Pilot Protection Based on Two-Dimensional Space Projection of Dual Differential Currents for Lines Connecting MMC–HVDC Stations

As an important topic of power system protection, protection algorithm for transmission lines connecting modular multilevel converter (MMC)-based converter stations has attracted extensive attention. This article proposes a new time-domain pilot protection based on two-dimensional (2-D) space projection of dual differential currents for lines connecting converter stations. The dual differential currents, i.e., original and virtual differential currents, are projected into 2-D space. Subsequently, the dynamic trajectories of dual differential currents under various circumstances are elaborated. On this basis, the nonoperating zone and internal fault index are defined, whereby the criterion of pilot protection is developed. Afterwards, the operating characteristic of the proposed pilot protection is analyzed under various circumstances. The performance of proposed pilot protection is widely assessed using power systems computer aided design (PSCAD) and real time digital simulator (RTDS). The contribution of this article lies in a new time-domain pilot protection based current trajectory of dual differential currents, which exhibits exceptional performance in operating speed, sensitivity, complexity, tolerance to fault resistance, current transformer saturation and abnormal data, and adaptability to operation mode of MMC.