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Electrical Frequencies - Soft Foot( 2xLF -100hz)

Symptoms: 2x Lf 100hz Peak radial - SoftFoot (Stator Eccentricity)

Soft foot and warped bases can produce an eccentric stator. Altering the tension on the hold down bolts, or repairing the foundation can resolve this problem.

 SoftFoot (Stator Eccentricity) is characterised by:

Spectrum: The peak at 2xLF will be high. For a two-pole motor this peak will be close to 2X running speed – you will need sufficient resolution to separate them.

 

  • A live spectrum may reveal beating – the 2xLF/2xTS peak may appear to rise and fall if you do not have sufficient resolution to separate the peaks.
  • The vibration will be strongest at the point(s) where the stator is closest to the rotor. 

 

  • Move the accelerometer around the motor housing to see if the peak is highest in one or two locations.

We expect to see a high peak in the spectrum at 1X turning speed of the shaft. It is often higher in the horizontal direction compared with the vertical direction due to stiffness.
Waveform:

  • The waveform will be a combination of 1xTS, possibly 2xTS and 2xLF and may therefore include a "wobble” or take on the "M” or "W” shape. 

  • Beating between 2xLF and 2xTS (2-pole motor) may be observed if the time waveform covers more than a few seconds.

    TS = Turning Speed 

    LF = Line Frequency (50 or 60 Hz)

Phase:

  • Not Used

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