1. Power System Voltage Stability
At any point of time, a power system operating condition should be stable, meeting various operational criteria, and it should also be secure in the event of any credible contingency. Present day power systems are being operated closer to their stability limits due to economic and environmental constraints. Maintaining a stable and secure operation of a power system is therefore a very important and challenging issue. Voltage instability has been given much attention by power system researchers and planners in recent years, and is being regarded as one of the major sources of power system insecurity. Voltage instability phenomena are the ones in which the receiving end voltage decreases well below its normal value and does not come back even after setting restoring mechanisms such as VAR compensators, or continues to oscillate for lack of damping against the disturbances. Voltage collapse is the process by which the voltage falls to a low, unacceptable value as a result of an avalanche of events accompanying voltage instability . Once associated with weak systems and long lines, voltage problems are now also a source of concern in highly developed networks as a result of heavier loading.
The main factors causing voltage instability in a power system are now well explored and understood [1-13]. A brief introduction to the basic concepts of voltage stability and some of the conventional methods of voltage stability analysis are presented in this chapter. Simulation results on test power systems are presented to illustrate the problem of voltage stability and the conventional methods to analyze the problem. Limitations of conventional methods of voltage stability analysis are pointed out and the scope of the use of Artificial Neural Networks as a better alternative is discussed.