Influence of Rotor Position in the Broadband Impedance Response for SFRA Rotating Machine Diagnosis

Sweep Frequency Response Analysis (SFRA) applied to rotating machine diagnosis and monitoring lacks of widespread industrial applicability up to this date. Several authors identify the rotor position influence as one of the main obstacles for an on-site and reliable diagnosis. This work provides a thorough investigation on how the rotor affects the broadband impedance for different rotor topologies. The rotor DC field is identified as a strong influence on the measured broadband impedance. First, a theoretical analysis is performed to study the effect of an external DC field in the broadband impedance. Then, a 4.7 kW PMSM is thoroughly analyzed including magnetostatic Finite Element Analysis (FEA) and experimental measurements. Finally, the influence of magnetic remanence on the broadband impedance is experimentally studied. To this aim, two induction machines with two different rotor types (i.e., wound-rotor and squirrel cage) are analyzed. This collection of results is aimed to clarify the physics behind the rotor position influence and to enhance the reliability of SFRA diagnosis for rotating machinery.