The magnetic circuit of power transformers is built with magnetic oriented grain sheet. These modern
sheets present a more and more narrow static hysteresis cycle, as well as an important remanent flux density,
generally larger than 1 tesla. Although such a magnetic circuit necessarily includes joint air gaps, the experiment
shows that these don't lead to an appreciable weakening of remanent fluxes.
In order to explain the “paradox” of the existence of an important remanent fluxes in the magnetic circuits
including air gaps, we propose a new model of joint called "pseudo-variable air gap" allowing 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 remanent when the overlap
joint has been used (which corresponds to the power transformer 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 improvement of the transformer models deriving from the circuit
theory.