Residual Flux Density Measurement Method for Transformer Core Considering Relative Differential Permeability

Abstract

The residual flux measurement is one of the difficulties in the transformer research field. This article presents a residual flux density (B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> ) measurement method considering the relative differential permeability (μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sub> ) of the core material. First, the basic relationship between μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sub> and B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> is analyzed on the basis of the magnetic domain theory. Then, combining the experimentally measured relationship between B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> and μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sub> , using μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rd</sub> as an intermediate variable, the relationship between B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> and time constant is derived. Furthermore, a square iron core model is established by the finite-element method, and the empirical formula for calculating B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> is was fit. Finally, the feasibility of this method and the accuracy of the proposed empirical formula are verified through experiments.