Time harmonics investigation of stator and rotor currents of a dedicated induction machine

Condition monitoring of electric machines is of increasing importance. The continuous assessment of the machine performance allows to schedule appropriately maintenance operations, thus increasing machine operating life and reducing repair cost. The input current spectrum is a wide spread procedure for non-invasive diagnosis of induction machines. Information on rotor variables are available only by computation, typically by FEM. Experimental results are difficult to achieve: specific sensors must be mounted on the rotor to detect currents or flux density. In this paper a dedicated machine and experimental set-up, developed at IEN, was used, that allows to detect single bar currents through sensors positioned on the rotor bars. So doing it is possible to compute both rotor phase currents and space vector spectra. The main phenomena, that introduce waveform distortion, are briefly recalled and the corresponding spectrum lines for both stator and rotor currents are reported and analyzed in this paper.