A novel duplicated main protection scheme suitable for both transmission lines and busbars

A new integrated directional relaying principle for transmission line and busbar is presented in this paper. This novel directional relay, which integrates the protective functionality of line directional protection and busbar protection, is implemented with the polarity comparison of the current travelling waves. The function of line directional protection of the integrated directional relay (IDR), which is actually the protective decision of IDR, is defined as the virtual directional protection (VDP). Using morphological gradient to characterize the initial current travelling wave into spike signal the direction of a fault can be determined by the polarity comparison of the formulated spike signals. A busbar fault can be detected if all the compared spike signals have the same polarities. Otherwise, a forward fault is identified by the VDP of one of the transmission lines connected to this busbar. In addition, the integrated directional relay is used to consist of the duplicated main protection scheme combined with the classical directional protection, classical distance protection and differential protection of busbar. By virtue of the individual protection principles and the measurements, the proposed duplicated protection scheme is promising to obtain higher reliability compared with the conventional schemes