Effects of end-shields and rotor on natural frequencies and modes of stator of small electrical machines

The effects of allowing for the end-shields, the rotor and the running condition on the natural frequencies and modes of the stator of a small electrical machine have been investigated by the modern experimental modal analysis technique. It was been shown that: because of the restricting effects, the end-shields significantly increase the values of the natural frequencies of the stator; by comparison the effect of the rotor is much smaller, however the rotor does cause important new natural frequencies to be introduced, in particular the first-order mode; and the modifying effects under a no-load condition are negligible, as is also likely to be the case up to rated load. The study has provided data which should assist further investigations, particularly in regard to the effects of the mounting feet on the natural frequencies and modes of stators, in developing vibrational models based on finite elements, as well as acoustic models.