Unintentional islanding and comparison of prevention techniques

When one or more distributed resources (DR) become isolated from the rest of the power system and inadvertently continue to serve loads separately from the utility system, the condition is known as "unintentional islanding". Utility engineers are seriously concerned about unintentional formation of islands. This is because the utility looses control of the voltage and the frequency during the islanding condition. Frequency deviation and out of limit voltage conditions can have severe consequences on utility loads. In this paper, various type of islanding is discussed. The focus is on the methods and special equipment used to detect and prevent islanding. Examples, advantages and disadvantages of each technique are also discussed.