Method of manufacturing transformer cores

A method of manufacturing a transformer core from electrical steel strip wherein said core comprises three frames each of substantially C shape in side view, the frames being arranged substantially 120.degree. apart, comprising:

• cutting a first strip of increasing constant taper from a minimum width to a maximum width;
• cutting a second strip having a decreasing constant taper from a maximum width to a minimum width;
• cutting each strip into a plurality of lamination lengths, each group of three lamination lengths being separated from the adjacent group at an end which is cut at substantially 90.degree. to its longitudinal axis, each said group forming a layer of the core, with three lamination lengths in the group being separated from each other by cuts at substantially 60.degree. to the longitudinal axis, the length dimensions of each layer being predetermined as a function of strip width of the layer such that the length dimensions vary in a non-linear manner from layer to layer;
• butt joining the ends of two of the lamination lengths cut at substantially 60.degree. to the sides of a third lamination length adjacent an end of the third lamination length cut at substantially 90.degree. to form a lamination layer;
• and
• assembling the lamination layers by butt joining the free ends of each lamination layer to form the assembled core such that the cross section of each substantially C-shaped frame is polygonal, and the side elevational profile of the exposed end of each substantially C-shaped frame is substantially wedge-shaped.