Head End Power - North America

North America

During the age of steam, cars were heated by low pressure saturated steam supplied by the locomotive. Electricity for car lighting and ventilation was derived from batteries charged by axle-driven generators on each car or from engine-generator sets mounted under the carbody.

The first advance over this system was developed on the Boston and Maine Railroad, which had placed a number of steam locomotives and passenger cars into dedicated commuter service in Boston. Due to the low average speeds and frequent stops characteristic of a commuter operation, the axle generators' output was insufficient to keep the batteries charged, resulting in passenger complaints about lighting and ventilation failures. In response, the railroad installed higher capacity generators on the locomotives assigned to these trains, and provided electrical connections to the cars. The cars used steam from the locomotive for heating.

When diesel locomotives were introduced to passenger service, they were equipped with steam generators to provide steam for car heating. However, the use of axle generators and batteries persisted for many years. This started to change in the late 1950s, during which time the Chicago and North Western Railway removed the steam generators from their EMD F7 and E8 locomotives in commuter service and installed diesel generator sets. This was a natural evolution, as their commuter trains were already receiving low-voltage, low-current power from the locomotives to assist axle generators in maintaining battery charge. In some cases, commuter cars were equipped with propane engine-powered air conditioning. The resulting separate systems of lighting power, steam heat, and engine-driven air conditioning increased the maintenance workload, as well as parts proliferation, thus leading to the full-scale adoption of HEP, where a single power source would handle all these functions.

While commuter fleets were quickly converted to HEP, long distance trains continued to operate with steam heat and battery-powered electrical systems. This gradually changed following the transfer of intercity passenger rail service to Amtrak, ultimately resulting in full adoption of HEP in the US and the discontinuation of the old systems.

Following its formation in 1971, Amtrak's initial locomotive purchase was the Electro-Motive (EMD) SDP40F, an adaptation of the widely-used SD40-2 3000 horsepower freight locomotive, fitted with a passenger style carbody and steam generating capability. The SDP40F permitted the use of modern motive power in conjunction with the old steam-heated passenger cars acquired from private railroads, giving Amtrak time to procure purpose-built cars and locomotives.

In 1975, Amtrak started to take delivery of the all-electric Amfleet car, hauled by General Electric (GE) P30CH and, later, EMD F40PH locomotives, both unit types equipped to furnish HEP. Following the introduction of the Amfleet fleet, the (also all-electric) Superliner railcar was placed into operation on long-distance western routes. Amtrak subsequently converted a portion of the steam heated fleet to all-electric operation using HEP, and retired the remaining unconverted cars.