AN INVESTIGATION INTO THE VALUE OF USING BALANCING CORRECTION ON GENERATOR WITH THERMAL BOW

  • By Ken Keith
  • one year ago
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Bearing vibrations are seen as major indicators for the dynamic performance and safe and reliable operation of a turbine-generator set. When a vibration alarm is received, efforts are concentrated to reduce the vibration at the bearing. The most common method used to reduce the fundamental (1xRPM) vibration is field balancing (weight correction). If the vibration is caused by mass unbalance of the rotor, weight correction on this rotor would be the most appropriate way to reduce the dynamic forces and stresses on the rotor and bearings. However, weight corrections are sometimes used to compensate generator thermal bow, bow due to uneven rotor temperature distribution often seen on generators with shorted turn(s). In this case, the bearing vibrations would be reduced, but the dynamic forces and stresses may not be, and thus a better dynamic performance and safe operation may not be achieved. This paper investigates into the value of using balancing weight to reduce bearing vibrations due to thermal bow with a case study on a 4-pole generator with a suspected shorted turn. The paper evaluates not only the end result vibrations, but also the shear forces, moments and stresses on the rotors. The evaluations are based on the results of a comprehensive rotor dynamic study, validated by field data.