Risk Assessment Of Grid Resonance Caused By Electrified Railway Harmonics

With the wide application of AC-DC-AC electric locomotives,the harmonic characteristics of electrified railway change accordingly,the contents of lower harmonics decrease significantly,and the contents of higher harmonics increase.The contents of higher harmonics in electrified railway penetrate into the power grid,and the risk of high frequency resonance in the power grid has gradually attracted attention.At present,the research on harmonic resonance of electrified railway is mainly concentrated in the traction power supply system,and there are few studies on harmonic resonance of power grid caused by electrified railway.Therefore,a comprehensive assessment of the risk of grid resonance caused by electrified railway harmonics is necessary for the power sector and the railway sector.This thesis mainly evaluates the risk of harmonic resonance in high-voltage system and medium-voltage system caused by electrified railway harmonics,and proposes measures to prevent and control harmonic resonance risk.Since the traction load is an asymmetric harmonic source for the power system,this thesis establishes three-phase harmonic model of each component of the power system and the harmonic model of the traction substation.Then,this thesis analyses harmonic characteristics of electrified railway and establishes harmonic source model.In this thesis,taking Henan local power grid as an example,harmonic power flow calculation and resonant mode analysis are carried out respectively.Combined with the penetration characteristics of electrified railway harmonics in power grid and modal impedance of each nodes,this thesis evaluates the risk of resonance in high voltage system caused by electrified railway harmonic current.The traction load connects to the high voltage power system directly,generates the total harmonic voltage distortion rate at the common connection point,and then transmits to the medium(low)voltage level system.This thesis establishes joint simulation model of traction station and distribution network,and uses it to analyse influence of conductor parameters,overhead transmission line length and system short-circuit capacity on the system resonance point distribution and harmonic amplification.The influences of capacitor capacity on the resonance of the system and the compensation branch are compared and analyzed,and the changes after the connection of series reactors are analyzed.Combined with the harmonic voltage content of common access point,the risk of resonance of distribution network bus caused by electrified railway harmonic and the risk of local resonance of reactive power compensation branch are evaluated.In this thesis,the prevention and control measures of power grid resonance risk are proposed from the perspectives of locomotive,traction station and power grid.From the perspective of locomotive,the measures to reduce the harmonic current generated by injecting traction network are proposed.From the perspective of traction substation,comprehensive compensation measures are proposed.From the perspective of power grid,the improvement measures of resonance condition are proposed.Finally,based on the harmonic resonance index,the capacity optimization method of reactive power compensation capacitor in distribution network is proposed,which can effectively avoid the resonance of reactive power compensation device caused by electric iron harmonics.