Simulation of undervoltage load shedding to prevent voltage collapse

Recent blackouts in USA, Italy and London discovered problems with systems in operation near to their limits. After deregulation of power systems in industrialized countries, large problems with voltage stability incurred due to the larger and larger amounts of power transmitted to larger and larger distances. Systems often work on their limits and single contingency is sometimes enough to cause system collapsing. Best way for voltage instability prevention is fast and enough local reactive power reserve. Also, building of new power plants and transmission lines helps in voltage collapse prevention. These projects often take several years to complete, and in a lot of cases there are big problems with acquiring suitable locations and corridors. One of the most economic methods to prevent larger scale voltage collapse is undervoltage load shedding (UVLS). In this article, most important characteristics of UVLS are shown and their implementation in New England test system. Loads are modeled with different amounts of motor load. Simulation of system behavior is presented as well.