Optimization of Shield Thickness of Finite Length Rotors for Eddy Current Loss Minimization

A high conductivity shield is often used for coating the rotor of solid rotor synchronous machines for reducing the surface eddy current losses due to the armature reaction space and time harmonics and/or tooth ripple. Since the design process for determining the optimal shield thickness can be very complicated and time-consuming, a simple analytical model based on Maxwell\´s equations was developed and presented in a previous paper to simplify the process. It has been shown that such an analytical tool can be used as an effective "screening tool" for determining the optimal shield thickness for minimizing rotor surface losses. In this paper, the design process is further refined by employing a special finite element method that accounts for the impact of finite axial length of the rotor. A number of comparisons are made between the analytical and the finite element results for significant space and time harmonic combinations to verify the validity of the proposed approach and to quantify the impact of the finite length of solid rotors