Today, the electrical system remains in operation largely as it was built. Wires, poles, signal and electrical equipment have been replaced as needed, but the bulk of the system endures intact.

Electrical power for the system is provided by the Montana Power Company, the Washington Water Power Company and the Puget Sound Power and Light Company.

The power is almost exclusively hydroelectrically generated from dams on various rivers in Montana and Washington.

Electricity from these utility companies is de­livered to the railroad at 10 of the 22 substations in the form of 100,000-volt alternating current. All the substations on each division are connected by a 100,000-volt high-tension transmission line which parallels the track. Through electrical equipment and transformers, the substations convert the current to the necessary 3,000-volt D.C. current.

At 3,000 volts D.C., electricity is fed from the substations into the copper feeder cable which parallels the track. The feeder is connected at frequent intervals to the two copper trolley wires suspended approximately 24 feet above the track from a steel messenger cable. The messenger cable in turn hangs from cross-arms attached to 40-foot poles alongside the track.

Each of the substations is primarily responsible for energizing a certain section of catenary, and intervals between substations were determined by probable power demand on that section of track. They are closer together on steep grades, for example, where power requirements are greater.

To obtain electricity from the catenary, the locomotive is equipped with a device called a pantograph. Spring-loaded, the pantograph rides underneath the wire, collecting energy and feeding it through control devices to the electric motor. When electricity is introduced into the motor, a magnetic field is created, causing the motor’s armature to revolve and, usually through gears, propelling the locomotive.

Strictly speaking, the term “electric locomotive” is a misnomer. Locomotive implies a completely self-driven machine, but the electric units contain no energy producing mechanism, only a motor. They convert electrical energy supplied from the wire into mechanical energy which moves the train.

The twin catenary supply system, developed especially for the Milwaukee, was designed to provide a steady supply of energy to the motor and eliminate sparking by ensuring that constant contact between the pantograph and the catenary would be maintained. Secondary tracks, yards and passing tracks normally have only one trolley wire.

To complete the necessary circuit, electricity is returned to the substation through the rails and in some areas through supplementary feeder cables atop the poles.

Of the 22 substations in the two zones, 11 are operated by supervised remote control and one is fully automated.

Although the eight substations on the Coast Division and the 14 substations on the Rocky Mountain Division are interconnected electrically on each division, each substation is equipped with circuit breakers, disconnect equipment and bypass circuits to allow continued operation on other parts of the line if the substation, wires or circuitry in one section should become inoperative.




Featrues of the electrical system:


- Power almost exclusively hydroelectrically generated


- Catenary - twin catenary developed for the Milwaukee


- Pantograph


- Electricity returned to the substations through the rails



document home

web version



full text

Click here for a guide to this website

Contact Webmaster

Last Updated: March 03, 2009