Induction machine diagnostics based on FFT analysis of current space vector

FFT analysis of one of the stator currents has become a standard procedure for diagnosing the state of an induction machine. In this procedure the harmonics are all as if positive. However, if the stator currents are aggregated to a space vector, a direction of rotation of complex harmonics is determinable. The sign of a harmonic conveys additional information, important for diagnostic purposses. The paper presents analyses of calculated currents, based on an FFT algorithm for two currents. As, typically, a machine is fed through three cables, two currents are sufficient to establish a space vector of stator currents. The space vector is a complex quantity which can be put into an FFT analysis. A developed software is fitted with graphical interface. Unlike traditional display, separate amplitudes of harmonics are displayed above and below a horizontal frequency axis. The harmonics rotating in positive direction are displayed above, and the others below the frequency axis. The software automatically indicates zones where the slot harmonics are expected. The algorithm for this is based on a specific harmonic balance model. Based on the frequency of a slot harmonic, the rotor speed is determined. Preliminary analyses are uncluded.