What is the critical speed of a steam turbine?
The critical speed of the steam turbine refers to the maximum speed that the rotor can withstand by axial deformation and failure, that is, the state that the rotation speed reaches a certain value and the vibration reaches a certain degree, resulting in the distortion vibration of the rotating parts. This state is called the critical speed of the steam turbine.
The critical speed of the steam turbine is an important parameter that determines the vibration characteristics of the steam turbine, for the modern high-speed, high-power steam turbine, it is necessary to conduct in-depth research on its critical speed, and reasonably regulate its design and manufacturing process, so as to avoid the instability caused by the natural frequency of the rotor following the change of external excitation.
The role and significance of steam turbine critical speed in steam turbine operation
The critical speed of steam turbine plays an important role and significance in the operation and use of steam turbine. Its main functions and significance are as follows:
1. Provide a basis for the design of steam turbine: the critical speed of steam turbine is one of the key parameters that need to be considered in the design of steam turbine. The critical speed of the steam turbine needs to be calculated according to the actual situation to ensure that the steam turbine will not resonate and cause damage during operation.
2. Guide the operation and maintenance of the steam turbine: The actual speed of the steam turbine needs to be controlled during the operation and maintenance of the steam turbine to ensure that the critical speed of the steam turbine will not be exceeded. At the same time, it is also necessary to pay attention to the balance of the steam turbine impeller and the no-load test operation to reduce the occurrence of resonance phenomenon.
3. Improve the safety and stability of the steam turbine: The calculation and control of the critical speed of the steam turbine can effectively reduce the resonance risk of the steam turbine, thereby improving the safety and stability of the steam turbine and ensuring the safety in the production and use process.
Factors influencing the critical speed of a steam turbine
1. Rotor structure
The structural parameters of the rotor have a great influence on the critical speed of the steam turbine. Rotor construction parameters include rotor geometry, number of dampers, support structure stiffness, and so on. The elastic properties, mass, and moment of inertia of the rotor also affect the critical speed.
2. Rotor support structure
The stiffness of the rotor support structure and the number and type of dampers will affect the critical speed of the steam turbine. In the case of less stiffness of the support structure and fewer dampers, the critical speed becomes lower.
3. Bearing stiffness
Both the stiffness and geometry of the turbine bearing affect the critical speed. Different bearings have different stiffness characteristics, and choosing the right bearing can effectively improve the critical speed of the steam turbine.
Points to note when passing the critical speed
1. When the critical speed is crossed, the critical speed should generally be crossed quickly and smoothly, but the practice of rushing through the critical speed can not be taken to prevent adverse consequences, and the current regulations stipulate that the rise rate when the critical speed is about 500 r/min.
2. In the process of passing the critical speed, attention should be paid to the comparison of vibration and speed to determine the vibration category and prevent misjudgment.
3. There should be no abnormality in the vibration sound, such as vibration exceeding the limit or there is a collision and friction sound, etc., the brake should be stopped immediately, and the cause should be found out and confirmed that there is no abnormality before it can be restarted.
4. After passing the critical speed, the speed rise should be controlled.
In short, for steam turbines, it is very important to grasp the critical speed, and only by in-depth study of the critical speed can we better ensure the normal operation of the steam turbine and improve the operation efficiency of the steam turbine.
