Amtrak's 25 Hz Traction Power System - History

History

25 Hz Power Supplies on the ex-PRR System

Legend Amtrak Hell Gate Line (12 kV 60Hz) Bowery Bay Phase Break Sunnyside Static Converter LI City GS (Ret) Waterside No.1 GS (Ret) New York Penn Station, NY KearnyPhase Break NJT M&E (25 kV 60Hz) WaterfrontPhase Break NJT M&E (25 kV 60Hz) MatawanPhase Break NJT NJCL (25 kV 60Hz) MetuchenRotary Converter Richmond Rotary Converter (Ret) RichmondStatic Converter Somerset Rotary Converter (Ret) Zoo Sub SEPTA ex-Reading Lines25 Hz from Wayne Junction Girard Ave. Phase Break Philadelphia 30th Street Station LamokinRotary Converter Parkesburg Sub Safe Harbor Dam Harrisburg, PA Perryville Sub Jericho ParkStatic Converter Benning GS Rotary Converter (Ret) Washington, DC Potomac Yard

The Pennsylvania Railroad (PRR) began experimenting with electric traction in 1910, coincident with their completion of the trans-Hudson tunnels and New York Penn Station. These initial systems were low-voltage direct current (DC) third rail systems. While they performed adequately for tunnel service, the PRR ultimately determined them to be inadequate for long distance, high-speed electrification.

Other railroads had by this time experimented with low frequency (less than 60 Hz) alternating current (AC) systems. These low-frequency systems had the AC advantage of higher transmission voltages, reducing resistive losses over long distances, as well as the typically DC advantage of easy motor control as universal motors could be employed with transformer tap changer control gear. Pantograph contact with trolley wire is also more tolerant of high speeds and variations in track geometry. The New York, New Haven and Hartford Railroad had already electrified a portion of its Main Line in 1908 at 11 kV AC 25 Hz and this served as a template for the PRR, which installed its own trial main line electrification between Philadelphia and Paoli, Pennsylvania in 1915. Power was transmitted along the tops of the catenary supports using four single phase, 2 wire 44 kV distribution circuits. Tests on the line using experimental electric locomotives such as the PRR FF1 revealed that the 44 kV distribution lines would be insufficient for heavier loads over longer distances.

In the 1920s the PRR decided to electrify major portions of its eastern rail network and because any sort of commercial electric grid simply did not yet exist at the time the railroad constructed its own distribution system to transmit power from a select number of generating sites to trains possibly hundreds of miles distant. To accomplish this the PRR chose to implement a pioneering system of single-phase high voltage transmission lines at 132 kV, stepped down to the 11 kV at regularly spaced substations along the right of way.

The first line to be electrified under this new system was between Philadelphia and Wilmington, Delaware in the late 1920s. By 1930, catenary extended from Philadelphia to Trenton, New Jersey, by 1933 to New York City, and by 1935 south to Washington, D.C. Finally in 1939 the main line from Paoli west to Harrisburg was completed along with several freight-only lines. Also included were the Trenton cutoff and the Port Road Branch. Superimposed on these electrified lines was an independent power grid delivering 25 Hz current from the point of generation to electric locomotives anywhere on nearly 500 route miles (800 km) of track, all under the control of electric power dispatchers in Harrisburg, Baltimore, Philadelphia and New York City.

Northeast railroads atrophied in the years following World War II; the PRR was no exception. The infrastructure of the northeast corridor remained essentially unchanged through the series of mergers and bankruptcies which ended in Amtrak's creation and acquisition of the former PRR lines which came to be known as the Northeast Corridor. The circa 1976 Northeast Corridor Improvement Project had originally planned to convert the PRR's system to the utility grid standard of 60 Hz. Ultimately, this plan was shelved as economically infeasible and the electrical traction infrastructure was left largely unchanged with the exception of a general traction power voltage increase to 12 kV and a corresponding transmission voltage increase to 138 kV.

During the 1970s, several of the original converter or power stations which had originally supplied power to the system were shut down. Also the end of electrified through freight service on the Main Line to Paoli allowed the original 1915 substations and their 44 kV distribution lines to be decommissioned with that 20-mile section of track being fed from 1930s-era substations on either end. In the decade between 1992 and 2002, several static converter stations were commissioned to replace stations that had or were being shut down. Jericho Park, Richmond, and Sunnyside Yard converters were all installed during this period. This replaced much of the electrical frequency conversion equipment, but the lineside transmission and distribution equipment were unchanged.

In 2003, Amtrak commenced a capital improvement plan that involved planned replacement of much of the lineside network including 138/12 kV transformers, circuit breakers, and catenary wire. Statistically, this capital improvement has resulted in significantly fewer delays, although dramatic system shutdowns have still occurred.

See also: PRR Rail Line Electrification Project