Contribution to the study of leakage fields at the ends of rotating electrical machines

A method is described for calculating the axial leakage field of the end regions of rotating electrical machines. The method subdivides the problem into the component fields of the magnetic sources that contribute to the axial field. The total field is then found by superposing these component fields. The method is compared with the traditional approach of analysing the magnetic field of electrical machines in terms of magnetic circuits. Measurements are presented of the field in air outside the laminated core of a slotless, cylindrical model. These measurements are in good agreement with the predictions of the method. The method is then used to consider qualitatively the behaviour of the field inside a laminated core. Conclusions are also drawn about the way in which the leakage field will alter with changes in the dimensions and operating conditions of the core.