Research Of Cable Fault Location Based On The Low Voltage Pulse Method

With the constant development of our economy,electric power network, communication network and Internet are expanding continuously,and the number of a variety of cable lines are increasing ceaselessly, the cable fault is also increasing.If we can’t find the location of the cable fault timely,quickly,accurately and remove the fault,and the fault will affect the quality of people’s lives and cause huge losses to the whole national economy. Therefore, analyzing the causes and types of cable fault and developing the way to find the fault fast and accurately is very necessary.According to the principle,the method of fault location can be divided into the bridge method and the traveling wave method. The bridge method has been used very little due to its accuracy and scope. Because the location principle of the traveling wave method is multiple,the traveling wave method can test different kinds of cable fault in different environment,thus the application of the traveling wave method is more and more extensively. According to the principle, the traveling wave method can be divided into the low voltage pulse reflection method, the pulsed voltage, pulsed current method, the second pulse method and some other improved ranging methods. We will introduce the principles, characteristics and scope of application of these methods systematically in this article.Ranging of the traveling wave method is using the propagation time of the traveling wave in the cable to determine the distance to fault. If the distance to fault testing is very far, the number of the traveling wave refraction and reflection will be very little and there is no overlap between the traveling waves, and the traveling wave method is correct.However,if the fault point is close to the test point, the ranging precision of these methods will be very low,these place we can’t test is called the blind spots of cables ranging. This article analyzes the the traveling wave in the blind spot,then we can learn that using a rectangular wave will be better if we test the open circuit or short circuit fault in the blind spots by the low voltage pulse reflection method.Using a rectangular wave,there will be an obvious inflection point between the launch wave and the reflected wave.We can find this inflection point manually or by wavelet transform.Then we can determine the time difference between the reflected wave with the launch and complete the ranging work.The visualization degree of the existing range finder is low,the operation is complex,the function is customized,the ability to adapt to a variety of fault and the environment is poor. This article describes a data processing system of a cable fault location based on virtual instrument.We get the waveform data by using a high-speed data acquisition board.We write interface and data processing code by the VB and MATLAB.Thus we can complet the work of data display and processing in the computer. We just need to drag the mouse,and the work of manual ranging wille done. And there are correlation algorithm,autocorrelation algorithm and wavelet transform three automation ranging methods in the data processing system. The system has a high degree of visualization,and is easy to operate.The result of the system is accurate.