Recent deep-bar induction motor developments

Deep-bar induction motors have rotor slots approximately one inch deep. Their excellent starting characteristics are due to skin effect. Since skin effect in copper at 60 cycles is approximately 0.4 inch, the copper losses and starting torque are as if the current were confined to a layer 0.4 inch deep. Thus, the rotor resistance of these motors is 2.5 or more times as great when starting as when running. These motors develop 150 per cent or more starting torque and are useful as a general purpose motor.