Modelling the vibrational behaviour of stator cores of electrical machines with a view to successfully predicting machine noise

Most modern large electrical machines are sold subject to a condition in the contract which limits the sound power generated. It is important to a large-machines manufacturer to be able to predict sound power which will be generated by his machine. One the biggest problems in this respect is the determination of the mechanical response of the stator core to electromagnetic forces acting on it. The predominant frequencies of interest are around rotor slot-passing frequency which is normally a small number of kHz. At these frequencies, the core of a machine cannot be modelled effectively in a mechanical sense using straightforward finite element methods because of the very modal density in this range of frequencies. This paper shows how a core model can be built up for each frequency by assembling a model for a single piece of core firstly into complete rings and subsequently connecting these rings into a cylindrical format.