Hello;

In our site one of the GT unit frame 5 Mark VI controller the bleed valves didn't close at 95% it closed at 100% during start sequence.
and when we stopped the unit the bleed valves closed directly after the command of stop from HMI.

is that a problem?
if so what is the solution for that case?

thanks..

 

Ayman,

When you post to a site like this, you need to provide much more information in order to get a more concise response. For example, you said the unit is a Frame 5, but is it driving a generator or a compressor or pump? In other words, is it a generator drive unit or a mechanical drive unit?

You may work with the units all day, week in and week out and be very familiar with them. We don't, and we need you to tell us as much about the machines as you can, and if you've done any troubleshooting what the results of the troubleshooting were. Otherwise, we are going to be asking for lots of information. So, try to anticipate the questions we might ask and to remember we're not sitting alongside you and don't know the details about your units and how they're operated. The more you tell us, the better our answers will be.

Some turbines have application code (sequencing; logic) that closes the compressor bleed valves at 95% of rated speed of the HP shaft, and some close it at 100% of rated speed, and still others close it at about 5 MW. It depends on many factors, mostly the vintage of the machine (when it was built; what hot gas path components it has; what kind of driven device it is providing torque to).

You would need to view the application code running in the Mark VI using Toolbox to see what the application code is written to do. The signal name is usually L20CB1X or something similar; when this logic signal is a logic "1" the compressor bleed valves are supposed to be closed. When it's a logic "0", the compressor bleed valves are supposed to be open.

If the compressor bleed valves are not operating the way they have been operating in the past on that machine, then something is possibly wrong. Not with the Mark VI application code, unless someone changed it.

Also, what Diagnostic Alarms and Process Alarms are active on the machine with the problems?

Lastly, when you post for help here on control.com it's customary to post feedback to the thread to let others know if the information provided was helpful or not, and what the ultimate resolution of your problem was. "Feedback is the most important contribution!"(c) here at control.com, and if you use the 'Search' feature of control.com to read past threads you will find that those with feedback are the most helpful and informative. If you have the time to post for help, you've got the time to post a couple of lines to let others know if you were able to resolve the problem with the help provided, or how you were able to resolve the problem.

 

Bleed valves should be closed by 14HS Speed Relay pick up, usually set at around 97% speed.

On shut-down, bleed valves should open when 14HS relay drops out, usually around 95% speed.

Check your operating logic and look at the settings for TNK14HS1/2, this will give you the exact settings.

It looks like everything is OK on your machine.

 

I checked the constant value and I found it:

TNK14HS1 = 95%
TNK14HS2 = 93%

But the bleed valve still closed when the turbine speed reaches 100%
(the gas turbine is generator drive and the starting system is Electrical starting motor)

Thank you all..

 

Dear Ayman,

Some unit bleed valves are closed /opened based on FUEL STROKE REFERENCE (FSR). In our Frame-6B machine is VA2 open & close based on FSR (18% & 24%) but in Frame-9E machine based on TNH (95%).

So please look your logic and write back what is being used.

Take care
G.Rajesh

 

Dear all,

I checked the logic of bleed valve. the command of bleed valve L20CB1X depended on two signals L14HS & L3 when these two signals become true {1} the bleed valve should be close. L14HS become true when the turbine speed reaches 95%, but the signal of turbine start sequence ended {L3} comes when the speed reaches 100% as a result of that the bleed valve command comes at 100%.

But I didn't know is that state is ok?
Is that turbine start sequence ended at 95% or at 100%?

Thank you all.

 

L3 is the Complete Sequence relay and I guess the name says it all. Usually it means you have reached 14HS and various things have then completed which are initiated by 14HS operating, Auxiliary pumps have shut-down,etc. By the time this all happens, the turbine will be at 100% speed but it all starts with 14HS.

 

There are some unit the bleed valve close when the main circuit breaker close and open when the main circuit breaker open. and some unit depend on the speed relay setting and this is not fix but usually it will be between 95% to 100% of the speed….

 

To add to Bob Johnston's excellent description, I've looked at the sequencing of several units and some used L3 as part of the permissive string for closing L20CB1X and some used L14HS.

Here is a <b>typical</b> rung for most of the sequencing I reviewed:<pre>
L52GX1 L4 L14HS L20CB1X
----| |----| |---------| |------------------( )
|
L3 |
----| |------------</pre>

<b>NOTE:</b> The rung above is <b><i>typical</b></i> and is only presented for the purposes of explanation.

Notice that in the rung above the compressor bleed valves won't be closed until the unit reaches L14HS <b>and</b> complete sequence (L3) has been reached. Once the generator breaker is closed (L52GX1) there is "seal-in" around L3. L3 will be dropped out when a STOP is initiated, but the compressor bleed valve solenoid will remain energized until the generator breaker opens or L4 drops out or L14HS drops out.

The original poster had said that "...the bleed valves closed [???] directly after the command of stop from HMI...." I interpreted that statement to mean the compressor bleed valves <b>opened</b> when the STOP command was initiated. Is that what you meant to say, Ayman? If not, what were you trying to tell us?

 

Dear CSA ,

Yes it's the same logic that I have , >> about bleed valve close after stop command yes i write it by error I mean open.

I understand from you that the logic is ok so that this unit bleed valve close at 100%

thank you very much..

 

Yes, I agree, but I think that you will find that that 52G cannot close until L3 has picked up.