Research On Circuit Design Of Railway Signaling SPD

As the artery of material circulation in our country,railway transportation makes great contribution to the national economic development.Railway signaling system is the"nerve center" of the safe transportation,whereas lightning is one of the most significant factors that affect the normal operation of railway signaling equipments.Installing Surge Protection Device(SPD)is the main lightning protection measures taken for railway signaling line.In recent years,frequent occurrence of train accidents which has been attributed to lightning shows the fact that the design of the existing SPD is of low reasonableness and low reliability.Based on this occasion,in order to improve the existing two-stage SPD circuit,this paper clarifies the performance and function of each device in SPD by theoretical analysis,simulation and test,in depth study of the working principle and design principles of SPD circuit,and improve the existing two-stage SPD circuit.The main content of this paper is as follows:Firstly,this paper studies the lightning current and lightning energy distribution from the frequency domain.Then a series of tests on the characteristics of common surge suppression device,such as metal oxide varistor(MOV)and gas discharge tube(GDT)has been made.These efforts provides precondition for the subsequent theoretical analysis.Meanwhile,for the purpose of testing the results of SPD circuit simulation,this paper makes an automatic surge test system based on the virtual instrument.This system can generate 1.2/50?s and 10/700?s these two standard voltage pulse waveform in the provisions of the GB/T 17626.5-2008 "Electromagnetic compatibility-Testing and measurement techniques-Surge(impact)immunity test ",and it has a friendly human-computer interaction interface,which can accomplish the task of automatic measurement,data storage,and can remarkably improve the efficiency of the test.Next,this paper analyzes the theory of the two-stage SPD protection circuit,the simulation and test of different SPD combinational circuits are carried out by using PSCAD/EMTDC simulation software and self-made surge test system.Based on the theoretical analysis,simulation and test results,the guiding principles of railway signaling SPD circuit design are given.The main results of this paper are demonstrated in the following:1.The primary protection of the two-stage SPD protection circuit should adopt single chip GDT parallel connected mode,and the multiple GDT parallel connected will lead to the increase of the breakdown voltage.2.The secondary protection of the two-stage SPD protection circuit adopts the multi-chip MOV device design,which can increase the flow rate of SPD,reduce the residual pressure,and improve the reliability of protection.3.The decoupling elements between the two-stage SPD circuits can be selected from inductance and resistance.Inductance plays the role of time delay and partial pressure,while resistance is to the partial pressure.By transient circuit analysis,the time delay of inductance can be obtained quantitatively.Inductance decoupling is suitable for the protection of low speed communication occasions,the resistance decoupling can be used for high speed communication occasions protection.4.Based on the above research results,the design and improvement of the existing two-stage SPD circuit are carried out,and the protection performance of SPD is improved.The SPD design guiding principle formed by the above research results has a certain reference value for improving the overall protection performance of SPD in practical application.