Protective Relaying for Distribution and Microgrids Evolving from Radial to Bi Directional Power Flow

As distributed energy resources (DER) achieve higher penetration levels in distribution systems, the normal flow of power (and fault current) is no longer unidirectional, from substation source to load (or fault). The increased importance of DER has also led to pending revisions in the DER interconnection standards, particularly voltage regulation and ride-through, with publication of a new IEEE Standard 1547 expected in early 2018. These changes have complicated normal distribution system operation, and they will also complicate distribution system protection. The US Department of Energy undertook a review of protection state-of-the-art for this new environment in order to identify gaps and propose near-term solutions.