Interharmonics injected into power system by a squirrel-cage induction machine in normal and faulty operation conditions

The paper aims at examining interharmonics injected into the power supply system by a healthy and faulty squirrel cage induction machine operated at steady state. The faulty operation discussed encompasses breaks in squirrel cage bars, breaks in squirrel cage end ring segments, combined static and dynamic eccentricity, clutch wobbling and vibration of bearings. The effect of these ailments is first investigated through simulations accomplished with a specially developed and implemented squirrel cage induction machine polyharmonic model, as the fundamental harmonic models are not capable of simultaneous accounting for eccentricities, slotting and actual winding configuration. Two case studies, based on preregistered currents of big industrial machines, confirm the frequencies of interharmonics predicted by theory and simulations. The case studies refer to broken bars and clutch wobbling. The case study analyses were accomplished with the system Sp4 developed for offline diagnoses of induction machines.