Research On Fast Fault Diagnosis Of DC Power Supply In Urban Rail Transit

In recent years,the development of urban rail transit has played an important role in alleviating urban traffic pressure,improving citizen's travel conditions,optimizing urban layout and promoting urban development.However the frequent DC power supply failure has brought new challenges to the safe operation of subway.According to the relevant research that the sudden short circuit fault caused by the fall of foreign bodies or thunderstorm is the most frequent failure which at the same time can not be early predicted or excluded.In the such event,the location of the fault point should be calculated to reduce the troubleshoot load and the time required for operation recovery.This paper mainly discusses the fast fault location diagnosis method after short circuit fault occured.Based on the model of short circuit fault in traction power supply system,a fast locating calculation method for short circuit fault is studied in this paper.The main work contents are shown as follow:(1)The structural composition,power supply mode and advantages and disadvantages of power supply system in urban rail transit are analyzed.The simplified equivalent circuit models of different power supply modes are studied,which provides theoretical foundation and circuit model for the establishment of the traction supply simulation model,the simulation of short-circuit fault and the realization of fault location method.(2)The key difficulty of calculating the electric parameter value of traction network lies in the calculation of the impedance of the rail.Due to the irregular shape and large area of the cross section of rail,the impedance value is seriously affected by the skin effect during the transient short-circuit fault.The calculation formula of the impedance value of the rail using an equivalent circular cross-section model is still complicated,which is not convenient for engineering popularization.The internal resistance value of rail is calculated by the empirical formula used in practical engineering application.A one-catenary line and two-rail model is used to calculate the external inductance of traction power supply circuit(3)The formation mechanism of DC side short-circuit fault is analyzed,the mathematical expression of transient current in the short circuit fault of the DC side is deduced,and the short-circuit transient current is analyzed qualitatively.A 24-pulse rectifier circuit model is established based on the actual equipment parameters,the traction network circuit model is established based on the calculation results of traction network's electric parameters,the short circuit fault simulation model of the DC traction power supply system is built,and the short-circuit fault of different transition resistance or different distance is simulated.The simulation result of fault transient current is consistent with the mathematical expression deduced ahead,which verifies the validity of the simulation model and provides data for the realization of the fault location method.(4)The classical impedance method requires the steady-state data of short-circuit fault to calculate the fault location.However,when a metal short-circuit fault occurs with extremely small transition resistance.The current rising rate will become extremely big that causes the circuit breaker to act and cut off circuits.The current cannot reach the steady state value and the impedance method is directly ineffective.A fault location method using single terminal data is arised to deal with such problem.First,the differential calculation of the voltage mathematical expressions of the line's both ends in the impedance method is carried out.Secondly,transient current expression deduced from forth chapter is used to replace the relevant parameter in the two-terminal voltage expressions to establish a new expression of the one terminal voltage.Finally,the fault location is achieved with the optimization function which is established by the single terminal fault voltage expression and the simulation value.The fault location method can adopt the little amount data after the fault occuring,and the influence of the accuracy which affected by transition resistance in the usual single terminal method is reduced,and the result has relatively high accuracy.