On the basis of introducing the causes and hazards of islanding, the paper classifies and generalizes the testing methods used currently about islanding. It is shown that applying single method to detect islanding will bring some wrong judgments. It is difficult to determine the protection thresholds by a single detection method, which will decrease protection sensitivity and result in system losses. This paper studies a method based on fuzzy clustering, which integrates variations of voltage amplitude and frequency change, mutations of current phase and voltage phase, as well as formation of voltage harmonics and so on, and determines the formation of islanding and the appropriate protection criterion.
