Understanding the Voltage Stability phenomena

Voltage stability in power networks has brought deep concern about  the problem, and nowadays is a subject of main interest due to the importance of the phenomena in the system security and power quality, in particular when power systems operate closer to their load limits, a fact that tends to takes place in the deregulated electric markets. To face this problem it is necessary to take some control actions, such as reactive power control or load shedding in order to reach network voltage profiles that guarantee a stable operation of the system. 

Voltage stability problem can be studied under the point of view of short-term or long-term. Concerning to the first case, the system response in the first seconds is analysed following a large disturbance, period at which is important to consider the dynamic behaviour of induction motors, SVC, SG, AVRs, etc., so dynamic models of the elements are required. In the second case, several minutes following the disturbance, the system behaviour must be studied considering the LTCs operation, overexcitation control, shunt compensation, etc.; this analysis can be performed using the simplified method of P-V and V-Q curves, but it is not appropriated when time-dependence of control actions must be taken into account. For this reason, a dynamic analysis is more accurate.

This web pages contain both theoretical and computing software developed by Rosa Mª de Castro and Horacio Díaz in the "Voltage Stability" Phd course developed at the Electrical Department, Universidad Politecnica de Madrid, Spain. 

All resources are free available