A mechanical strength evaluation of the permanent magnet in a rotating machine.

The small and light weight motor generator with permanent magnets is available in the field of a high-rotational-speed machine. The authors have developed a new-type uninterruptible power system with a high speed flywheel. This system carries continuous power to a computer immediately from the flywheel storage unit by changing kinetic energy into electric energy if the primary power source is temporarily interrupted. In this system, a cylindrical-type, synchronous motor generator with permanent 2-pole magnets on the inside periphery is adopted. The flywheel rotor rotates continuously at a high rotational speed of about 30 000 rpm. The stress and strain in the flywheel rotor is caused by centrifugal force. This stress and strain occurs in the rotor magnet at the same time. A crack in the permanent magnet would occur if the flywheel rotor were to reach a higher rotational speed because the material of the permanent magnet is brittle. This paper presents a mechanical strength evaluation of the permanent magnet in a rotating machine.