Studies On Traveling Wave Based Fault Location For Multi-Terminal Cable System

With the rapid development of society, power cable, especially the underground cable has been more and more widely used. On count of covering a small area, supply power reliably and being safe to person, cable gains social acceptance. But as the growth of the operating time, the probability of fault also gains. In the event of fault will lead to greater economic losses. Therefore the accuracy of power cable fault location is of great significance.The thesis introduces the basic principle of traveling wave based fault location. First describe the formation and propagation of traveling wave, including the equation and the phenomenon of refraction and reflection. The three-phase lines have significant electromagnetic coupling between conductors. Modal transformation can be used in order to decouple the traveling-wave equations in phase coordinates into independent equations for each mode. Then analyze the polarity of the traveling wave in lines, and introduce the typical methods of traveling wave based fault location.The thesis presents a novel wavelet-based fault-location scheme for two-terminal aged cable systems when synchronized digital fault recorded data are available at each busbar. To estimates the fault location in multiend-aged cable systems, we proposed a scheme using the theory of wavelet singularity detection, by which we can judge the fault section. In this scheme, the arriving time of the first and second voltage traveling waves at each buses must be identified reliably. Wavelet transform is applied on modal coordinates instead of the phase coordinates. Considering the big change in the propagation velocity of the traveling waves in aged cable, the new scheme has eliminate the impact of velocity on calculations. The scheme is also valid when the faults are very close to busbars.The thesis presents a novel wavelet-based fault-location scheme for multiend aged cable systems. To estimates the fault location in three-terminal cable systems, we classified them to continuous three-terminal cables and T-connected three-terminal cables. By analyzing the mathematic relation of the arriving time of the first voltage traveling waves of each busbar, we can identify the fault section. Using the data of two terminals of fault section, we can locate the fault. To fault location of multiend cable system, we propose a judge matrix, using which we can deduce the fault section. Analogously we can locate the fault using the data of two terminals of fault section.The simulation analysis has been done to this scheme about the various factors in various situations in power cable would be encountered by EMTP/ATP simulation software and MATLAB filtering. The new method provides very good accuracy. It presented quite accurate results for all fault conditions evaluated. It is not affected by the limitation of zero voltage point-on-wave faults, which is regarded as a major problem for pure traveling-wave techniques.