The GCV of the Fr5 twin shaft unit we have here is hunting, the above prioblem has appeared ever since the control system has been upgraded to MKVI from MKIV.

We are suspecting the problem from the MKVI panel itself as we have tried changing the servo valve, the actuator assembly and even the LVDT's but couldn't succeed in stoping the hunting of the valve.

The above hunting is not affecting the operation of the turbine and the speed of the HP shaft is almost stable, the only problem is in the fluctuation of the pressure after the GCV and the intervalve pressure the above both are fluctuating by around 1-2 bar and the GCV valve itself is hunting by around 4-5%, whereas the SRV is hunting less compared to GCV, the frequency of the above hunting is very slow if we trace the feedback of the GCV valve it will be like a small wave.

I would like to trouble shoot into some of the parameters of the MKVI panel which is directly going to control the above servo valves like the regulator gain which is set at 3, the dither amp which is set at 2.

Seeking expert advice before to touch the above parameters also would like to know whether the above parameters can be modified in the field.

Thanks in advance,

Brian
[email protected]

 

This is one of those questions that begs the answer: Why isn't GE contacted to resolve this issue since it's been associated with the control panel upgrade? Only GE can tell you if the servo-valve output is configured properly, and that is the source of expert advice for the configuration of the panel.

In general, on two-shaft machines fuel controls load and the HP shaft speed is controlled by the second-stage nozzle. The fuel is controlled by the Gas Control Valve (when operating on gas fuel). What is the second stage nozzle doing; how is it behaving? What is the load signal that is being used to control the fuel flow (the speed and power output of the LP shaft)? Is it stable?

Which division of GE provided the Mark VI control panel upgrade: Oil & Gas? Optimization & Control? Performance Services? Transactional Services? Or was it one of the business associates/packagers associated with GE? Have you been working with them to try to resolve the problem? Have you provided them with the same information you've posted here? What was their response?

If the GCV is not stable, it's likely that the P2 pressure will also fluctuate, also, though it would seem that the SRV should be able to control P2 pressure much better than you describe for the GCV fluctuations you describe.

There is usually a one-year warranty on GE control panels, but generally if you can show that the problem has existed for some time before the warranty expires and GE has been consulted and has been trying to help with the issue, they will usually continue working to try to resolve the issue even if the warranty has expired. So, what's the real problem here? You say the problem has existed for some time but it's not affecting the unit operation (though it certainly seems the parameters should be more stable than you describe). So, why aren't you working with the control panel supplier to resolve the issue? If it wasn't GE who originally provided the panel and the installation, have you considered contacting GE for assistance if you feel you haven't received the assistance you require?

It's just not recommended to go changing gains and dither values until all the various conditions and parameters are known, and if it's expert advice you seek it's probably going to come from the designer/manufacturer of the turbine.