A Pilot Protection Scheme for Pole-to-Pole Fault in Flexible DC Distribution Network

In the flexible DC distribution network, the pole-to-pole fault current has complex and controlled characteristics that challenge fault detection and protection. In the context of the multi-terminal flexible DC distribution network, this paper theoretically studies the short-circuit current characteristics of pole-to-pole fault, derives the analytical expression of the short-circuit current, and analyzes the variation characteristics. On this basis, a fault direction discrimination method based on the polarity characteristics of short-circuit current fault components and a directional pilot protection scheme is proposed. At the same time, countermeasures are put forward for the T-type structure and the special operating condition of the single-ended power supply to improve the protection's applicability and reliability. Simulation results show that the proposed scheme can reliably identify faulty lines. The protection principle does not require sampling synchronization and is easy to apply in engineering.