General/ Motors



Purpose: This study is to explain how a troubleshoot was carried for a high vibration issue in a motor where vibrations were fluctuating at 1x and 2x of RPM    01


During solo run test of a 850kW/3575 RPM/4160V Horizontal motor it was observed that vibrations were in Unsatisfactory level 4.6 mm/sec rms as per ISO 10816-3 class-3.

FFT spectrum indicated dominant 1x and 2x frequencies which kept fluctuating with time. Phase angle was unsteady but cross phase noticed was around 105from horizontal to vertical direction.

Challenge:    02

The challenge was to reduce the vibrations at 1x and as well as 2x which were fluctuating up and down with respectively changing amplitudes.

Need to identify that rotor is flexible or normal.

Such behavior of the machine is rare, the trim balancing of the motor with 2plane balancing method was recommended during technical discussion and was performed.



  1. Two Plane balancing using Pruftechnik – Vibexpert kit.
  2. After performing couple of trials vibrations were reduced to maximum 1.0 mm/sec rms which is Good limit as per ISO 1081-3 class-3 and achieved balance quality was in acceptable limit.

Conclusion: 03.

  1. Proper diagnosis is required to address the problem in the machine to decide the corrective action. The machine diagnosed being a flexible rotor during analysis is very much important before performing any correction for vibration issue in the motor.

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