Heating in deep-bar rotor cages

Redistribution of current in deep-bar cage rotors as a result of temperature-dependent electric conductivity alters the distribution of thermal sources in the bar and provides complex temperature variation in the bar area. The temperature distribution is also widely affected by the conductivity of the interface area between the bar and inner surface of the slots. In the majority of existing work this effect is overlooked by assuming adiabatic boundaries around the bar during the first few seconds. It is shown that unless there is good insulation around the bar, which is unlikely to be practical in copper bars and impossible in die-cast aluminium cages, this boundary is not valid even for the first second after starting. Also the effect of redistribution of current in the bar is studied.