Establishment of Flux in Magnetic Cores

The same fundamental propagation and diffusion processes that establish current in conductors are also involved in establishing flux on the surface of magnetic cores and laminations but the spatial positions of the E and H fields are interchanged in the insulating medium. The E fields appear around the magnetic cores when the flux changes (∫Edl = dφ/dt), and the H fields are normal to idealized core surfaces. In the case of conductors, the displacement current plays an important part in layering any current changes onto the conductor surface during each transition of the line. However, in the case of magnetic cores, it is the ‘leakage’ flux that builds up the surface core flux, and adds any changes in dφ/dt to the core surface, on each transition of the magnetic line. Once set up on the surface the flux, and hence the surface H field, slowly diffuses into the interior of the core until it is uniformly distributed throughout its cross sectional. Thus leakage flux is essential for the operation of magnetic circuits, inductors, and transformers and exists even in the case of idealized systems with materials of infinite permeability.