MCSA Case Histories—Cyclic Loads Can Cause False Positives of Cage Winding Breaks

This chapter focuses on case histories where cyclic loads in squirrel cage induction motor (SCIM) drive trains can cause false positives of cage winding breaks. The industrial case histories demonstrate the complexity of applying motor current signature analysis (MCSA) to SCIM drive trains, from which the mechanical dynamics are reflected back into SCIMs. The first case considers the effect of gas recycling in a centrifugal compressor on the spectral content of the current spectrum for detecting broken rotor bars. The chapter presents interpretation of current spectra and photos of the rotor with the broken rotor bars. It focuses on false positive of cage winding breaks caused by fluid coupling dynamics in the drive train. The chapter suggests that extreme caution should be exercised, when interpreting spectra from SCIM drives with gas compressors in a gas recycling mode, or with a fluid coupling or any mechanical load variations that are reflected back into the SCIM.