Bringing ROCOF into spotlight in Smart Grids: new standardization and UFLS method

The development of Smart Grid applications in electric power systems has highlighted larger frequency variations and disclosed misunderstandings related to frequency and its derived quantities. This paper discusses the mathematical and physical background behind frequency variations in the electric power system and the contribution of International Electrotechnical Commission (IEC) in standardizing the performances of frequency and frequency-related protection relays. Last but not least, the paper brings the focus on frequency-related measurements (frequency and its rate of change) with a new concept for underfrequency load shedding's decisions which is expected, thanks to its simplicity and intuitive design, to contribute to the frequency stability in electric power systems.