Study On Impact Of Rail Transit On Urban Distribution Network Power Quality

With the rapid development of city rail transit construction, its impact on the powergrid gradually presents. Different from other load in power network, Metro load isspecial. First of all, the subway traction power supply network is a AC-DC network, andthe operation is more complicated and changeful. Secondly, the load is affected by manyfactors, the harmonic content is rich, and showed significant volatility change with time.Nowadays people are demanding better power quality, the problems that urban rail transitsystems connected to the grid need to be solved.This paper analyzes the structure, operation mode, the train rules of the entire railsupply system, analysis of the city rail transit power supply system power quality indexvalue calculation method. According to the power quality evaluation content, evaluationindex, evaluation criteria and evaluation purposes divide the evaluating point of powersupply system, test and analysis power quality index limit of different evaluation point,assess the extent of the impact on the grid, then seek further cause of power qualityproblems.Theoretical analysis the main harmonic source of rail power supply system,including6-pulse rectifier,12-pulse rectifier,24-pulse rectifier, analysis theircharacteristic harmonics and analyzes the reasons for producing Non-characteristiccurrent harmonics in rectifying system. Studied the problem of reactive power with urbanrail transit power supply system, reactive power problems mainly due to the low voltageload of traction substation, step-down substation. The reactive power produced bytraction substation has relationship with traction transformer operation mode and railtransport diagram, the reactive power produced by low voltage system has relationshipwith train operation peak period and low valley period.Proposed power quality management program of urban rail transport access todistribution network. Analysis the effect of Active filter in low voltage system. Ensuring400V bus power factor above0.9, series reactor, choose fit reactance rate, in order toachieve economy and ensure that less harmonic currents flowing through the reactivepower compensation device. Medium voltage system uses parallel inductive reactivepower compensation device, ensuring reactive power don’t reverse feed at fundamentalstate, taken two ways to suppress harmonics: series7times or11times second-orderhigh-pass filter branch, and simulation analysis to verify the validity of the harmonicsuppression,so providing guidance and ideas for power quality control under differentcircumstances.This paper comprehensive and depth studies the power supply system of city railtraffic, propose solutions to its harmonics and reactive power compensation issues, to improve the power quality of urban rail transit power supply system has a certainreference value.