Diagnostics Insights on Single and Three-Phase Induction Motors in Healthy and Single-Phasing Conditions

In this work, an investigation on permanent-capacitor single-phase induction machine, healthy three-phase and three-phase induction machine in single phasing condition is presented. The study focuses on the analysis of one-phase current signal, radial and axial stray fluxes, and also torque signal for the single phasing condition. The steady state signals are initially analyzed in the time-domain and then sidebands around the supply harmonic are studied in the frequency-domain. Firstly, new insights are presented for the permanent-capacitor motor, very rarely treated in literature. Then, the presence of a significant harmonic in stray flux signals is highlighted or all machines and conditions. An investigation over a wide frequency range is also carried out proposing a new rule of thumb to locate a supply unbalanced condition looking at third and fifth harmonics. Two Low Frequency Torque Oscillation (LFTO) conditions are considered and evaluated. Finally, the derivative of the phase current is examined, and its interaction with the stray flux signals' variations in shape and amplitude is evaluated for several conditions. Some correlations between these signals and the current derivative are found, providing interesting diagnostic insights.