Technical assessment of 6¿% (wt.) silicon iron for possible application in power transformers

A comparison of the properties of 6¿%(wt.) and 3%(wt.) silicon iron has been made, based on measurements of the magnetostriction constants, the anisotropy constants, the static hysteresis loss and the power loss at 50c/s, of single-crystal specimens. The loss measurements were made on small stacks consisting of six 0.013 in-thick picture frames cut with their limbs along [100] directions. The results show that: (a) the power loss of single-crystal 3% silicon iron is about 0.3W/kg lower than that of commercial material at 15kGs (b) the power loss of single-crystal 6¿% silicon iron is 0.2W/kg lower than that of single-crystal 3% silicon iron at 15kGs (c) the magnetostriction constant is reduced to about one-tenth of the value of 3% silicon iron (with obvious advantages from the point of view of noise reduction) (d) the first anisotropy constant is about two-thirds of that of 3% silicon iron, so it will still be necessary to produce the silicon iron in oriented form. Although it is expected that a reduction in power loss of about 20% can be achieved by increasing the silicon content from 3% to 6¿%, this is accompanied by a reduction in the magnetic saturation induction. After taking all factors into account it is unlikely that an extra cost of more than £30 per ton can be paid for commercial grain-oriented 6¿% silicon iron.