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Electric Locomotives in the 20th Century

By Dr M.C. Duffy

From the November 2006 Newsletter.

Electric locomotion grew from 19th Century electrification of quarries, mines, light railways and cable-ways. Basic forms were established in the street tramways of 1880s in the USA. Heavy duty electric traction evolved in the 1890s on rapid transit railways in large cities like Chicago, or New York. LVDC technology, using rotary converters and conductor rails, was needed for terminal and tunnel lines, where locomotives were required. Locomotives equal in power to any steam locomotive were working in the period 1900-1910. Overall energy efficiency was low if power came from coal stations and electric traction was employed to meet legal requirements or operational needs. Early locomotives took many forms. Some used body-mounted motors driving through rods and shafts. Others used geared axle-mounted nose-suspended motors. Outside heavy-duty rapid-transit railways, electric traction could not replace steam traction on general purpose railways. The Pennsylvania RR and New York Central terminal lines, and the Detroit and Baltimore tunnel lines were early locomotive worked railways.

During 1900-1920, other electric transport systems appeared, including cable ways (Germany, Switzerland), monorails (Langen, Kearney) and funiculars (Italy). Electric rail "mules" were used to haul ships through the Panama Canal locks. The rail-less trolley-bus, locomotive and train, drawing power from an overhead line and running on road wheels appeared before the 1914-18 war. Road locomotives powered from batteries found use. The hybrid vehicle, with engine, generator, and accumulators, was invented, and today is finding use in passenger transport over routes too lightly used to justify electric tramways. Heavy dumper trucks, drawing power from an overhead supply line are currently at work in quarries. The use of electric rail-less road vehicles, declined with the rise of motor transport. Many electric trolley systems were dismantled but there has been a general revival of electric tramways since 1970.

The early heavy-duty electric railways, with 3rd rail DC distribution were not suitable for long distance main line work. The three-phase railway dated from the Lugarno tramway (1896) and was extensively used in Italy, on the Simplon Tunnel route (Switzerland) and through the Casade Tunnel (USA). The need for two overhead wires, and speed-control limitations prevented widespread use. By the early 1930s it had been replaced by monophase systems in Switzerland and the USA, though it survived in Italy until after the 1939-45 war. The single-phase AC railway dates from 1902 with the introduction of a reliable, powerful single-phase commutator motor. The 1905 tests of 11kV single-phase AC locomotives on the Pennsylvania in 1905 established the system and in 1907, it was used on the New Haven lines into New York. In 1914 it was installed on the Philadelphia Paoli Division of the Pennsylvania RR. In Europe, the 1908 Loetschberg line in Switzerland used 15kV, 16.66 Hz which became standard in Austria, Switzerland, Germany, Sweden and Norway until replaced by the 25 kV 50 Hz European standard in the 1950s. Tests on the Seebach-Wettingen line between 1901 and 1905 with phase converter locomotives investigated various motor and control systems drawing power from a single contact wire. The first locomotive to use industrial frequency (50 Hz), at 15 kV, was tested here. By 1913 locomotives of 2500 hp were in use. AC motors of great power were large and often body mounted, with rod and jackshaft drive. Many engineers favoured the DC motor. Converter locomotives used single-phase AC supply with DC motors by having an on-board rotary converter. These were heavy, large machines. The first in the USA, was constructed in 1925 by Henry Ford at the Rouge River Plant for the Ford-owned Detroit, Toledo and Ironton RR. Supply was 11 kV, 25 Hz. Traction power was 3100KW. Weight was 393 tons. Converter locomotives were never numerous. The final American examples were supplied in 1948 to the Great Northern Railway (320 tons, 5000 hp) and to the Virginian Railway (454 tons, 7800 hp). The type was rendered obsolete by the locomotive mercury-arc rectifier, and the solid state rectifier. The Hungarian Kando experimented between 1927 and 1941 to combine single-phase AC supply with DC motors, but size, weight and complexity prevented general use. By the mid-1930s rectifier locomotives using mercury vapour were under trial. Phase-splitting locomotives, which converted single-phase AC to 3-phase supply to induction-type traction motors were used on the Norfolk & Western Railway in 1915 and on the Virginian Railway. Supply was single-phase 11 kV 25 Hz.

