Domain reconstructions of g.o. SiFe during rotational magnetization considering also 3-D flux components

Abstract

Domain analyses of modern types of grain-oriented (GO) transformer steel are rare, and they are focussed on single grains under academic magnetization patterns. The present Kerr effect study reveals that grains of industrial, polycrystalline materials react in specific ways according to individual crystallographic orientations. The amount of parameters is very large, especially if additional flux components are given as a further impact. The paper reports a procedure for statistical evaluations of quasi-dynamic Kerr effect images. The instantaneous area ratios of bar domain portion BD, oblique domain portion OD and saturation S are determined with consideration of peak induction BRD in the rolling direction (RD), axis ratio a of rotational magnetization, the angle ψ between B and RD, additional flux Bx in RD or Bz in normal direction. Focus is put on OD(t) which is assumed to be a key function for λ(t), i.e. the course of time of magnetostriction. As the most distinct tendencies, OD increases strongly with increases of a and ψ. OD(t) shows non-sinusoidal course of time with differences of the two halves of cycle. Rotation out of the RD yields sharp onsets of ODs, especially after half-cycle saturation. Additional off-plane flux enhances ODs in a general way.

Printed detector bands for measurements of strain in core interior of transformers

“…The higher intensities can be explained by the strong rotational magnetization that appears within the T-joint region. As shown in [6], the periodic annihilation and generation of oblique domains under rotational magnetization causes a distinct increase of magnetostriction, hence also of the measured strain.…”

“…An overview of several not-typical and rarely used direct and in-direct measurements methods like dilatometry are presented in [5]. Magnetostriction can also be estimated by observation of magnetic domains [6], however the latter is extremely laborious and requires a removing of coating.…”