| With the continuous development of urban population,the subway has alleviated the pressure of urban traffic to a certain extent,but the stability of subway power supply system is the primary guarantee to ensure its safe operation.As far as the national subway traction power supply system is concerned,most of them use DC power supply,and the biggest safety hazard is that the subway can not run normally due to the short-circuit fault of catenary.Therefore,when a short-circuit fault occurs,it is of great research value and significance for operation and maintenance to distinguish the effective current waveform and locate the short-circuit fault,and accurately measure the scope of the fault.Firstly,the composition and structure of Metro DC traction power supply system are briefly introduced,which provides a basis and reference for establishing the 24 pulse DC output model of its traction power supply system.For the short-circuit fault of Metro catenary,it can be equivalent to the first-order RL equivalent series circuit.The short-circuit current when the DC side fault occurs is mathematically analyzed and calculated,which provides theoretical support for the current waveform verification of subsequent fault model simulation.The calculation of electrical parameters of DC traction network also provides a good basis for the setting of fault model parameters.By using PSCAD electrical simulation software,the 6,12 and 24 pulse DC output models of Metro rectifier units and the short-circuit fault models at the near and far ends of the DC side of catenary are simulated.Through the simulation results,we can know that: first,the 24 pulse DC power output can obtain the stable power more suitable for the locomotive;second,when the near end and far end short-circuit faults occur in the contact network,there will be a huge short-circuit impulse current in an instant.Secondly,there are similarities between the measured locomotive starting current and the current waveform of remote fault.Therefore,in practical engineering,it is necessary to distinguish the normal locomotive current waveform and fault waveform.In this paper,the wavelet transform algorithm and high-frequency decomposition are used to verify that the wavelet can make a good discrimination between the fault current and the normal current waveform when the locomotive is started,so as to distinguish the fault current and the normal current when the locomotive is started.At the same time,the wavelet analysis and fault current identification provide effective bedding and help for the short-circuit fault location and location of the rear catenary.Then,the traveling wave theory is adopted in this paper.Because it has the advantage of less affected by electrical parameters,it can be better applied to the fault location of Metro DC catenary.Finally,for the short-circuit fault on the DC side of Metro DC traction power supply system,the single ended traveling wave method is used for fault location.PSCAD / EMTDC software is used to simulate the occurrence of short-circuit fault of catenary,collect and analyze the short-circuit fault current signal,then use MATLAB software for programming,select common and appropriate DB wavelet for transformation,and judge the more accurate time point information of fault occurrence through the singularity(modulus maximum point)of fault current signal,so as to determine the transmission time of fault wave,The distance between the short-circuit fault point and the measuring point can be obtained by calculating the fault distance combined with the single ended traveling wave algorithm when the fault occurs.Through verification,it is found that the error is within the acceptable ideal range.The simulation results show that the single ended traveling wave fault location method is applicable in the case of near and far end grounding or inter pole short circuit fault of Metro catenary,and its fault location accuracy is within the feasible range. |
