Research On Key Technologies Of Fault Location For High Voltage Transmission Lines

High voltage transmission line is the lifeline of the power system, when it fails, fast and accurate location is very important. As there are many defects in the existing transmission line fault location methods, the research of this paper is based on the following issues:The current algorithms of unsynchronized two-terminal fault location may lead to failure to locate the fault because of the false root. To overcome the defect, a new two-terminal fault location algorithm is proposed. Based on distributed parameter model for the power transmission line, the paper uses the ratio of positive to negative sequence component of voltage or the ratio of voltage positive and fault positive sequence component to eliminate the asynchronous angle and then proposes a new algorithm of two-terminal fault location with asynchronous data based on the monotonicity of the phase. The algorithm without the false roots and the bisection method or secant method can be used to find out the fault position quickly. The algorithm can be applied not only to the single-circuit transmission lines, but also to the double-circuit lines on the same tower.The traditional methods for fault location of teed lines can't identify the fault section correctly when the fault occurs near the teed node, thus failing to locate the fault. To solve this problem, two new branch identification criterion algorithms are proposed based on the principle of equal positive sequence voltage detected at both ends. It is concluded that, the amplitude of fault location function has the following characteristics:the amplitude of the fault location function is monotonically decreasing and over zero at fault point in the fault branch, but it is monotonically decreasing and the value is greater than zero in the healthy branch, so the zero-cross characteristic of the fault location function in the fault branch can be used as the criterion of fault branch; the phase of fault location function has the following characteristics: the phase of fault location function is monotonical and at the head and end the two values differ by approximately 180° at the fault branch, but it is monotonical and at the head and end the two values are approximately equal at the healthy branch, so the size characteristics of the fault location function at the head and that the end can be used as the criterion of fault branch. After identifying the fault section, using the analytical expression for fault distance gets the fault distance. The two branch identification criterion algorithms do not have dead zone of fault location, and remedies the defect of traditional fault location methods in which dead zone of fault location exists. And the two algorithms do not require fault type identification, and only in a few points in the corresponding formula can get the faultdistance, so the procedure is implemented simply, fast. The phase of fault location function used as the criterion of fault branch can be applied not only to T-shaped transmission lines, but also can be used in the multi-terminal transmission lines(N>3).In allusion to the problem that existing traveling wave fault location method for T-shaped transmission line cannot cope with the change of line length, a new traveling wave fault location algorithm for T-shaped transmission line is proposed. Based on existing traveling wave fault location method for T-shaped transmission line, the occurrence moment of the fault obtained by three-terminal calculation or the relation among the traveling wave speeds can be used to judge whether the fault occurs in a certain branch or not, and further the position of the fault point can be calculated.Considering the impact of ling length change, the distance range, within which the misjudgment may appear due to fault point adjacent to the T-connection point, is given.In both the criterion of the fault branch and the expression of the fault location the three-terminal measurement data are fully utilized, and the impact of the error brought by the conductor sag and the change of line length on the measurement data is eliminated a certain extent.