Design and comparison of UFLS schemes of isolated power systems based on frequency stability margin

Increasing penetration of RES affects stability and, in particular, frequency stability of island power systems like the Canary Islands. System protection involves underfrequency load shedding (UFLS) as a last resort tool. The objective of this paper is to tune the parameters of a UFLS scheme based on the frequency stability margin (FSM) and compare its performance with the conventional UFLS scheme. The performance is assessed by simulating the outage of generating units of a real isolated Spanish power system. The results of this study demonstrate that the introduction of the FSM in the UFLS scheme contributes to a significant improvement in its performance. The load shedding is delayed for moderate rate of change of frequency (ROCOF) values, and the amount of disconnected load is reduced.