Reliable detection of induction motor rotor faults under the influence of rotor core magnetic anisotropy

Motor Current Signature Analysis (MCSA) has become a popular test method for medium/high voltage induction motor rotor cage condition assessment in industry. However, cases of false alarms due to rotor core magnetic anisotropy resulting in unnecessary rotor inspection have recently been reported. In this paper, a method for testing the rotor under the startup transient based on the application of the Short Time Fourier Transform (STFT) is presented as a solution for averting anisotropy induced MCSA false alarms. An experimental study is performed on medium voltage motors operating in an oil refinery, and on custom built lab motor samples for verification of the proposed method. It is shown that the STFT based startup detection method provides reliable identification of rotor faults immune to the influence of magnetic anisotropy and external supply interference.