Polarized Distribution Protection Coordination Strategy Under the Impact from Various Distributed Energy Resources (DER) Generation Points

The present design of protection systems is based on power flowing in a single direction, which allows for unpolarized (non-directional) protection schemes. With the large influx of renewable technologies recently introduced into the electric power system, referred to as distributed energy resources (DER), creates many challenges to adequately maintain existing protection schemes. Protection engineers design protection systems to safely eliminate faults from the electric power system that was exclusively built with rotating machines (which have quite a different behavior under fault than inverter-based sources). As the penetration level of DER increases, the adverse impacts from DER is no longer to be considered minimal. With DER becoming influential in the distribution system, the current utility protection strategy merits a comprehensive investigation. This paper discusses major protection issues caused by DERs and provides utility-verified solutions based on more than 500 DER interconnection project system impact studies. An optimized coordination flow chart is provided in this paper along with software CYMEDIST-verified real US utility radial distribution feeders, which were used for simulations and related validation.