Dimensional factors affecting magnetic properties of wound cores

Abstract

The magnetic properties of wound cores constructed from electrical steel strips have been found to be affected by their geometry, in particular the inner and outer diameters, the strip width and the build-up thickness of the toroids. Assessment of the effect of aspect ratio and winding ratio have been carried out in various sizes of toroid. An increase in aspect ratio resulted in better magnetic performance, whereas increase in winding ratio degraded the original magnetic properties. However, when the inner and outer diameters are varied with constant build-up and strip width, better performance is obtained by increasing the winding ratio.The initial rate of rise of temperature technique using thermistors has been used to measured power loss on the inner and outer wraps of a wound toroid. The power loss of a 60 × 44 × 40mm toroid at 1.0 T before stress relief annealing was 0.88 and 0.52 W kg−1 at the inner and outer layers respectively. After stress relief annealing, the power loss fell to 0.44 and 0.43 W kg−1 at the inner and outer layers respectively. This indicates the higher stress produced by small diameter wrapping can be reduced by normal stress relief annealing.