Skin Effect Factor in the Bar Extension of Large Two-Pole Induction Motors by Three-Dimensional Finite-Element Simulations

An accurate estimate of the skin effect factor in the rotor bars of squirrel cage induction machines is important for the calculation of starting torque since the developed torque is directly proportional to the bar resistance. Past studies have given good estimates of this factor for the portion of the bars embedded in the rotor iron, but little is known about the effect in the rotor bar extension beyond the rotor core before entering the end ring. Depending on the length of the bar extension, the effect on the starting torque calculations has the potential to become significant. In this study, the end region of the machine was modeled using a commercial three-dimensional finite-element package in order to gain some insight into this phenomenon