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 twospeed 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.