A A three-phase system was used to provide the electrical power to Great Northern units. A portion of the locomotives had two trolley poles to engage overhead wires while the running rail carried the third phase. In the booklet, “New Cascade Tunnel” published by the Great Northern for the opening of the tunnel in the 1920s, the railroad wrote: “An unusual feature of the Great Northern’s electrification is the combination of the alternating-current and direct-current systems. Alternating current is used for transmission from the source of power to the locomotives and direct current is used in the traction motors. The locomotives themselves carry the transformers and motor-generator sets, which change the high-tension alternating current to low-tension
direct current.” — Seth Bramson, historian and author
