The issue of the critical speed of steam turbines

In my personal opinion: if they are driven by turbines for centrifugal compression, then they are connected by the same main shaft, and the critical speed of each one should be taken into consideration. If it is motor-driven, the output power of the motor is fixed; it is the compressor that needs to reach its critical speed. For detailed brief answers, listen to the analysis downstairs.

Both the critical speed of the turbine and that of the centrifuge need to be taken into account.

All of these need to be taken into consideration; for details, please refer to page 5 of http://bbs.hcbbs.com/viewthread.php?tid=192213

All critical speeds must be considered (including those of the turbine, compressors I, II..., as well as those of the gearbox and the entire unit)!

If it is a single-turbine unit, the critical speed of the turbine refers only to the critical speed of the turbine itself; whereas in the case of a turbine-driven compressor unit, the critical speed of the compressor is also taken into account when determining the critical speed. In particular, it is important to note that for a two-stage unit, the critical speed of the booster compressor must be calculated based on the speed ratio, in order to determine the critical speed at the operating speed of the turbine within the unit. Typically, turbine manufacturers provide the critical speed of turbines, while compressor manufacturers provide that of compressors. The turbine or compressor manufacturer is responsible for configuring the speed-up curve, taking all critical speeds into account during this process.

The single-unit test relates to the critical speed of the turbine; when a centrifugal compressor is installed on the turbine, the critical speeds of both components need to be taken into account

If it is driven by a turbine for centrifugal compression, then they are connected by the same main shaft, who said that?

There is a first-order critical speed, a second-order critical speed, and a third-order critical speed. Generally, turbine manufacturers provide the critical speed of turbines, while compressor manufacturers provide that of compressors. The acceleration curve is configured by either the turbine manufacturer or the compressor manufacturer, and all critical speeds must be taken into account during this configuration process.

Each rotor has first and second critical speeds! ! !

The turbines of Hangzhou Automobile Industry that I have come into contact with are all of rigid rotor design, and their operating speeds are all below the +10% range of the first-order critical speed; therefore, when in operation, only the critical speed of the compressor needs to be taken into consideration.

I agree with the discussions of the other users. 1. The critical speed is the speed at which the value equals the natural frequency of the rotor. If the rotor operates at its critical speed, severe vibration will occur, and the bending of the shaft will increase significantly. Prolonged operation can lead to serious bending deformation of the shaft, or even its breakage. 2. Although the rotor of a centrifugal compressor is carefully balanced, extremely slight eccentricities still exist inevitably. 3. Due to its own weight, the rotor always develops a certain degree of deflection between the bearings. 4. For the reasons mentioned above, it is impossible for the center of gravity of the rotor to coincide exactly with its axis of rotation; as a result, a periodically varying centrifugal force is generated during rotation, and the frequency of this force is undoubtedly consistent with the rotational speed of the rotor. When the frequency of variation of the periodically varying centrifugal force equals the natural frequency of the rotor, the compressor experiences severe vibration, known as \"resonance\". Therefore, the critical speed of the rotor can also be considered as the speed at which rotor resonance occurs during the operation of the compressor. 5. A rotor has several critical speeds, which are referred to as the first-order critical speed, the second-order critical speed, and so on. The value of the critical speed depends on factors such as the shaft’s structure and diameter, the mass and position of the impeller, and the way the shaft is supported. The purpose of understanding the critical speed is to find ways to keep the operating speed of the turbine away from this critical speed, in order to avoid resonance. Typically, the rated operating speed of a turbine is either lower than the first critical speed of the rotor, n1, or it lies between the first critical speed n1 and the second critical speed n2.

For a 1-to-2 unit, what issues need to be considered when the turbine reaches its critical speed during startup? Please provide a solution

The turbine itself has a critical speed. The critical speed changes when connected to a device that needs to be dragged.

The normal operating speed should be between the first critical speed and the second critical speed. So far, I haven’t heard of any case where there are two critical speeds before reaching the operating speed.

Yes, that’s possible. Usually, the rated operating speed of a turbine is either lower than the first critical speed of the rotor, n1, or it falls between the first critical speed n1 and the second critical speed n2. The former is called a rigid shaft. The critical speed of a turbine with a flexible shaft depends on various factors, including the magnitude of the critical speed itself, the structure and thickness of the shaft, the mass and position of the impeller, as well as the way in which the shaft is supported. There is a critical speed reached at the rated speed; in some cases, there are 2 to 4 such critical speeds. The turbine is connected to the equipment it drives, and there is also a critical speed for the unit.

I have a question: for turbogenerators, are there any machines that have two critical speeds? In other words: below the designed operating speed, are there two critical speeds? Thank you!

There are turbines with 2, 3, and 4 critical speeds. The turbines in my previous workplace had 2 critical speeds, while another unit had to pass through 3 critical points during startup.

Both need to be considered. The increase rate beyond the critical speed also needs to be set according to the manufacturer’s requirements.

The amplitude of the rotor increases as the speed increases; it reaches its maximum value at a certain speed. Beyond this speed, the amplitude gradually decreases as the speed keeps rising, and remains stable within a certain range. The speed at which the rotor amplitude is at its maximum is known as the rotor’s critical speed. This rotational speed is equal to the natural frequency of the rotor. As the speed increases further and approaches 2 times the natural frequency, the amplitude increases again. When the speed equals 2 times the natural frequency, it is referred to as the second-order critical speed; similarly, there are third-order and fourth-order critical speeds…………