Study Of Optimal Reclosure Method On Transmission Line

With rapid development of electric power network, transmission lines put forward new requirements for reclosure. The optimal reclosure which provides with the feature of adaptive reclosure and capturing the optimal reclosing time becomes the relay protection research hotspot. It can not only accurately identify the nature of the failure and determine the arc extinction time, but also further improve the power system transient stability margin. This thesis revolves around the two key technologies of the optimal reclosure which contains adaptive reclosure and optimal reclosing time to carry out the research.Recognition the nature of fault and capture the arc extinction time are the core content of the adaptive reclosure. Since the EHV transmission line fault mainly manifests single phase ground fault, this thesis studies on single-phase adaptive reclosure technology.Firstly, fault arc dynamic characteristics when single-phase fault occurs are analyzed. Using EMTP simulations obtain the characteristics of arc curves and fault phase terminal voltage waveform.Secondly, aimed at the transmission lines with shunt reactors, analysis of the mechanism of the change of faulty phase terminal voltage and the frequency calculation formula of free component is presented. Using the Hilbert transform extracts the envelope of fault phase voltage. Envelope analysis shows that the complexity of the fault phase voltage envelope value can accurately reflect the nature of fault and arc extinction state. Then, an adaptive reclosing scheme based on fault phase terminal voltage envelope analysis is proposed. The simulations verify the accuracy and validity of the scheme.Finally, for transmission lines without shunt reactors, the cause of the fault phase terminal voltage appearing DC offset phenomenon is analyzed. Due to system transmission power containing zero sequence component after fault, the instantaneous zero sequence power (ZSP) of line side is computed. The instantaneous ZSP calculation results show that instantaneous ZSP frequency components are inconformity under different fault. Based on the fundamental frequency component of ZSP which appears at the moment of arc extinction during the transient fault, an adaptive reclosure scheme is proposed.Optimal reclosing time ensures reclosing operation to furthest damp oscillation of the system and benefit the stable operation of power grid. The thesis analyzes the reclosing operation sequence influence on system transient stability and deduces the optimal reclosing time calculation method under different nature of fault. Moreover, the mating strategy between the optimal reclosing time and adaptive reclosing theory is developed.