الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 168 |  |  |
| | | from | 168 | | |
Abstract
With the improved optimized operation and increase in loading of a power system, the phenomenon of voltage instability and hence the voltage collapse attracts more and more attention due to this reason. The phenomenon of possible steady state voltage instability is creating serious concern among operation of large interconnected power system. A voltage collapse can take place in power systems or subsystems quite abruptly. continuous monitoring of the system state is required.
Mehtods for predicting voltage stability in power system can be categorized either into steady state or dynamic methods. the methods of dynamic ones are very consuming in computation time. The static methods with their much less computing time, provide senstive information of the system. steady state methods are widely used to provide a close observation of the voltage instability phenomenon.
There are different methods to study this phenomenon. some of these methods are the jacobain method, the simplified jacobain method, the multiple load flow method and the voltage collapse proximity indicator VCPI method.
To prevent the voltage instability process, a load shedding is carried out at the weakest buses. The load shedding can be performed locally or centrally, depending on the level of information and the avilable control means in the control center. The main feature of load shedding is that performed at all network buses belonging to a certain region. In this way, all regional buses contribute to the voltage recovery at the critical weakest bus, in addition, this approach implies load reduction by disconnecting certain types of customer loads. The load shedding can be solved with the aid of the optimization technique model. The suggested procedure of load shedding consists of several sequential regulation steps which are executed at regular time intervals until the voltage instability is eliminated.
The methods of steady state voltage instability assessments are reviewed and discussed. in this thesis, it is suggested to use the voltage collapse proximity indicator method VCPI to detect the weakest buses under the optimal operating conditions. the optimal operating conditions used in this study are minimum fuel cost, minimum transmission losses and minimum fuel cost with minimum transmission losses.
The voltage collapse proximity indicator method under the optimal operating conditions and hence the load shedding at the weakest buses are applied to three different power systems. these studies illustrate that the indicator can provide useful and necessary information about the system state at any operating point.