The core material of a electric transformer is primarily made from magnetic materials. Due to the high magnetic permeability of ferromagnetic materials, ordinary iron sheets were used as core materials in the early development of transformers. Later, hot-rolled magnetic steel sheets were developed for transformer core manufacturing. In 1934, Gauss invented cold-rolled oriented magnetic steel sheets, which gradually replaced hot-rolled magnetic steel sheets. After the 1970s, high-permeability magnetic steel sheets (Hi-B) were developed, which have lower unit losses and exciting ampere-turns compared to ordinary grain-oriented magnetic steel sheets. In the 1980s, even lower loss magnetic steel sheets were developed through magnetic domain refinement (using laser irradiation or mechanical indentation methods).
In 1960, the United States developed amorphous alloy materials, and in 1974, iron-based amorphous alloys were produced. The core losses of amorphous alloys are smaller than those of oriented magnetic steel sheets, and they also have higher magnetic permeability. Transformers made from amorphous alloys have been in trial operation in power grids for about 20 years, during which time amorphous alloys have been widely used in distribution transformers worldwide.
