Implementation and comparison of different under frequency load-shedding schemes

In the context of power system restructuring, the maintaining of adequate levels of security and reliability will be operated also through direct load control, thus considering load as the potential provider of ancillary services such as regulation, load-following, frequency responsive spinning reserve. In any case load-shedding still remains the ultimate resource for emergency conditions. In the paper several load-shedding schemes for underfrequency operation are examined. Both traditional schemes, based only on frequency thresholds, and adaptive schemes, based on frequency and on its rate of change, are considered. An IEEE test system for reliability analysis is used to compare the behavior of the proposed schemes when selecting different thresholds and percentages of load to be disconnected. Results are reported into detail and considerations on possible advantages and drawbacks also related to the framework provided by the electricity market are presented.