Research On Fault Location Algorithm For Complex Transmission Lines

Accurate fault location for transmission lines can achieve quick elimination of faults and immediate recovery of power supply,which is beneficial to reduce the economic loss caused by power outage.With transmission capacity of power system increasing,limits of transmission line corridor are becoming increasingly more obvious,and in the process of renovation and expansion for transmission lines,new types and new structures for lines appear considering the commercial and cost reasons,different from existing single-circuit and double-circuit lines.These new structures tend to contain some circumstances,such as installing series-compensated device,expanding lines' length and increasing line numbers based on existing lines,and crossing lower voltage classes for power transmission when constructing new lines.The paper has chosen three kinds of line types,including the series-compensated double-circuit transmission lines,incomplete-journey double-circuit lines and crossing span transmission lines,and they are called by a joint name,complex transmission lines.The paper has conducted research on fault location for complex transmission lines base on these three line structures,and the main researches and achievements are as follows:(1)Based on the distributed parameter model,a fault location algorithm of the time domain and power frequency quality for the series-compensated double-circuit transmission lines are presented respectively.Both simulation and comparison are made in both of them.In the proposed power frequency quality algorithm,voltage of series compensated device are eliminated based on the features that sequence voltages at the fault point calculated from opposite buses are equal,and that current directions through series compensated device remain constant,and utilizing that transition resistance is pure resistant at the fault point,the two-terminal fault location algorithm which is suitable for all fault type can be implemented.In the fault location algorithm for the series-compensated double-circuit transmission lines based on distributed parameter model in time domain,the current of the series-compensated device can be derived by the relationship between currents and voltages at the fault point based on the Bergeron model.Then,the universal fault location can be implemented by using the relationship between currents of two sides of the series-compensated device.The location equation adopts different constraint conditions about the fault distance according to the fault position relative to the series-compensated device,and can be solved by the least square method.Thus,the optimal solution along the line is the correct fault location.Both of the proposed algorithms do not depend on the equivalent model of series compensated device and is not affected by the nonlinear V-A characteristic of MOV.In addition,they do not demand the fault type,and there exists no fault-location identification and pseudo root elimination problem.Both of them can be chosen according to practical situations an demands on site.The simulation results show that both of the proposed algorithm have high accuracy.(2)Aimed at the incomplete-journey double-circuit lines,a fault section identification and accurate fault-location algorithm based on the distribution parameter model is proposed.Based on the positive-sequence component network,in the demarcation points of incomplete-journey double circuits,the section positionfunctions are constructed by utilizing the phase step jump characteristic of hyperbolic tangent function.Judging the denominator of section-identification functions and the plus or minus of identification functions phase can determine the fault section,and distinguish the single line fault from interline fault.Fault section identification has simple theory and clear procedure.After determining the fault section,the phase transformation theory can be applied to choose modulus to achieve the fault accurate location.The simulation results verify the correctness of this algorithm.(3)Focus on angled space crossed transmission lines,the calculation method for mutual impedance isdeduced in the paper,and the characteristic of mutual impedance coefficient along the line is analyzed.Based onthe segmented nominal-? line model,in which mutual impedance of each section is obtained by Neuman's Integral,the location equation is derived by utilizingthe feature that the voltages calculated from two sidesare equal at the fault point.Simulations in PSCADcompare the differences of fault-location resultsbetween in the condition of considering and ig noringcoupling effect of space crossed transmission lines.Thecalculation results demonstrate that the proposedalgorithm has higher accuracy,and is not affected byfault types,which has certain engineering practical value.