Power Flow Solvability And Power Supply Capability Assessment Of Traction Power Supply Systems

The requirements of transport capacity of electric railways are higher and higher with the developments of high-speed and heavy-haul railways.The power supply capability(PSC)of a traction power system(TPSS)is a part of transport capacity.The lack of PSC decreases the transport capacity.There have been many cases of insufficient PSC reported in recent years.The phenomena include traction transformer overload,inadequate overhead contact system(OCS)current capacity,and low OCS voltage.The PSCs of TPSSs should be mastered for the design,maintain and reconstruct of electric railways.It helps to avoid accidents,maximize the carrying capacities of railways,and operate them safely and efficiently.Therefore,it is significant to assess the power supply capability of TPSSs.The TPSS is a kind of electricity transmission and distribution system.Its PSC is a concept of maximum transfer power from the circuit property.The maximum transfer power is constrained with the power flow solvability.However,the viewpoint is focused on the safety constraints in the relative researches.There have not been references assessing the PSC of the TPSS from the power flow solvability.This dissertation treats both the power flow solvability and the safety constraints as the influencing factor of power supply capability,which relates the PSC assessment and the power flow analysis.The maximum transfer power is calculated to provide a new viewpoint to the researches,which is instructive for the elaborate design and economic operation of electric railways.Maximum transfer power calculation needs repeated power flow to approximate.Meanwhile,the moving train loads make the number of calculation rise.A fast power flow algorithm is needed.A noval power flow calculation algorithm of the TPSS is proposed in this dissertation.The node voltage equations are converted into port equation(s)based on the Thevenin equivalence,and solved by the mathematical or numerical method.Case stydies verify that this algorithm has the advantage of fast convergence,short calculation time and easy approach to multiple solutions,which is applicable to the calculation of the system maximum transfer power.The PSC is constrained with the capacities of the power supply equipment.It is clear to assess the capacities of traction transformers,breakers and disconnectors.Nevertheless,the OCS current capacity is complex because it depends on current capacities and distribution ratios of several conductors.The existing calculation method did not consider the influence of the return circuit,which leads to a modal error.A new method of calculating the OCS current capacity is proposed to avoid this error,which takes the electromagnetic coupling of the OCS and the return circuit into account,and verified with case studies.The electromagnetic coupling makes the current distributed to the OCS conductor nearest to the return circuit,which decreases the current capacity utilization ratio of other conductors.On the basis of maximum transfer power calculation,the method of power supply capability assessment is proposed under different needs.If the power supply capability needs to be increased,the restriction should be determined according to the maximum transfer power under every constraint.Then the appropriate measures should be taken.The applicable situations and priority of measures in common use are analyzed.The reconstruction of Beijing-Tianjin Intercity Railway is taken as an example to assess whether the power supply capability satisfies the operation of Fuxing Hao EMU at the speed of 350 km/h.The reconstruction schemes are proposed.