MCSA Case Histories—SCIM Drives With Slow Speed Gearboxes and Fluctuating Loads Can Give False Positives Of Broken Rotor Bars

This chapter presents case histories focusing on the influence of slow speed gearboxes in 3‐phase induction motors (SCIMs) drive trains which are driving fluctuating mechanical loads. A significant cause of forces in a SCIM drive train applicable to all drive trains is misalignment across the coupling between the shaft of the electric motor and the driven load, causing an external mechanical force to be transmitted to the cage rotor in the motor. Misalignment in the drive train can cause changes to airgap eccentricity within a SCIM, therefore it is necessary to define the different types of airgap eccentricity. In practice it is not possible to separate static from dynamic airgap eccentricity using classical motor current signature analysis (MCSA) when the only information available is the nameplate data and hopefully the number of rotor bars from the motor manufacturers (OEMs). The chapter provides knowledge via MCSA to help avoid false positives of broken rotor bars via MCSA.