On-line Monitoring Research On MOA In Railroad System

Electric railway develops promptly in our country, at present it has exceeded twenty thousand kilometers, so it is important for railroads system to keep its operation safety. Since metal oxide arrester (MOA) has excellent volt-ampere characteristic, it is widely usded in electric railway to ensure power supply reliability. Rail-traction power supply system has many problems, such as much high harmonics , unstable frequency,. voltage fluctuation, many interference sources etc. All these questions can affect and even damage MOA. Once MOA is in failure, it can threat the reliability of railroad power supply. Though the on-line monitoring technology of MOA in power system was a mature technology, yet the on-line monitoring technology of MOA in electric railway is a new question to be discussed .Therefor ,it is very significant for us to research on the on-line monitoring technology of MOA in electric railway.Firstly,The paper simply introduces the present situation and characteristics of electric railway , then imports the concept and working principle of MOA . From the property of MOA, we can know that the current flowing through it is very small in the normal running state, but the capacitive current has little change and resistive current will greatly increase when the arrester damaged. So it is an effective method for MOA to judgeg its health by monitoring resistive current .The system adopts this way to realize detection function. The rail MOA works in different environment with MOA in power supply, yet they have the same theory of monitoring. So the paper combines the development trends of power supply MOA home and abroad with the technical difficulties to analyse them. We study on the lifting wavelet to eliminate much high harmonics and interference source. We also research on correlation analysis method, which is excellent in analysing two signals relativity. The system adopts improved fundamental wave measurement method as control scheme, which is a means combining traditional fundamental wave measurement method with lifting wavelet filtering and correlation analysis method. Comparing to traditional way,it can avoid frequency spectrum leakage of FFT for inaccuracy sampling, and it also can solve the noise question and interference in system.Based on large MATLAB simulation of lifting wavelet and PSPICE simulation for system ,we design the on-line monitoring system of MOA in railroad traction power supply system.It contains three parts: upper PC, slave computer and communication circuit.The the main function of upper PC is to control salve computer and finish the function of monitoring interface.The slave computer is a measuring apparatus for resistive current of railroad MOA.The hardware circuit of system uses DSP TMSLF2407 as a core control chip,this circuit can finish sampling signals, eliminating noise, filtering, data processing and communication to upper PC.We select CAN as the communication bus to achieve communication function, which is facility and easy to enlarge system.Considering the system working in complicated interference environment , we take the double measures to carry out anti-jamming.At last ,we make simulation experiment in laboratory for this system.Through the precision experiment, veracity experiment of itself ,we can prove that the system is correct and credible. Through measuring MOA resistive leakage current experiment of monitoring system, it proves that the system satisfies the need of engineering measurement.