We have a problem in Frame 5 turbine Mark2 run on gas. only in the case of normal shut down, speed reach about 80-82% and stop to continue down (no there any alarm). then the operator by pressing the emergency button to stop the unit.

What is responsible for extinguishing the flame in the combustion chambers in the case of normal shut down

 

i think the problem with speed card in mark 2 .

 

MK, if I understand your question problem correctly, you are saying that when the turbine is in a shutdown (L94X) the unit decelerates to around 80-82% speed, then stops decelerating.

During a typical shutdown, logic is written to set VCE or FSR to a level that allows the turbine to decelerate smoothly(via a shutdown fuel curve), and controls temperature of hot gas parts, until the unit falls to around 30% speed and flame out occurs. This fuel curve is generally set during commissioning. Unfortunately due to differences in ambient temperatures it does not always perform as desired. As a backup there is usually a timer that will stop all fuel after a timer expires, usually started when breaker opens.

Other factors can also influence how a shutdown occurs. If fuel valve calibrations have drifted this can also cause problems with shutdown fuel control.

As with many other posters I would ask if anything has recently changed with this unit, maintenance/repairs/changes/trips? This is always your best place to start looking. Also have any ambient conditions changed? It is possible that a change to shutdown fuel control may be required, but I would check other factors like calibrations etc. first since if logic worked ok before it should still work now, as long as the inputs and outputs that define the logic are correct.

I hope that this helps some, my answers are based on my experience with newer controls which are usually quite different than the earlier speedtronic/MARK systems.

 

1. My recollection is that Mark II and older controls did not have the "fired" shutdown which keeps flame on until around 40% speed.

2. I am guessing that your machine is 5001R, mechanical drive (compressor or pump) rather than a generator drive, and the minimum operating speed is around 80%. If so, my recollection is that the normal shutdown sequence would run the unit down to minimum speed and would sequence valves as required to put the load equipment in a shutdown condition. This part would be custom designed for each project. Once feedback from the process confirmed that load sequencing was complete, and the unit was at minimum operating speed, the unit would be tripped.

3. If, on the other hand, you do have a generator drive, the standard shutdown sequence would unload the generator until reverse power was sensed, at which point the turbine would be tripped.

4. So, this leads to the question of what changed with your unit? Have you changed the process equipment in a way that would change the shutdown interface to the turbine control?

Need more information.

 

The originator did not tell us what fuel the unit is burning, nor when the unit normally loses flame during shutdown.

MIKEVI is also very correct in his line of questioning that we should always begin with: What has changed? New fuel nozzles? Recent Speedtronic calibration? Recently replaced cards in the Speedtronic? There was a lot of "calibration" that had to be done with a Mark II, not so difficult, but with potentiometers and such for control, things needed tweaking and adjusting more often than with digital controls.

New Liquid Fuel Control "Valve" (some older machines used an axial piston high-pressure liquid fuel pump with a variable "swash" plate that was driven by a hydraulic actuator via an electro-hydraulic servo-valve as the means for controlling liquid fuel flow, not a bypass valve as in many more modern units). There's a lot we don't know about the unit and the circumstances.

I don't have a ton of experience with Mark II Speedtronic, mostly only troubleshooting grounds and some basic I/O problems, and I've been hoping that otised would respond to this one as he likely has more experience with this than most on this forum.

The good news is that GE doesn't change things too much from one version of Speedtronic to another, but this may be one of those things that is different.

I believe MIKEVI is mostly correct, that the fuel during shutdown is likely ramped down as a function of speed, but, because the Mark II didn't have much in the way of compute horsepower I don't think they were really able to do a lot of fancy things when it came to protecting hot gas path parts like they started doing with the Mark IV (they called it "Low Cycle Fatigue" protection).

I've been told that on some older Speedtronic control systems, that ramping the fuel down during shutdown wasn't done, and that on some machines the fuel was just shut off once the unit reached a particular speed level. I've even heard that on some machines it was at 95% speed!

But, I would also believe there was some kind of timer to shut off the fuel if flame hadn't gone out in some "reasonable" amount of time after the shutdown was in progress and the unit had decelerated below 14HS.

One would need to look at the Mark II Speedtronic elementary (which was not done in ladder logic format which was a change from Mark I and then GE went back to ladder logic format with the Mark IV and now they've gone to function block diagrams with the Mark VIe) to see what drops out the Master Protective Logic signal, the "4" relay(s) during a normal fired shutdown (maybe a signal called 94X?) and then work backwards from there.

Lastly, units which run on liquid fuel usually have to shut the fuel off much sooner than units running gas fuel. This is because there is insufficient atomizing air during low-speed operation and as a result there may be a LOT of smoking (thick, billowy, white smoke). So, many Frame 5s and Frame 6s running liquid fuel have to shut of fuel as high as 50% or 60% speed to reduce the amount of smoking from the exhaust.

 

Our machine to drive a generator and no any change we do before the problem. it work on gas and diesel and the problem on gas because today when we make shut down on diesel the shutdown is normal and at 75% machine trips with 14HS by 4 signal, so we doubt with servo valve GCV or its card.

 

OK, apparently you do have a fired shutdown on a Mark II control, and it was set up to trip the unit after the speed drops below 75%, and the control works properly on distillate fuel. On gas fuel, the speed fails to drop below 80%.

Assuming no one has changed control settings for gas fuel, my guess would be that your gas supply has changed (either you changed suppliers or your provider has changed) and you are now burning a "hotter" gas. For gas fuel, I think you may need a lower VCE setting for the fired shutdown. I recommend you contact GE about this, and provide them with a current fuel analysis.

 

We found the feedback at GCV card (LVDT) incorrect so we recalibrated again. Now problem solved.

thank you very much for all.