Research On Electromagnetic Transients Of Uninterruptible Power Passing Neutral Section Of Electric Railways

The power supply mode adopted by the electrified railway is AC,single phase,power frequency,and commutation.In order to avoid phase-to-phase short circuit,an electrical isolation device,i.e.a neutral section device needs to be set at every distance on the contact network.The common auto-passing neutral section methods have certain transient problems of over-voltage,ferromagnetic resonance and magnetizing inrush current,which endanger the safe operation of electrified railways.In addition,the long power-off time will cause the locomotive speed to drop significantly and affects the transportation efficiency.Therefore,it is urgent to research an auto-passing neutral section technology with safety,reliability,and a short power-off time.Firstly,the common schemes and technical characteristics of auto-passing neutral section are sorted out.From the perspective of technological development,this thesis determined to focus on two improved auto-passing neutral section schemes:the ground switch scheme using electronic switches instead of vacuum circuit breakers,and the flexible scheme based on two-level converter.Both of these schemes have the advantages of short power-off time and effective suppression of transient overvoltage,and with the rapid development of power electronics technology,such schemes have broader application prospects.Then,the topology and passing neutral section mode of the traction power supply system are analyzed,and the technical characteristics of the three traditional methods and the new methods in the research stage are summarized.This thesis deeply investigates the transient problems that are common in the process of passing neutral section,analyzes the occurrence probability and damage degree of over-voltage phenomenon with the measured data,and research the electromagnetic transient process from the theoretical point of view.Aiming at the electronic switch scheme,this thesis proposes a method using a set of anti-parallel IGBTs as ground switches instead of vacuum circuit breakers.The accuracy of the model is verified by comparing simulation and measured data.The minimum power-off time of the scheme is calculated and the simulation results at that time are given The relationship between the closing angle and the overvoltage level is analyzed.For the transient overvoltage phenomenon,the suppression measures of the parallel RC protection device are proposed,and the simulation results verify its effectiveness under different closing angles and different operating conditions.Aiming at the flexible scheme,the two-level converter is selected as the main circuit structure of the flexible device.Then the simulation model of this scheme is built and the control strategy of the converter is given.Research have shown that the electronic switch scheme can weaken the operating overvoltage problem and shorten the train’s power-off time.The suppression scheme of the parallel RC protection device can effectively suppress the transient overvoltage under different closing angles and different operating conditions.The flexible scheme can well realize the uninterruptible power process of passing neutral section,and there is almost no transient phenomenon in this process.