Insights on diagnostic signals in single-phase and three-phase induction motors in single-phasing fault

The aim of this paper is twofold. On the one hand, the applicability of the well-known diagnostic techniques, based on the motor current and stray flux signature analysis, has been experimentally tested both on small single-phase induction motors and on large on-field three-phase induction motors. On the other hand, the single phasing fault in three-phase induction motors, which has rarely been treated in the literature, has been experimentally analyzed and compared to the behavior of the single-phase motor, in order to find characteristic signatures of this fault. Time and frequency domain analyses were performed on current, axial and radial stray flux, and torque signals. The experimental study highlighted the following insights: i) classical motor current signature analysis cannot be easily applied to permanent-capacitor single-phase machines; ii) stray flux analysis reveals the presence of additional harmonic sidebands, even in healthy three-phase induction motors; iii) a rough analysis of the third harmonic in the current spectrum may be sufficient to diagnose the single phasing fault.