Islanding

Islanding is the intentional or unintentional division of an interconnected power grid into individual disconnected regions with their own power generation.

Intentional islanding is often performed as a defence in depth to mitigate a cascading blackout. If one island collapses, it will not take neighboring islands with it. For example, nuclear power plants have safety-critical cooling systems that are typically powered from the general grid. 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.[1][2]

Grid designs that lend themselves to islanding near the customer level are commonly referred to as microgrids. In a power outage, the microgrid controller disconnects the local circuit from the grid on a dedicated switch and forces any online distributed generators to power the local load.[3][4]

Unintentional islanding is a dangerous condition that may induce severe stress on the generator, as the generator must match any changes in electrical load alone. If not properly communicated to power line workers, unintentional island can also present a risk of electrical shock. Unlike unpowered wires, islands require special techniques to reconnect to the larger grid, because the alternating current they carry is not in phase. For these reasons, solar inverters that are designed to supply power to the grid are generally required to have some sort of automatic anti-islanding circuitry, which shorts out the panels rather than continue to power the unintentional island.

Methods that detect islands without a large number of false positives constitute the subject of considerable research. Each method has some threshold that needs to be crossed before a condition is considered to be a signal of grid interruption, which leads to a "non-detection zone" (NDZ), the range of conditions where a real grid failure will be filtered out.[5] For this reason, before field deployment, grid-interactive inverters are typically tested by reproducing at their output terminals specific grid conditions and evaluating the effectiveness of the anti-islanding methods in detecting island conditions.[4][6]

  1. ^ Autorité de sûreté nucléaire. "Îlotage provoqué des deux réacteurs à la centrale nucléaire de Saint-Alban". ASN (in French). Retrieved 2019-02-25.
  2. ^ "Centrale nucléaire de Fessenheim : Mise à l'arrêt de l'unité de production n°2". EDF France (in French). 2018-07-14. Archived from the original on 2019-02-26. Retrieved 2019-02-25.
  3. ^ Saleh, M.; Esa, Y.; Mhandi, Y.; Brandauer, W.; Mohamed, A. (October 2016). "Design and implementation of CCNY DC microgrid testbed". 2016 IEEE Industry Applications Society Annual Meeting. pp. 1–7. doi:10.1109/IAS.2016.7731870. ISBN 978-1-4799-8397-1. S2CID 16464909.
  4. ^ a b "IEEE 1547.4 - 2011". IEEE Standards Association Working Group Site & Liaison Index. IEEE. Retrieved 3 March 2017.
  5. ^ Bower & Ropp 2002, p. 10.
  6. ^ Caldognetto, T.; Dalla Santa, L.; Magnone, P.; Mattavelli, P. (2017). "Power Electronics Based Active Load for Unintentional Islanding Testbenches". IEEE Transactions on Industry Applications. 53 (4): 3831–3839. doi:10.1109/TIA.2017.2694384. S2CID 40097383.