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Rail transport is an energy-efficient but capital-intensive means of mechanized land transport. The electrification system provides electrical energy to the trains, so they can operate without a prime mover onboard. This allows lower operating costs, but requires large capital investments along the lines.

In addition, the presence of track guiding the wheels allows for very long trains to be pulled by one or a few engines, even around curves, which allows for economies of scale in energy use. Due to these benefits, rail transport is a major form of passenger and freight transport in many countries. In Asia, many millions use trains as regular transport in India, China, South Korea and Japan while it is widespread in European countries. Freight rail transport is widespread and heavily used in North America.

Mainline and tram systems normally have overhead wires, which hang from poles along the line. Grade-separated rapid transit sometimes use a ground third rail. Power may be fed as direct or alternating current. The most common supplies are 600 and 750 V for tram and rapid transit systems, and 1,500 and 3,000 V for mainlines. The two dominant AC systems are 15 kV AC and 25 kV AC.

Railway signalling is a system used to control railway traffic safely to prevent trains from colliding. The signalling process is located in small buildings that house the transformers, the switches and signal equipment. These are placed at various intervals along the route of a railway, controlling specified sections of track.

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Tram and underground

A tram, is a rail vehicle which runs on tracks in streets. It may also run between cities or towns, or partially grade separated even in the cities such as light rail or light rapid transit. Some trams may also run on ordinary railway tracks, a tramway may be upgraded to a light rail or a rapid transit line. Most trams today use electrical power, usually fed by a pantograph; in some cases by a third rail and if necessary, they may have several power systems.

A rapid transit, metro, subway, underground, or elevated railway system is an electric passenger railway in an urban area with high capacity and frequency, and which is grade separated from other traffic. Rapid transit systems are typically either in underground tunnels or elevated above street level. Outside urban centres, rapid transit lines sometimes run grade separated at ground level.

Rapid transit is used in metropolitan areas to transport large numbers of people at high frequency. The extent of the rapid transit system varies greatly between cities, with several transport strategies: in larger metropolitan areas the underground system may extend only to the limits of the inner city, or to its inner ring of suburbs with trains making frequent station stops.


Milan – Metro New Generation

  • Third rail Voltage 750 V DC
  • Line Filter Single Phase Inductance L = 6 mH Weight = 390 kg
  • Routine test – Insulation voltage 12 kV for 60 sec – Coil immersed in water
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Regional trains

Regional rail is a passenger rail transport service that operates between towns and cities. It operates with more stops and lower distances than does intercity rail, but with fewer stops and faster than commuter rail. Other terms include local train and stopping train. Regional rails operate beyond the limits of urban areas, and either connect similarly sized smaller cities and towns, or connect cities to the surrounding towns, outside or at the outer rim of the suburban belt.

Regional rail normally operates with an even service load throughout the day, although slightly increased services may be provided during rush-hour. The service is less oriented around bringing commuters to the urban centers, although this may generate part of the traffic on some systems. Other regional rail services operate between two large urban areas, but make many intermediate stops.

TSR Auxiliary converter reactors

  • Overhead line Voltage 3000 V DC
  • Line Filter Single Phase
  • Inductance L = 39 mH Effective Current Ieff = 310 A DC
  • Chopper Filter Single Phase Inductance L = 2 mH Effective Current Ieff = 400 A DC
  • LC Filter Inverter Output 3 Phase Inductance L = 1 mH Effective Current Ieff = 150 A AC
  • Routine test – Insulation voltage 12 kV for 60 sec – Coil immersed in water
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High speed trains

There are a number of different definitions for high-speed rail in use worldwide and there is no single standard. EC Directive 96/58 defines high-speed rail as systems of rolling stock and infrastructure which regularly operate at or above 250 km/h on new tracks, or 200 km/h on existing tracks. In the United States high-speed rail is defined as having a speed above 110 mph (180 km/h) by the United States Federal Railroad Administration. In Japan high speed Shinkansen lines use standard gauge track rather than narrow gauge track used on other Japanese lines. These travel at speeds in excess of 260 km/h (160 mph) without at-grade crossings. By building a new rail infrastructure with 20th century engineering, including elimination of constrictions such as roadway at-grade (level) crossings, frequent stops, a succession of curves and reverse curves, and not sharing the right-of-way with freight or slower passenger trains, higher speeds (250–320 km/h) are maintained.


TGV High Speed Train

  • Overhead line Voltage 25000 V AC
  • Water Cooled Smoothing reactor Inductance L = 3 mH Effective Current Ieff = 426 A
  • Routine test – Insulation voltage 9,5 kV 50 Hz for 60 sec – Coil immersed in water
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A traction substation or traction current converter plant is an electrical substation that converts electric power from the form provided by the electrical power industry for public utility service to an appropriate voltage, current type, and frequency to supply railways, streetcars, and/or trolleybuses with traction current. Inside substations there could be installed also signalling and standard distribution devices and transformers.

The transformers rated power for a traction application has to be identified with a cycle described in EN 50329 or EN 60146 standards.

Metro Madrid substation

  • Power 3,3 MVA
  • Primary Voltage 15 kV
  • Secondary Voltage 2 x 1225 V
  • Protection IP00
  • Cooling AN
  • Weight 9.000 Kg
  • Rectifier traction substation
  • 12 pulse
  • Overload capacity according to EN 60146 Class VI