Novel Rotor Design for High-Speed Solid Rotor Induction Machines Daniel Tunc MCGUINESS, Mehmet Onur GULBAHCE, and Derya Ahmet KOCABAS Dept. of Electrical Engineering, Istanbul Technical University, Istanbul, Turkey mcguiness@itu.edu.tr, ogulbahce@itu.edu.tr, kocabasde@itu.edu.tr Abstract Solid rotor induction motors (SRIM) became increasingly prominent in high-speed drive applications with the development of efficient power electronics systems. These types of motors are easier to manufacture compared to conventional caged rotor induction machines (CRIM). In addition to that their high material integrity and high thermal properties makes them suitable to be used for high- pressure and high-speed drive applications. This paper proposes a new innovative rotor type for SRIM using in high-speed drive applications. This rotor type consists of hybrid construction of axially slitted and coated solid rotor structures and it is named as Shielded Axially Slitted Solid Rotor Induction Machine (SASSRIM) by the authors. In order to obtain performance characteristics of the novel designed rotor type, transient magnetic model is analyzed by finite element method (FEM). Finite Element Analysis (FEA) results show that rated output torque of SASSRIM is higher and more stable than other solid rotor structures. The brand new design also decreases the total losses, thereby making it more efficient than other conventional solid rotor designs. 1. Introduction This paper complements another paper by the same authors [1] where comparison of known solid rotor types for the same rated speed (slip) used in this study. Due to its simple structure, the usability of high speed induction motors have become increasingly popular in the fields of high pressure pumps, high speed gas compression systems and in small energy compression units [2]. Structure of a conventional solid rotor consists of steel to set up both main flux-carrying parts and the shaft itself which has worse ferromagnetic properties. Due to their simple rotor structure and high thermal properties, Solid Rotor Induction Machines (SRIM) became a cheap and reliable alternative to Caged Rotor Induction Machines (CRIM) in high speed applications. Even though their main principle operation is similar to other induction motors, considerable attention is needed for current density of rotor, temperature properties, magnetic properties and mechanical stress for a successful design [3, 4]. Although a SRIM has good mechanical and fluid dynamical properties, its electromagnetic properties are unsatisfactory. When the properties of solid rotor are questioned, its low power factor and its high time-spatial harmonic losses are prevalent. The most common type for solid rotors is the smooth steel cylinder (SSRIM) [5]. As a result of its simple structure, it has the best mechanical, fluid and thermal dynamics than that of other rotors [6]. However, its electromagnetic properties are not as good as other types. Its rated slip value is much higher for same output torque. Furthermore, depending on its geometrical properties, SSRIM cannot filter any of time and spatial harmonic losses in the air-gap. This causes high rotor losses and low efficiency. Different rotor types have been investigated in order to improve the electromagnetic and electromechanical performance, such as axially-slitted solid (ASSRIM) and coated solid rotor (CSRIM). However, their mechanical integrity is inferior to that of a SSRIM [7]. Axially slitted rotor helps to reduce the impacts of rotor losses caused by the air-gap harmonics [2]. The fundamental component of magnetic flux penetrates deeper into the rotor resulting in an improvement in the electromagnetic performance of the motor. In addition, the output torque of ASSRIM is higher than that of SSRIM [8]. This technique also reduces the rotor surface eddy current losses. However, because of the changed geometric shape of the rotor, the air-friction loss becomes more prominent at high-speed values. Another improving method is to coat the rotor with a thin sleeve of highly conductive material together with conductive end rings on both ends. Coating material is usually chosen with high conductivity and high thermal capability [2]. The eddy currents are mainly concentrated inside the coating material [9, 10]. Coating the rotor reduces the effects of air-gap harmonics and it acts as a low-pass filter. In addition, electromagnetic performance and mechanical operational properties of motor improves. Previous studies show that coated rotor is better than previously mentioned SRIM types at high-speed operation [11]. When designing a solid rotor induction machine, the electromagnetic and mechanical properties of the rotor material must be chosen accordingly. This choice greatly affects the field distribution and the mechanical stress on rotor structure. In this study, design of a motor having a new rotor type named as Shielded Axially Slitted Solid Rotor Induction Motor (SASSRIM) is proposed for high-speed drive applications. The new rotor type seems mainly a combination of two different conventional rotor designs. Axially slit are radially-covered by a thin layer of high-conductive coating material. Due to high- conductivity and high thermal integrity, coating material is chosen as copper. Slitted rotor material is chosen as steel-1010 depending on its availability in the market and its magnetic properties. Proposed new structure is analyzed by FEA tools for numerous speed levels in order to obtain performance characteristics, the distributions of magnetic flux and eddy current density in rotor. Only simulation results for 11300 rpm is presented to visualize one of the obtained results for the proposed design including the distributions of magnetic flux and eddy currents, and besides calculated core-loss, total loss and efficiency are given. 579