Abstract
This paper presents a new balancing method pertaining especially to significantly eccentric, flexible rotors. When dealing with these rotors in service facilities, standard balancing methods often require excessive runs, and vibration problems are frequently experienced upon rotor reinstallation in the field. The method presented here is based on a novel view of the unique rotordynamic behavior in these cases. The key is to fully compensate rigid modes first to bring the effective principal mass axis coincidental to the rotor’s designed geometric axis, preventing a switch of precession axes through the critical speed region. This must incorporate proper axial distribution of weights using 2N+1 balancing planes (where N is the highest operating mode). The end result is a “dynamically straight” rotor that remains balanced without distortion or bending at any speed. This method requires fewer runs, and the rotor is guaranteed not to need field balancing upon properly aligned installation.
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Notes
- 1.
Rotors operating under these conditions will eventually self-correct these moments, but as a result may develop coupling face deformations or even develop cracks.
- 2.
In operating plants, “relative shaft vibration readings” are often used as a limit for “safe” operation, often unnecessarily forcing a turbine-generator unit to shut down over safety concerns for what is very often a benign cause with minimal true transmitted forces. Worse yet is the situation when balancers reduce the displacement amplitudes below “alarm level,” but only by unintentionally creating a disproportional, damaging increase in bearing reaction forces.
- 3.
This mean mass axis becomes the principal axis of rotation/precession above the critical speed region, when inertia forces become dominant in controlling rotor behavior.
- 4.
That is, to shift the effective radial center of gravity at any given radial plane of the rotor to coincide with the geometric axis, but not to bend the rotor in any way.
- 5.
Significant eccentricity existing outside the journals must be corrected by machining only.
References
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Racic Z, Hidalgo J (2007) Practical balancing of flexible rotors for power generation. In: Proceedings of the ASME IDETC/CIE conference, Las Vegas NV, USA, Sept 2007
Racic Z, Hidalgo J (2007) The effect of applied high speed balancing method on flexible generator rotor response in operation. In: Proceedings of ISCORMA-4, Calgary, Canada, Aug 2007
Racic Z, Racic M (2014) Behavior of eccentric rotors through the critical speed range. In: Paolo P (ed) Proceedings of the 9th IFToMM International Conference on Rotor Dynamics, Mechan. Machine Science, vol 21. Milan, Italy, 22–25
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Racic, Z., Racic, M. (2015). Development of a New Balancing Approach for Significantly Eccentric or Bowed Rotors. In: Pennacchi, P. (eds) Proceedings of the 9th IFToMM International Conference on Rotor Dynamics. Mechanisms and Machine Science, vol 21. Springer, Cham. https://doi.org/10.1007/978-3-319-06590-8_4
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DOI: https://doi.org/10.1007/978-3-319-06590-8_4
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