2022 Fault Zone Series: Part 5 Rotor

Returning to the Fault Zone approach to electric motor troubleshooting we continue this series with Rotor. When PdMA refers to the Rotor Fault Zone in a squirrel cage induction motor, it is referring to faults in the rotor bars, end rings, and rotor laminations. It’s important to remember that a fault in any one of these components identified early enough will not restrict the operation of the motor and can be corrected before any severe or secondary damage occurs.

Like in other fault zones a variety of root causes should be considered when trying to get ahead of a rotor faults. Rotor faults, if not identified as the root cause may result in a motor failure blamed on another fault zone. Without correcting the rotor anomaly you are doomed for a repeat failure in the short future. The following are some potential indications of rotor faults:

  • Lower Start-Up Current and Longer Motor Start Times
  • Increasing Current Modulations
  • Audible Hunting Sounds Heard Near the Motor
  • Excessive Vibration
  • Non Symmetric Heating of Rotor Laminations
  • Non Sinusoidal Inductance Pattern on Rotor Influence Check
  • Increased Pole Pass Frequency (FP) Side Bands Around Line Frequency
  • Increased (FP) Side Bands Around the 5th Harmonic
  • Stator Inductance

Note that many of the fault indications above are based on a comparison to a baseline or trend. Remember…Trend is Your Friend.

For more examples of Rotor anomalies and alarm standards applied to your electric motor reliability view our website at https://pdma.com/diagnostic-tools/fault-zone-rotor/