Three-phase AC electrification of Ferrovie dello Stato

Three-phase AC railway electrification was used in Italy, Switzerland and the United States in the early twentieth century. Italy was the major user, from 1901 until the 1976, although lines through two tunnels also used the system; the Simplon Tunnel

Simplon Tunnel

The Simplon Tunnel is an Alpine railway tunnel that connects the Swiss town of Brig with Domodossola in Italy, though its relatively straight trajectory does not run under Simplon Pass itself. It actually consists of two single-track tunnels built nearly 20 years apart...

in Switzerland from 1906 to 1930, and the Cascade Tunnel

Cascade Tunnel

The Cascade Tunnel refers to two tunnels at Stevens Pass through the Cascade Mountains, approximately to the east of Everett, Washington. The first Cascade Tunnel was a 2.63-mile long single track railroad, built by the Great Northern Railway in 1900 to avoid problems caused by heavy winter...

of the Great Northern Railway in the United States from 1909 to 1939. The first line was in Switzerland, from Burgdorf to Thun (40 km (24.9 mi)), since 1899.

The system provides regenerative braking with the power fed back to the system, so is particularly suitable for mountain railways (provided another locomotive on the line can use the power). The locomotives use three-phase induction motors without commutators which require less maintenance. The early Italian and Swiss sysyems used a low frequency (16⅔ Hz), and a relatively low voltage (3,000 or 3,600 volts) compared with later AC systems.

The overhead wiring, generally having two separate overhead lines and the rail for the third phase, was more complicated, and the low-frequency used required a separate generation or conversion and distribution system. Train speed was restricted to one to four speeds, with two or four speeds obtained by pole-changing or cascade operation or both.

The system is only used today for four mountain (funicular or rack) railways using powered carriages, where the overhead wiring is less complicated and restrictions on the speeds available less important; the Corcovado Rack Railway

Corcovado Rack Railway

The Corcovado Train is a mountain railway in Rio de Janeiro in Brazil, from Cosme Velho to the summit of the Corcovado Mountain at an altitude of . The summit is known for its statue of Christ the Redeemer and its views over the city and beaches of Rio....

in Rio de Janeiro Brazil, Gornergratbahn

Gornergratbahn

The Gornergratbahn is a nine-kilometre metre-gauge mountain rack railway, with Abt rack system. It leads from Zermatt, Switzerland , up to the Gornergrat...

and Jungfraubahn

Jungfraubahn

The Jungfraubahn is an gauge rack railway electrified at 3-phase 1,125 volts 50 Hertz, which runs 9 kilometres from Kleine Scheidegg to the highest railway station in Europe at Jungfraujoch...

in Switzerland and the Petit train de la Rhune

Petit train de la Rhune

The Petit train de la Rhune is a metre gauge rack railway in France at the western end of the Pyrenees. It links the Col de Saint-Ignace, some to the east of Saint-Jean-de-Luz, to the summit of the La Rhune mountain...

in France). They are industrial rather than low frequency (50 Hz, or 60Hz (Brazil)), using between 725 and 3000 volts.

This category does not cover railways with a single-phase (or DC) supply which is converted to three-phase on the locomotive or power car, e.g. most railway equipment from the 1990s and earlier using solid-state converters. The Kando system of the 1930s developed by Kando

Kando

Places and things known as Kando or kando include:* Kando, Burkina Faso, a village in Burkina Faso* Jiandao, an area in China* Kálmán Kandó a Hungarian engineer and inventor of the Kandó system of railway electrification...

and used in Hungary and Italy used rotating converters on the locomotive to convert the single-phase supply to three phases, as did the Phase-splitting system on the Norfolk and Westren Railroad in the USA.

Locomotives

Usually the locomotives had one, two or four motors on the body chassis (not on the bogies), and did not require gearing. The induction motors are designed to run at a particular synchronous speed, and when they run above the synchronous speed downhill, power is fed back to the system. Pole changing and cascade (concantation) working was used to allow two or four different speeds, and resistances (often liquid rheostats) were required for starting. In Italy freight locomotives used plain cascade with two speeds, 25 and 50 km/h (15.5 and 31.1 mph); while express locomotives used cascade combined with pole-changing giving four speeds, 37, 50, 75 and 100 km/h (23, 31, 46 and 62 mph). With the use of 3,000 or 3,600 volts at 16⅔ (16.7) Hz, the supply could be fed directly to the motor, so not requiring an onboard transformer.

Generally the motor(s) fed a single axle with other wheels linked by connecting rods, as the induction motor is sensitive to speed variations and with non-linked motors on several axles the motors on worn wheels would do little or even no work as they would rotate faster.This motor charactership led to a mishap in the Cascade Tunnel to a GN east-bound freight train with four electric locos, two on the head and two pushing. The two pushers suddenly lost power and the train gradually slowed to a stop. But the lead unit engineer was unaware that his train had stopped, and held the controller on the power position until the usual time to transit the tunnel had elapsed. Not seeing daylight, he finally shut down the locomotive, and found that the wheels of his stationary loco had ground through two-thirds of the rail web.

Overhead Wiring

Generally two separate overhead wires are used, with the rail for the third phase, though occasionally three overhead wires are used. At junctions, crossovers and crossings the two lines must be kept apart, with a continuous supply to the locomotive, which must have two live conductors wherever it stops. Hence two collectors per overhead phase are used, but the possibility of bridging a dead section and causing a short circuit from the front collector of one phase to the back collector of the other phase must be avoided. The resistance of the rails used for the third phase or return is higher for AC than for DC because of the "skin" effect, but lower for the low frequency used than for industrial frequency. Losses are also increased, though not in the same proportion, as the impedance is largely reactive.

The locomotive needs to pickup power from two (or three) overhead conductors. Early locomotives on the Italian State Railways used a wide bow collector

Bow collector

A bow collector is one of the three main devices used on tramcars to transfer electric current from the wires above to the tram below. While once very common in continental Europe, it has now been largely replaced by the pantograph.-Origins:...

which covered both wires but later locomotives used two pantographs side by side. In the United States, a pair of trolley pole

Trolley pole

A trolley pole is a tapered cylindrical pole of wood or metal, used to transfer electricity from a "live" overhead wire to the control and propulsion equipment of a tram or trolley bus. The use of overhead wire in a system of current collection is reputed to be the 1880 invention of Frank J....

s were used. They worked well with a maximum speed of 15 miles per hour (6.7 m/s). The dual conductor pantograph

Pantograph (rail)

A pantograph for rail lines is a hinged electric-rod device that collects electric current from overhead lines for electric trains or trams. The pantograph typically connects to a one-wire line, with the track acting as the ground wire...

system is used on four mountain railways that continue to use three-phase power (Corcovado Rack Railway

Corcovado Rack Railway

in Rio de Janeiro, Brazil

Rio de Janeiro

Rio de Janeiro , commonly referred to simply as Rio, is the capital city of the State of Rio de Janeiro, the second largest city of Brazil, and the third largest metropolitan area and agglomeration in South America, boasting approximately 6.3 million people within the city proper, making it the 6th...

, Jungfraubahn