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Under Frequency Load Shedding

About This Metric

The purpose of Under Frequency Load Shedding (UFLS) is to balance generation and load when an event causes a significant drop in frequency of an interconnection or islanded area. The UFLS activation metric measures the number of times it is activated and the total MW of load interrupted in each Regional Entity and NERC-wide. The table illustrates a history of UFLS events from 2003 through 2012. Notably, single events had a load shedding range from 24 MW to 17,644 MW. The activation of UFLS is the last automated reliability measure associated with a decline in frequency in order to rebalance the system. Further assessment of the MW loss for these activations is recommended. Because of the large range of load lost in UFLS events, the need to establish a UFLS total load loss threshold is under evaluation. The significance of a UFLS activation compared to the total activation load loss will be assessed over time.




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