To avoid stray current and maintain the benefit of no phase-split in the DC traction power supply system,an AC traction power supply system was proposed for the urban public transport such as metro and light rail transit. The proposed system consists of main substation (MSS)and cable traction network (CTN ). MSS includes a single-phase main traction transformer (MTT ) and a negative sequence compensation device (NCD ),while CTN includes double-core cables (DCC ),traction transformers (TT),overhead catenary system (OCS),rails (R),etc. Three key techniques of the proposed system were discussed. First,power supply principle,equivalent circuit and transmission ability of CNT were introduced and cable-catenary matching technique,catenary voltage level selection were discussed. Second,the segmentation technology,status identification method for traction power supply network,distributed and centralized protection schemes,etc. were discussed. Third,single-line main substation supply scheme,and two or more lines shared main substation scheme were presented. Given that the excellent technical performance,good economy and high reliability of the proposed system,it provides a new alternative for metro and urban rail transit power supply system.%在地铁、轻轨等城市轨道交通中，为了避免现行直流牵引供电系统的迷流，同时发挥其无分相的优势，提出并研究了一种交流牵引供电系统。该系统由主变电所（MSS）和电缆牵引网（CTN）构成，主变电所由单相主牵引变压器（MTT）和负序补偿装置（NCD）组合而成，电缆牵引网由双芯电缆（DCC）、牵引变压器（TT）和接触网（OCS）、钢轨（R）等构成。讨论了该系统的3项关键技术：电缆牵引网的供电原理，等效电路和输电能力，电缆与接触网的匹配技术，接触网电压等级选择等；牵引网分段供电技术，牵引网供电状态辨识方法，分布式保护与集中式保护方案等；单条线路主变电所供电方案，2条及以上线路共用主变电所的供电方案。该系统技术性能优良，经济性好，可靠性高，为地铁、轻轨等城市轨道交通提供了新的、更好的选择。
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