The development of an accurate finite element model to investigate the factors which influence the fault-indicating components of current in 3-phase induction motors

This paper has reported on the development of an accurate finite element model of an induction motor suffering from rotor faults. The model has been used to provide a clearer understanding of how such faults are manifest in the line current and should therefore aid the development of more accurate condition monitoring techniques. The results have shown that when there are broken rotor bars, the lower sideband component of current is initially established as per standard theory. In the absence of magnetic saturation and speed ripple, this would be the only effect of the broken bars and measuring the magnitude of the lower sideband component would give a reasonable indication of fault severity. When speed ripple is introduced, as it would be in practice, the lower sideband component is modulated about the 50 Hz component and an upper sideband is created while, at the same time, the magnitude of the lower sideband component is attenuated. The effect of magnetic saturation is to introduce a further upper sideband component and this, in turn will affect the lower sideband through the modulation process described above. The resulting sideband magnitudes are therefore seen to be a result of several influencing factors