Dear All
I am Working on G.E frame 6 mark 5 gas turbine.

the turbine is using fuel distillate for a long time. Suddenly some times not fixed the turbine starts hunting of 3 MW at full load(30mw). remains for 2 hours nearly then normalizes. Fuel lines were vented for air if present from Low pressuee and High pressure filters and pumps During hunting. But no changes were observed. High pressure filter in service weer changed too but no changes observed. This problem arise suddenly and go suddenly...

Please share ur Views...

 

It would seem this problem just recently started; was it after some maintenance outage?

Are there any Diagnostic Alarms annunciated during this hunting?

What Diagnostic Alarms are present before and after the hunting?

What Process Alarms are present before and after the hunting?

You seem confident that all air has been removed from the piping and filter canisters; that's good.

The above presumes the unit has a Liquid Fuel Bypass Valve and screw-type, positive displacement High-pressure Liquid Fuel Pump with an electric clutch coupling the pump shaft to an output shaft of the Accessory Gear Box. It also presumes the combustors are conventional (i.e., not DLN combustors). If the arrangement is different, you will need to tell us.

Possible causes include:

--Electric Fuel Pump Clutch slipping (need a photo tachometer or other non-contact tachometer to troubleshoot)

--Servo-valve problems (sticky servo spool; failing or intermittent servo coil)

--Mark V servo-valve output problems (<b>NOT</b> likely unless there are also related Diagnostic Alarms!)

--Liquid Fuel Bypass (Control) Valve hydraulic actuator problems (leaking o-ring(s); etc.)

--High-pressure Liquid Fuel Pump problems (not likely, but possible)

--Liquid Fuel Forwarding Pressure Regulator problems (or the pressure regulator of the Liquid Fuel Supply system) such as a cracked or broken diaphragm/spring, sticky actuator/valve stem, etc.

--Unstable IGVs (should be easily spotted or determined, and may be accompanied by Diagnostic- and/or Process Alarms)

If the unit has Water- or Steam Injection for NOx emissions reduction, the problem could also be related to unstable water- or steam flows.

If you write back for more information it would be helpful to know if the Mark V is SIMPLEX or TMR.

 

Sounds to me like a servo valve or liquid fuel control valve problem. Could be a sticky servo valve just at that particular load and valve stroke. If you have a replacement servo, at least you can eliminate that. Is your hydraulic supply pressure steady and correctly set? Please report back with any more info. available

 

Dear All,

There are no process alarms nor diagnostic alarms during hunting..
As said the lines were vented for possible air in it....
There was no recent inspection or maintenance the unit is on load from 5 month from its last inspection. the problem arised a week ago.

The above possible causes mentioned by you all are been checked. fault when traced will get back to you.. if there is any other possibility please let me know....

thanking you

 

The hydraulic pressure is constant as observed nearly 90 bar.inspection to ur possible causes in process
thanking you

 

13 barg hydraulic system pressure seems a little on the high side, but not excessive if I recall correctly.

Is the pressure set using VPR-3 of the hydraulic pump, or VR-21 on the hydraulic manifold? It should be set using VPR-3, NOT VR-21.

Is there a hydraulic accumulator in the hydraulic system? If so, is it properly charged and properly valved in (block valve open; bleed valve closed)?

 

Rafi... for another point of attack, see thread: http://www.control.com/thread/1026226787

Regards, Phil Corso

 

Dear csa

yes we have relief valve VR21 and VR22 on the hydraulic manifold....
We also have hydraulic accumulator Ah1 and Ah2.which are charged and valved..

The details for this hydraulic system because you think the hydraulic oil operating the fuel valves...?

 

Dear all

The notorious part has been caught with your help...it was the fuel by pass system vc3-1 operated through 65fp servo valve.the controlling valve here was providing wrong operation positions to valve vc3-1.the hydraulic system is ok with no pressure variations..

Any further information if required please do ask...
Thanking you

 

Thanks for the feedback!