Research On Fault Location Of HVDC Line With Distributed Multi-source Coupling Method

In recent years,with the development of the high voltage direct current(HVDC)transmission technology,large capacity HVDC transmission lines are increasing rapidly.As a result,the fault type and the fault probability of HVDC transmission lines also increase.The locating inaccuracy of the line fault point will extend the maintenance time,thus extend the break time of the HVDC transmission lines,which will cause serious economic losses.Therefore,the rapid and accurate detection of fault point has great significance to ensure the reliability and stability of HVDC transmission and increase the power quality of the users.When electromagnetic wave propagates in long distance current transmission lines,the transmission lines can be equaled to a long line model.As the electromagnetic wave propagates in the long line model,a reflected wave will be produced if there is an impedance mismatch point in the transmission line.Based on this principle,this paper put forward a new method applicable to fault detection and localization of high voltage DC long-distance transmission line,using multiple distributed pulse signals.Firstly,inject several signals generated by several distributed signal generating devices into the DC transmission line and receive the reflected waves from the DC transmission line using a signal detecting device;secondly,analyze the characteristics of the reflected waves signal through the data processing terminal.Then,determine whether there is fault point in the DC transmission line according to one group of the reflected waves signal,and determine the fault position through the coupling calculation of multiple groups of reflected waves signals.Simulation results show that the new method using multiple distributed pulse signals can be used for the fault detection and localization of HVDC transmission line over a long distance,the reflected waves have high degree identification,and the fault waveform is clear.In order to determine the starting point of the reflected pulse,and improve the fault location accuracy of the transmission line,wavelet analysis methodis used to determine the input wave head time and the reflected wave head time.Accurate wave head time is obtained through wavelet analysis.Finally,modeling and training the BP neural network algorithm using the wave head time obtained through wavelet analysis as the input and the fault distance as the output to determine fault location.Reasonable BP neural network fault location model is obtained.Combined with wavelet and BP neural network analysis,this new method can identify the fault type accurately and locate the fault point precisely.The new method using multiple distributed pulse signals can improve the accuracy of fault point location of HVDC transmission lines effectively.Also,the accuracy of fault diagnosis and reliability of the fault location of the long distance HVDC transmission line can be improved through on-line monitoring using this new method,which will guarantee the safe and stable operation of power system.