Shutdown VS Trip in Mark VI for GE frame V gas turbine

R

Thread Starter

Raza HAider

What is the difference between trip and shutdown in Mark VI. There are few interlocks in gas turbines which will generate a normal shutdown of the unit and will not generate a trip command.

These interlocks are

1. Turbine wheel space temperature
2. Seismic vibration
3. Turbine inlet air filter differential pressure
4. Shutdown button from HMI

For shutdown is there any sequence?What is deceleration rate in case of shutdown?
 
Trip instantly cuts off the fuel to the gas turbine.

Protective shutdown initiates a "normal" shutdown sequence - unloading followed by fired shutdown. This is done where it is not necessary to stop the fuel flow instantly, but it is necessary to shut the machine down and not permit a restart until the problem is corrected. Or, to put it another way, any additional damage done by going through the sequential shutdown is less than the damage done by a thermal shock of a trip.
 
To add to what otised said very well, that's a pretty interesting list of "interlocks". I've seen some units tripped by high wheelspace temperatures, but never one that went into an automatic shutdown on high wheelspace temperatures.

Also, I've never seen a unit go into an automatic shutdown on high vibration; they are almost always tripped on high ("high-high") vibration.

Typically--and every unit is NOT the same as every other unit, and this thread just exemplifies the differences between units!--when an automatic shutdown is initiated by some event or condition the shutdown rate is the same as the automatic loading/unloading rate.

When an operator initiates a STOP (shutdown) from the operator interface, the Speedtronic starts reducing TNR (the turbine speed reference) at a pre-programmed rate. This is called the "AUTO" loading/unloading rate (loading/unloading because the same rate is typically used for loading the machine as well as for unloading the machine). And, when an automatic shutdown is initiated the same rate is typically used.

Typically, because there are eight (8) different loading/unloading array values available in most digital Speedtronic turbine control systems. In digital Speedtronic turbine control systems, the loading rates are Control Constants (adjustable values), and the typical name is something like TNKR1_0 through TNKR1_7, or something similar. Not all eight array values are used on every job.

BE VERY CAREFUL when reading GE descriptions of Control Constants, because they are very generic. One MUST review the sequencing or application code running in the Speedtronic to determine exactly what a particular Control Constant does. In other words, the written descriptions provided with the Speedtronic DO NOT always correspond to exactly how the Control Constant is used or what it does--only a review of the sequencing or application code can reveal exactly what the Control Constant does or how it's used to control or protect the unit.

The loading/unloading rates for GE-design heavy duty gas turbines vary from machine to machine, and the same Control Constant signal name is not always used for AUTO or MANUAL or any of the other rates, so without being able to see the sequencing or application code running in the Speedtronic turbine control panel at your site we can't say for certain what the auto loading/unloading rate is for the unit at your site.

And, since there are a couple of unusual "interlocks" it's a safe bet that there may be some unusual sequencing or application code for different conditions at your site.

I wish we could have been more help, but I hope this does help some!
 
B

Bob Johnston

Never say never CSA. The gentlemen from Italy who supplied our new Frame 6 generators have added a few new "wrinkles". If the turbine runs for >24 Hrs. with a high W/space Temp. Alarm, it shuts the machine down (Normal Shutdown). Maybe I'm getting old, but I sometimes think that the faster and bigger that control systems get, the more that office design engineers dream up new Bells and Whistles to add on.
 
Bob Johnston,

There's no review of any of these functions by a team of experienced engineers and operators--except that if they shut the unit down (shutdown or trip) then it's likely the OEM or packager will get a call for service.

I remember many years ago hearing a prominent Customer of the OEM tell them at a major meeting of their senior management that the OEM needed to listen to operators because they knew more about operating the machines than the OEM's engineers. But that was back when operators had to progress through the ranks before becoming operators to learn the machines and how to respond to events and conditions and alarms.

Nowadays, the problem is that operators do not have the proper training for running these machines. The salespeople have sold the control systems as completely protecting the machines, not requiring any operator intervention. But the documentation is so lacking that the owners/operators never find out about these new "features" until after the shutdown or trip.

It is getting to be out of control, pun intended!

As we both know, Bob, there are MANY times after maintenance outages when wheelspace T/Cs don't get re-inserted properly and erroneously cause high wheelspace temperature alarms. I wonder if the Firenze boys have code to detect that to prevent unnecessary shutdowns. I wonder if the new wheelspace T/C code looks at trends of wheelspace temperatures to determine if there is a problem, or just looks at the magnitude like the original code did.
 
Hi.

I have a similar question pertaining to Mark VI vibration settings.

We have in the GT m6b file, in the vibration logic module, two setpoints; a trip setpoint of 1.0in/s and a shutdown setpoint of 1.1 in/s.

What is the difference in these two setpoints?
 
Hi.

Well, if the shutdown settings are above the trip settings, then the unit would always trip BEFORE it went into a normal fired shutdown on excessive vibration.

It could be that someone wanted to "disable" the shutdown on high vibration and just have the unit trip on excessive vibration by making the shutdown setpoint(s) higher than the trip setpoints. Sometimes the people who program Speedtronic control systems use "unconventional" means to enable or disable some functions.

I, personally, have never encountered a unit that went into a normal fired shutdown on excessive vibration. And, then would trip if the vibration increased even more during the shutdown--which is what would happen if the setpoints were reversed in your description. If the vibration exceeded 1.0 ips the unit would go into a normal fired shutdown (STOP), and if during that shutdown the vibration continued to increase above 1.1 ips the unit would be tripped.

But, the setpoints you described just seem to be configured to trip on high vibration, because once a unit is tripped it can't be restarted until it's coasted down to near or at zero speed (depending on the unit and starting means configuration).

Hope this helps!
 
Yashiv,

Are you sure your set point is 1 in/s and 1.1?

Our is 0.5 in/s for alarm and 1 in/s for trip. Even my old plant too having the same setting.

take care
G.Rajesh
 
Thanks a lot CSA. That makes things much clearer now. I must say, that is a rather unconventional way to do things.
 
i think you will find more detail about the answer in both document if you have access to them
functional description / cause & effect
 
H
> Are you sure your set point is 1 in/s and 1.1?

> Our is 0.5 in/s for alarm and 1 in/s for trip. Even my old plant too having the same setting.

excuse me, but i read Yashiv's question, he did not talk about alarm level. he said 1 in/s for trip just like your constant and the second value 1.1in/s which refers to the shutdown of the turbine.
 
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