An islanding detection method for distributed generations using voltage unbalance and total harmonic distortion of current

Distributed generation (DG) units are rapidly increasing and most of them are interconnected with distribution network to supply power into the network as well as local loads. Islanding operations of DG usually occur when power supply from the main utility is interrupted due to several reasons but the DG keeps supplying power into the distribution networks. These kinds of islanding conditions cause negative impacts on protection, operation, and management of distribution systems; therefore, it is necessary to effectively detect the islanding conditions and swiftly disconnect DG from distribution network. Generally, if there are large changes in loading for DG after loss of the main power supply, then islanding conditions are easily detected by monitoring several parameters: voltage magnitude, phase displacement, and frequency change. However, in case of small changes in loading for DG, the conventional methods have some difficulty in detecting such a particular islanding condition. This paper presents a new islanding detection algorithm for DG effectively working in the most of DG loading conditions. This paper proposes two new parameters for detecting islanding operation of DG: voltage unbalance and total harmonic distortion of current. The proposed method effectively combines the conventional parameters with the newly proposed parameters for detecting the islanding conditions. The proposed methods were verified using the radial distribution network of IEEE 34 bus.