Locking Frequency Band Detection Method for Islanding Protection of Distribution Generation

An islanding condition refers to an undesired event in which a portion of utility system, including both distributed generator(s) (DG) and local loads, remains energized while the main grid is disconnected. Unintentional islanding incident can result in serious personnel safety issues, interference to grid-protection facilities, power quality degradation, and equipment damage. Accordingly, anti-islanding protection for DG system is required by standard and utility codes. In this paper, an active islanding protection method is proposed called locking frequency band detection. The proposed method functions by introducing a virtual detection band only based on local grid frequency measurements at the point of common coupling. Hence, it has little or no impact on DG output and its power quality, and it does not get affected by a number of DGs. In addition, the proposed protection method eliminates the dreaded nondetection zone for DG systems typically observed during most severe power system transient conditions. In this paper, detailed description of the algorithm is explained and its performance and efficacy are evaluated through simulation and hardware experiments for different load quality factors.