Study On Fault Location Based On Curving Fitting Method

Accurate fault location for high voltage transmission line is an important act to ensure the safety, stabilization and economy of the power system and pays increasingly important role in social life. For many years, accurate fault location of high voltage transmission line has been paid much attention to.Firstly, some existing methods of transmission line fault location are summarized and classified and those methods' primary merits and disadvantages are analyzed as well in this dissertation. Analyzing the algorithms based on fundamental frequency fault location, we know that the precision of extracting the fundamental component of fault voltage and current influences the precision of fault location directly. Secondly, two common methods of extracting the fundamental component are introduced and analyzed. Algorithms based on sinusoidal function model just need short data window and compute uncomplexly, but the actual power signals usually contain nonperiodic component and high frequency component, so the band-pass filter is cooperated with. Algorithms based on periodic function model contain full-cycle fourier algorithm and half-cycle fourier algorithm and are adapt to extracting the fundamental component. The full-cycle fourier algorithm needs one cycle of sampling data and needs at least one cycle to respond; although the half-cycle fourier algorithm only need half cycle of sampling data, the precision of it is not as good as the full-cycle fourier algorithm. The actual recording data show that the corresponding relays can cut off the fault line in one cycle after the fault occurs.It's impossible to compute the fundamental component exactly with the full-cycle fourier algorithm when the recording data is less than a cycle. In this dissertation, a math-model based on fourier series is set up to fit the fault voltage and current, obtain the coefficients of fourier series with the least-square method, select and confirm the fitting equation by residual plot and sum of squares due to error of fault voltage (current) and fitting voltage (current), and then a whole cycle of fault voltage (current) can be calculated from the fitting equations, the fundamental component of them is calculated by the full-cycle fourier algorithm finally. Simulation of faults in HV transmission line is performed in ATP-EMTP. First, the fault voltage (current) is fitted with the method based on fourier series. The results show that there are good fitting equations to most of the faults. Second, the author locates the fault point with fitted fault voltage and current and compares with the fault location results that obtained from half-cycle fourier algorithm and full-cycle fourier algorithm. The results show that the precision of fault location with fitted fault voltage and current are close to those obtained from full-cycle fourier algorithm and much better than those obtained from half-cycle fourier algorithm.