Transformers: A joint model explaining remanent fluxes

The magnetic circuit of power transformers is built with magnetic oriented grain sheet. These modern sheets present a more and more narrow static hyst eresis cycle, as well as an important remanent flux density, generally larg er than 1 tesla. Although such a magnetic circuit necessarily includes join t air gaps, the experiment shows that these don't lead to an appreciable we akening of remanent fluxes. In order to explain the "paradox" of the existe nce of an important remanent fluxes in the magnetic circuits including air gaps, we propose a new model of joint called "pseudo-variable air gap" allo wing to account for the nature of the type of joint: butt or overlap. It is shown that the new model fully explains the existence of an important rema nent when the overlap joint has been used (which corresponds to the power t ransformer case), as well as the nearly total disappearance of the remanent fluxes in case of butt type joint. In addition, this model could be easily implemented in a global transformer model; which contributes to the improv ement of the transformer models deriving from the circuit theory.