T. Wolbank, R. Wöhrnschimmel, R. Kunicky, J. Machl:
"'Detecting rotor bar faults in induction machines at low and zero load based on flux modulation";
Talk: International Power Electronics Conference IPEC, Niigata, Japan; 04-04-2005 - 04-08-2005; in: "The 2005 International Power Electronics Conference", (2005), ISBN: 4-88686-065-6; 1225 - 1230.

Besides rotor bearing faults and isolation breakdown, rotor bar faults in induction machines are a major concern in critical industrial processes and many detection techniques have been suggested. Most of them demand a minimum load for a clear identification of the failure. Especially in high power applications this may make an expensive test set-up necessary. This restriction doesn´t apply if the modulation of the electrical rotor time constant in different magnetizing directions with respect to the rotor surface is monitored. Because its evaluation is not limited to a certain load level and can even be performed on an idle running machine by magnetizing and demagnetizing the machine with respect to certain angles in the rotor coordinate system and measuring the time constant. The resulting magnitude of the modulation is then used as a fault indicator.
The applicability of this technique was verified for an idle running machine in recent publications. This work shows an extension of the method for the case when a certain low and inevitable load is applied, what is a realistic point of operation since there is always a load originating i.e. from cooling fans or when the machine under test is part of a production line and its decoupling has to be avoided.

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