Theory and application of magnetic shells

Every current-carrying circuit, whether isolated or in the presence of iron parts, is magnetically equivalent to simple or complex distributions of magnetic poles. This equivalence can be of considerable practical value, since, when computational, graphical or analogue methods of solution are used, the field problem can often be expressed more simply in terms of the equivalent pole sources than in terms of the actual currents. The paper examines the magnetic-shell principle and its application to the solution of magnetic fields in the vicinity of the windings in machines, transformers and other electromagnetic devices. It is shown that every solenoidal or vector-potential field can be transformed into many different scalar-potential equivalents and that the appropriate field sources are easily derived.