Automatic 3-dimensional flux analyses of a 3-phase model transformer core

Abstract

For the development of new strategies for reduction of energy losses and audible noise of transformer cores, the assessment of the induction distribution is essential. The results confirm that the core represents a strongly inhomogeneous 3-dimensional magnetization system. For a full understanding of distributions, measurements in the core interior are necessary. For the first time the paper presents detailed analyses of induction distribution in a multi-package model core. Automatic measurements were performed in 112 local positions within 3-phase, 3-limb transformer core stacked from three packages of different width of grain oriented material. As a completely novel approach, a soft magnetic Fe-pin (of 2.4 mm diameter) with pick up coil was used as an a priori calibrated pin sensor. 25 measurement channels (of 3 mm diameter) were established through the entire core. Z-profiles of the induction through the channels were determined in an automatic way for a nominal induction of 1.7 T. They confirm that the core represents a system that is magnetized in a strong inhomogeneous way. Strong variations of the induction up to 10% were observed not only for the in-plane direction, but also along the normal direction (off-plane). Maximum induction values were detected in the widest main package, minimum ones in the narrowest peripheral package. An exception is the corner area where the inhomogeneity of B decreases, linked with a balancing off-plane flux. The paper proposes a model for the flux distribution through the three packages of the core.