Stray Fluxes Amplitude and Phase Shift Monitoring for Interturn Short Circuits Detection in Induction Motors

In this paper considerations about the time-domain amplitudes and phase shift between diagnostic signals measured in induction machines will be presented. In particular, the line to line voltage, stator current and axial and radial stray fluxes have been considered in various conditions. Since the phase shift between signals is rarely considered in the diagnostics of electrical machines, even in multi-sensor system, this represents a quite strong novelty of the presented method. The machine considered, a small-size induction motor, has been fed by the mains and with an open-loop PWM inverter. Tests with different load conditions and with three severity levels of stator inter-turn short circuits are presented. The phase-shifts between the fundamentals and third harmonics of the signals are considered, giving good diagnostic results.