Passive Method for Distributed-Generation Island Detection Based on Oscillation Frequency

This paper aims to present a passive island detection technique for synchronous distributed generation (DG). The technique is based on frequency oscillation estimation in order to distinguish the islanding from other events that may occur in distribution systems. The island detection uses a small window to estimate the oscillation frequency, obtaining faster responses than the existing methods which use larger windows to estimate the damping and frequency of oscillation. The algorithm performance has been tested considering different generation and load scenarios, including short circuits, load, and capacitor switching, DG outage, and islanding. The technique is reliable since it does not trip for a nonislanding event; the island detection time is less than 40 ms and its nondetection zone is less than 1.6% of the DG nominal power. The proposed method has been compared with one of the most common algorithms used in practice-the rate of change of frequency. The results show that the algorithm based on frequency oscillation detection performs better than the ROCOF, and its mathematical simplicity is adequate for practical relay implementation.