Transient High-Frequency Impedance Pilot Protection for Urban Flexible DC Distribution Network

With the development of new energy, switching from AC to DC has become a development trend of the power system. The urban distribution network has high requirements on power quality, and the use of flexible DC technology is the best choice at present. Different from traditional motors, the flexible DC system has low inertia and small damping. When the fault occurs on DC line, the current rising rate is extremely fast, which seriously threatens the safe operation of the urban distribution network. It is necessary to design high-reliability and fast protection according to its fault characteristics. This paper proposes a pilot protection method based on transient high-frequency impedance by analyzing the variation characteristics of transient electrical quantities after a DC line fault. And regional protection can also be formed through the cooperation of adjacent lines. Finally, a simulation was built to verify the accuracy of the principle.