Investigations of impacts of distributed generations on feeder protections

Recently increasing connections of various kinds and sizes of distributed generators (DGs) on the distribution feeders have imposed considerable impacts on the existing feeder protective devices that were designed for traditional distribution systems of mostly radial configuration. The DG connections have laid tremendous challenges on reliability of existing feeder protections, for both operational dependability and security, as the presence of DGs almost fundamentally changes the existing radial feeder circuit structure and radial flow of power. Therefore the research reported in this paper investigates problems in existing feeder protections particularly those caused by DGs, and aims to increase the operational dependability and security of distribution feeder protections. This paper presents findings of detailed investigations on DG-imposed protection issues, typically sympathetic tripping, failure of fuse saving practice, mis-protection due to feeder-network reconfiguration, reduction-of-reach protection, unintentional islanding operation, and mis-coordination. This paper proposes simple solutions to the protection issues caused by the connections of DGs on the power distribution systems.