Abstract It is widely recognized that the rotor-bar skin effect strongly influences induction-motor operation during unbalanced conditions. However, classic induction-machine dynamic models ignore this effect. A more general machine representation is derived that can predict the rotor-bar skin effect over the full range of dynamic induction-machine operation. The model is used to examine the starting of a motor fed by an open-delta transformer bank. The need to account for the rotor-bar skin effect is explained, and comparisons between motors starting with open-delta and balanced feeds are made.