Study On Fault Location Algorithm For High-Voltage Transmission Line Under Dynamic Conditions

As an important elements of power system, high-voltage transmission line is the lifeblood of the power system. So, precise fault location method for high-voltage transmission line plays a very important role in ensuring security, stability and economic operation of power system. Yet, it is a complex and dynamic system for power system itself, and long and heavy transmission line systems are often running in the critical stable state based on some economic benefits. When some disturbances or faults occured, a variety of complex and dynamic process will inevitably exist in transmission line system. Due to inability to express the dynamic characteristics of power system, existing fault location algorithms for high-voltage transmission line can not provide an accurate fault location estimate.To solve above problems, a fault location algorithm based on equivalent line parameters for two-terminal transmission line is studied. At the first, the distributed parameter model of two-terminal transmission line and the conventional static fault location algorithm are studied, which is based on two-terminal’s electrical quantities. The algorithm can approximately express the dynamic characteristics on time-domain of power signal using the amplitude change rate of synchronized phasor at two ends of line. Furthermore, the algorithm not only can build the dynamic equation of power transmission line, but also supply the equivalent wave impedance and the equivalent propagation coefficient which are able to express dynamic characteristics of power signal to modify the errors of the conventional static location algorithm under dynamic conditions. Finally the fault location equation under dynamic conditions is established, and an accurate fault location estimate can be attained via Newton iteration method for solving this nonlinear equation. A variety of PSCAD/EMTDC simulation tests under different conditions show that the algorithm is correct and effective, and can yield an accurate fault location estimate independent of fault locations, fault types, fault impedance, operation modes and fault angles. In addition, the simulation results still show that the algorithm has a precise estimate not only under steady conditions, but also under dynamic conditions.A fault location algorithm based on parameter modification for multiple-circuit transmission line on same tower is proposed. Firstly, on the basis of study on the coupling theory of double-circuit transmission line on same tower,6sequence component method is supplied. Then, in-depth study on the decoupling theory of four-circuit transmission line on same tower, the line parameters of actual six-layer vertical tower can be simplified in according to Carson formula. So,12sequence components that are independent from each other can be obtained via decoupling of coupled four-circuit line by the using of12sequence component simplify method. Similarly, because the fault location for multiple-circuit transmission line under power oscillation will have significant errors, a detailed study on the differential equation of positive sequence network for multiple-circuit transmission line is achieved in this paper. After wave impedance and propagation coefficient of positive sequence network are modified by revised parameters, positive sequence fault location equation can be solved via Newton iteration method. PSCAD/EMTDC simulation results show that the proposed algorithm has a higher accuracy compared with the traditional static algorithm when power system is under dynamic conditions, and the results have nothing to do with fault locations, fault types and fault impedance.A fault location algorithm for three-terminal transmission line under dynamic conditions is proposed via extending the fault location algorithm for two-terminal line to three-terminal line when power system is under oscillation. Power signal dynamic model is built using information at three ends of three-terminals, and equivalent parameters at three ends line are estimated. Meanwhile, in according to long line equation, electrical quantities at the trap point can be estimated by electrical quantities of non-fault section and fault section. Then the three-terminal line is equivalent to the two-terminal line. By the using of the principle of the fault location algorithm based on equivalent line parameters for two-terminal transmission line, the three-terminal fault location indices have be obtained, and correct fault section and fault location index are attained according to the fault section identify method. PSCAD/EMTDC simulation results indicate that the proposed algorithm can correctly indentify the fault section under dynamic conditions, and not only has a higher accuracy compared with the traditional static algorithm, but also is independent of fault locations, fault types and fault impedance.A set system of theory and application is built in this paper, including the fault location algorithms for two-terminal line, multiple-circuit line and three-terminal line under dynamic conditions.