Adaptive fault identification for multi-level relays using fault tree and user-defined inverse-time characteristics equation

The traditional inverse-time overcurrent (ITOC) protection setting method relies on a fixed topology, and the setting workload in large-scale networks is very large and difficult to adapt to topology changes. An adaptive fault identification (AFI) scheme is proposed, which is applicable to ring or large networks, and does not require prior knowledge of the primary/backup coordination relationships between relays or the stepwise setting of inverse-time characteristic parameters. First, the positive sequence fault component voltages (PSFCVs) with natural distribution characteristics is analyzed. By utilizing the communication channels in existing wide-area protection systems (WAPS), only the protection action signal (PAS) of primary protection is transmitted, generating a fault tree that automatically reflects the relationship between each relay and the fault point. Secondly, a user-defined inverse-time characteristic equation (ITCE) and an online adaptive method for setting parameters are provided. The calculated tripping time depends solely on the parameters of the individual lines. Finally, an IEEE 30-bus test system is built in PSCAD/EMTDC to verify the effectiveness of the proposed scheme under different network topologies and when distributed generation (DG) is connected.