Keywords: magnetic hysteresis, mechanical stress, magnetic field computation.

The paper deals with the numerical analysis of a modified Epstein-frame, which is able to measure the magnetic characteristic of the transformers laminations under applied mechanical stress. The measurement proved, that the magnetic properties of material are sensitive to the applied stress, the stray energy losses decreased by increasing the tensile force [1].

The stress dependent Preisach model approximates the hysteresis characteristic of the laminations, and is inserted into the finite element method (FEM) that has been applied in the simulations. According to the results of the measurements the model parameters have been installed.

A Preisach-based stress dependent model has been developed, where the Preisach distribution function P(alpha,beta,sigma) contains the stress value, where sigma is the value of the mechanical stress. The scalar Preisach model is the main building block for the vector model, which is constructed as a superposition of the scalar models. In the anisotropic case the hysteresis characteristics are different for the easy and for the hard axes. Between the two axes the distribution functions have been interpolated [2].

Maxwell equations can represent the magnetic behaviour of the magnetic material in the field calculation. The Fe-Si laminations of the modified Epstein frame was calculated with linear and with hysteretic media. In this case the time-varying and the eddy current field has been tested with the stress dependent Preisach-type magnetic model.

The T,Phi-Phi potential formulation have been applied for the calculation, because this formulation allows the use of the hysteresis operator directly.

The main task is to solve the Maxwell differential equations, substituting the T,Phi-Phi potential formulation, for the iron coupled with the equations for the air with respect to the interface conditions between the air and the conducting material.

In nonlinear media the relationship between the magnetic flux density B and the magnetic field intensity H contains hysteretic behaviors B=H(H), where, with the fixed point technique the hysteretic relationship H(.) can be separated into a linear and a residual nonlinear R part, B=µ_FPH+R [3].

The nonlinear partial differential equations of the time-varying and eddy current problems are solved using a finite element model for the magnetic field calculation.

1

A. Sipeky, A. Ivanyi, "Magnetic hysteresis under applied stress", Physica B, 372, 177-180, 2006. doi:10.1016/j.physb.2005.10.042

2

A. Sipeky, A. Ivanyi, "Preisach-type stress-dependent magnetic vector hysteresis model", Physica B, 403, 491-494, 2008. doi:10.1016/j.physb.2007.08.082

3

M. Kuczmann, "Simulation of a vector hysteresis measurement system taking hysteresis into account by the vector Preisach model", Physica B, 403, 433-436, 2008. doi:10.1016/j.physb.2007.08.068

purchase the full-text of this paper (price £20)

go to the previous paper
go to the next paper
return to the table of contents
return to the book description
purchase this book (price £95 +P&P)