Influence of Magnetic Saturation on Diagnostic Signal of Induction Motor Cage Faults

Induction motor rotor cage diagnostics bases on additional components in stator phase current with (1-2s)f_o and (1+2s)f_o frequencies. The (1-2s)f_o component arises as the main effect of the cage asymmetry whereas the (1+2s)f_o component is a secondary effect. It is commonly known, that it arises due to speed ripples, which are generated by alternating component of electromagnetic torque in a motor with faulty cage. This paper shows that magnetic saturation of a main magnetic circuit also generates the (1+2s)f_o component in stator currents. A special mathematical model accounting for saturation is used to prove this thesis. Results of quantitative analysis of an influence of inertia and saturation on the (1+2s)f_o component is shown.