The problem of voltage stability is becoming a more acute and indispensable topic given the major and sensitive role it plays in the electrical system. It can be considered a major factor in the initiation of blackouts around the world. Hence, the need for reliable and fast tools to detect and control the approach of instability points throughout the network, namely, voltage stability indices and flexible alternating current transmission systems (FACTS) devices for the control and management of the electrical network. In this paper, an update on the existing blackouts in the world has been presented. Based on the brief overview of the most significant definitions of voltage stability presented in this work, a new definition of voltage stability has been proposed. A detailed comparative study on voltage stability analysis methods has been conducted. Furthermore, an exhaustive discussion on the various voltage stability indices and FACTS devices existing in the literature with their contribution to voltage stability prediction and improvement has been proposed.

Presently, voltage stability indices are ones of powerful tools used to monitor and evaluate power system stability. The purpose of the presented work is to analyse, assess and compare different indices from the point of view of the sensitivity to the network disturbances. The proposed method allows to locate the sensitive area and also to monitor the behavior of indices in order to select the best ones that can be used. The study is achieved through the analysis of IEEE 14 busbar as the test system and several scenarios of contingencies are considered. The results are validated by using PSAT software.

To aid the decision maker, the optimal placement of FACTS in the electrical network is performed through very specific criteria. In this paper, a useful approach is followed; it is based particularly on the use of Kalai-Smorodinsky bargaining solution for choosing the best compromise between the different objectives commonly posed to the network manager such as the cost of production, total transmission losses (Tloss), and voltage stability index (Lindex). In the case of many possible solutions, Voltage Profile Quality is added to select the best one. This approach has offered a balanced solution and has proven its effectiveness in finding the best placement and setting of two types of FACTS namely Static Var Compensator (SVC) and Thyristor Controlled Series Compensator (TCSC) in the power system. The test case under investigation is IEEE-14 bus system which has been simulated in MATLAB Environment.

Voltage stability indices are one of the powerful means of power system monitoring. With the existence of several ones in literature, some of them are less accurate and insensitive to some kinds of disturbances and especially when the power system operates near to its load ability limit. In this paper, a static and dynamic analysis were conducted to assess and analyze the performances of few line Voltage Stability Indices namely Lmn index, FVSI index, NLSI index, LQP index, VSI index, VLSI index, and SFVSI index. The methodology is applied on an IEEE 14 bus test system and has made it possible to estimate the degree of, sensitivity, trust, and accuracy for each one.