The turbine speed control is unstable
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In our hydrogen compressor turbines, significant speed fluctuations occur when the opening degree of the speed control valve is between 31-33%; the speed remains stable when it is below or above this opening degree. The electro-hydraulic converter was also replaced, and the error in the throttle of the hydraulic actuator was cleaned, but this issue could still not be resolved. During static testing, both the valve opening and the secondary oil pressure responded as expected. Have other experts encountered the same problem?
There may be various reasons for unstable turbine speed control, requiring more detailed troubleshooting. Here are some possible reasons: 1. The control parameters of the speed regulation system are set improperly or not adjusted correctly. 2. Internal damage to the speed control valve or uneven valve opening. 3. A fault occurred in the booster pump system, resulting in unstable speed control oil pressure. 4. There are problems with the compressor system, such as damaged impellers, loose blades, blocked gas pipes, and so on. 5. There are problems with the sensors, such as the speed control oil pressure sensor, the rotation speed sensor, and so on. It is recommended that you check the above conditions and find the relevant technical personnel for further repair and troubleshooting. -
Consider the issue of overlap in valve opening; check pages 31-33 of the manual to see if there is a valve disc that is exactly open at that moment
After on-site inspection and disassembly by the manufacturer’s technical staff, it was found that there was no damage inside the speed control valve, the oil pressure was stable, the compressor was not damaged, and both the speed probe and related components had been replaced. The parameters of the speed control system were also checked and adjusted through testing, but none of these measures were able to eliminate the fluctuations in speed at a fixed opening.
If the above possible causes have been ruled out, it is recommended that you further check the following aspects: 1. The stability of the control circuit of the speed regulation system: including components such as the governor, tachometer, and proportional integrator. 2. Check whether the signal transmission lines of the speed control system are properly connected, and whether there are any breaks or poor contacts. 3. Check whether the position feedback device of the speed control valve is functioning properly, such as whether the movement status of the speed control motor and the speed control valve is consistent (by comparing the position feedback signal with the actual position of the speed control valve). 4. Is the gap between the speed control valve and the rotor even? This can be confirmed by measuring the dimensions of components such as the rotor and bearing covers. 5. Check the speed control oil circuit system for issues such as blockages, leaks, and whether the filters are clean. 6. Check the operation of automatic regulation: for example, verify whether the gain of automatic regulation is set appropriately and whether the set adjustment parameters are correct. 7. Check whether the PID control algorithm is appropriate, such as whether it is necessary to adjust the controller parameters or the PID algorithm itself. If no issues are found in the above areas, it is recommended that you contact the turbine manufacturer or a professional maintenance service for further inspection and repair. -
Was the problem solved? Have you carefully checked the size of the oil holes in the valve spools of those faulty pumps?
The same is true for our turbines: when starting up and increasing the speed, if the control valves are set at around 28-31%, the speed fluctuates and vibration levels become very high. The problem goes away once the valves are set outside this range. This phenomenon did not exist before; it started appearing 6 years ago. The electro-hydraulic converters and hydraulic actuators have been checked; next, we plan to take advantage of the every-8-years major maintenance of the turbine to inspect the valve stems of the speed control valves. There is suspicion that the stems might be loose, or there could be issues with the overlap in valve adjustment. Since it only exists at startup, no special action was taken to deal with it. Previously, it was found that the mesh size of the filter on the control oil circuit was incorrect; replacing it did not improve the situation. I hope to maintain communication with the original poster
Our turbine experiences large speed fluctuations at low load levels (when the control valve is open at around 30%), and the speed control provided by the governor is unstable. Later, we switched to using the opening degree of the inlet shut-off valve to control the speed, which proved to be more stable. (Analysis later showed that it was likely due to an oversized diameter of the steam inlet pipeline in the turbine, a low opening degree of the governor, and poor control over the amount of steam.)
The factor of overlap still needs to be ruled out when considering other reasons
I agree with you; I also thought of the issue of overlap between the valve butterflies right away. By taking out the valve beam and measuring the travel distance of each valve, we can find out. Over time, wear and tear may occur, causing the travel distance to increase
Come in and take a look, learn something:*lol