Chemical Process Machinery Area: [Weekly Topic] What are the causes of turbine speed fluctuations? (2011.7.4~7.10)

This post was last edited by YTH-Gavin on 2011-7-4 09:16. 1. Fluctuations in the speed control valves caused by pressure fluctuations in the steam pipeline system； 2. Fluctuations in the throttle valve caused by improper adjustment of the PID parameters for the throttle valve, as well as fluctuations in the secondary oil pressure ； 3. Fluctuations in the speed control valve caused by oil pressure fluctuations in the control system ； 4. Fluctuations in the speed control valve caused by poor quality of the control system oil (presence of water, air intrusion, etc.) ； 5. Turbine load fluctuations caused by variations in system load, which in turn lead to fluctuations in the throttle valve ； 6. Fluctuations caused by mechanical wear faults in the speed control valve actuator ； 7. Water entrainment in the steam injection of condensing steam turbines causes speed fluctuations ；

First, check whether the speed increases first or the valve setting changes first. If the door doesn’t move but the rotation speed fluctuates, it’s likely due to mechanical issues such as the blades. If the valve moves first, then check whether there is any change in the overall valve position command. If the change in the valve opening is caused by the command, it indicates a logic issue; examine the logic related to speed control. If the valve moves while the overall valve position remains unchanged, it suggests a problem with the local servo card or the hydraulic actuator.

Normally, the pressure of the power steam is unstable

In actual production, we have encountered turbine speed fluctuations caused by the following factors: 1. Fluctuations in main steam pressure； 2. Compressor load fluctuations ； 3. Fluctuations caused by PID parameter settings during startup.

Water has accumulated in the main steam, causing fluctuations in steam pressure; the turbine blades have been damaged, the PID parameters are incorrect, and the operation of the main steam valve is unstable. The vibration levels are now too high

This issue should also be considered from two aspects, in terms of steam: 1. Fluctuations in the pressure of the steam pipeline network, which lead to fluctuations in the throttle valves； 2. If the quality of the main steam is poor, such as containing excessive water or impurities, the firing test will fail ； 3. In the case of a back-pressure turbine, fluctuations in the pressure of the back-pressure pipeline network can also cause fluctuations in speed ； 4. Water entrainment in the steam injection of condensing steam turbines causes speed fluctuations ； Regarding steam turbines: 1. Fluctuations in the throttle valve caused by improper adjustment of the PID parameters for the throttle valve, as well as fluctuations in the secondary oil pressure ； 2. Fluctuations in the speed control valve caused by fluctuations in the oil pressure of the control system (it may be due to problems with the accumulator ahead of the control mechanism or issues with the filter in the oil cooler at the pump outlet) ； 3. Fluctuations in the speed control valve caused by poor quality of the control system oil (such as water content, air intrusion, or impurities resulting from mechanical wear) ； 4. Turbine load fluctuations caused by variations in system load, which lead to fluctuations in the throttle valve (such as too rapid acceleration or deceleration) ； 5. Fluctuations caused by mechanical wear faults in the speed control valve actuator (e.g., damage to the actuator’s packing as well) ；

As a supplementary point, it’s also possible that the packing on the main stem of the newly replaced control valve is too tight

Reply to 8# franktree: Compared to valve stem packing, valve disc packing is more prone to problems; similarly, this issue also exists with the packing of hydraulic actuators.