RELEVANCE OF STEP-LAP JOINTS FOR MAGNETIC CHARACTERISTICS OF TRANSFORMER CORES

It has been stated that multistep-lap (MSL) jointed cores show distinc t improvements regarding power losses P in comparison to single-step-l ap (SSL). On the other hand, model core experiments tend to yield cont radictory results. In the paper, special emphasis was put on the under lying physical mechanisms, taking into consideration that model cores usually show 'perfect' stacking, while full-size cores exhibit conside rably high air gap lengths g as well as shifts s between the overlap r egions of adjoining packages. It is shown that an increase of the numb er N of steps reduces the sensitivity of the core in respect to variat ions of g and s. This is due to increasing 'critical induction' B-C as of which the excitation V-L of the overlap region steeply increases. Low V-L corresponds to lower balancing interlaminar flux in the overla p/gap regions and thus to a generally more homogeneous flux distributi on linked with lower P. The quantity B-C can be assumed to be of high practical relevance for the design of transformer cores.