What is the critical speed of a back-pressure steam turbine?
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This post was last edited by chengkang on 2010-8-1 16:49. What is the critical speed of a back-pressure turbine? Are the critical speeds of all back-pressure steam turbines the same?
Of course it’s different–our first one is 4573.5R and the second one is 17350R
Not all are the same; ours is BCL403 with a critical speed of 7777
Not only are they different, but the operating speed of some low-power turbines is also below the critical speed; such shafts are commonly referred to as rigid shafts. One of our company’s compressors is like this: its operating speed is around 14,000, but its critical speed is even higher; therefore, the operating procedures do not specify what the critical speed is. There is no need to take the critical speed into account when accelerating or running the compressor, and there is even no need to turn it by hand after it has been shut down. The manufacturer’s design does not include a turning motor, nor a manual turning mechanism.
Can the critical speed be calculated based on power and rotational speed?
The critical speed of each machine is different, and this is related to the shaft. Each compressor undergoes a critical speed test upon leaving the factory; a trial run is carried out before startup, followed by an overspeed test, and it is through these tests that the relevant data are obtained.
This parameter is determined based on several sets of manufacturing specifications; for my unit of type NK32/12/16, it is 4879–5089 RPM. The client should refer to the manufacturer’s instructions when formulating the operating procedures, as it is necessary to pass through the critical point quickly.
I asked if it’s 3964.5–4964.5r
Regardless of the model or load capacity, each machine has a different critical speed; any similarity is purely coincidental. Even twin machines of the same model that are produced and shipped at the same time will have different critical speeds, although they tend to be quite close to each other. This number is determined by the manufacturer through individual testing of each machine. Each machine generally has two critical speeds: one is the low-speed critical speed and the other is the high-speed critical speed. The low-speed critical speed must be quickly exceeded during the startup acceleration process to prevent resonance ； The high-speed critical speed is generally well above the normal operating speed, and it is highly unlikely to be reached; with an overspeed protection system in place, there is basically no need to consider the high-speed critical speed