Railway system of electrification

A railway system of electrification is the whole of the means implemented to supply with electrical energy the trains (electric Locomotive or electric motorized oar).

These systems can be classified according to various criteria:

standard of food (conductor Catenary rail or )
standard of current:

D.C. current or electric Alternative course
Tension
Frequency (in alternative course)
running Three-phase Single-phase current or

A little history

To propel an electric engine it is necessary:

an electric propellent system
a system of variation the speed
a system of production and of transport of electrical energy.

… and it is there that the pack wounds. The only easily producible and transportable current is the polyphase alternative course. Three-phase current today, the diphasic one or quadriphasé yesterday. The only electrical motor naturally adapted to traction is the engine with D.C. current of the series type because to very great beach variable speed and very strong couple with starting (but on the other hand inapt to recover energy with braking). By dividing into sheets the stator of an engine with D.C. current and by taking a very great care on the level of the brushes (phenomena of commutation) it is possible to supply an engine with D.C. current with alternative course. The higher the frequency of this current is, the more the losses iron (Eddy current Hystérésis and ) are important, from where the idea to use the weakest possible frequency: the 16 Hz 2/3.

No system not being perfect, all was tested: in tensions, frequencies, types of engine, systems of variation speed, system of transmission of the power to the wheels, in systems of collecting of current. From where the very great number of manufacturers of railway material in first half of the 20th century, and the very large variety of schools of engineers training the specialists able to include/understand and make evolve/move this multitude of systems.

The whole of these problems was solved today with the semiconductors of power which make it possible to juggle with tensions and frequencies. Today the electrical motors of traction are synchronous alternate engines at variable frequency, supplied with static inverters. The only economic tension with the use is thus 25.000 V at industrial frequency.

D.C. current

The first electric systems used relatively low tensions in D.C. current. The electrical motors were fed on line on the network and were controlled by a combination of resistance S and Relais which connected the engines in parallel or series.

The current tensions are 600 V and 750 V for the Tramway S, Trolley S and Métro S, and 1500 V and 3000 V for main road of iron. Formerly, of the rotary converters or the rectifying with mercury arc was used to convert the alternative course provided by the public network into D.C. current to the desired tension. Nowadays, it is generally carried out by Redresseur S with Semi-conducteur S.

The system with D.C. current is very simple, but requires thick drivers and imposes short distances between the sub-stations which feed the network. Moreover, there are notable losses because of resistance of the drivers.

The auxiliary equipments, such as Blower S and compressing S, are also animated by engines connected directly on the electrical communication. Consequently, these engines are often unusually bulky.

The D.C. current 1500 V is used with the Netherlands, the Japan, in certain parts of the Australia and partially in France (South-eastern networks and South-west). With the the United States, the D.C. current 1500 V is used in the area of Chicago by the Metra (in the past Illinois Central Railroad) and the line of interurban tram South Shore and South Bend.

With the the United Kingdom, the D.C. current 1500 V cd. was used in 1954 for the electrification of the route of trans-Pennine (now closed) by the Tunnel of Woodhead. The system used braking by regeneration, allowing the transfer of energy between the up-trains and descending the slopes from approach of the tunnel. The only network currently using this type of current in the United Kingdom east that of the Subway the Tyne and Wear.

The D.C. current 3000 V cd. is used in Belgium, in Italy, Poland, in the north of the Czech Republic, in Slovakia, in old the Yugoslavia and the countries of the ex- Soviet Union. The D.C. current 3000 V cd. was also used formerly by the Delaware, Lackawanna & Western Railroad (currently NJ Transit before it is converted with the alternative course 25 Kv).

The tensions indicated (such as 1500 V) are face values likely to fluctuate in a direction or the other, for example between 1300 V and 1800 V according to various factors:

number of trains collecting the current on the line,
distance since the sub-station.

The current tensions are often simple multiples one of the other:

1500V DC = 2 X 750V DC
3000V DC = 2 X 1500V DC
1200V DC = 2 X 600V DC

Conductor rail

The majority of the systems of electrification resort to overhead lines, but the third rail is an option for the systems with low tension, to 1200 V approximately. Whereas the use of the conductor rail does not imply necessarily that of the D.C. current, in practice, the systems with conductor rail used all of the D.C. current because it can transport 41% of energy in more than one system to alternative course to the same tension of peak. The third rail is more compact than the overhead line and can be installed in tunnels of lower diameter, criterion which has its importance for the subways.

The systems with conductor rail can be conceived with a higher, side or lower contact. The higher contact is more dangerous, the rail under tension being exposed to the free air and accessible to the people likely to go above, unless a mask insulating was installed over. The contacts inferior or side can more easily be equipped with integrated protections of safety, carried by the rail itself. The third rails with higher contact are also vulnerable to disturbances by the ice, snow, even by dead sheets.

As the third rails and the systems with D.C. current are limited to relatively low tensions, that can be a factor limiting for the power of the trains (length, load, speed) like for the secondary equipments like air-conditioning. That constitutes a factor favorable to the use of overhead lines and higher tensions even for an urban use. In practice, the fastest trains in conductor rail are limited to 160 km/h because of the constraints of collecting of the current between the “shoe” and the rail. It is in particular the case of oars EUROSTAR when they circulate on the British south-eastern network, out of the new line.

