Power Quality Evaluation And Simulation Platform Development For Electric Railways Connection To The Power Grid

At present,Chinese electrified railways are still in a period of large-scale development.However,due to the problems of negative sequence and harmonics of electrified railways,the power quality of the power grid has also been affected to various degrees.Subsequently,both the power grid and the railway relative departments have paid more attention to the power quality.Thus,how to accurately pre-evaluate the power quality in the early stage of electrified railway construction is the key to the problem.A feasible way is to develop a set of software system including the functions of measurement data analysis and simulation calculation.Therefore,using the measurement data of existing electrified railway lines as the electric load of the simulation model,one can pre-assess the power quality when new traction substations of similar railway lines connecting to the power grid.At first,this thesis analyzes the current problems of traction substation access assessment and some applicability problems in the national standard of power quality,and proposes some suggestions for improvement.Then,the power system component models and three-phase traction substation model are established based on the analysis method to three-phase systems.The three-phase fundamental and harmonic admittance matrices of traction substation are formulated;and the operation data of the traction substations are obtained through measurements.The distribution of traction load harmonics and negative sequence in power system is calculated according to the current injection method.On the basis of the analysis and conclusion of the characteristics of traction load distribution,fitting the probability density function of the feeder current of a traction substation is fitted by using logarithmic normal distribution,meanwhile,in order to improve the accuracy of the collected data,using C#language,a software for power quality measurement and analysis is developed for German imc measurement devices.As a result,the reliability of the data acquisition is guaranteed.Using the imc,the electric load data of Zhouliying traction substation on both traction and grid sides are acquired.The measurement data are analyzed by the developed software,and fitted by the logarithmic normal distribution.A power quality simulation software,ErailLink,is further developed by using the C#language and SQL database technology.Its visual operation mode is convenient tosimulate the power grid surrounding the traction substation.It can analyze the influence of the harmonics and negative sequence the traction substation to the power grid.At the same time,taking the use of the analysis data of Zhouliying test as the current source,using the ErailLink it is analyzed that the harmonic and negative sequence current of power grid surrounding Tianjin Xinxing village,Liuzhuang traction substation in order to verify the feasibility of the software.Finally,the ETAP simulation software,which is uniformly used by both electric research power institutes and electric power design institutes for now,is used to analyze the harmonics and negative sequence at access point of the Xinxing village and Liuzhuang traction substation as well.Then,the results of ETAP simulations,ErailLink simulations and imc measured data are compared respectively.Based of the comparisons of the accuracy of ETAP and ErailLink,some shortcomings of ETAP are pointed out.At the same time,to improve the accuracy of ErailLink some improving approaches are proposed correspondingly.