The Impact of Off-Plane Flux on Losses and Magnetostriction of Transformer Core Steel

• Published in: IEEE transactions on magnetics 2014-11, Vol.50 (11), p.1-4
• Main Authors: Shilyashki, Georgi, Pfutzner, Helmut, Hamberger, Peter, Aigner, Martin, Hofbauer, Franz, Matkovic, Ivo, Kenov, Anton
• Format: Article
• Language: English
• Subjects: Magnetic domains; Magnetic hysteresis; Magnetic losses; Magnetism; Magnetization; Magnetostriction; Transformer cores
• ISSN: 0018-9464; 1941-0069
• DOI: 10.1109/TMAG.2014.2324017

Transformer cores are assembled from several packages of different widths. Furthermore, circular limbs tend to be combined with semicircular yokes. These characteristics mean that the core represents a complex 3-D system. A consequence is balancing off-plane flux (z-flux) perpendicular to the core plane. Measurements of z-induction on model cores show that mere inhomogeneity of stacking may yield significant values of flux density B z in the normal direction. Close to overlapping regions of corners and T-joints, the order of 10 mT was observed. Losses prove to increase in a nonlinear way with increasing Bz for both alternating magnetization (AM) and rotational magnetization (RM). Effects become significant for B z = 10 mT, with losses showing increases of order of 30%. The corresponding increases of magnetostriction are much more pronounced, reaching 100%. These increases are clearly supported by the results of Kerr effect studies of domains. They reveal distinct increases of oblique domains. For 1-D AM, they are restricted to inner lancet slopes. For 2-D RM, the latter merge to inner plate domains. For the 3-D case of additional z-flux, the formation of plates is significantly enhanced. Plates can be assumed as a main source of both rising hysteresis losses and increasing magnetostriction.