A coordination protection scheme for high-voltage DC grids without line boundary reactors

• The analytic expressions reveal the features of fault current traveling wave. • The operation traveling waves have different polarities under internal and external faults. • Both the fault and operation traveling waves are used to construct the protection. • The proposed protection can cover the whole DC line without boundary reactors. • The protection uses local measurements to detect high-resistance faults. Local measurement-based protections of DC transmission line without boundary reactors are important for the safe operation of high-voltage DC grids, however, existing protections have dead zones or cannot tolerate high-resistance faults. To address these issues, this paper proposes a local measurement-based coordination protection scheme, which is based on the traveling waves generated by the fault and DC circuit breakers. First, the analytic expressions of the fault current traveling waves are derived, which reveal the relation between the fault position and the decay time of the protection current slope. Then, the traveling wave processes generated by the DC circuit breakers are detailed to present the voltage slope difference during internal and external faults. The proposed protection uses the decay time-based criterion to protect most area of the DC line and uses voltage slope-based criteria to protect the whole DC line. The proposed protection scheme can protect the full DC line using local measurements, and it is independent of the line boundary reactors and can tolerate high-resistance faults. These characteristics are validated using various simulations in PSCAD/EMTDC.