TABLE OF CONTENTS The vibration spectra produced by rotating electric machines are similar in many respects to the vibration spectra produced by other rotating machines. Vibration frequencies caused by mechanical forces at running speed, and multiples of running speed vibration, as may be produced by rotor unbalance or the forces produced by shaft misalignment are the same. Vibration produced by bearings, such as the rolling element frequencies produced by rolling element bearings are also the same. But, in addition, rotating electrical machines produce a multitude of other vibration frequencies that are generated by the electromagnetic forces inherent in the operation of the machine.
Each machine, whether it is a motor or a generator, has its own individual vibration signature. The characteristic vibration signature is determined by the running speed, the number of poles on the rotor, the number of slots in the rotor and stator, and other variables. Certain vibration frequencies are fixed by the basic design and construction of the machine, but others may develop due to wear or deterioration of some components. This makes the monitoring of the vibration signature particularly useful for predictive or preventive maintenance purposes.
The stators of most modern motors and generators contain the armature winding, and the magnetic stator core provides part of the magnetic circuit of the machine. The stator core is made of thin steel laminations to control losses, and the bore of...
