Monitoring gearbox oil viscosity by means of motor current signal analysis

Pieter A. Van Vuuren, Yuandong Xu, Fengshou Gu, Andrew D. Ball

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review


A number of gearbox failures can be attributed to lubricant related problems. One measure of the condition of gearbox oil is its viscosity. In electrically powered systems, motor current signal analysis allows online estimation of the viscosity of gearbox oil without requiring additional sensors. Previous work on this problem entailed monitoring the power (and change in power) of sidebands of the shaft frequency in the induction motor current spectrum. Sideband frequencies in the current spectrum can however be influenced by other potential problems in the electromechanical system ranging from bearing faults to gearbox teeth damage. Changes in the lubricant viscosity result in changes in the mechanical and thermal losses in the system. These small deviations in the mechanical and thermal losses in the system become visible in the ratio of the electrical energy demanded by the induction motor to the kinetic energy of the rotating mechanical parts. Speed and load invariance can be ensured by normalizing the measured energy ratio with lookup table values obtained when the system attained thermal equilibrium. Speed or load perturbations in the system give rise to small deviations in the normalized energy ratio curve. The distributions of these deviations are significantly different (in a statistical sense) for different oil viscosity values.
Original languageEnglish
Title of host publication1st World Congress on Condition Monitoring
Subtitle of host publication(WCCM 2017)
PublisherBritish Institute of Non-Destructive Testing
Number of pages12
ISBN (Print)9781510844759
Publication statusPublished - 2017
Event1st World Congress on Condition Monitoring - ILEC Conference Centre, London, United Kingdom
Duration: 13 Jun 201716 Jun 2017 (Link to Conference Website)


Conference1st World Congress on Condition Monitoring
Abbreviated titleWCCM 2017
Country/TerritoryUnited Kingdom
Internet address


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