A novel directional protection based on transient energy for HVDC line

Using the characteristic difference of transient energy, a transient energy based directional unit protection is proposed. Assuming the positive direction of current is from DC busbar to DC line, for an internal line fault, the detected transient energies on both ends of the line are all negative, which denote the positive direction fault. When an external fault occurs, the transient energy on one end is positive, which denotes a negative direction fault, but the transient energy on opposite end is negative, which means that the fault direction is positive. Through comparing fault directions on both ends, the internal or external DC line fault can be identified. Besides, according to the magnitude difference of transient energy, the faulty line can also be discriminated for bipolar line. Finally, this paper constructs a ±800kV DC transmission system model, and simulation results verify the validity and feasibility of the proposed method.