Abstract
Voltage stability has become one of the most important issues in electrical power systems. The power system ability to maintain acceptable bus voltage is a very important characteristic of a network. This paper analyzes the performance of line stability indices. These indices were tested in IEEE 14 and IEEE 57 busbar test systems, with satisfactory results. Simulation results show that using line stability indices the most critical line and the weakest bus of the system can be correctly identified.

Abstract
This paper proposes the use of available PMU measurements for establishing network observability State estimation is an important EMS application for providing real time, reliable and qualitative information on the system state. The observability analysis is the necessary function of the whole network state estimation. This paper addresses the incorporation of PMU measurements with the purpose of full network observability. The methodology is validated by the results on IEEE 14, 30 and 57 bus test system.

Abstract
This paper aims to characterize accurately each incident main cause, to analyse their occurrence with the intrinsic characteristics of the Portuguese territory, including geographical and meteorological data, and to define the requirements and guidelines to use this information as input for a risk assessment methodology, whose main purpose is to support control room operators in their continuous task.

Abstract
Nowadays the total sum of Distributed Generation (DG) in the Portuguese Distribution Network (DN) is extremely significant. Previously, load shedding schemes were designed without taking into consideration this type of generation. In this paper, the Portuguese Electrical System is studied through a static analysis using real data, and the new relay parameters to be applied in substations are evaluated, continuously bearing in mind the strict coordination with those of the DN. In order to achieve these purposes, an algorithm was developed to rank possible candidate substation feeders to the load shedding plan, using Ms Excel to process data and perform the calculations. The obtained results show that by using the designed algorithm it is possible to find a systematic process for determining under-frequency relay parameters considering the trade-off between shedding critical consumers and shedding DG. © 2009 IEEE.

Abstract
Taking into account that the non renewable recourses are less and less available worldwide we need to use renewable energies to produce electricity. The wind energy is nowadays the most attractive renewable energy, after hydropower, to produce electricity. Wind energy is the renewable energy source that had a higher growing in the last decades and can be considered a hope in future based on clean and sustainable energy. All over the world, energy companies are investing in technologies to make better use of renewable energy to generate electric power. Wind energy is the renewable energy source that had a higher growing in the last decades and can be considered a hope in future based on clean and sustainable energy. Unlike conventional fuels, wind energy is a massive indigenous power source permanently available in virtually every nation in the world. Wind power delivers the energy security benefits of fuel costs, no long term fuel price risk, and avoids the economic and supply risks that can arise with reliance on imported fuels and political dependence on other countries. The problems resulting by the production of electricity using wind power and by the interconnection of wind parks to the grid are discussed in this paper.

Abstract
In a world with a global market that is continually increasing, the productivity management plays an important key role to keep the competitiveness. The productivity can be achieved through the availability that can be increased through the adoption of efficient maintenance practices, by focusing the organisations on adequate type of maintenance strategy. Condition Based Maintenance (CBM) uses primarily non destructive testing techniques, as environmental indicators, visual inspection, monitoring functioning variables and performance data. This kind of maintenance replaces tasks of scheduled maintenance by warranted interventions predicted by on-condition limits previously defined. The interventions occur only when the equipments presents abnormal symptoms. The intervals of CBM are determined based on the expected delay to fail and are managed through the frequency by which the predictive interventions have to be done. The technological advances are accepted and applied on CBM systems, which includes improved knowledge of failure mechanisms, advancements in, failure forecasting techniques, monitoring and sensor devices, diagnostic and prognostic software, communication protocols, and computer networking technologies. The measurement precision and sensitivity of the Condition Monitoring (CM) techniques are used because they affect the reaction time available to reduce or eliminate the consequences of the functional failure. CBM maintenance tasks must be applicable under the situation of cost effective improvement, including external costs. The base of development of this paper is supported by an integrated system called SMIT (Terology Integrated Modular System), that permits to manage the maintenance itself, including on-condition maintenance, but it is modular enough to permit to associate new features, namely this last approach, in order to maintain the system up-to-date and, always possible, to anticipate the future.