Diagnosing And Monitoring Methods Of Power Cables Fault

Since the power cable having many advantages such as smaller volume, much more safety, it is extensively used in power supply system. But once fault occurs in the power cable, it is difficult to determine the fault location, and may disable the power supply. So it is of great significance to make on-line fault diagnosis and monitoring on the power cable. Off-line fault location for power cable and on-line fault location for overhead transmission line have been accomplished in the past several decades. In this paper, normal fault location methods and new technologies are analyzed and compared systematically. Several important and difficult problems should be thought of carefully. Firstly, whether or not can effective traveling wave due to cable fault be found to locate the fault point in cable system whose transformer neutral point non-grounded? Secondly, what's the characteristic of the traveling wave during its propagation? Thirdly, will the fault point characteristic affect the traveling wave? Fourthly, how will the traveling wave change at the measuring point? And the last but not the least, how to determine accurately the arrival time of the traveling wave?This paper created a sample power cable system model with a transient simulation tool PSCAD/EMTDC based on a 35kV XLPE power cable. Within this model, the characteristic of fault current is simulated in different grounding modes, and so to answer the question whether or not effective traveling wave can be found in cable system whose transformer neutral point non-grounded. The characteristic of fault point is simulated to determine its effect to traveling wave. Besides, a spectral analysis is made to the fault current traveling wave. Using wavelet transform and local module maximum method to find break point is adopted, and judged the question whether or not the fault is happened by the criterion of fault traveling wave singularity. If that's ture, the fault distance is worked out with the traveling wave arithmetic of fault location. As a case, on-line fault location is made to a sample power cable using wavelets, and thus to validate the feasibility of on-line fault location.For the usability of further testing the thesis and studying, design hardware and software of a on-line monitoring system of power cable fault location. The hardware of the system mainly including DSP(Digital Signal Processing) minimal system design, A/D conversion circuit design, power supply module design, the memory modulecircuitis designed, and the logical control module circuitis designed, and data transmission based on GPRS network. Data processing systems sotf mainly includinganalgorithm to pick-up the arrival time of the traveling wave based on Bd wavelet. Wemake simulation experiment and on-line debug in laboratory for this system, it provesthat the system satisfies the need of engineering measurement.