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Started from a simple analysis on the position of subways in urban life and current subway developments at home and abroad, and based on the medium-voltage power Supply system for the south extension of Nanjing Subway Line#1, this article studies the grid structures and operational manners of the centralized power supplies frequently applied in China in detail, analyzes the requirements of subway systems for power supply equipments and the advantages of selecting P139 and P521 as the protection for this subway line, studies P139 and P521 functional features, details the protections for and control logics of all main power supply station and substation inlet wires, outlet wires, bus connections, station transformers, reactors, feeder transformers, rectifier transformers etc through logical diagrams, and specifically analyzes P139 and P521 communications.At first, this article analyzes the current subway developments at home and abroad, the benefits of subways to our urban lives; then the general mode of subway power supplies and the advantages and disadvantages of centralized power supplies are compared in detail; the tasks for and working mechanisms of medium-voltage power supply systems during subway operations are analyzed; subways and the power supplies to subways are preliminarily summarized.The power supply grid structures, power supply combination distributions, traction power supply and feeder power supply distributions, and the manners how power grids are shifted under different operational modes etc for the south extension of Nanjing Subway Line#1; in addition, the protective functions to be configured to the GIS cabinets at different loads are generally analyzed. The specific requirements of the power supply systems to subways for the hardware and functions of protection devices, the technical features of P521 and P139 protection devices, and the ways how they can satisfy the requirements of the power supply systems to subways are analyzed in detail.Based on the mixed substation including all power distribution and consumption equipments of the south extension engineering of Nanjing Subway Line#1 as the background, the roles played by, the inter-relationship between, and their respective specific protection for and control logics of each equipment such as inlet wires, outlet wires, bus connections, station transformers, reactors, feeder transformers, rectifier transformers etc are studied in detail. Some specific conditions of the feeder lighting systems and traction power supply systems are analyzed in detail. The structures and functions of general main stations, the similarities and differences between main station and substation power supply and consumption equipments, and the roles of reactor sets in the power supply to subways are analyzed as well.Finally, the compositions and working mechanisms of subway power supply monitoring systems are studied, and a detailed list of signals at typical stations under the subway power supply monitoring systems are also given.By now, the south extension engineering of Nanjing Subway Line#1 has been operated for nearly one year, while such power supply systems have been operated in good conditions. This article provides good references for construction of future subway power supply systems.
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