Cross-magnetisation effects in electrical machines

Examples of cross-magnetisation effects in electrical machines are collated and the physical characteristics of the phenomena are reviewed qualitatively. New experimental results to clarify the phenomena are introduced. This subject has also been called a cross-axis, cross-magnetisation, cross-saturation, intersaturation or cross-reactance effect. Cross-magnetisation encompasses the magnetic behaviour of saturable machine materials when the vector of the main magnetomotive force (MMF) is applied in a direction that is not geometrically or analytically favoured in the magnetic structure of the machine. The phenomenon is important because it controls the magnetic behaviour of components that are closest to the highest field strengths in operating machines. A number of cases in electrical machines where this can occur are considered and conclusions drawn. These can be used to allow the cross-magnetisation effects from field calculations of electrical machines to be quantitatively represented and qualitatively explained, particularly for machines of unusual topology, in which key components are not subjected to a magnetic field in the preferred direction.