Research On Short-circuit Fault Location Method For Cable-overhead Hybrid Distribution Lines

The basis and precondition of distribution power supply network's fault isolation,removal and restoration are the fault of the network located reliable and accurate.With the wide application of cable lines,the number of the hybrid distribution network is increasing.Therefore,it is of great practical significance to study the fault location of the hybrid distribution network.Because of the complexity of the fault travelling wave in distribution power supply network,it is very difficult to identify the fault reflection wave from the traveling waves which measured from the single side of the line.Single terminal method of traveling wave fault location,which has no external signal sources,is not suitable for the fault location of the hybrid distribution network.Double terminal method of traveling wave fault location only needs to detected the time of the initial fault traveling wave to the both ends of the line.It does not have to consider the refraction waves and reflected waves.So it can accurately locate the fault of the line.Double terminal method of traveling wave fault location is adopted in this paper.Due to the great difference between the traveling wave velocity in the overhead line and the cable line,the principle of the traditional traveling wave method is no longer applicable to the overhead-cable hybrid line.For hybrid transmission lines,the current fault location method used in engineering is wave speed coincidence method which based on the double end distance measurement.In order to solve the problem of different parameters of the two section line,the cable parameters have converted into overhead line parameters,which may bring deviation.To solve this problem,a fault search algorithm based on VMD algorithm and time variable is proposed in this paper.Based on the length of each line and wave velocity on different lines,the algorithm transforms the space length of each line into the corresponding time length.Then it starts the search of the time points corresponding to the fault from the beginning of the line.By using phase mode transformation and spectrum analysis,the method is based on the double end traveling wave method.It extracts fault line wave head with more accurate VMD algorithm.To reduce the error,time interval screening method is used to determine the time interval of wave head acquisition.This paper uses the algorithm to locate the fault in hybrid transmission lines.Finally,To prove the effectiveness of the method,this paper obtains the fault data through PSCAD simulation and program with MATLAB software.The traveling wave will attenuates or distort during transmission,which makes a certain error in the detection of the wave head.A fault location method of hybrid transmission lines based on phase comparison is presented in this paper.In order to reduce the fault interval,a number of current measurement points are installed on the line model.So the accuracy of wave head detection is raised.To solve the error which caused by the spectrum leakage,a phase comparison method based on Kaiser self convolution window's FFT is proposed by this paper.The fault section is judged by comparing the phase difference between adjacent measured points,which makes the fault interval and phase difference determinate accurately.In this method,the wave velocity is measured online,which eliminating the influence of the wave velocity's uncertainty on the positioning results.The simulation result proves that this method has a high accuracy on multi branch hybrid transmission lines.