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 to avoid an overloaded condition should be the last alternative. Controlled system separation and adaptive or intelligent control could also be used.
Control of transformer tap changers
Tap changers can be controlled, either locally or centrally, so as to reduce the risk of voltage collapse. Microprocessor-based OLTC controls offer almost unlimited flexibility for implementing ULTC control strategies so as to take advantage of the load characteristics.
Under voltage load shedding
For unplanned or extreme situations, it may be necessary to use undervoltage load-shedding schemes. This is similar to under frequency load shedding, which is a common practice to deal with extreme situations resulting from generation deficiency.
Strategic load shedding provides cheapest way of preventing widespread voltage collapse. Load shedding schemes should be designed so as to differentiate between faults, transient voltage dips and low voltage conditions leading to voltage collapse.
Operators must be able to recognize voltage stability-related symptoms and take required remedial actions to prevent voltage collapse. On-line monitoring and analysis to identify potential voltage stability problems and appropriate remedial measures are extremely helpful.