Fourth rail

The Métro of London is one of the rare networks in the world to use a fourth rail. This additional rail ensures the return of the current of traction, role ensured by the guide rails in the systems conductor rail. In the subway of London a third traditional rail with higher contact is placed along the way and subjected to a continuous tension of + 420 volts and the fourth rail, also with contact by the top, is laid out with the center of the way between the guide rails with a tension of - 210 V, which provides a current of traction to 630 volts. Special devices exist when the same ways must be traversed by subway trains (envisaged for 4 rails) and oars of suburban trains (planned for three rails with return of the current by the guide rails), section of Gunnersbury to Richmond on the District line for example.

The interest of the fourth rail is that the two guide rails are available exclusively for the circuits track. In addition, the reduction in the tension compared to the ground (“potential of ground”) is likely to make less dangerous the fall of a passenger on the way.

Low frequency alternative course

The current electrical motors, with Commutation, can also be fed in alternative course (universal Moteur), because the inversion of the direction of the current at the same time in the Stator and the Rotor does not change the direction of the couple. However, the Inductance of a rolling up does not make it possible to produce large engines at the standard frequencies of the distribution networks. A certain number of European countries, whose Germany, Austria, the Swiss , Norway and Sweden, standardized the alternative course single-phase current to 15 Kv 16,2/3 Hz (a third of the standard frequency) (before of the tensions of 6 Kv and 7,5 Kv had been employed). With the the United States (with their electric delivery system with 60 Hz), the frequency of 25 Hz (an old standard frequency, from now on obsolete of distribution) is used under 11 Kv between Washington and New York. A section equipped in 12,5 Kv 25 Hz between New York and New Haven (Connecticut) was converted into 60 Hz in the last third of the 20th century.

The engines are supplied via a Transformateur switch which makes it possible to modify the tension, also resistances are not necessary. The auxiliary equipments are controlled by engines with low tension with commutation, are supplied by a separate rolling up of the principal transformer, and are of reasonably small size.

The unusual frequencies suppose that electricity is converted starting from the current provided by public network by engine-generators or static reversers in the sub-stations of food of the network, or produced by electric stations completion separate.

Alternative course at standard frequency

The first attempts to use alternative course single-phase current at the standard frequency of 50 Hz took place in Hungary in the Années 1930, then in Germany. However, it is only in the Années 1950 that the use of this current called “to industrial frequency” began (around Annecy, under the impulse of Louis Armand), then was really spread, in particular with the electrification of the North-eastern transversal (Valencian - Thionville) in France.

Nowadays, some Locomotive S in this system use a Transformateur and a Redresseur which provide a D.C. current to low tension with the engines. The speed is controlled by commutation of rollings up of the transformer. More sophisticated engines use circuits with Thyristor S or transistors IGBT to produce a vibrated alternative course or even at variable frequency which then directly feed the driving of traction.

This system is economic. To avoid imbalances of phase in the external feeding systems, one appealed, in the beginnings, with transformers three-phase/single-phase currents or three-phase/diphasic. These two types of transformer reduce imbalances between phases without removing them. They on the other hand make it possible to direct suitably the vector of phase resulting with the secondary each time necessary and in particular in the case or one wants to put in parallel several under stations which do not present the same time index to the primary education (ex: 0-4-8 for 225 Kv and 3-7-11 for 63 Kv). This solution was applied to 3 pennies stations of the suburbs 25 Kv Western, Is and Northern of Paris about years 1966/1968, with an aim of feeding these three networks in parallel. Today, the engines thanks to the IGBT with engines of traction at variable frequency, have a weak ringing current to starting. That makes it possible to take the food of under stations directly between two phases. That generates imbalances on the third phase but is regarded as acceptable because avoiding the acquisition of these very expensive special transformers. It should be noted that a system of too unbalanced currents can on the one hand generate electromagnetic interferences notable and on the other hand to pose problems on the level even of the production of current (the alternator).

The alternative system single-phase current 25 Kv 50 Hz is used in France, in Great Britain, Finland, with the Denmark on certain lines in Belgium in particular LGV, in the countries of the ex Soviet Union, the ex- Yugoslavia, in India, with the Japan and in certain parts of Australia (all electrifications of the Queensland and Western Australia), while with the the United States one commonly uses currents of 12,5 and 25 Kv with 60 Hz. 25 Kv 50Hz is the current one of reference for all the lines at high speed and the long distances, even when the remainder of the network is electrified with another type of current. It is the case in particular in Spain, in Italy, in South Africa, in Taiwan, in China, etc

Engines polycourant

Because of diversity of the systems of railway electrification, which can vary even inside a country, the trains must often pass from one system to the other. One of the means of doing it is the change of engines in the stations of contact. These stations are equipped with overhead lines which can rock of a type of current to the other, so that a train can arrive with an engine and set out again with another. It is however a system which presents disadvantages and overcosts: waste of time, need for having various types of engines.

Another means is to have engines polycourant able to function under currents of various types. In Europe, one can find engines quadricourant (D.C. current 1,5 Kv and 3 Kv, alternative course 15 Kv 16-2/3 Hz and 25 Kv 50 Hz). It is the case for example oars Thalys PBKA. These engines can pass without stop of a type of current to another, however they are generally not also effective under all the currents, and their costs of construction is higher. One finds of the engines bicourant more usually, for example in France whose railway network is shared between the D.C. current 1,5 Kv and the alternative course 25 Kv 50 Hz.

the trains Eurostar are tricourant to be able to circulate on the lines at high speed (CA 25 Kv 50 Hz, the old lines with 3rd rail British (DC 750 V) and the Belgian lines (DC 3000 V).

With the the United States, the New Jersey Transit uses engines polycourant ALP-44 for its services Midtown Direct towards New York.

See too

List of the currents used in electric railway traction
Electrification of the railroads in the United States

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