Comparison of flux distribution in three-phase transformer cores assembled from amorphous material and grain oriented silicon iron

Model stacked three-phase transformer cores were assembled from amorphous material and from grain-oriented silicon iron, and both types were magnetized under sinusoidal flux density conditions. Small search coils were located at selected points on individual strips of material in both cores in order to monitor the localized flux density distribution from analysis of the voltages induced in the coils. The distribution of the fundamental and third- and fifth-harmonic flux density in the plane of the core was recorded at chosen instants in time, and the locus of the flux density at each measuring point was plotted. Three important differences were observed. First, the flux in the amorphous core tended to vary in direction as it proceeded around corners, whereas in the other core the flux density was directed along the rolling directions of the laminations almost everywhere. Second, there was a high degree of rotational flux in the T-joint of the amorphous core that did not occur in the core assembled from silicon iron. Third, the flux was more uniform in the amorphous core. On the basis of these results, the building factor of the amorphous core should be far less than that of the silicon iron core of the same geometry.>