The Research To Distinguish Remote Short Circuit Current Of Urban Railway Transit

It is one of the most important segments in relay protection of traction power supply system in urban railway transit to effectively avoid locomotive starting current and extraction short circuit current information. The DDL protection system based on the transient characteristics of current increment and rise rate may be failure, therefore, the key problem is to research a kind of comprehensive solution.This paper’s target is to effectively make a distinction between starting current and remote short circuit current, and build a new identify criterion make the most of computer simulation and the field measured data. It explained that the time constant of starting current is unchangeable on the basis of characters of starting current and remote short circuit current, at the same time, the time constant of short circuit current is changeable because of skin effect of the rail. Theory basis of this paper is that the time constant is whether changeable or not.First of all, the paper calculated rail transient parameters under influence of skin effect and verified the time constant is changeable with the development of the short circuit process, which proved the theoretical basis is veracity. Then it established the traction substation model based on the24pulse rectifier that is used widely. In order to analysis the locomotive starting current, at the same time, this paper established locomotive starting model use DC motor traction transmission system and AC three-phase asynchronous motor traction transmission system and got the starting current based on Matlab/Simulink. Afterwards, analyzing the influence of skin effect of parallel P type, serial S type and chain type three orbital equivalent structures, so as to form an S series for the foundation, through the PSCAD/EMTDC simulation platform got remote short circuit current. Finally, using the wavelet multiresolution analysis and wavelet packet analysis of the experimental data was studied and the wavelet base db6is used in continuous wavelet transform of the starting current and short circuit current. Through analysis these two current wavelet transform coefficient, this paper proposed the identify criterion and validated it based on measured data.The measured data validation showed that the identify criterion based on wavelet transformation of the locomotive starting current and remote short circuit current have good identify results, thus it can provide reliable guarantee for relay protection of traction power supply system.