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A New Protection Scheme for Two-terminal DC Grid

DC grid enables power system more flexible and efficient, and increases absorptive capacity of the renewable energy, which will be an important part of the future smart grid. However, higher requirement of protection is a significant barrier to more widespread adoption of dc grid. To solve the drawbacks of the existing protection methods, a new protection scheme which delivers fast operation for a two-terminal DC network is presented in this paper. The proposed scheme comprises a communication-assisted fault detection and an isolation method through differences of fault current directions. The scheme uses multiple intelligent electronic devices (IEDs) to exchange digital signals of zone current direction, which can distinguish line and bus fault, then combines with circuit breakers to cut-off DC faults within sub-millisecond timescales. Converter and battery protection are also presented to perfect grid protection. The effectiveness and practicability of the proposed protection strategy is validated through PSCAD.