Inverse-time Backup Protection Based on Unified Characteristic Equation for Distribution Networks with High Proportion of Distributed Generations

The setting work of backup protection using steady-state current is tedious, and mismatches occasionally occur due to the increased proportion of distributed generations (DGs) connected to the power grid. Thus, there is a practical need to study a backup protection technology that does not require step-by-step setting and can be adaptively coordinated. This paper proposes an action sequence adaptive to fault positions that uses only positive sequence fault component (PSFC) voltage. Considering the influence of DGs, the unified time dial setting can be obtained by selecting specific points. The protection performance is improved by using the adjacent upstream and down-stream protections to meet the coordination time interval in the case of metallic faults at the near- and far-ends of the line. Finally, the expression and implementation scheme for inverse-time backup protection (ITBP) based on the unified characteristic equation is given. Simulation results show that this scheme can adapt to DG penetration scenarios and can realize ^the adaptive coordination of multi-level relays.