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Rotor Analysis Techniques (Part 2 of 2)

Last week we discussed rotor analysis techniques (1 - 3) performed on motors that are de-energized. This week we will discuss rotor analysis techniques (4 – 6) performed on motors that are energized.

  • Technique #4 is a quantitative evaluation of the amplitude of the pole-pass frequency sideband (FP) around line frequency (FL). This is an age old accepted approach where the analyst evaluates the difference in dB between the amplitude of the FL and the amplitude of the FP. Elevated FP under a 40 db difference from the FL should be monitored closely and trended.
  • Technique #5 is a qualitative evaluation of the 5th harmonic of FL looking for FP sidebands created by the phase shift in the air gap flux surrounding a broken rotor bar. The presence of three harmonic FP peaks to the left of the 5th harmonic in conjunction with technique #4 above, adds significant confidence to the assessment of a rotor bar anomaly.
  • Technique #6 is a quantitative/qualitative evaluation of the FP amplitude after filtering out the FL and spectrum noise through a demodulation process. Although relatively new compared to the other evaluation methods, this technique is quickly becoming a favorite for trending rotor bar anomalies in larger two-pole motors.


Click here to read more information about rotor analysis techniques.

Click here to read more information about the demodulation process mentioned in technique #6.

 

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Rotor Analysis Techniques (Part 2 of 2)
June 22, 2015
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