Negative sequence impedance based islanding detection for distributed generation (NSIID)

This paper introduces a novel method of islanding detection for distributed generation networks employing negative sequence impedance measurement. The negative sequence impedance islanding detection method (NSIID) is an improvement on previous impedance measurement techniques for islanding detection because it has a small non-detection zone and large threshold window, which previous techniques have had difficulty achieving. Experiments were conducted on a distributed generator fed commercial building by measuring naturally occurring and injected negative sequence components. Results indicate that naturally occurring unbalanced load conditions are readily measurable and correlate to the system Thevenin impedance. The experimental measurements also confirmed the accuracy of the negative sequence components exhibited in simulations, which were employed to analyze islanded conditions. This work further demonstrated that injecting negative sequence current into the distribution network increases the measurability of negative sequence currents, improving the accuracy of our proposed islanding detection technique.