| dc.description.abstract | A large, double ended drive synchronous motor experienced
severe, limiting lateral vibration during commissioning of a major
plant expansion. The motor driving a centrifugal compressor
providing process air is decoupled during startup from a gearbox
and steam turbine by a clutch. Steam generated by waste heat from
the process drives the turbine under normal operation and the
synchronizing clutch is engaged, reducing the motor load
requirements. Excessive running speed ( 1 x) lateral vibrations
came to light when the motor was run solo during field
commissioning. Extreme sensitivity to small trim balance weight
changes on the exciter end led to extensive field tests to identify
the source of the problem. Rotordynarnic analyses and coupled
running tests confirmed an overhang resonance, and revealed the
only possible short term solution to be the addition of a third
bearing on the motor shaft to control the overhang mode. Field
installation of a 14 inch diameter tilting pad bearing, located on the
clutch hub at the motor shaft end, was completed quickly to allow
plant startup to proceed. In situ machining of the hub on the shaft,
while the motor remained installed in the field, was required to
assure proper journal shape and rapid project completion. This
paper describes the process of problem identification,
measurement/verification, rotordynarnic analyses, resolution, and
field implementation. Before and after field vibration
measurements are presented to illustrate the success of the solution
and demonstrate the additional instrumentation required. | en |
