Determining torque-speed curve of two-speed deep cage lift asynchronous machines

Typical rated slip for most induction motor applications lies below 15%, and the concern about their torque-speed curve, when existing, refers to slips of only up to 100%, and then usually with somewhat loose requirements (like minimum or average starting torques). However, for two-speed lift motors, a very reliable determination of the T-n curve is necessary, especially at the extremely high slips of up to 300% appearing in their working cycle. Therefore a precise determination of leakage reactance together with an accurate analysis of bar current displacement and end-ring current distribution become unavoidable. A systematic investigation is made on four gradually more sophisticated steady-state models (the first three of them rather well known to specialists) used to predict the T-n curve from machine design data. The comparison of all model results with the T-n curve measured in more than 30 industrial lift motors makes evident, and allows a clear appreciation of, the limitations and range of validity of each model when faced with such a demanding application and, at the same time, confirms the suitability of the proposed fourth model.