Head End Power
In an earlier post, I wrote about the cars Union Pacific sold to Amtrak, and how some of them were rebuilt by Amtrak with what it calls HEP, or Head End Power.
To put Amtrak’s use of head-end power in context, I started looking at the idea of using electricity on trains, and the story soon became very compelling. Research in the U.S. patents brought some basic information about the first use of electricity on passenger trains, and its full adoption by 1910. Individual generators were attached to passenger car axles, with the design usually referred to as either “axle lighting,” or “axle lights.” But there were limitations in the early designs, mostly due to the small size of the generators themselves, known as dynamos. To obtain more capacity, in about 1903-1904, larger steam-driven dynamos were installed in baggage cars, with electrical wiring being run along the length of the train, usually in the form of conduits along the rooftops. Baggage cars were, in almost every case, operated at the front of the train, at the head-end, and the steam-driven dynamos soon took on the name of head-end power plants.
These head-end power plants used what were known as turbo-generators, which were steam-powered electrical generators intended for use in industrial applications where steam power needed to be converted to electrical power. The railroads were looking at having more electrical power available on their passenger trains, more power than axle generators of the period could supply. It likely seemed to be an easy solution to adapt these industrial steam dynamos for use on a moving passenger trains. They were big and heavy, and needed a steady supply of steam, so locating them in the baggage car was an obvious solution. A supply of steam was already available, since every passenger train made use of steam heat, using steam supplied by the locomotive at the front of every train. Electricity at the time was a developing combination of science and early materials engineering, and many of the components, such as switches and relays, required large panel installations. These control panels, along with the dynamos themselves, meant that a full-time attendant was needed to keep the equipment properly maintained and operating.
Union Pacific adopted the concept of head-end plants in about 1905 with at least 15 wooden baggage cars being equipped with steam dynamos; these cars were labeled as Baggage Dynamo cars, and were considered by many to be cutting-edge technology. Several steel cars were delivered in 1909 and 1910, and in about 1914, the dynamos in the wooden cars were removed and installed in the steel cars. More steel cars were delivered in 1913, 1914, and 1921, making for an overall fleet of 63 baggage cars that used large steam dynamos to furnish electricity on the passenger trains of Union Pacific and its subsidiary companies.
The design for axle generators continued to improve, allowing more powerful generators to be installed on individual cars on either the truck and wheel assemblies, or to the underbody of the passenger cars. These new designs improved the economics of axle lighting, making the cost of steam dynamo head-end plants, including a full-time attendant in each car, a factor that needed to be addressed.
Union Pacific interchanged numerous passenger trains every day with Southern Pacific at Ogden, Utah, operating over what is still known today as the Overland Route. Southern Pacific had adopted Baggage Dynamo cars at the same time as Union Pacific, from the fact that the two companies shared overall corporate ownership, and a shared concept of equipment design known as Common Standard. Southern Pacific’s passenger car fleet has been thoroughly researched and published by the Southern Pacific Historical & Technical Society, in the form of a heavily illustrated, multi-volume history. This published history of Southern Pacific equipment shows that in the two decades between 1900 and 1920, SP history is much the same as Union Pacific’s, and the SP society thankfully has chosen to include an unbelievable amount of Union Pacific equipment history in its publications. This history of Southern Pacific passenger cars shows that axle generators were included when SP began receiving steel cars in 1909. Earlier cars had been equipped with gas lighting, which was replaced by axle lighting beginning as early as 1914. A program was established in 1924 that formalized the changes for cars that were not delivered with axle lighting.
By this same 1924 date, SP adopted a change in axle lighting from truck-mounted generators to body-mounted generators, allowing for a larger, more efficient design. These improvements in axle generators brought an end to the steam dynamos installed in head-end baggage cars. In 1924, UP’s Los Angeles & Salt Lake subsidiary modified its nine Baggage Dynamo cars by removing the dynamos, converting the cars to become full Baggage cars. Although documentation has not yet been identified, Union Pacific and its other two subsidiary railroads, Oregon Short Line and Oregon-Washington Railroad & Navigation Co., were closely tied together, making one think that at about the same time, they also began conversion to larger body-mounted axle generators, and removing their steam dynamos from the Baggage Dynamo cars. Research continues.
Similar to axle generators for electrical lighting, is the subject of air conditioning. Early designs for air conditioning on passenger cars used a concept known as steam injection. Another design used air blowing over ice, which was then distributed throughout the passenger car with electric fans. Refrigerated air conditioning became available in the early 1930s, using either axle-diven compressors or propane-powered internal combustion engines driving compressors. Waukesha was one of the more successful companies and their designs for underbody-mounted propane-powered generators and compressors replaced axle-driven designs. Waukesha designs remained in use to the end of regular passenger trains, when Amtrak started in May 1971, and continued until Amtrak’s last Heritage cars were retired.
During the early and mid 1950s, new designs for railroad commuter cars were placed in service to modernize the commute service in the New York and Chicago areas, and included all-electric cars that took their power from the locomotive that pulled the train. These designs were adopted as consideration of cost saving for the new cars. Money was saved in the initial purchase price by not having to add electrical generating equipment to each and every car, and money was saved in overall operating costs because each car was lighter by about five tons, and therefore more economical to operate. These commuter cars from the 1950s were the start of today’s 480 VAC systems, and continued to be specified as new cars and locomotives were delivered throughout the 1970s. The 480 VAC design was carried over when Amtrak began buying its first Amfleet cars and GE locomotives in 1975, and today is the recognized standard for both self-contained power, and for electrical power provided by the locomotive to the entire train.
