Pulse power drilling assembly transformer with a core having insulative and electrically conductive materials

An apparatus comprises a sub-section of a pulse power drilling assembly including a transformer encircling a center flow tube. The transformer comprises at least one primary winding that encircles the center flow tube and a core that encircles the at least one primary winding. The core comprises an insulative material and an electrically conductive material, wherein the insulative material is positioned relative to the electrically conductive material to create at least one break to prevent an electrical path for current within the electrically conductive material during operation of the transformer. The transformer comprises a secondary winding that encircles the core.