Protection Of Transmission Line Traveling Wave Longitudinal Direction

With the continuous development of Extra high voltage (EHV) transmission lines and Ultra high voltage (UHV) lines carried out in china, higher requirement bring forward for the power system security and stabilization and the transmission line protection. High speed clearance of transmission line fault is recognized as an effective way for increasing power transmission capability and improving the transient stability. However, conventional protection techniques used fundamental frequency components. To extract accurate fundamental components, it needs a longer period of time filtering transient components. That is, conventional protections have inherent shortages in improving operation speed. On the other hand, protections based on travelling waves can not only operate at ultra high speed, but avoid the influence of fault resistance, power swing, CT saturation, series compensation capacitor and so on. Therefore, travelling wave based protections are theoretically meaningful and practically useful for modern power system.Based on the formerly proposed travelling wave protection principles and in-depth analysis of the travelling wave propagation and fault transient travelling wave characteristics, the dissertation proposed a novel travelling wave based directional pilot protection scheme for EHV/UHV transmission lines. For a forward fault, the magnitude of forward voltage travelling wave is less than reverse wave, and for a reverse fault, the magnitude of forward wave is greater than reverse wave. The directional relay determines fault direction by a ratio of two integrations. The first one is based on forward voltage travelling wave, and the second one is based on reverse voltage travelling wave. The paper presented the detailed protection algorithm process. EMTDC based simulation experiments showed that the protection could overcome most of the drawbacks existing in traditional travelling wave protection scheme, such as immunity to the influences of bus structure, fault initial angle, fault on one of the parallel lines, and other factors.The dissertation analyzed the characteristics of the UHV transmission line, introduced both domestic and foreign UHV relay protection schemes, and established the accurate system model of the UHV demonstration line. Simulation tests showed that the novel ratio directional protection was feasible to UHV transmission lines.Theoretical analysis and simulation results have shown that the proposed ratio directional protection is both reliable and sensitive, and can reach ultra-high-speed.