Adaptive DC grid fault reclosing scheme using second-order TET-corrected Reconstructed-traveling-waves

• DCCB operational sequence design ensures safe and secure reclosing process. • Second-order TET analysis eliminates dead zones and significantly enhances fault. • sensitivity. • Fault nature discrimination is achieved independently without communication reliance. • The proposed method demonstrates high fault resistance coverage, up to 1427 ohms. Half-bridge modular multilevel converter (HBMMC) based direct current (DC) grids, using overhead lines and DC circuit breakers (CBs), face an urgent demand for selective reclosing methods due to the high DC line fault-probability and the limited overcurrent-tolerance of power electronic equipment. Existing methods, which enhanced reclosing performance, still face challenges such as safety concerns, dead zones, sensitivity, and dependence on communication. To address the safety issue, this paper reveals the mechanism by which the operational sequence of the direct current circuit breaker (DCCB) transfer branch influences overcurrent. Furthermore, a transfer branch operational sequence is designed to strictly avoid the overcurrent during the reclosing process. Regarding the dead zone and sensitivity problems, the low-frequency component of the local voltage measurement generated after signal injection is corrected using the second-order transient extraction transform (TET). The time-domain traveling wave characteristic, i.e. the reconstructed measurement local voltage (RMLV), is then compared with the reconstructed theoretical local voltage (RTLV), enabling the discrimination of fault nature using a low setting threshold. Case studies indicate that the proposed method can discriminate the fault nature of the DC line to be reclosed without relying on communication, eliminates dead zones, and demonstrates a 300-ohms’ resistive coverage along the entire DC line.