Tangential forces matter [rotating electrical machines]

It is known that radial forces acting in the airgaps of rotating electrical machines on the tips of stator teeth account for a major portion of the vibration of these machines. Despite apparently widespread belief, however, these are not the only significant forces at work. Tangential forces acting on the teeth are invariably many times smaller than their radial counterparts. However, tangential motions of tooth tips are often many times larger than the radial motions in important natural modes of machine vibration. Hence the ability of the tangential tooth-tip forces to excite these modes can be comparable with the radial tooth tip forces. This paper shows that tangential forces acting on the tooth tips should not be neglected in large machines