A High Speed Single-Ended Fault Detection Method for DC Distribution Feeder—Part I: Feasibility Analysis of Magnetic Ring as Line Boundary

DC distribution network has a lot of advantages over traditional ac distribution network and it is considered as one of the best power supply modes in the future. However, protection relay design for dc distribution network is a major challenge due to the requirement of high speed fault detection for the vulnerability of converters. In this paper, it is proposed that the boundary protection is very suitable for dc distribution network since it can protect the whole line only based on local measurement and does not need to coordinate with neighboring relays. However, it needs to find suitable line boundary for dc distribution network. Impedance features of magnetic ring is tested and difference in steepness and peak time of voltage travelling wave in case of internal and external faults when magnetic ring installed at both ends of dc distribution line is analyzed. Results show that magnetic ring is feasible to be used as line boundary. Besides, a wide band model of magnetic ring is proposed based on vector fitting and circuit synthesis method. It paves the way of analysis on features of internal and external faults at dc distribution line and validation of proposed fault detection method.