Research On Short-term Grid-connected Switching Technology Of Two Utility Systems In Traction Substation

In order to ensure the reliability of the power supply for electric traction loads,the two utility systems in the traction substation(TSS)of electrified railway usually adopts one primary and one backup power supply scheme.According to the operating conditions of electrical equipment and the maintenance requirements of the electricity company,it is often necessary to perform some switching operations on the utility system or traction transformer.However,the conventional switching scheme has the following drawbacks: 1)Each switching operation results in a power interruption in TSS,which affects the railway traffic;2)The switching plan usually cannot be approved as required,results in the ineffective maintenance of electrical equipment.On this basis,this paper studied the feasibility and the technical conditions of implementing the switching operation under the condition that the two utility systems in TSS are short-term connected.The main works are as follows:(1)It analyzed the circulation characteristic during the process of grid-connected switching of the two utility systems in TSS in different operating conditions with the established simulation model.Primarily,it analyzed the operation principles and the modeling methods of electrical equipment based on the operating mechanism and topology of the traction power supply system(TPSS).Then,it established a general simulation model of gridconnected switching of the two utility systems in TSS using MATLAB/SIMULINK software.Moreover,It simulated the circulation characteristic during the process of grid-connected switching under no-load and loaded operating condition in an ideal condition.The results show that grid-connected switching will not affect the protection of the system in an ideal conditions.(2)It analyzed the calculation method as well as the influencing factors of the circulation current generated when the two utility systems in TSS are short-term grid-connected.Primarily,it analyzed the calculation method of the circulation current based on a simplified equivalent circuit,and discussed the influencing factors of which.Moreover,it explored the discipline of various influencing factors on the circulation current,and a sensitivity metric is applied to identify the key influential factors.Ultimately,the technical conditions for grid-connected switching are summarized.The simulation results show that the voltage amplitude deviation between the two utility power sources is the most sensitive factor on the circulation.Typically,grid-connected switching does not affect the regular operation of the system when the voltages meet the requirements of the national voltage deviation standard.(3)It carried out a field test with a complete grid-connected switching scheme.Primarily,it designed a complete implementation scheme of grid-connected switching considering the actual situation of TSS.Moreover,it elaborated a detailed procedure for the field test in the Huzhou TSS of Nanjing-Hangzhou high-speed railway.The fluctuation characteristics of the three-phase current and 27.5k V side current were analyzed respectively.The analysis results demonstrates that,1)The circulation current is increasing with the increasing of the gear difference between traction transformers,and the current will not affect the operation of the system,which verified the feasibility of the grid-connected switching scheme;2)The fluctuation characteristic of the measured circulation current is completely consistent with the simulation analysis results,and the effective value error of the circulation current is less than1 A,which verified the correctness of the simulation model and analysis methods in this paper.(4)This paper developed a set of simulation software for short-term grid-connected switching of two utility systems in TSS.It introduced the constructure of the simulation platform as well as the functions of the main platforms.This software is useful,which can provide technical support for the engineering application of grid-connected switching of two three-phase power system in TSS.Finally,the work of this paper is summarized,and the shortcomings of this study have prospected.