Assessing the incorrect undervoltage blocking of frequency-dependent relays for anti-islanding protection of a synchronous generator

Anti-islanding protection of synchronous generators is performed by the protection functions of under/overvoltage, under/overfrequency and rate of change of frequency. These frequency-based functions may include undervoltage blocking parameters, which keep the trip blocked if the voltage is below a threshold and maintain the blocking during a dropout time. This paper presents an analysis of these parameters in the incorrect blocking during islanding events in which the protection should trip. An improvement in the setting map method is developed to evaluate the effect of undervoltage blocking for a synchronous generator with constant impedance and induction motor loads. Then, a detailed simulation-based analysis is carried out, which shows a process that can be replicated to properly adjust the undervoltage blocking. The results indicate that larger dropouts can pose a risk, that operating conditions with higher power imbalance should be simulated to adjust this parameter and that combined analysis with under/overvoltage and overcurrent functions helps avoid overly conservative settings.