| A Metro is an important measure to address the traffic congestion in the central city and the best name card to show the comprehensive strength for the modern transportation system.All metro vehicles adopt electric control,but Metro DC traction power supply system(TPSS)is easy to make threatening and harmful faults in feeder lines.Due to the high traffic density and changeable vehicle operation,a nuisance tripping for current feeder protection was made frequently,which seriously affects the safety of metro transportation.Therefore,based on the qualitative analysis of traction load characteristics,it is virtually necessary to study a new feeder protection principle based on impedance characteristics by establishing the wire-ground loop model and carrying out real-time simulation of power supply system.Firstly,the structure of Metro TPSS is described,and a protection configuration and working principle is analyzed in detail.According to the difference of time series waveform,the short-fault current and the traction load current with large value are distinguished,and the special load current is the main reason that causes the DDL protection nuisance tripping.Based on the waveform similarity,the traction load current is divided into system-oscillation current and locomotive-oscillation current,and the essential characteristics of short circuit current and two kinds of special load current are qualitatively analyzed by Fractal correlation dimension algorithm.Secondly,the DC TPSS is divided into power component modules suitable for RT-plus modeling of real-time simulation platform.According to the equivalent circuit and electrical parameters of the existing power elements and lines,the simulation parameters of each power element are calculated and configured into the simulation model of each function module.Build the traction power supply system and vehicle equivalent circuit simulation model,and find out the cause of special traction load current through simulation analysis.A balance reactor is qualitatively analyzed by simulation leading to the high-order harmonic of the feeder current.Finally,a new metro traction feeder protection algorithm based on the impedance characteristics is constructed by making the short-circuit impedance characteristics as the entry point and theoretical derivation,and the setting principle is proposed.RT-plus platform was used to test the reliability of the new protection algorithm by setting short-circuit points and different vehicle operating conditions.It is verified that this protection algorithm can effectively avoid the influence for oscillating currents amounts of experiment data and it has advantages of clear concept,convenient criterion,so it is suitable for feeder protection in a Metro TPSS. |
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