Abstract
Islanding phenomenon of the utility interconnected photovoltaic(PV) power generating systems mainly installed in residential houses is a most serious problem for the safety of utility distribution lines. The 3rd harmonic voltage detecting method is one of the recommended measures in the Japanese guidelines on utility interconnection. However, detailed conditions of the method when detecting have not been clarified yet. This has prevented establishing the optimum islanding prevention method including combinations with other prevention measures. In this study, detailed detecting conditions of the 3rd harmonic voltage detecting method were analyzed by a simulation developed based on demonstration tests in Rokko Island. The simulation showed the following:
• 3rd harmonic voltage increases remarkably and can be detected clearly when the imbalance of load currents of each phase is more than about 15%.
• There are conditions of PV power output and relationships between PV power outputs and loads at which islanding detection fails, when the imbalance of load currents of each phase is less than about 15%. The ratio of PV power output and load in the case of failed detection tends to be less than 1.0.
• The 3rd harmonic voltage detecting method is a useful supplement when other islanding prevention measures fails in combined methods.
