Islanding occurs when a feeder, a section of network or a single site keeps running on its own generators or inverters after the connection to the wider grid has opened. An unplanned island is dangerous: crews may find a supposedly dead line still live, and the island drifts in voltage and frequency, so reclosing onto it out of phase can wreck machines. Grid-tied inverters carry anti-islanding protection, often rate-of-change-of-frequency or vector shift, that disconnects them within about two seconds.
Sub breaker opened but the solar farm held the feeder up for three seconds, the anti-islanding settings need another look.
Also heard as
- loss of mains
- LOM
Do not mix it up with
- Backfeed: Backfeed is energy arriving from an unexpected direction; an island is a whole section kept alive by its own sources.
Related terms
Backfeed
Power arriving at a circuit from an unexpected direction, such as a generator or second supply feeding back.
Auto-reclose
Automatic closing of a breaker shortly after a fault trip, restoring supply when the fault was only transient.
Black start
Restarting a power system from total shutdown using generators that can start without any outside supply.