High turbine shaft vibration
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The operating speed of the turbines in our plant ranges from 8,240 to 10,300 revolutions per minute, while the critical speed is between 2,040 and 8,240 revolutions per minute. During recent startups, the shaft vibration of the turbines was around 20 units before reaching 7,500 revolutions per minute; after that, the vibration level increased rapidly. The maximum vibration levels reached 130 units at one bearing point and 80 units at another, which led to a shutdown of the turbine. Can it be determined whether this is due to a mechanical fault or an issue with dynamic balance?
It’s not easy to analyze this – has the temperature increased?
The critical range is too wide; the exact value isn’t clear. If it’s above 7500 rpm, the vibration could be caused by imbalance. If there is no critical speed above 7500 rpm, waveforms and frequency spectra need to be provided to determine whether issues such as rubbing are occurring.
The critical speed of a high-speed rotating rotor is determined through theoretical calculations based on the stiffness of the shafting system and through actual tests. When the stiffness of the shafting changes, the critical speed also changes. Of course, it is inseparable from the quality of maintenance and installation.
After running for a period of time, the shaft vibration fluctuations decrease, but the shaft vibration increases again when the reduction is significant
It is suspected to be related to rotor scaling; planning to open it for inspection after the New Year
Your vibration level is high; it is recommended that you check what frequency the vibration is at Is it equipped with a status monitoring system?
The half-frequency component constitutes the main part, with a small amount of first-frequency component. Vibration decreases significantly when the oil temperature is reduced and the oil supply volume is increased; vibration increases markedly as the oil temperature rises