Vibrations and noise produced by special purpose permanent-magnet synchronous motors in variable frequency operation

Synchronous motors with solid-state power supply are widely used for variable speed applications. To keep the machine size to a minimum and maximize efficiency, high speed synchronous motors are used wherever possible. Such motors are inevitably a source of considerable magnetic, windage and mechanical noise. Developments in the field of rare-earth permanent magnets have made it possible to design and build synchronous machines of large power ratings with high efficiency and high power-to-weight ratio. For speed control, generally solid-state inverters are used. This paper presents a brief description of the theoretical and experimental investigations conducted on a variety of permanent-magnet synchronous motors in connection with the problems of noise and vibrations. In order to illustrate the procedures to determine the mechanism of the production of the noise and vibrations and to reduce them, two specific motors are considered here. The first motor has a power rating of 1.1 MW with 16 pairs of poles. The second motor is of a power rating of 1.5 MW, and has a very special design suitable for high speed operation.