Recovering of deteriorated iron loss parameter of sheared and perforated grain-oriented electrical steels

Abstract

This article focuses on improving more efficient electric transformers through research on core steel processing. By examining the mitered and perforated M5 grade grain-oriented electrical steel core components, many trials have been executed to understand and reduce the deteriorating effects of the cutting and perforating discontinuities on the magnetic properties of grain-oriented electrical steel laminations. Specifically, trials and experiments are focused on the no-load loss parameter of laminations and prototype cores. For these purposes, as-cut versus annealed samples are compared using the Epstein frame test with standard and non-standard test samples. Iron loss parameters of non-standard stacked M5 Grade samples showed 3.7% to 6.4% recovery by annealing at 800 °C for 2 hours. By promoting and guiding Epstein frame test results, four units of 40 kVA-rated identical cast-resin type transformer cores were produced. Two sets of legs and yokes of core components were perforated for stacking purposes, and others were processed without centering holes. One was imperforated, and one of the perforated core sets was annealed under vacuum at 750 °C for 3 hours. The remaining two sets were left as-cut. No-load loss measurement of prototype cores executed by gradually leveled induction. Comparison results of prototype no-load loss parameters showed the recovery of iron loss at a ratio of 14.5% to 16.5% as W/kg on perforated cores by the contribution of annealing.