A method has been described for the calculation of the stall temperature rise rate for the hottest bar in a rotor cage. It has also been demonstrated both theoretically and experimentally that this rise rate can differ very significantly from bar to bar in a machine of conventional design. The method for calculating the maximum bar temperature variation requires three basic steps. First the maximum bar current must be determined, and it has been shown that this can be accomplished via the conventional equivalent circuit. Secondly the loss distribution must be calculated, and this may be achieved using a simple stratified model of the bar and an impedance matrix. Finally a thermal model has been described, leading to a time-stepped finite difference solution for the bar temperature.
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