Practical Balancing of Flexible Rotors for Power Generation

Abstract

Balancing technology is still relatively new. Thirty years ago it was primarily still part of the skilled trade and was often obscured. Today there is enough reference literature printed during the last 20 years alone on general balancing and balancing of flexible rotors, that could fill a room, (Ref: N. Rieger). The majority of papers and other references deal with theoretical derivation of equations based on Jeffcott rotor model. With the growth of rotor sizes specifically of electric generators in power plants, so grew the need to develop not only a theory, but also the way to practically balance these rotors. The economy of manufacturing required pushing the rotors to more and more slender; lower and lower stiffness (∝ EIxx/L3) designs, in relation to its mass moment of inertia (Im), these rotors were more difficult to balance. The first to encounter the problem of balancing these rotors were the OEMs. On two different shores of the Atlantic Ocean, two basic balancing theories known as balancing in “N”, or in “N+2” balancing planes and operating rotor modes were developed. Later, with the development of the microcomputer the influence coefficient method had gained popularity among the power plant community and despite good experiences from both sides the controversy over which one produces better results was left open. In this paper a review of the “N” and “N+2” methods including notes on influence coefficients (IC) is conducted from a practical standpoint. The conclusion by the Authors is that there is no “better” or “worse” balancing method, only the more or less economical in a given situation, and neither gives a unified method to satisfy every rotor. General guidance is also provided over which method to use for best results in balancing large turbo-generator sets.

An investigation into the balancing of high speed, flexible shafts by external application of compensating balancing sleeves

“…The figures show that external application of balancing sleeve methodology is feasible for shafts with large overhung discs, thus enabling considerable reductions in disc deflections to be achieved, especially at higher operating speeds. It is also apparent that the dynamic requirement of encastre simulation to achieve optimum compensation, as defined in the earlier work by Knowles et al., 15 has been met for the portion of the shaft supporting the overhung disc, since the shaft slope at the first bearing is approximately zero.…”

“…A good review of current balancing methods 13 concludes that the capability/availability of today’s high powered computers makes the differences in balancing methods more a question of economics than capability.…”

The Effect of Rotor Balance During Crushing of Intermetallic Compounds in Hammer Crushers

“…The influence of the imbalance of the parts that rotate on different mechanisms, the analysis of these actions and solutions to this problem are considered in scientific works of different areas of science and allow us to take this experience into account [5][6][7][8].…”

Аналіз Дії Незбалансованості Ротора Молоткової Дробарки На Його Опори

“…У ще у роботах запропоновані: альтернативна методика врівноваження ротора, де попередньо проводиться: низькочастотна балансування ротора, кероване складання й багатоплощинне балансування ротора з заданими параметрами напрямків і розміщення залишкових дисбалансів [4], а також дослідження про економічну і раціональної складової балансування великих роторів [5].…”