UHVDC Line Traveling Wave Protection Based On Mode Component Decomposing Of Voltage

In recent years, with the UHVDC(Ultra High Voltage Direct Current) transmission technology developed, the application of UHVDC transmission project is becoming more and more popular, for its the ability of transmit power of long distance, high capacity, and the requirement of protection performance is also getting higher and higher, especially the requirement of line protection. Nowadays, the TWP(traveling wave protection) is used in UHVDC transmission project as the main protection of line, which has the advantage of responding rapidly, short cycle data, and the protection performance of TWP would not be influenced by current transformer saturation, system oscillation. However, reliability of Circuit Protection Device of domestic is not high, within easily disoperation and other issues, among the actual project; In theoretical, the research of line protection are more concentrated in the application of new algorithms to improve the speed relay and the use of new mathematical methods to analyze faults, since the algorithm has more stringent requirements on the operating conditions and the actual working conditions constrained by factors such as operating systems and restrictions, which made more difficult to carry out the practical application and promotion.In this paper, the status and applications of UHVDC line TWP protection were analyzed, and then the DC line traveling wave theory and its propagation characteristics were introduced. Combined with the TWP scheme applied in practical engineering, the advantages and disadvantages of the current TWP criterion were analyzed. The UHVDC transmission system is introduced, based on the PSCAD/EMTDC simulation software, and the typical TWP faults are simulated and studied. Based on the respond characteristics of characteristic parameters of TWP under different kinds of faults, the aerial mode component and earth mode component of the fault voltage were decomposed to analyze the criterion of internal or external faults, and propose the criterion of faulty pole. And the operation equation of TWP was concluded and criterion setting value was calculated. And then the impact of the transition resistance of the TWP criterion was analyzed. Finally, this criterion was proved validity by the yun-guang UHVDC model using a set of logic control system to protect two polar lines.