Evaluation of the influence of rotor axial air ducts on condition monitoring of induction motors

Sungho Lee, Jongman Hong, Sang Bin Lee, Ernesto J. Wiedenbrug, Mike Teska, Heedong Kim

Research output: Contribution to journalArticlepeer-review

65 Citations (Scopus)


Rotor axial air ducts are used in large motors for cooling and for reducing weight and material. The rotor axial ducts can produce twice-slip-frequency $(2sf-{s})$ components in the vibration or a current spectrum that can be misinterpreted as induction-motor rotor faults. There is currently no practical solution to the air-duct-induced false positive indications, which is an ongoing problem in the field. However, there are only a few publications that report the issues caused by rotor axial ducts. In this paper, the influence of the rotor air ducts on motor condition monitoring is analyzed and investigated through testing in the field on 6.6-kV motors and in the laboratory. The experimental study shows that the magnitude of the $2sfs component due to axial ducts depend on the design, material, construction, and operating conditions of the motor. It is also shown that the $2sf s component can even decrease with broken bars, depending on the fault position relative to the ducts, which makes online condition monitoring difficult. Guidelines for reliable motor testing and interpretation of test results are also provided.

Original languageEnglish
Article number6506101
Pages (from-to)2024-2033
Number of pages10
JournalIEEE Transactions on Industry Applications
Issue number5
Publication statusPublished - 2013
Externally publishedYes


  • AC machine
  • axial cooling duct
  • condition monitoring
  • diagnostics
  • electrical fault detection
  • induction motor
  • magnetic asymmetry
  • shaft spider

ASJC Scopus subject areas

  • Control and Systems Engineering
  • Industrial and Manufacturing Engineering
  • Electrical and Electronic Engineering


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