Thermal Management Issues of Rotors in Rotating Electrical Machines

Advanced electrical machines such as permanent magnet and switched reluctance types are very compact and have high power densities, usually 2 - 5 kW/lb. Nearly 20% of the rated power capacity is dissipated as heat within the machine. Thermal stress, deterioration of magnetic and insulation properties, and loss of power are caused by the overheating of the machine resulting from poor cooling. Because of the enclosed and rotating nature of the rotors in these machines, it becomes increasingly difficult to cool. In this paper, a thorough literature review on this subject is presented. A general description of the thermal management issues and some possible solutions are discussed. Rotating heat pipe rotor shaft and spray cooling heat exchanger solution is suggested. This study was conducted in support of the Air Force more-electric aircraft technology development.