Ahmad Ebrahimi - Organization: University of Shahid Rajaee, Faculty of Electrical & Electronic Engineering Tehran, I.R. of Iran.

Reducing loss in laminated cores during ac magnetization is the aim of steel manufacturers as well as the wish of the users. A microprocessor controlled system for magnetizing and measuring the characteristics of magnetic materials was employed to calculate the losses and other magnetic properties of electrical steel material. The characteristics of 0.27 mm thick high permeability grain oriented 3% siliconiron, "Unisil – H" material, have been studied at large angles of magnetization to the rolling direction over the range during the magnetization process, was measured in different stacking units of Unisil-H materials. It has been established that the magnetization angle to the rolling direction is the main factor which controls the magnitude of normal flux density and resulting loss. The angle of 0o shows very low losses and also low normal flux density, because of the low reluctance magnetic path along this, the rolling direction. The effect of surface scratching on the normal flux density and power loss was investigated. Static domains were observed by using a Bitter Technique system. A decrease in the main domain wall spacing tended to reduce the power loss, whereas wall deviation from the rolling direction has a major effect on increasing the normal flux and eddy current loss. The comparative measurement of the localized power loss and normal flux density over an area showed a reasonable correlation with the observed static domain configuration in the Unisil – H material. The effects of different stacking methods and different magnetization direction on the power loss, due to the normal flux, were investigated by conducting a systematic comparison between five different stacking methods. The stacking method and number of strips per stacking unit has an important effect on controlling the normal flux and power loss particularly at the T-joint and corners in 3-phase laminated cores. The low nominal loss and low magnitude of normal flux density materials are preferred in laminated transformer cores, because of low building factor. It was found that low magnetic reluctance along the magnetizing direction decreased normal flux density and eddy current loss, consequently improving the building factor.

Unisil – H: A high permeability grain oriented magnetic material Building factor (B.F.): Actual loss / Nominal loss BN: Normal flux density transfer between strips BL: Longitudinal flux density through the strips