Under-voltage load shedding is the least and lowest cost solution to severe voltage problems [13].
Precisely, it can complete the under-frequency and under-voltage load shedding protection of the whole substation, strengthen the function of accurate load tripping based on traditional under-frequency and under-voltage load shedding protection, and realize comprehensive decision making with the combination of off-line strategy and on-line measurement information.
Meanwhile, it can realize automatic control functions, for instance backup power supply automatic switch-on (auto backup) of the whole substation, under-frequency and under-voltage load shedding protection, and breaker failure protection, etc.
Some under-voltage load-shedding strategies including real and reactive power load curtailments are adopted to mitigate system voltage instability [13, 14, 15, 16, 17, 18] in real-time operation of power systems.
Currently, the widely used load shedding methods mainly involve overall load shedding strategy [14] and under specific voltage load shedding strategy [15].
After performing load shedding for all influenced nodes, the under specific voltage load shedding strategy will be applied for remaining nodes.
For the previous example, the voltage variance after shedding load is used to evaluate the system stability, and the value when using the proposed strategy is only 10% of the value when using under specific voltage load shedding strategy.
For example, regarding the obtained failure chain l 1, l 14, l 44, l 26, l 6, l 7 and l 8 in IEEE-39 test system, if using under specific voltage load shedding strategy, the load losses will be 1138.2 MW, while when using the proposed load shedding strategy, the load losses are only 446.5 MW.
Examples of SIPS include [55]: generator rejection, load rejection, under frequency and voltage load shedding, system separation, dynamic braking, and turbine valve control.
