The coolant loops typically lie on a separate circuit that can also operate off of reactor power or emergency diesel generators if the grid collapses.
Unlike unpowered wires, islands require special techniques to reconnect to the larger grid, because the alternating current they carry is not in phase.
[9][10] Synchronous generators may not deliver sufficient reactive power to prevent severe transients during fault-induced island formation,[11] and any inverters must switch from constant-current to constant-voltage control.
[14] Islanding reduces the economic efficiency of the wholesale power market,[10] and is typically a last resort applied when the grid is known to be unstable but has not yet collapsed.
[8] In particular, islanding improves resilience to threats with known time but not location, such as terrorist attacks, military strikes on electrical infrastructure, or extreme weather events.
[15] Following the 2019 California power shutoffs, there was a rise in interest in the possibility of operating a house's electrical grid as an island.
In principle, this technique has a vanishingly small NDZ, but in practice the grid is not always an infinitely-stiff voltage source, especially if multiple inverters attempt to measure impedance simultaneously.
[20] At the utility level, protective relays designed to isolate a portion of the grid can also switch in high impedance components, such that an islanded distributed generator will necessarily overload and shut down.
When the main grid disconnects, the power factor on the island suddenly decreases, and inverter's current no longer produces the proper waveform.
The phase-locked loop then becomes unstable when the grid signal is missing; the system drifts away from the design frequency; and the inverter shuts down.
[26] A very secure islanding detection method searches for distinctive 2nd and 3rd harmonics generated by nonlinear interactions inside the inverter transformers.
Even noisy sources, like motors, do not effect measurable distortion on a grid-connected circuit, as the latter has essentially infinite filtration capacity.
[28] Utilities have refused to allow installation of home solar or other distributed generation systems, on the grounds that they may create uncontrolled grid islands.
[29][30] In Ontario, a 2009 modification to the feed-in tariff induced many rural customers to establish small (10 kW) systems under the "capacity exempt" microFIT.
Supervisory Control and Data Acquisition (SCADA) systems can be set to alarm if there is unexpected voltage on a purportedly-isolated line.