Mario Klarić

Undervoltage load shedding using global voltage collapse index

Increasingly higher demand in power created problems in power system operation since the growth of the transmission system is restricted. System often function close to their stability limits and sometimes loads need to be shed in order to prevent system from collapsing. In this paper one undervoltage load shedding (UVLS) method to prevent voltage collapse is presented. This method is based on a global index, which indicates voltage collapse proximity and voltage magnitudes on critical buses. Global index for voltage collapse proximity determination is calculated based on power flow Jacobian matrix operations. Considering that on the voltage stability limit Jacobian matrix becomes singular, it cannot be inverted. Therefore method involving eigenvalue calculation is used here. IEEE 14 bus system was used as a numerical example, which showed how loads and system in general can be saved from voltage collapse using UVLS.

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.

Grid integration of wind power plants in congested line

Wind power projects in Croatia are in commencement but are also being demanded on a larger scale in the recent few years. However, Croatian Transmission System Operator (TSO) has many problems with the quantity of capacity asked for grid connection resulting in many places with large scale line congestion, especially in 110 kV network. In many places grid is not ready for such big penetration of intermittent power which was proven with many load flow analysis carried by system operator. In this paper one example of two different developers asking for grid connection on the same 110 kV line is presented. Also, current and future states of network are analyzed. Main problems are detected and measures for grid integration of both wind power plants are suggested.

Example of undervoltage load shedding implementation

After deregulation of power systems, large problems with voltage stability incurred due to the large transits of power transmitted to large distances. Systems are very stressed and often work on their limits. Therefore, single contingency is sometimes enough to cause system collapsing. One of the most economic methods to prevent larger scale voltage collapse is undervoltage load shedding (UVLS). In this article, implementation of UVLS scheme is tested in New England Test System and then modeled in part of Croatian power system. Simulation of system behavior is presented as well.

Optimal grid integration of wind power plants in Croatian 110 kV network

Wind power projects in Croatia are demanded on a larger scale in the recent few years. However, Croatian Transmission System Operator (TSO) has many problems with the quantity of capacity asked for grid connection resulting in many places with large scale line congestion. Transmission network is not ready for such big penetration of real power with stochastic nature produced by a large number of wind power units which was proven with many load flow analysis carried by system operator. In this paper one example of two different developers asking for grid connection on the same 110 kV line is presented. Also, current and future states of network are analyzed. Main problems are detected and measures for grid integration of both wind power plants are suggested.