Impact of load variation on the synchronous DG frequency-based anti-islanding protection

The performance of passive islanding detection techniques, such as frequency-based and voltage-based relays are affected by the active and reactive power imbalance and by the voltage dependence of the system loads. The combination of the load variation at different nodes of the power distribution grid with the DG power output can create similar power imbalance scenarios but with different voltage profiles. Therefore, the dynamic behavior of the loads after the islanding can be quite different in these situations, affecting the performance of the anti-islanding protection. In this context, this paper investigates the influence of the load variation on the performance of frequency relays employed for islanding detection of distributed synchronous generators. The analyses were carried out by running real time closed-loop simulations with a commercial frequency relay. The results have shown that, for the same relay setting, the performance of the relays can be strongly affected by the load variation, and such issue should be taken into account to correctly adjust the frequency-based anti-islanding protection.