to AUTO or FIRE). However, for unmanned stations, with remote start and stop capability, at least one additional automatic attempt to was generally made. If the end user required it, additional firing attempts were permitted. Note, purging was required between attempts. Back in those days, cranking speed and firing speed were usually the same (about 18% speed).

 

MIKEVI,

I haven't had a lot of exposure to some of the newer machines that have, hence the reason for my question. People are ALWAYS telling that their unit trips on a "Failure to Ignite" and while I have been told by other experienced controls people they DID work on units which actually tripped on "Failure to Ignite " each one also told me that it was unusual in their experience--that usually the unit continued to "crank" indefinitely.

You and I know that the 4's are still picked up and a START is still active if the unit is still at CRANK speed after a "Failure to Ignite" but that the Speedtronic won't "do" anything to try to re-fire (unless that legacy sequencing is present and active). And we also know that it's not written anywhere in any documentation that when a "Failure to Ignite" occurs the operator must select CRANK then FIRE or AUTO to re-initiate the firing sequence, or initiate a STOP and wait for the unit to coast down sufficiently to get a "Ready to Start" indication to try another fired start.

GE does such a disservice to their customers by not providing good documentation, and this basic operation description is a perfect example of the harm caused by the lack of documentation. The same people who tell me the unit tripped on "Failure to Ignite" say they had to trip the unit or give it a STOP in order to try another START. It didn't really trip, but they couldn't get the unit to do anything even by clicking START again--it would just keep cranking--and selecting CRANK then re-selecting FIRE (or AUTO) is not very intuitive, so they just think it "must have tripped."

I wasn't trying to slight anyone's experience, just asking to get an idea of the percentage of units you have worked with that tripped on "Failure to Ignite." Nothing more than that. I do believe there are actually units that are programmed to trip on "Failure to Ignite" but they are the exception rather than the rule, and it really goes counter to GE's philosophy of trying to reduce the number of trips.

Again, no slight was intended--none. Just trying to get a feel for the number of units that actually trip on "Failure to Ignite."

 

Mr CSA,

No slight was taken in your question or comments. I wanted to be truthful to you and the original poster that my experience and exposure while growing is still somewhat limited. I have had the pleasure to go through several commissioning activities where I think one can gain the most experience. And have the chance to test various parts of logic that may never get used or tested. But so far I have not had a unit ever have a problem firing that caused a failure to ignite that I can directly comment on.

I think GE could do a much better job of documenting logic. When talking about control systems, certain OEM's do specific things very well, and others not so much. But I have not seen the perfect control system yet in my opinion. I enjoy working with the GE speedtronic systems, but they definitely do some things that make me scratch my head.

Again no slight was taken from your comments or question. I like many others very much appreciate the time and effort you contribute to this site. And I count on you to catch me if I make a comment that may not be correct, or is based on my limited exposure to the GE fleet. I am here to learn, and hopefully help others with what knowledge I can share.

 

As a reference for the DLN 2.6 combustion mode changes are made:<pre>
1D - 100 F
3 1650 F
6.2 1850 F
6.3 2230 F</pre>
Values can look at the Toolbox