Measurements of the influence of core geometry, eddy currents and permeability on the axial flux distribution in laminated steel cores

Measurements are described of the axial flux distribution inside the laminated steel core of a slotless model machine. The measurements were made over a range of frequencies and coreplate permeabilities, and the model could accomodate cores of different radial depth both with and without an end screen and a steel rotor. The measurements show that the axial flux distribution can be considered as being controlled by large physically identifiable sources of axial magnetic field. In particular, results show that the magnetic surface polarities on the core end surface have a considerable influence on the internal axial flux, whereas the rotor steel surface polarities do not. Coreplate eddy currents become the controlling source provided only that the radial depth of the core is large. The internal magnetic volume polarities are controlled by coreplate permeability, and the results show that, as the volume polarities are weakened, the penetration of axial flux increases. The presence of a core end screen alters the axial flux at the screen location, but does not greatly reduce the flux penetration deeper into the core.