Comprehensive investigation of the voltage relay for anti-islanding protection of synchronous distributed generation
Interconnection standards prevent islanding operation of distributed generations (DGs) to keep the safety and avoid the equipment failure. To meet this requirement for synchronous DGs (SDGs), the frequency-based relays are commonly used in the active distribution networks. This paper shows that in some conditions, a voltage relay has better islanding detection performance than a frequency relay regarding the SDG operating point, power factor of loads, and network characteristics. In this paper, a method is proposed for adjusting and evaluating a voltage relay based on application region and power imbalance application region to satisfy the islanding detection and safe and abnormal voltage variation criteria and to eliminate the false operation for the non-islanding disturbances including load shedding, load restoration, and 3-phase short-circuit fault, as far as possible. The relay false operation is studied for a combination of the control mode of SDG excitation system and the load type that leads to the highest possibility of relay false operation for the non-islanding disturbances. A number of dynamic simulation case studies are conducted to investigate the characteristics and capabilities of the proposed SDG anti-islanding protection scheme in both single- and multi-DG systems.