Non-unit transient based boundary protection for UHV transmission lines

Different from EHV transmission lines, the boundary of UHV transmission lines naturally consists of busbar stray capacitance, shunt reactor and/or series capacitor. The frequency characteristics of the UHV line boundaries with different structures are analyzed deeply, which have significant attenuation on both high frequency signal and low frequency signal. The attenuation is the inherent characteristic of UHV line boundary. Based on the UHV boundary characteristic, a novel boundary protection principle utilizing backward traveling wave is proposed. The fault direction is identified by means of the time-domain energy of the backward traveling wave. The high frequency energy and the low frequency energy of the backward traveling wave are extracted by wavelet transform, and then the forward internal and external faults are discriminated by the product of high frequency energy and low frequency energy. An adaptive setting calculation method in terms of fault type is presented, which is able to improve effectively the right discriminating rate for internal faults. The simulation model of Jindongnan-Nanyang-Jingmen UHV transmission project is established in ATP/EMTP. The simulation results show that the boundary protection possesses stable performance under various fault situations, and the operation time is less than 2 ms, which is appropriate as the non-unit ultra-high-speed protection element for UHV transmission lines.