Abstract: This transformer core and coil assembly comprises (a) a low voltage coil surrounding a coil window and including first and second coil legs on opposite sides of the coil window, (b) a first plurality of side-by-side amorphous-steel core loops surrounding one of the coil legs, and (c) a second plurality of side-by-side amorphous-steel core loops surrounding the other of the coil legs. Extending between said coil legs in a position between two of said side-by-side core loops in the first plurality and between two of said side-by-side loops in the second plurality is a brace of plate form and of electrical insulating material for blocking motion of said coil legs toward each other in response to coil-collapsing forces developed by short-circuit currents through the low voltage coil, thereby protecting the amorphous-steel core loops from damage by these short-circuit produced forces tending to collapse the coil.