The knowledge of rotor quantities in induction motors allows the improvements of failure diagnosis and device design. In the first problem category, diagnostic techniques utilizing current analysis are based on the increase of specific frequencies of the current spectrum. This increase is directly related to anomalous conditions or machine non-idealities. Hence, to achieve a very accurate diagnosis, the whole current spectrum must be interpreted and this requires the deep knowledge of the machine behaviour, which can be acquired only by experiments or models[1-2]. In the second problem category, the high frequency currents produced in the rotor by the stator teeth, give rise to stray Joule losses (additional losses), which can be an important term in the energy balance of the machine, especially under non sinusoidal supply[3]. In both cases the precise knowledge of the rotor quantities is a crucial issue.
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