Excitation current and power loss characteristics for mitered joint power transformer cores

The 45° mitered-overlap joint is commonly used in the construction of large power transformer cores. There are several variables which affect the performance of such cores with respect to core loss and exciting current. The major variables investigated in this paper are 1) overlap distance, 2) stagger layer thickness, and 3) overlap method, namely, simple staggering versus step-lap. Also investigated to a lesser degree were the effect of frequency and the effect of series air gaps at the corners. One set of results in this paper is not in agreement with a previous paper and reasons for this are speculated. The other sets of results are new, and indicate that staggering beyond two laminations per stagger is not advisable, that the difference between one and two laminations per stagger is marginal, and that the use of a step-lap joint reduces exciting current requirements but not core loss.