Research On Electromagnetic Transient And Safety Protection Of Grounding System Of Electric Multiple Units

With the rapid development of high-speed railway(HSR),the requirements for safe and reliable operation of electric multiple units(EMUs)are more stringent,which bring new challenges and technical issues for researchers.In the operation,EMUs inevitably goes through many electromagnetic transient processes including rising and lowering pantograph,passing electrical split-phase insulator and vibration detachment arcing between pantograph head(PH)and catenary.These scenarios cause surges on the train body(TB),influencing the grounding safety of EMUs.Considering that the TB surge over-voltage may cause damage to on-board equipment,logic disorder of control system,burning of electronic components,etc.,and the excellent TB grounding pattern is an important factor of limiting TB over-voltages,it is necessary to analyze the electromagnetic transients and the safety protection of grounding system under multiple working conditions,on the basis of establishing accurate vehicle-grid equivalent models.These works help to provide accurate data sources and theoretical research basis for ensuring the safety and long-term reliable service of on-board equipment.The main work of the thesis is summarized as follows.1)The traction network model of viaduct path and tunnel path is extended.Aimed at the traction network system of viaduct path and tunnel path,with the consideration of the nonlinear impedance frequency characteristics of grounding steel bars,broadband-circuit model is applied to express the electrical grounding system.From the inside and outside of EMUs,the influential factors of the TB voltages and the return traction currents of entering TB are investigated and determined.On this basis,the construction method of the electric coupling model of grounding system of EMUs applicable to all kinds of electromagnetic transient scenarios is improved.Combined with the testing data of the experiments in the passenger dedicated railway line from Xian to Chengdu and the existing literatures,the comparison with the simulation results of traditional methods and so on,the validity and accuracy of the extended models is proved.2)The TB over-voltage distributional behaviors considering the typical operating conditions of EMUs' leaving HSR station,including rising PH,normal drive and passing insulated joints at the traction return current cut-off points,are investigated.CRH2-type EMUs is taken as an example and vehicle-grid equivalent circuit model is established.On the basis of verifying the accuracy of vehicle-grid model,the effects of the grounding layout of roof high-voltage cable shielding layer and the grounding mode of TB on the TB over-voltage behaviors are revealed using simulation.Some countermeasures of TB over-voltage are given from the angle of grounding optimization.3)Focusing on the electromagnetic transient process of short marshalling EMUs passing the articulated split-phase insulator with ground-switch automatic convertor,the CRH2-type EMUs is taken as instance for analyses.Vehicle-grid equivalent circuit model is built and Habedank arc model is added to simulate the arc generated by the operations of vacuum breakers.The behaviors of PH over-voltages and TB over-voltages caused by the operation of switches are obtained,as well as the influential laws of switching phase angle and different TB grounding patterns on the TB over-voltages.Then,taking the CRH380BL-type EMUs as instance,the process of long marshalling EMUs passing articulated split-phase insulator with locomotive-breaker automatic convertor(LAC)is investigated.By the means of numerical solution and software simulation,the over-voltage behaviors of PH and TB and the influential laws of the factors including instantaneous phase angle of catenary voltage,etc.,on the over-voltages are obtained for the each transient process.In the studies of numerical solution,the vehicle-grid distributed parameter models,fully involving the influential factors of TB over-voltages,are established.Based on the transmission line theory,the distributed parameter transmission line elements are simplified as the lumped parameter elements by using Bergeron algorithm.Further,over-voltages are solved by using the general lumped parameter numerical solution method.In the studies of software simulation,the influential factors of TB over-voltages are fully involved to establish the simulation models for the each transient processes.In addition,traditional lumped parameter circuit is adopted to simulate the vehicle-grid system in the area of EMUs.The comparison of numerical solutions and software simulations proves that it is still effective to adopt the equivalence of lumped parameter circuit to simulate and analyze the over-voltages.The broadband impedance behaviors of viaduct grounding system and the coupling between traction network loop circuit and viaduct pier loop circuit are further considered to build the vehicle-grid electrical simulation models for long marshalling EMUs passing articulated split-phase insulator with LAC on the viaduct path.The TB over-voltage distributions in the transient processes of ordinary path and viaduct path are compared.The over-voltage suppression measures from the angle of changing the TB grounding layout are proposed and its effectiveness is verified.4)Because multiple EMUs may run on the same path of power supply feeder and splitphase insulator at the same time,in order to simulate and analyze the impact of PH arcing on the vehicle roof from multi-angled,more comprehensive,multi-operating,and more closely related to the reality,the multiple scenarios of multiple EMUs encountering PH arcing are focused.The vehicle-grid equivalent models are established to deeply analyze the electromagnetic transients.The scenarios to be analyzed are divided according to the case if there is running EMUs in the split-phase region.The one includes the case of multiple EMUs running on the same feeder and the case of multiple EMUs running on the different feeders.The other one refers to the case that multiple EMUs run on the split-phase region and the feeder path at the same time.For the above scenarios,the over-voltage behaviors of PH and TB are achieved,including the mutual effects of over-voltages of multiple EMUs and the comparison of different scenarios.5)The failure event that a door of EMUs could not open normally in Chinese Wuxi Station and the failure event that wrong closure of a door of EMUs occurs at Chinese Chang-chun station are focused.On the basis of figuring out the electromagnetic interference(EMI)mechanism of TB over-voltages on the speed sensor detection of EMUs in the different scenarios,the electromagnetic coupling model which can reflect the relational formula between the TB voltage and the EMI of speed sensor is established.On this basis,this paper proposes the evaluation scheme for the EMI of speed sensor detection.The evaluation scheme for two failure events are,respectively,verified according to the testing results of Chinese Nanjing electric multiple unit station and the testing results of literature.Based on the verification,the applications of evaluation scheme under multiple operational scenarios are made.Taking the EMUs with the decentralized ground as example,the fact that the increase of TB groundings is an effective method of lowering TB surge over-voltages is considered,and the feasibility of increasing TB groundings to suppress the EMI of speed detection under different electromagnetic transient scenarios is investigated.The relationship between the voltage waveform behaviors of TB and the interference voltage of speed sensor is further revealed.