## Voltage Stability:

**Mathematical Formulation of Voltage Stability**** :** Mathematical Formulation of Voltage Stability – The slower forms of voltage instability are normally analysed as steady state problems using power flow simulation as the primary study method. “Snapshots” in time following an outage or during load build up are simulated. Besides these post-disturbance power flows, two other power flow based methods are often used; PV curves and VQ curves. These two methods give steady-state loadability limits which are related to voltage stability. Conventional load flow …

**Prevention of Voltage Collapse**** :** Prevention of Voltage Collapse is given by Application of reactive power-compensating devices. Adequate stability margins should be ensured by proper selection of compensation schemes in terms of their size, ratings and locations. Control of network voltage and generator reactive output Several utilities in the world such as EDF (France), ENEL (Italy) are developing special schemes for control of network voltages and reactive power. Coordination of protections/controls Adequate coordination should be ensured between equipment protections/ controls based on dynamic simulation studies. Tripping of equipment …

**Trends in Voltage Stability**** :** Trends in Voltage Stability – The present day transmission networks are getting more and more stressed due to economic and environmental constraints. The trend is to operate the existing networks optimally close to their loadability limit. This consequently means that the system operation is also near voltage stability limit (nose point) and there is increased possibility of voltage instability and even collapse. Off-line and on-line techniques of determining state of voltage stability and when it enters the unstable …

**Voltage Stability**** :** Voltage control and stability problems are very much familiar to the electric utility industry but are now receiving special attention by every power system analyst and researcher. With growing size along with economic and environmental pressures, the possible threat of voltage instability is becoming increasingly pronounced in power system networks. In recent years, voltage instability has been responsible for several major network collapses in New York, France, Florida, Belgium, Sweden and Japan. Research workers, R and …

**Voltage Stability Analysis**** :** The voltage stability analysis for a given system state involves examining following two aspects. Proximity to voltage instability: Distance to instability may be measured in terms of physical quantities, such as load level, real power flow through a critical interface, and reactive power reserve. Possible contingencies, such as a line outage, loss of a generating unit or a reactive power source must be given due consideration. Mechanism of voltage instability: How and why does voltage instability take place? What are …