Electric railway traction - Railway dynamics and substations

Today in France, 54% of the national rail network, i.e. 15,350 km (of which 9,380 km electrified at 25 kV-50 Hz) out of 28,500 km, is electrified and handles over 90% of national rail traffic.

Electric rail traction is currently characterized by the following aspects:

• given the power required for trains with a unit capacity of several hundred passengers, it is the sole vector for both very high-speed rail and urban and suburban traffic. Beyond or ahead of high-speed lines, high-speed trains use electrified conventional lines to serve numerous towns and cities;

• the pre-eminence of single-phase electrification over DC electrification (cost, capacity) means that new electrifications are almost always 25 kV-50 Hz, with the exception of a few short extensions to the 1.5 kV network. Converting lines electrified at 1.5 kV to single-phase 25 kV, with the requirement for reduced service interruption times, is a current challenge;

• major innovations in powertrains, particularly in energy converters and the associated three-phase traction motors. Increased power-to-weight ratios make it possible to produce "polycurrent" traction motors. Thanks to a power factor very close to 1 in all operating conditions, and reduced harmonic spectra, they now make better use of fixed single-phase traction systems. Developments in power converters also concern fixed traction installations (imbalance compensation, improved line power supply through controlled injection of reactive energy);

• its strong involvement in the rail interoperability process launched at European level, as part of the development of "technical specifications for interoperability" in the "Energy" domain. This process concerns both the high-speed and conventional rail networks. The Energy subsystem has major interfaces with the Rolling Stock subsystem, in the field of electric traction.

This file includes :

• A reminder of railway dynamics and the characteristics of electric motors, which are fundamental to the dimensioning of fixed traction installations subject to moving and highly fluctuating loads;

• the respective principles of 1.5 kV DC traction power supplies and 25 kV-50 Hz traction power supplies, including the so-called 2 × 25 kV variant, which was introduced in France in the early 1980s, when the first high-speed line, Paris-Lyon, was electrified.