The Research Of Operation Over-voltage In Traction Power Supply System

In electrical railway, single-phase breakers are used to control switching on at the primary side of main traction transformers and substation transformers in certain traction substation. The asynchronous movement of the breakers will cause overvoltage, magnetizing inrush current and etc. Those electromagnetic transients may result in blown fuse, explosion and bus support insulator flashover. In addition, electromagnetic transient process will also appear during EMU lifting pantograph and switching traction transformer. That is a serious threat to the normal operation of electrical equipment, vehicle communication and control system and no conducive to EMU normal operation. Research on operation over-voltage is mature and systematically in electric power system. However, lacking of research in this area of railway traction power supply system. In this paper, the theoretical and simulation analysis of operation over-voltage for railway traction power supply system is carried out.Electromagnetic transient process was studied in the case of no-load switching on main traction transformer and station transformer in substation; lifting pantograph and no-load switching on traction transformer in CRH2EMU high voltage system. Firstly, the circuit model is established and the theoretical analysis and calculation are carried out for the above three kinds of cases. Theoretical analysis shows that closing angle is the main factor affecting the electromagnetic transient process of switching on main traction transformer and station transformer, followed by the other causes, equivalent inductance of source and equivalent capacitance to ground. Pantograph-catenary voltage when pantograph of EMU lifting was influenced by the inductance and capacitance value of system equivalent power supply. In addition, if the parameters of roof system are constant, the electromagnetic transient process during the no-load switching on EMU traction transformer will primarily concern with closing angle and residual magnetism.Secondly, simulation model of the above three circuit models is built by the electromagnetic transient simulation software PSCAD/EMTDC and the simulation results are verified by the simulation software. Simulations results show that:if the system parameters are certain, the maximum over-voltage of YNdll type main traction transformer, three-phase asynchronous no-load switching on is bigger than the same period switching on in high voltage side. The minimum over-voltage appears when switching phase is near 0°. When switching phase is near 90°, over-voltage is maximum and 2.7 times of rated voltage. The 2% statistics showed that asynchronous time difference is bigger, the bigger the switching overvoltage. When switching angle is 0°/180° of A and 90° of B, over-voltage of station transformer no-load switching on is maximum which is 4.37 times of rated voltage and inrush current is 184 times of the rated excitation current. When switching angle of A is 90° and B is 0°, there are 1.98 times over-voltage and no excitation current. The contact wire overvoltage during lifting pantograph of CRH2EMU is about 60-70kV. The traction transformer switching on over-voltage is large and inrush current is small when switching phase is near 90°. Over-voltage is small but inrush current is large when switching phase is near 0°.Finally, the technical measures conformed by simulation for each case to suppress over-voltage for electromagnetic transient are proposed. Simulation shows that closing resistor, phase selection technology and installation of surge arrester can effectively reduce the over-voltage of traction main transformer,110/27.5kV, high voltage side three-phase asynchronous no-load switching on. The utilize of intermediate relay can make the normal closing for station transformer. Inserting resistance and adding RC filters can improve the electromagnetic transients. Closing resistors can effectively reduce the over-voltage of traction transformer.