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Vibration spectrum analysis

  1. Oct 6, 2014 #1
    I want to ask about spectrum of Ac induction motor, first of all, we measure points at non drive end + drive end - radial+axial direction.

    At horizontal direction we measure not only velocity but also acceleration. Two questions:

    1. I see a peak around 65000 rpm with sidebands at running speed (1500 rpm) , I suspect it not a bearings failure but as electrical problem.

    2. Here, too, I guess it electrical problem – suddenly the g' of the motor jumping and characterized by high peak around the 160000 – 200000 rpm, also with sidebands but at line frequency relative to motor running speed. For example, motor running speed is 1490 rpm the sidebands will be close to 6000 rpm. Even in case the motor has VFD (motor 3000 rpm 50-60Hz) and the running speed is close to 3600 so the sidebands will be 7200 rpm . Sometimes, it supported at the velocity spectrum by high harmonics at line frequency (6000 rpm).

    I hope you're familiar to these problems and can tell me ''recommended action'' to prevent or reair it.
  2. jcsd
  3. Oct 6, 2014 #2


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    Science Advisor

    Welcome to PF.
    Why do you suspect electrical?
    Is the vibration in phase with the motor rotation or the supply voltage? Induction motor slip will help discriminate between vibration of bearing/rotor/load and electrical/supply.

    Are these new vibrations? or were they there last time you measured the motor?
    Does the motor drive a gearbox?
    How many slots are there in the stator?

    A damaged ball or a track imperfection can be analysed by knowing bearing details. Record bearing size and manufacturer, number of balls in the bearing, ball rotation rate and frequency of balls passing a track imperfection.
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