islanding

Islanding refers to the condition in an electrical power system in which a portion of the grid remains energized by distributed generation after it has been disconnected from the main utility network. This can occur unintentionally due to faults, protection miscoordination, or device failures, or intentionally in the operation of microgrids that continue to supply local loads when the broader grid is down.

Unintentional islanding poses safety risks to utility workers and the public, as well as technical challenges such as voltage and frequency variations and possible backfeeding into de-energized lines. To prevent unsafe islanding, utilities and manufacturers implement anti-islanding protection. These include passive methods that monitor voltage, frequency, and other electrical parameters, and active methods that introduce small, controlled perturbations to test for grid presence. Some schemes rely on communications or coordinated control in a microgrid context. Standards such as IEEE 1547 (interconnection and interoperability of distributed resources) and UL 1741SA specify requirements for anti-islanding performance and interconnection equipment.

In microgrid applications, islanding can be part of planned operation, where a local network remains powered by distributed energy resources during a broader outage, improving reliability and resilience.

Islanding also appears in ecology and geography, where it describes the separation of habitat or populations into isolated patches akin to islands in a sea of unsuitable environment. Island biogeography studies how island size, isolation, and time influence species richness and extinction risk, with implications for habitat fragmentation, conservation planning, and ecosystem restoration.