A communication-less overcurrent protection for distribution system with distributed generation integrated

The increasing penetration of distributed generation (DG) in distribution systems has resulted in a challenge for the conventional protection methods, due to the bi-directional power flow and the variation of fault current contribution. Moreover, the operation of distribution system in islanded mode is still an issue due to the difference between the short circuit current in islanded mode and grid-connected mode. This paper proposed a novel adaptive protection method, measuring only the local information rather than using the communication, to adapt the protection settings to the states, such as the change of operation mode (grid-connected or islanded), the change of network topology (radial or meshed) as well as the disconnection of some DG. The directional overcurrent relays (DOCR) is adopted in the distributed system to shorten the tripping time in order to maintain the DG´s connection. The relay settings are calculated offline and modified online according to the state detection, including the islanding detection, the power flow detection and the fault section detection. This protection method is verified by simulating a distribution system of Denmark in DIgSILENT PowerFactory.