The traction power network of Amtrak uses 25 Hz for the southern portion of the Northeast Corridor (NEC), the Keystone Corridor, and several branch lines between New York City and Washington D.C. The system was constructed by the Pennsylvania Railroad between 1915 and 1938 before the North American power transmission grid was fully established, which is why the system's frequency is 25 Hz, as opposed to 60 Hz, which became the standard for power transmission in North America. The system is also known as the Southend Electrification, in contrast to Amtrak's 60 Hz traction power system that runs between Boston and New Haven, which is known as the Northend Electrification system.
In 1976, Amtrak inherited the system from Penn Central, the successor to the Pennsylvania Railroad, along with the rest of the NEC infrastructure.
Only about half of the system's electrical capacity is used by Amtrak; the remainder is sold to the regional railroads that operate their trains along the corridor, including NJ Transit, SEPTA and MARC.
The system powers of the NEC between New York City and Washington, D.C., the entire Keystone Corridor, a portion of NJ Transit's North Jersey Coast Line (between the NEC and Matawan), along with the entirety of SEPTA's Airport, Chestnut Hill West, Cynwyd, and Media/Wawa lines.
History
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 found it 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 25 Hz AC 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, two 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 a commercial electric grid did not exist at the time, the railroad constructed its own distribution system to transmit power from generating sites to trains, possibly hundreds of miles distant. To accomplish this, the PRR implemented 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 tracks.
The first line to be electrified using 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 unfeasible, 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 that 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 section of track being fed from 1930s-era substations on either end. 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.
Specifications and statistics
The 25 Hz system was built by the Pennsylvania Railroad with a nominal voltage of 11 kV. The nominal operating voltages were raised in 1948 and are now:
Catenary (Traction) Voltage: 12 kV Transmission Voltage: 138 kV Signal Power: 2.2 kV Hz – NY Penn Area. 60 Hz used 1910–1931. 100 Hz installed but quickly changed to avoid interference caused by simultaneous AC and DC electrification 3.3 kV 100 Hz – Paoli/Chestnut Hill. 60 Hz used 1915/18–1930 6.9 kV Hz – all electrification work from 1930 onward
As of 1997, the system included of 138 kV transmission lines, 55 substations, 147 transformers, and of 12 kV catenary.
Over 550 GWh of energy is consumed annually by locomotives on the system. If this were consumed at a constant rate over the entire year (although it is not in practice), the average system load would be approximately 63 MW.
The system power factor varies between 0.75 and around 0.85.
Power sources
Electrical power originates at seven generation facilities or traction current converter plants. The nameplate capacity of all the power sources in the system is about 354 MW. The instantaneous peak loading on the system is 210–220 MW (as of 2009) during the morning rush hour and up to 225 MW during the afternoon.Forczek 2009, p. 18. Peak load has risen significantly over time. In 1997, the peak load was 148 MW.
Regardless of the source, all converter and generator plants supply power to the transmission system at 138 kV, 25 Hz, single-phase, using two wires. Typically, at least two separate 138 kV circuits follow each right of way to supply the line-side substations.
Currently, the following converter and generating plants are operable, although all are rarely in operation simultaneously due to maintenance shutdowns and overhauls:
Location Capacity (MW) In service Comments Sunnyside Yard 30 1996 Static inverter Metuchen 25 1933 Motor–generator Metuchen 60 2017 Static inverter Richmond 180 2002 Static inverter Lamokin 48 1928 3 motor–generators Safe Harbor Dam 81 1938 2 water turbines; 1 motor–generator Jericho Park 20 1992 Static cycloconverter System total capacity 354
Several types of equipment are currently in operation: static inverters, motor–generators (sometimes called rotary frequency converters), water turbines (hydroelectric generators) and a static cycloconverter.
Hydroelectric generators
Safe Harbor Dam, PA – The Safe Harbor Dam has two 28 MW single-phase turbines dedicated to 25 Hz power generation. A 25 MW bi-directional motor–generator-type frequency converter is also installed. The total 25 Hz capacity of the dam is 81 MW. Power from Safe Harbor is transmitted via the Conestoga substation to Royalton, Pennsylvania, Parkesburg, Pennsylvania (two circuits), and Perryville, Maryland (four circuits), where it is fed into the lineside 138 kV network.
The 25 Hz turbines at the dam are scheduled by Amtrak but operated by Safe Harbor Water Power Company. Like other hydroelectric plants, it has excellent black start capability which was most recently demonstrated during a 2006 blackout. After a cascade shutdown of converters had left the network de-energized, it was recovered using Safe Harbor's generators, and the other converters were subsequently brought back online.
During the twelve-month period ending August 2009, Safe Harbor supplied about 133 GWh of energy to the Amtrak substation at Perryville.Forczek 2009, p. 12 Typically, two-thirds of the Safe Harbor output is routed through Perryville, the remainder being sent through Harrisburg or Parkesburg. This suggests that Safe Harbor supplies around 200 GWh of energy annually into the 25 Hz network.
Motor–generators (rotary frequency converters) Motor–generators and steam turbine generators were the original power sources on the PRR traction power network. The last steam turbine shut down in 1954, but some of the original motor–generators remain. Although the converting machines are frequently called 'rotary converters' or 'rotary frequency converters', they are not the rotary converter used frequently by subways to convert low-frequency alternating current to DC power. The converters used are more precisely described as motor–generators and consist of two synchronous AC machines on a common shaft with different ratios of poles; they are not electrically connected as in a true rotary converter.
Principal advantages of motor–generators include very high fault current ratings and clean output current. Solid-state electronics can be damaged very quickly, so the microprocessor control systems react very quickly to over-correct conditions to place the converter in a safe, idle mode or to trip the output circuit breaker. Motor–generators, being of 1930s design, are heavily overbuilt. These rugged machines can absorb large load transients and demanding fault conditions while continuing to remain online. Their output waveform is also perfectly sinusoidal without noise or higher harmonic output. They can actually absorb harmonic noise produced by solid-state devices, effectively serving as a filter. These attributes, combined with their high fault-current capability, make them desirable in a stabilizing role within the power system. Amtrak has retained two of the original converter plants and plans to overhaul them and continue their operation indefinitely.
Disadvantages of motor–generators include lower efficiency, generally between 83% (lightly loaded machine) and 92% (fully loaded machine). In comparison, cycloconverter efficiency can exceed 95%. Also, motor–generators require more routine maintenance due to their nature as rotating machines, given the bearings and slip rings. Today, the outright replacement of motor–generators would also be difficult due to the high manufacturing cost and limited demand for these large 25 Hz machines.
Metuchen, NJ – 25 MW Motor–generator. Upgrades to transmission lines and circuit breakers are planned for 2010.