The HVDC railway generally used a supply voltage of 1500 V, or 3000 V. This was proven in 1911 on the Butte, Anaconda & Pacific Railway in Montana, and used on the Montana Division electrification scheme (438 miles) of the Chicago, Milwaukee & St Paul Railway, completed in 1915. This showed that a general purpose steam railway could be better worked by electric traction. All sections used 3000V DC. These installations influenced strategy world wide and HVDC became a world standard.

The spread of railway electrification was encouraged by the construction of high-efficiency thermal power stations; the use of the mercury-arc rectifier as a static rectifier and phase converter; and the standardization of grid supply after 1930. In Europe, electrification was aided by national ownership of railways. The wars, economic difficulties, and political crises of Europe and Asia between 1914 and 1950 delayed many electrification projects. In the USA, the diesel-electric locomotive met the needs of general purpose railways and electric locomotive development ceased until the 1980s. By the late 1930s, electric locomotives were outperforming steam traction in every field. In the 1950s there were increasing demands for much higher speeds, well in excess of 100 mph, and the superiority of electric traction became evident. The ability of electric locomotives to integrate closely with electric signalling and control technologies was advantageous.

After WW2, the 25 kV 50 Hz single-phase system became the world standard. High speed trials in France, under the 1500 V DC system, set a world speed record of 331km/h (205mph) with locomotive BB9004 in March 1955. This stood until 1981 when a SNCF TGV train reached 371km/h. The locomotive-mounted mercury-arc rectifier combined the single-phase AC supply with DC traction motors. Hibbert conducted pioneer experiments in 1913, but regular use began in 1950. Locomotive mercury rectifiers proved unreliable, and were replaced by solid-state devices from the mid-1960s. The success of solid-state rectifiers, inverters, and controllers enabled any type of supply system to be used with any kind of traction motor. In the 1970s Brown-Boveri developed variable speed control for modem 3-phase traction motors. Solid state devices provided multistage transformations of energy between supply and motors with minimal loss. They introduced reliable, compact technologies for suppressing interference between traction equipment and signalling and control networks. On-board information processing systems shifted trackside signalling into the locomotive and made possible the automated, driverless mainline railway. Driverless railways were previously simple systems like the London Post Office Railway of the 1920s. Rapid transit lines in San Francisco, London, and other large cities, were automated after the 1960s. Mine railways were worked without drivers in the USA, and driverless goods trains tested on mainlines in Germany. Today it is possible to monitor all locomotive operations from a control satellite in geostationary orbit. Automatic control of all operations is likely in the near future.

In the 1970s the "universal" electric locomotives was designed for most duties. The DB Class 120, introduced in 1979, is one example. Today, the "modular" philosophy dominates, and a range of locomotives, from shunting engines, to very high speed machines use components in common. Design is "globalized" by the formation of world-wide combines. European based industries like Adtranz, and Alstom are moving towards partnership with American companies like General Electric and General Motors. In Great Britain, privatization of the nationalized railways has slowed new electrification because private operators find diesel traction cheaper. In North America, the diesel remains the norm, despite occasional proposals to use dual-mode locomotives over partly electrified routes. On the high speed railways, now found in most industrialized countries, both multiple-unit and locomotive-hauled trains run at speeds of 350 km/h. Speeds of 515km/h (320mph) have been attained. The limits of wheel-on-rail transport have not been reached, and conventional TGV trains have outperformed Maglev, jet-trains, tracked hovercraft and monorails. Apart from short run passenger conveyers, long-distance Maglev routes are unlikely, despite the engineering success of the German and Japanese test installations. In passenger carrying capacity, loads moved, and speed, the electric railway worked with conventional locomotives and multiple units has much unrealized potential. The effects on railways of applying electronic control and guidance to road vehicles and modem road-trains (the "automated highways" concept) have yet to be determined.

If you have enjoyed this article, you may also be interested in the following articles by the same author:

Diesel traction

Dr M.C. Duffy's history of diesel traction on the railways from the turn-of the last century to the present day.

The Worldwide development of steam locomotives in the 20th Century from the 1900s to the present day


Dr M.C. Duffy's very extensive discussion on the development of high speed railways around the world from the end of the 19th century to the present day.  


Dr M.C. Duffy's history of Railway Mechanics to examine the mechanical properties and behaviour of railway systems

Steam Locos High Speed Rlys Railway Mechanics