Software Development For Feeder Protection Setting Of DC Traction Power Supply System Based On MATLAB Simulation

In recent years,metro construction has become an important direction for the development of urban rail transit.Short circuit faults of system may destroy related electrical equipment.In some severe cases,these accidents may even cause casualties.Therefore,the safety of the DC traction power supply system is the key to ensure the stability and reliability of the metro system.Feeder protection is one of the core technologies of the DC traction power supply system.When a short circuit fault occurs,reasonable determination of the setting value will enable the system to remove the fault quickly and accurately.In consequence,it is of great significance to make research on the setting of feeder protection in DC traction power supply system.Firstly,the composition and power supply mode of the metro power supply system are analyzed.Based on the MATLAB/Simulink platform,a simulation model of DC traction power supply system is established.The simulation model consists of the external power supply of AC system,the rectifier unit,the traction network and the vehicle load of DC system.The feasibility of the proposed model is verified by comparing with the measured data.Next,the configuration and setting methods of DC feeder protection are studied.The protections include quick-brick protection,current change rate and incremental protection(DDL protection),definite time overcurrent protection,low voltage protection and so on.The factors which may affect the correct operation of the feeder protection are summarized from three aspects: the accuracy of the protection device,the determination of the setting value and the special operation of the system.Besides,the thesis concludes that the identification of multi-vehicle starting current and remote short-circuit current can be a difficult problem in the study of feeder relay protection.Then,a simulation model of multi-vehicle DC traction power supply system is established based on Beijing metro.The simulations of short circuit fault and multivehicle starting are conducted.Because traditional DDL protection can't identify the multi-vehicle starting current and remote short-circuit current effectively,a new method is proposed.This new method takes the current integral value and the ratio of the current integral average value to the maximum value as the setting values.It can improve traditional feeder protection as a backup of DDL,and provide a new idea to study the problem of multi-vehicle starting.Afterwards,the reasonableness and effectiveness of the improved feeder protection strategy and setting values are verified by simulation.Finally,based on the MATLAB/GUI platform,the setting software of feeder protection in the DC traction power supply system has been developed.The main functions include parameter management,transient simulation,setting calculation,protection verification and result output.The software can help normal users understand the structure of the traction power supply system and the principle of feeder protection.What's more,it can also support the system operators to determine the setting values and maintain the relay system efficiently.