The railway power supply and distribution system is an important component of the power system. Based on their functions, the railway power supply and distribution system can be divided into the railway traction power supply system and the railway electric power supply system. The railway traction power supply system supplies power to electric locomotives or EMUs, and it mainly consists of traction substations and the traction network. The railway electric power supply system supplies power to non-traction loads such as railway stations and sections along the line. The railway electric power supply and distribution system consists of external power sources, substations, high-voltage distribution systems, and low-voltage distribution systems, which are described below:
The railway power supply and distribution system preferentially uses external power sources, i.e., connections to local substations. The low-voltage level of the external power source is generally 10kV, with a few using 35kV. Railway substations (10/10) or transformer substations (35/10) are located every 40 to 60 km along the railway line to improve the reliability of the railway power supply system. Two 10kV power lines are installed on both sides of the railway between any two substations.
One type is called the Primary Load Through-Line (Automatic Power Supply Line), a high-voltage power line that primarily supplies power to primary loads along the railway line, with adjacent substations and distribution stations acting as backups. The other type is called the Comprehensive Load Through-Line (Through Line), a high-voltage power line that primarily supplies power to various small and medium-sized loads along the railway line, with adjacent substations and distribution stations acting as backups. It can serve as a backup for the Primary Through-Line and also supply power to secondary and tertiary loads along the railway line. In my country, ordinary railways generally use overhead lines for both automatic power supply lines and through-lines, rarely using cable lines. However, overhead lines have relatively poor power supply reliability, and to ensure power supply reliability, the proportion of power cable lines is continuously increasing.
Railway substations are generally set up using a "one station, one substation" approach. For railway dual-power 10kV substations supplying primary loads, one power source should ideally be a dedicated panel and line. Adjacent substations supplying power to through-line power lines should meet dual-power requirements, with one substation ideally having two power sources. Other substations should have one reliable power source, and ideally two power sources if possible. Considering the long power supply arm and light load of railway substations, voltage regulators are installed to improve the power supply quality of automatic or through lines, ensuring that a fault in the railway power supply system will not affect the local power grid. Lines supplying power to station loads using 10/0.4 transformers are called station feeders. The structure of a railway 10kV power supply and distribution system is shown in Figure 1-1.
Figure 1-1 Schematic diagram of railway power distribution system
Railway power lines, whether automatic or continuous, typically have dry-frame substations or prefabricated substations installed approximately every 3 km to supply power to station loads and loads along the line. Prefabricated substations integrate high-voltage switchgear, transformers, and low-voltage switchgear, featuring strong integration, small size, compact structure, high reliability, minimal on-site installation work, short installation and commissioning cycle, and portability. Station loads mainly include railway station power supply loads such as station signaling equipment, communication equipment, overhead contact line remote control switch operating power supplies, lighting, air conditioning, and ventilation. Railway section loads mainly include fiber optic repeaters, signaling equipment, wireless communication base stations, tunnel lighting, etc. Signaling and communication, which are closely related to controlling train operation safety, are classified as Level 1 loads. Dedicated air conditioning for machine rooms and fire-fighting level power supply loads are also included; specific load level classifications can be found in TB10008 "Railway Power Design Code".
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