Research On Fault Location Algorithm For HV Transmission Lines

Fault location for HV transmission lines can detect the fault point promptly and accurately, which can not only reduce labor intensity of line patrol and repair the damaged line in time, but also find out indiscoverable faults to ensure power supply reliability. Accurate location has great significance for safe, stable and economic operation of power system. Based on fault analysis method, fault location methods for HV transmission line are studied and discussed from the following aspects:One-end power frequency fault location algorithms mainly include linear equation method, iterative method, quadratic equation method and the last two ones are more commonly used. Both iterative and quadratic equation methods need system impedance and have pseudo problem. For earth faults, the analytic solution of fault distance can be directly obtained from linear relationships among short-circuit currents of three sequence networks at the fault point, so pseudo problem can be solved. Based on distributed parameter model, location equations for different types of faults are deduced according to boundary conditions and pure resistance character of fault impedance, so the effect of distributed capacitance can be overcomed.There is not enough information for one-end power frequency fault location, so it cannot overcome the effect of fault resistance and system parameter at the same time. To eliminate effect of fault resistance, most one-end methods bring in system impedance. When system impedance varies, fault location accuracy will be influenced inevitably. The influence of system impedance at remote end is analysed from theory and simulaton. To reduce error produced by given vaule of system impedance, we can calculate impedance using measuring quantities when normal operation and there are disturbances in superior system.Whether fundamental component of fault signals is extracted precisely or not will directly influence fault location accuracy of power frequency algorithms. Besides fundamental and harmonic components, fault signals include much decaying DC component and non-integral harmonics, which will reduce filter accuracy of traditional Fourier algoirithm and increase fault location error. Using low-pass filter to filtrate high-frequency component and improved Fourier algorithms to eliminate the influence of decaying DC component can lower filter error, and therefore fault location accuracy will be improved. With the development of communication techniques, research on two-end fault location methods made great progress. Though two-end method needs communication channel, it can improve location accuracy by overcoming the effect of fault resistance and system impedance. Two-end methods are divided into two-end data synchronized and without synchronization algorithm. The second method has better practical value. For the location error produced by line parameter change with environmental condition, a two-end time domain fault location method based on line parameter estimation is proposed. The algorithm calculates positive sequence parameter and asynchronous time, and then implements location in time domain. The method can not only overcome error produced by the uncertainty of line parameter and two-end being asynchronous but also avoid the effect of filter method. Besides, result of location is expressed by the ratio of fault distance to whole-length of transmission line, so the location result will not be influenced by line real length change. The simulation results show this algorithm can realize accurate fault location in several milliseconds.Besides phase coupling, double-circuit lines own line coupled inductance and can be decoupled by six-sequence component transform. There is no system impedance in differential network, with what a new one-end fault location algorithm is proposed based on distributed parameter model. A universal location equation is obtained under general fault condition. According to the boundary conditions of different single-line faults, unified relations between common sequence and differential sequence currents at the fault point are founded, and then common sequence currents in the equation are removed, so the unified location equation for single-line faults could be obtained. This method can be implemented easily and there’s no need for phase selection. Theoretically, this method is not influenced by single-line fault type, distributed capacitance, fault resistance and system impedance. The simulation results show this algorithm owns high accuracy.