Transformers: A joint model explaining remanent fluxes

¹ Laboratoire des Systèmes Électriques-ENIT, BP 37, Le bélvédère, 1002 Tunis, Tunisia
² Laboratoire d'Électrotechnique de Paris 6, 4 place Jussieu, 45252 Paris Cedex 05, France
³ Laboratoire LETAU-ENIS, BP W, 3000 Sfax, Tunisia

Corresponding authors: mohamed.elleuch@enit.rnu.tn mpo@ccr.jussieu.fr mba.kamoun@enis.rnu.tn

Received: 12 May 2000
Revised: 12 December 2000
Accepted: 12 December 2000
Published online: 15 February 2001

Abstract

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.