Research On Power Cable Fault Location Method

With application costs decreasing of power cable and rebuilding of power network, power cable is being widely used. But, until now, there have not efficient methods on power cable fault location. Through research on principle and approach, this paper puts forward three new methods in power cable fault location. The first method is based on wavelet reconstruction, and the measured signal which is the difference between the faulty and sound phase current under the high voltage pulse excitation, is transformed using wavelet, and the high frequency component is reconstructed at single scale. Compared with conventional methods, the proposed method is not disturbed by reflected waves from tee joints or other resistance discontinuities, and is not influenced by fault type, and can recognize the reflected wave from the fault point even when the fault point is near to the measuring terminal (so-called dead-zone), and simultaneously, the method reduces the influence of wave speed uncertainty. In the second method, wavelet transform is combined with modal transform, and transient travelling-wave signal is used. After three phase signals are decomposed into their modal components, the wavelet transform coefficient of ground mode can be used to identify approximate position of fault, and the wavelet transform coefficient of aerial mode is used for identifying arrival time of traveling-wave. Because the method utilizes modal transform, the problem of fault inception angle can be avoided , which occurs in almost all conventional methods. The last proposed method is based on the distributed parameter model, the algorithm utilizes searching and iteration methods to locate the fault point. Only using data of single-terminal, the algorithm can eliminate the influences of the fault resistances and it needn't resolve the complicated equation of long line. The methods above have been simulated using EMTP and MATLAB, and the simulation results indicate that, (1) In the fault location method based on wavelet reconstruction, the influences of reflected waves from tee joints or resistance discontinuities except the fault point can be eliminated when the current difference between faulty phase and sound phase is used in fault location. And the problem of wave arrival time and dead-zone can be resolved through wavelet transform of current signal.(2) The influences of wave propagation speed uncertainty can be reduced when the measured current is decomposed using wavelet transform, and the high frequencycomponent is reconstructed at single scale.(3) The location result is not influenced by fault resistance and inception angle when wavelet transform coefficient of aerial mode current is used in fault location.(4) The location results are always affected by fault resistance in almost all conventional impedance methods in fault location, but the application of power balance theory can overcome the shortcoming.(5) The proposed methods have high accuracy in fault location, and the methods are feasible.