Stator Looseness Trouble Analysis

Reactor jacketing pump which located in polymer plant have no stand-by equipment.

460V, 3phase, 100HP, 6 pole, 60Hz, TEFC Type
Maker : Reliance (Baldor) / Frame : 444T
1187 RPM at FLA (118A)

Chronology of events
Reactor Jacketing Pump (no stand-by equipment) vibration gradually increase 1.75g to 4g and maintain vibration about 4g for 2month.

- By looking at 2FL side band(Acceleration Spectrum), RBPF was expected cause.
However this is uncertain, as number of Rotor bar is unknown.
- Electric Fault was expected by 2FL frequency in the envelope spectrum.

Due to occurred RBPF & 2FL, testing to check rotor bar trouble at first.
But, Sideband frequency (frb) of rotor bar didn’t occur at this motor.

Lessons Learned
- For rotor bar fault analysis in mechanical view, rotor bar data must be needed, but electrical analysis for rotor bar can be performed without data. If data is not sufficient for mechanical analysis, electrical analysis can be good alternative
- In stator trouble, twice line frequency side band can be shown in the acceleration trend and it can be considered as rotor bar fault. For accurate diagnosis, MCSA (Motor Current Spectrum Analysis) must be performed.
- For rotor bar passing frequency analysis, detail rotor data should be include at the purchasing stage.