High speed synchronous homopolar and permanent magnet machines comparative study

Two types of high-speed (30000-r/min) synchronous machines, a homopolar and a permanent magnet, have been designed and constructed. The authors discuss possible applications of such machines and problems associated with high-speed operation. Details of machine geometry and design procedures are described. In comparing the two types of synchronous machines, it is shown that the power/mass ratio of a homopolar machine is lower because of relatively low utilization of the magnetic circuit, typical for homopolar machines. The construction of a homopolar machine is complex and therefore seems to be less reliable. the first critical speed of a homopolar machine is lower as a consequence of a higher rotor length