Research On Electrical Distribution Characteristics And Optimization Of Train Network System Under Short Circuit Impulse

After a short-circuit fault occurs in the traction network,the feeder protection in the substation needs a short delay time to remove the fault.During the fault period,the shortcircuit current will cause a series of over-voltage and over-current problems in the train and network systems.For example,the current in the conductors of the traction network(contact wires,return wires,rail,etc)will rise rapidly;short-circuit current is injected into the rail to make the rail potential too high;the short current flows into the train body through the protective grounding and generates train body overvoltage and train grounding system overcurrent.Focusing on these electrical problems,this thesis studies theory derivation,distribution characteristics,influencing factors and restraining measures of the traction network conductor current,rail potential,train body potential and body return.The research results for safety of railway operation and equipment reliable work is of great significance.First of all,the expressions of the traction power supply system’s short-circuit impedance and the current distribution in conductors of the traction network is giving when the T-R is short-circuited.Based on the obtained current distribution,the rail potential,space power frequency magnetic field,train body potential and body return current is calculated and analyzed.Among them,when deriving the rail potential expression,the mutual inductance between the conductors and the influence of the on-line shunting are considered;when deriving the expression of the train body potential and body return current,the calculation result can be more accurate by taking into account the influence of the inductive coupling between train and traction network.Taking the CRH3 train grounding method as an example,the phasor expressions of the conduction current and the induced current of the train body are deduced.Through the analysis of the phase relationship between the two,it is concluded that considering the inductive coupling between train and traction network will increase the train body potential and body return current.Secondly,according to the electrical coupling relationship between the traction network,the train grounding system and the ground,a "train-network-ground" coupling simulation model is constructed.Using simulation to calculate and compare with the measured data,it is concluded that the simulated value of the potential difference between the train body and the rail when considering the inductive coupling between the vehicle network is 1.04 V smaller than the measured value,and the error is 8.9%.When the inductive coupling is not considered,the simulated value is 6.30 V smaller than the measured value,and the error is 54.0%,which verifies the correctness of the theoretical analysis and shows that the simulated result considering the inductive coupling will be more consistent with the measured value.Then,on the basis of the accuracy of the simulation model,the study of the rail potential,train body potential and body return distribution characteristics during a short circuit was carried out.The influence of the power supply mode of the traction network,the leakage resistance of the rail on the rail potential,the equivalent impedance of the train body to the axle end,the position of the short-circuit point,the position of the train and the leakage resistance of the rail on the train body potential and body current are successively analyzed.Finally,the simulation model is used to carry out the research on rail potential,train body potential and body current suppression scheme during short circuit.In terms of rail potential:Analyze the suppression effects of the three schemes of horizontal rail connection between up and down,adding integrated grounding conductor and horizontal rail connection + integrated grounding conductor.In terms of train body potential and body current: As the original protective grounding scheme of the train has the disadvantage that the potential difference between the terminal car body and the rail is large,the pros and cons of three new schemes,direct grounding,series resistance grounding and asymmetric grounding,are analyzed to suppress train body potential and body return current.