Under-frequency Load Shedding Schemes Characteristics and Performance Criteria

Our work focuses on the European Network Code on Emergency and Restoration (NC-ER) which introduced an harmonization requirement of Under-frequency Load Shedding (UFLS) schemes. This new requirement implies that in the medium term, the UFLS scheme of all European countries will have to evolve. It stipulates an acceptable range for the main factors that define an UFLS scheme, namely: the number of load shedding steps, the percentage of load shed in each step, and the accuracy of the frequency measurement that is implemented in the protection relays. In this context, the contribution of this paper is twofold: first, we define a new performance criterion for UFLS schemes; and second, we apply this criterion to two opposite archetypal schemes, in order to highlight the pros and cons of both approaches.