An Overview of UFLS in Conventional, Modern, and Future Smart Power Systems: Challenges and Opportunities

As power systems continue to expand, the need arises for more robust monitoring, control and protection techniques especially under abnormal conditions. In the event of generator tripping or major tie-line disconnection due to a fault, the system frequency might drop to unacceptable levels, well below secure threshold values. Under such conditions, under frequency load shedding (UFLS) protective schemes are implemented to balance quickly generation and demand. In this paper, the merits and weaknesses of different UFLS schemes are discussed. In particular, focus is placed on wide area monitoring systems (WAMS)-based UFLS schemes, which are becoming popular due to the availability of real time measured phasors. A comprehensive comparison between the different UFLS techniques is provided and research gaps and future research trends are highlighted.