good morning,

we have a MS-5002c gas turbine, and we have a trouble in nozzles. this problem is occurred after an MI revision!

the nozzles sticks in 1.3 degrees and stop there, serv_ref go to 0, and tsnz at -5°!

and remains in this position, any one have a idea?

thank you in advance.

 

Good morning to you!

The problem started after a Major Inspection "revision." What is a MI revision, please?

Exactly what was done to the second stage nozzles/actuator during the MI?

I don't recall if there is a "trip" solenoid/hydraulic trip relay valve in the second stage nozzle actuator circuit. If so, is it energized?

Have you tried stroking the nozzles using the Manual feature of AutoCalibrate? (You indicated the turbine has a digital GE Speedtronic turbine control system, all of which have the ability to manually position ("stroke") any servo-operated device equipped with LVDT feedback.) If so, what were the results? (This stroking would be done with the turbine off-line, at zero speed.)

Have you tried moving them open, as well as closed, and if so, what were the results?

Are you certain there is hydraulic pressure to the second stage nozzle actuator?

If the unit has hydraulic accumulators, are you sure they are charged and properly valved in?

If the Speedtronic turbine control panel is putting out servo current, and the servo current has reached saturation (likely positive saturation to close the nozzles) then it's likely the nozzle actuator is stuck--mechanically bound--and is not capable of moving. Have you inspected the nozzle ring and actuator to ensure there is nothing preventing them from moving?

Have you monitored the servo currents during attempts to stroke the nozzles?

Were the LVDTs "calibrated" after the MI revision? If so, what were the results?

What Diagnostic Alarms are present and active when the nozzles should be moving?

What Process Alarms are present and active when the nozzles should be moving?

What version of Speedtronic turbine control panel is in use on the turbine? Is the Speedtronic a SIMPLEX or redundant controller (DUAL or TMR)?

 

good morning,

thank you CSA for your helpful response. we have made a standard MI, and we did not much things in nozzles, and we tested nozzles (off-line) its works properly. all things was normal at offline. we think that the problem is the actuator or the MOOG, what do you think?

 

Troubleshooting is quite often a process of logical troubleshooting. It is logical to question the servo-valve and the actuator.

However, if everything worked fine before the MI and during off-line testing after the MI, then it's likely to presume the problem is the actuator or some kind of mechanical binding of the linkage. If the nozzles are stuck at one position and won't open or close from that position, then I would suggest it's either a lack of hydraulic pressure/flow to the actuator (through the servo-valve) or some problem with the nozzle linkages that's preventing the nozzle ring from moving--open or closed.

Of the two, <b>from the information provided,</b> I would suggest the latter. If the nozzles are stuck in one position and won't open or close then it's most likely some mechanical problem with the linkage.

If the servo-valve was replaced, or the hydraulic system was "disturbed" during the outage, then it could be that dirt in the hydraulic piping has made it's way to the servo-valve and is causing it not to allow high-pressure hydraulic fluid to get past the servo-valve to the actuator. This is not likely, but it can--and has--happened.

EVERYONE always suspects the servo-valve, because they are such mysterious, mythical devices. It's not usually the servo-valve (almost never is), but they usually get (incorrectly) blamed for the problem. If you replace the servo-valve and still have the same problem, then you've wasted a lot of time and effort--and used a perfectly good servo-valve to replace a good servo-valve. Not a productive use of time or spares. Replacing the servo-valve should only be done as a last resort during troubleshooting--unless the Speedtronic is indicating (usually through Diagnostic Alarms) a problem with the servo-valve currents/outputs.

Have you tried using a hydraulic jack/ram to try moving the nozzle linkage to see if it's mechanically bound up? It should be relatively easy to move the linkage either direction from the reported position with a small hydraulic ram or bottle jack. If not, then I would suspect a mechanical binding problem with the linkage/actuator.

I believe if you look at the Piping Schematic (P&ID) for the second stage nozzles you will see that in the absence of any signal the servo-valve and/or a hydraulic trip relay/dump valve will direct hydraulic pressure to move the nozzles to the either the open or the closed position (I can't recall which without being able to look at a Piping Schematic drawing). So, if the mechanical linkage were free to move and there was hydraulic pressure the nozzles should move to either the full open or full close position.

You could also look at the Speedtronic and see what the nozzle reference angle is when the unit is at rest and hydraulic pressure is available and check the servo-valve currents to see if it's trying to move the nozzles to the reference position.

Again, my most likely suspect from the information provided, is some kind of mechanical binding of the linkage or actuator, or the inability of hydraulic pressure to get to the actuator. A small hydraulic jack/ram would easily prove or disprove that theory.

I do NOT believe this is a Speedtronic controls problem; most problems like this never are. However, you were asked to provide the list of active Process- and Diagnostic Alarms and haven't done so, so we can't help with troubleshooting the Speedtronic....

Please write back with more information, and to let us know how you fare with troubleshooting and resolution!