The Research Of Urban Rail Transit DC Traction Power Supply System Grounding Scheme

In recent years,the urban railway system has been a rapid development, more people pay attention to operational safety and reliability of DC traction power supply system for urban rail transit.The DC traction power supply system grounding plays an important role to solve the stray current, rail potential anomalies and systematic short-circuit fault.This paper will divide the research of grounding into two parts,including the three-track rail system and four-track rail system.The main contents:Building and analyzing the model of floating ground and directly grounded. Rail-to-earth distributed parameter model is established,and by the boundary conditions of floating ground and directly grounded, mathematical modesl of suspended ground and directly grounded are obtained.Under the different insulation levels, the suspended ground is simulated to observe characteristics;In the simulation of directly grounded, its characteristics are obtained by comparison between suspended ground and directly grounded.Establishing the diode grounding model. Firstly, by comparative analysis among a single diode grounding, suspended ground and solidly grounded, characteristics of a single diode grounding model are gained. Due to the interaction between the diodes, a mathematical model of the adjoining diode grounding is built, by changing the position of the locomotive,the situations of the adjoining diodes were analyzed and validated by matlab, then the entire line diode grounding model is built, its characteristics are analyzed and the model is illustrated by examples, optimization measures are taken.The analysis of controllable rail potential grounding.The working principle of controllable rail potential grounding is analyzed.Followed,there is a discussion for the relationship between track short circuiting device and protection framework at the different short-circuit fault. Then, a selective protection optimization is proposed.Proposing the optimal voltage control strategy. Due to status quo of track short circuiting device acting frequently, the optimal voltage control method is proposed to make the acting number of track short circuiting device minimize for reducing stray currents.The research on the four-track system grounding. Firstly, the structure of the grounding will be explained, and then in different states of the locomotive, the short-circuit fault protection is analyzed and the grounding principle is indicated,a measure is proposed to determine the fault location inside the locomotive. Finally,the neutral earthing is applied to the four-track system and the method of grounding are designed and its characteristics are analyzed.Through the study of the grounding scheme, solidly grounded causes serious stray current, while the problem of rail potential anomalies exists in the suspended ground and diode grounding,so controllable rail potential ground is the best choice, the selective optimal control make protection of the ground more selective, and the optimal voltage control strategy can minimize stray current in a safe condition; in the four-track system grounding,the maglev and monorail can not determine fault locationin side the locomotive, this problem can be solved by optimizing. The Four tracks reflux system grounding can reduce electromagnetic interference,and the use of neutral earthing make programs improve output voltage by one time without increasing its insulation grade.