Study On The Failure Of Traction Return System Under Direct Power Supply Mode

Traction return is a continuous high current,and many devices are associated with its return path.Abnormal traction return will threaten the safe operation of the railway system.The general-speed railway is an important part of the main railway in my country.Its traction network mainly adopts direct power supply.This paper establishes the traction power supply system model of this type of railway based on CDEGS software,and simulates and analyzes the main return conductors in the traction return system under different conditions.Voltage and current characteristics,and two common faults caused by traction return on this type of railway were studied in detail.The thesis focuses on the following aspects:The first is the establishment of a traction return research model.A suitable traction power supply system model is the prerequisite for studying the relevant laws of traction return.The article briefly introduces the software CDEGS used for modeling,and gives the measured data related to the modeling of the traction power supply system.Combined with the characteristics of the simulation software and the measured data,the traction power supply system is equivalent according to the research needs,and the main explanation is The equivalent processing process of the soil,traction network,electric locomotive and traction substation in the model is established,and finally the traction power supply system model of single and double track railway under direct supply mode is established.Then,based on the established single-line traction power supply system model,the voltage and current characteristics of the main return conductors in the traction return system under different conditions are studied.Based on the simulation data,the traction return distribution law of the traction substation under the complete state of the traction return system,the rail potential and current distribution law,and the return line current distribution law are summarized based on the simulation data.Two traction return systems with open rails on one side and open on both sides of the rail are discussed.The abnormal changes in the traction return state of the open circuit state and the rail through the signal cable shielding layer and the signal building ground net short-circuited state,and the possible damage to the railway equipment caused by the abnormal change is explained.The unbalanced return flow of the two rails may cause overvoltage faults on the secondary side of the choke transformer.In this article,the BES2 type choke transformer is taken as an example.A simulation circuit model of the choke transformer is established based on the Multisim software,and the choke transformer is simulated.The occurrence process of overvoltage on the secondary side,and the occurrence characteristics of overvoltage faults on the secondary side of the choke transformer are studied.Finally,the influencing factors of the overvoltage fault on the secondary side of the choke transformer are analyzed,and the change law of the secondary side voltage of the choke transformer under the influence of the unbalanced traction current is discussed.Studies have shown that after the air switch of the choke transformer is disconnected under the influence of a large unbalanced traction current,the secondary circuit impedance increases sharply,resulting in the occurrence of secondary side overvoltage faults;the secondary side voltage U2 and the rail unbalanced current Iub meet:U2=0.09Iub(switch closed);U2=15.3Iub(switch tripped).From the perspective of phenomenon,the breakdown of the insulation pad between the rail and the fixed steel plate of the switch machine is caused by the leakage of the rail traction return flow.Based on the simulation results of the failure state of the traction return system,it is guessed that the ground resistance of the fixed steel plate of the switch machine is too small.It is the cause of the insulation pad breakdown.Based on the principle of series partial pressure,a set of measurement plan for the ground resistance of the fixed steel plate of the switch machine was designed.Through field measurement,the fact that the ground resistance of the fixed steel plate of the switch machine was too small was confirmed;through excavation The investigation found that the direct cause of the insulation pad breakdown was the wrong connection between the cable shielding layer and the junction box of the switch machine,and targeted preventive measures were proposed.