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The cooling system of unregulated self-ventilated motors operating in the pulp area can be severely deteriorated by pulp fibers deposited in the motor frame and in the air intake area. As a result, these motors can become overheated even with operating currents below the rated current. This paper presents and evaluates three thermal models that are capable of detecting the effect of the pulp in the dissipation of the operating losses to the ambient. One model is a simple 3rd-order model, which frame-to-ambient resistance is affected by the presence of pulp partially blocking the air inlet. The other two models recognize the asymmetrical dissipation produced by the pulp coating the upper sector of the motor frame by defining flow paths for the different radial quarters of the motor. Through an extensive testing program, the effects of the different pulp situations on the quarter and/or equivalent thermal resistances are determined. Using these values, the temperatures rises in the spots of interest using the proposed models are evaluated, showing excellent agreement with the experimental values. Finally, the different options for the use of the models for motors with and/or without temperature sensors are analyzed.
Date of Conference: 21-23 June 2010