Issues regarding the valve position of backpressure turbine control valves
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The turbine speed is set at 6000 rpm, and the opening degree of the steam valve is adjusted to fluctuate steadily between 50% and 60%. It seems that such large fluctuations shouldn’t occur; the steam pressure, temperature, and flow rate are all normal and stable. What could be the reason for this? Also, I would like to know how the percentage value for adjusting the steam valve’s opening degree is determined – is it calculated based on the 4 to 20 mA current range?
If the fluctuations are not caused by changes in the load at the load side, adjust the valve flutter; there’s no need to focus on the percentage of opening – as long as the valve passes the calibration tests, that’s sufficient
Adjusting the opening degree of the steam valve is related to the speed you have set. If opening the valve enough to achieve the desired speed is not possible, the valve will continue to open further until the speed requirement is met! I have encountered this situation before as well. I suggest setting the controller to manual mode for now, so that the output of the steam valve remains unchanged; after some time, try switching it back to automatic mode and see if the problem you mentioned disappears Personal advice, for reference only!
Learn a bit about it; if you don’t understand, ask questions. How is the controller adjusted manually? Is it done by controlling the current?
Fluctuations in the process medium also have a significant impact
Set it to manual on the DCS, and switch to automatic once it’s stable
The control valves of the steam turbines are all controlled by 505; how do I switch the DCS to manual mode?
I just saw that you commented on someone else’s reply. What you said makes some sense, but in practice it is indeed 505 that controls the turbine speed. Yet who controls 505? In the control loop, the turbine speed is the main parameter; its value is used to adjust the oil pressure via device 505, thereby changing the opening degree of the main steam valve and ultimately achieving the goal of adjusting the speed. By controller, I mean this control loop in the DCS. Switch to manual mode, and once it’s stable, switch to automatic mode.
I’ve learned it, I’ve learned it… Is this controller in the cabinet at 505? I really don’t quite understand it
The controller is not located in 505; we colloquially refer to 505 as our \"my own\" speed control system. It works by altering the pressure in the oil circuit to change the stroke of the hydraulic actuator – it is a mechanical system. As for the \"brain\" that controls it, it is either found in the DCS or in an independent speed control system. There is a lot to learn about these mechanical systems, but sometimes it can be very boring, as it’s difficult to understand their internal structure or imagine how they work; that’s why I know very little about them... I’m ashamed!
It is recommended that the poster consider two aspects: 1. whether there are fluctuations in the pressure of the backpressure steam pipeline network, and 2. whether there are any process fluctuations on the load side; an increase or decrease in the load on that side can also cause fluctuations in the rotation speed