DC Line Protection for Flexible MVDC Distribution Grid With Renewable Energy Resources

A line protection scheme for multi-terminal flexible MVDC distribution systems was proposed to identify and isolate faults by cooperating with DC circuit breakers. Firstly, the architecture of the dc distribution system was presented. Secondly, a fast-operating main protection was designed for pole-to-pole faults and pole-to-ground faults with low fault resistance. It takes advantage of the current information and the current status matrix of each relay, and can identify and isolate the fault typically within 5ms. Subsequently, a backup protection scheme was designed to deal with the pole-to-ground fault with high fault resistance. It utilizes the unbalance voltage as the starting criterion, and the unbalance current between the positive and negative pole currents to identify the fault. Finally, simulation results in PSCAD/EMTDC verify the effectiveness of the proposed protection scheme.