Complete protection scheme for active closed-loop distribution systems

With increasing integration of distributed generation (DG) to the active distribution systems, the existing grid structure and protection configuration cannot meet the requirements of reliability. Adopting closed-loop configuration and reasonable protection schemes, it is possible to reduce the range of power outage and ensure continuous supply of DG. Firstly, an IED (intelligent electronic device) based complete protection structure consisting of several protection functions is proposed, including line protection, load protection and node protection. The protection principles of each protection function is described. The paper also studies the single-terminal weak-infeed issue of closed-loop distribution system by theoretical and simulation analysis. It is proved that the current phase variation based line protection function is not affected by the magnitude of fault current. It could correctly identify the fault under single-terminal weak-infeed condition.