Likelihood of Islanding in Distribution Feeders with Photovoltaic Generation

The probability of islanding in residential and commercial distribution feeders with varying penetrations of distributed photovoltaic generation is investigated. A necessary condition for islanding is that load should closely match available generation. Extensive load measurements were made on residential and commercial laterals in a utility system. The load data were combined with generation data based on measured insolation in the same areas to estimate the probability of load- generation match. The probability, frequency and duration of islanding events were estimated for varying levels of penetration and are reported in the paper. Although load-generation match is only a necessary condition, making these estimates "worst case" results, they underscore the fact that anti-islanding measures are essential in uncontrolled systems.