Hello;

We have Frame 5 gas turbine in gas plant.

When we start turbine, at full speed no load the bleed valves 86 CB1/2 closed, but after 05 seconds change to position open.

Please anyone has answer.

Regards

 

KADDOURI,
The axial compressor bleed valves are not, technically, part of the Mark VIe turbine control. They are opened and closed by air pressure which is controlled by the position of a solenoid which is energized/de-energized by the Speedtronic (Mark I, Mark II, Mark IV, Mark V, Mark VI, or Mark VIe).

Precisely, what Process Alarm(s) and Diagnostic Alarms(s) are present when this problem occurs? Don't give us drop numbers--provide the full text of the alarm message(s).

The most important question to be asked when a problem like this occurs is:

<b>When did this problem start?</b>

If the bleed valves were operating correctly, and now they're not--what has changed between the time they were and now?

After a maintenance outage?

After a turbine control upgrade?

Are these units generator drives, or compressor drives?

Is speed not being maintained, and decreasing, that's causing the compressor bleed valve solenoid to be de-energized?

Have you examined the application code using ToolboxST to see what might be causing the solenoid to be de-energized?

Is there a leak in the air piping between the solenoid (20CB-1) and the actuators of the bleed valves?

Have you checked to see if current is still being applied to the solenoid coil, but for some reason the solenoid coil is not holding?

There are many possibilities, but you haven't told us what you've done to try to resolve the problem and what the results of your efforts were. It's really NOT very likely that the evil Mark VIe is the cause of the problem--if it were, there would most likely be Diagnostic Alarms trying to alert conscious operators to an internal problem. And, application code (logic; sequencing) doesn't change by itself. If someone was messing with logic and downloading to the Mark VIe that could be a possible cause, also.

If you want more help, you are going to have to provide more information. Tell us as much as you can about what you've done to try to troubleshoot the problem and the results of your efforts. Tell us when the problem started, and what happened before the problem started that might possibly be related (did someone change a printed circuit card, or replace the compressor bleed valve solenoid, or was wiring disturbed during a maintenance outage).

Last but not least, have you checked the wire terminations everywhere along the circuit to be sure they are tight?

If this is a gas processing plant, there is likely IS barriers in the wiring somewhere. Are you sure they are working properly?

Has there been a lightning strike in the plant recently?

You see--the possibilities, while not endless--are many. Many, indeed. And if you can tell us more about the conditions and what troubleshooting you've done and the results of that troubleshooting we can help narrow them down, probably considerably.

Please write back to provide more details and information and to let us know how you fare in troubleshooting the problem.

 

1) Whether bleed valve is a new installation or the problem started in the existing installation itself. Exactly when this problem started.

2)Is there any Mark-VI e programming download has been done with any logic modification.

3) What is the command generating for 20CB from Mark-VI e during opening of bleed valves after FSNL.

4) Whether the 20CB solenoid is checked for passing of air. Also check the bleed valves operation by directly applying air to the same.

 

On Frame 7 B and EA on the bleed valve system, check you pour stone filter and clean. Install a control air source downstream of the filter, apply test air and cycle the Laurence 20CB valve open and feed air to both bleed valves, check for air leaks, and checking air pressure to valve position movement, the valve should have say 20 psi break away and 70 psi full close and seated, and make any adjustment to the valve by loading or un load the spring. Remember you have two valve is open limit switches and two closed limit switch and their wired in series, make sure wiring connection is good, relay limit switch operate and are clean cycle freely and no resistance or ohms good and voltage pass through (no contact issues) and relay mounting and setting of the relays are good, these are what tell your controls I am open and closed. If you have an actuator that is air cylinder to spring air to open we have used Dow high temperature graphite lube to keep actuator free and no binding movement. We have also piped clean dry air to the unit and quit using the wet air from the turbine combustor this help resolve air system contamination. The other item is clean the steam of and pivot point on the 20 CB valve and bleed valve and make sure the bleed valve bushing are not wear out. The last item is check the voltage to the 20CB and ohm the coil and make sure your coil has not shorted turn and is a magnet to open the valve, full cycle close to open .5 seconds. our older frame 7 the bleed valve close at 95 % speed 14 HM and will trip the unit if the bleed valve are not in a close state from signal given to close, our frame 7 ea close at FSNL and have 1.5 seconds to close. Make sure on your new controls speed is not dropping if the valve close at 3600, I do not remember what speed drop to the valve will open back up under 3600 RPM or normal speed on a frame 6. Are over all cycle time to signal to close to close on both bleed valve is around 1 to 1.2 seconds.

 

When the turbine reach full speed, the bleeds valves closes but after 10 second opened.

I check thr 14HP was dropped before closing the bleed valves.
i have some hinting in SRV valves.

Thanks