505 governor control

With a steady hand, of course.

There is so much you would have to tell us to be of any real help. Let's start with the basic questions:

1) When did this problem start? (In other words, was the unit working fine and then it started experiencing oscillations?)

2) What kind of actuator does the control valve have: hydraulic, pneumatic (compressed air), mechanical?

3) Is the control valve oscillating all the time or just sometimes? If it only oscillates sometimes, what is happening when the oscillations occur? (For example, it doesn't oscillate until the unit reaches 35% load, and if the load can be increased the oscillations will stop after increasing above 55%. Like that. Or does it just oscillate during synchronization attempts?)

4) You say the unit is operating in parallel mode--is it in parallel with a large (infinite) grid? Or just with another unit or couple of units at the plant? If so, what are the sizes of the units at the plant?

5) Do the oscillations only occur when a particular other generator is operating?

6) We presume you are referring to load (kW; MW) oscillations. Or are you referring to voltage/kVAr/MVAr oscillations? Or does this steam turbine drive some mechanical load (such as a centrifugal compressor or pump)? Is the speed of the steam turbine/generator also changing/oscillating when the oscillations occur?

7) How long has it been since the steam turbine and stop- and control valves were serviced/refurbished?

8) What is the source of the steam for steam turbine? A fossil fuel-fired boiler? Combustion turbine exhaust into a waste heat recovery boiler?

9) You say the steam turbine is being operated in parallel with other generator(s). Is this steam turbine in Isochronous Speed Control or Droop Speed Control during the oscillations?

10) Is the unit being operated in Power Control Mode or some other kind of mode? Other modes might be Inlet Pressure Control Mode, or Exhaust Back-pressure Control Mode, etc.

11) When these oscillations occur, are the other turbine(s)/generator(s) also oscillating?

12) Is the grid the unit is synchronized to stable (meaning is the frequency of the grid stable or is it fluctuating/oscillating)?

And this is just a partial list of things we need to know. If the answer to #12 is that the grid the unit is synchronized to is unstable, well, you can't do anything about oscillations in that case. If the unit is synchronized to a large grid an the grid frequency is unstable--your steam turbine/generator speed AND LOAD are also going to be unstable. Full stop. Period.

And even a steady hand isn't going to fix that. No matter what the Operations Supervisor says or thinks. It's the way AC (Alternating Current) generation, transmission and distribution systems work.

But, if you can answer most of the above questions to the best or your ability we might be able to offer some suggestions. Unless you have reason to believe the 505 is faulty or failing or has failed, and if the inputs to the 505 are calibrated and working properly the problem is most likely NOT the control system. It could be a worn hydraulic actuator, or poor air pressure regulation, or dirty hydraulic oil--it could even be a combination of things. But, again, unless you have reason to suspect the turbine control system (the 505) OR its inputs or outputs, it's probably not the control system. And, this isn't an operator's responsibility--restoring system stability.

Best of luck!