Magnetic flux distribution in transformers

It is customary when discussing magnetic leakage in the transformer to consider the primary and secondary windings as having a counter e. m. f. induced by a flux surrounding the coil and having the core for a part of its path. This leakage flux is frequently represented by closed lines. Since the main flux is also represented by closed lines in the core, apparently two fluxes are to be found in the core under a given coil, namely, the leakage flux and the main flux. The main flux is the flux found in the core at a point not under either the primary or secondary winding, and has been commonly considered as being the flux which causes the secondary induced voltage. If the leakage fluxes have a separate existence, i. e., if they are to be represented by closed lines, then the flux along the edges of the core would consist largely of leakage lines while that to be found in the middle portion of the core would be the main flux. Since these fluxes are out of phase with one another it should be possible to identify them if they are present as separate fluxes. Using a simple test core-type transformer, provided with belt exploring coils under both the primary and secondary windings, data concerning the magnitudes and phase positions of the fluxes in different sections of the core were secured. The results show that leakage fluxes do not exist as separate fluxes in the core. It is also shown that the primary and secondary induced voltages are equal to the primary and secondary terminal voltages diminished and increased respectively by the corresponding I R drops.