Abstract
Maintenance management is a subject that, instead of reducing importance, with the increase of equipment reliability, it increases its role in the companies and obliges the increase of the level of demand of professionals involved because of the new technical and environmental demands. Sometimes, scientific developments anticipate the company's needs while other times it is the company that challenges science. The maintenance area is an example that offers challenges to both science and companies in order to optimize the performance of equipment and facilities. This is also the case of wind generators, because their expansion, evolution, maintenance and reliability guarantee, needs to be adequately articulated in order to maximize production time and, obviously, to optimize maintenance interventions. It is because of this kind of challenge that the authors are developing new methodologies in the area of wind generators that aims to optimize the cycles of production and, consequently, reduce other kinds of energy production. The new features include on-line measures and the corresponding on-time treatment, using algorithms based on time-series forecasting and wireless technology to transmit the signals. The prediction models uses regression techniques based on SVR, ARMA and ARIMA models, modified according to this specific case. The weather, conditions and the technical and construction characteristics of wind generators are only some variables that we have in account in the models that are under development. But, if these conditions are important, it is also very important to collect, read and treat data from sensors placed in wind generators that, because their geographic dispersion, and difficulty of transmission, must be solved adequately and conjugated with the above referred algorithms, in order to implement an adequate system. This is the ambit of the present article that reports a wide approach of a subject that usually is managed separately, this is, the hardware from one side and the prediction algorithms from other side. This is possible because the team has being researching and developing algorithms and an information system, since many years ago, around the terology subject that is a wider vision of maintenance. Then, the new methodologies, above mentioned, will be, later, incorporated through new predictive maintenance modules in an integrated maintenance management system called SMIT (Terology Integrated Modular System). The base of SMIT is accessed through a client-server system and a browser system that includes the main modules of a traditional system, as well as a fault diagnosis module, a non-periodic maintenance planning module and a generic oncondition maintenance module, among other innovations.

Abstract

Abstract
Today, the State Estimation is considered as the heart of nearly all modern network control centers. Among other factors, the technical developments in fast data communication network technology opens up the possibility of parallel and distributed implementations of the state estimation function. This paper provides an overview of the state of the art in Power Systems State Estimation.

Abstract
In this paper a combined Monte Carlo-extended equal area formulation for the transient security assessment of a multimachine power system is proposed. This approach evaluates a probabilistic measure of the transient stability, instead of just a particular response to a specified disturbance. Due to the large number of calculations required, the application of the extended equal area criteria reduces drastically the computing time, since it allows to evaluate the critical clearing times and the stability margins without solving numerically the differential motion equations. The probabilistic software package TRANsySTEM, developed by the authors to study the transient security of a multimachine system, is applied to a test network. During the simulation time, the occurrence of disturbances and the subsequent protective actions are assumed as a stochastic process. Finally, the obtained results are discussed and some conclusions that provide a valuable contribution to the understanding of the system dynamics are pointed out.

Abstract
The increasing competitiveness of the power systems' environment has created new challenges to the power system security assessment, demanding the development of new methodologies. Important aspects of this evolution are the unbundling of generation, transmission and distribution, caused by regulatory changes and creating a more competitive environment, the increased environmental concerns making it more difficult to build new assets, and the strong incentives to the generation from renewable energy sources. These factors contribute to the increasing stress on operating conditions and, consequently, cause more vulnerable networks. In recent years, the daily routine of transmission system operators has become more complex. The interconnected network is no longer just for mutual support; nowadays it has become the base platform for trading electricity allowing the shifting of increasing volumes of power across the system. Despite all the benefits that doubtless are many, from the operations perspective, the free electricity market presents more unpredictable and less stable power flows, a market-dependent generation pattern, also more unpredictable and less controllable. In addition to the latter, the significant amount of generation from renewable energy sources also contributes to place the system closer to its security limits. Therefore, and despite the bigger complexity and increased quality of service requirements, the energy supply and the optimization of resources remain a permanent goal, fulfilling all the security principles used for system operation. Incidents are naturally unpredictable and after the large disturbances which occurred in recent years (such as the blackouts on 9th May of 2000 in Portugal, on August 14th 2003 in the United States of America, on September 28th 2003 in Italy and in the European UCTE Network on November 4th 2006), the awareness of the risk of unpredictable disturbances has increased, and it has become essential for the decision-making process to have security indices that allow the operator to react in advance and to be aware of inherent risks, preventing harmful situations. The use of methodologies that take advantage of the actual real-time conditions in combination with past knowledge is extremely interesting in the system operation environment, because it gives a more accurate overview to the control room operators. Since long, the deterministic security assessment has been used to guarantee a high level security in system operations of Transmission Systems, being known as N-1 criterion. It tends to provide a conservative security region for protecting the system against severe contingencies. In the deterministic approach only the consequences of contingencies are assessed, but it does not consider likelihood, or better it does consider likelihood equal to one for all contingencies, therefore it cannot address increased or decreased uncertainty in operating conditions, such as adverse meteorological conditions or risk of forest fires. The advantages of probabilistic methods in comparison with deterministic ones are further developed in [1, 2]. Hence, the probabilistic assessment has become an important topic for researchers and engineers, because by combining consequences and probability it is possible to evaluate risk of contingencies, as in (1): Riskcontingency i = probabilitycontingency i × severitycontingencyi (1) Through the historical data, it is possible to affirm that most incidents originate from overhead lines (OHL). From 2001 until the end of 2008, OHL represent on average 91% of the incidents with origin in the Portuguese transmission system. Overhead lines, due to their dispersion over a wide geographic area and because of the many different ground characteristics where they are deployed, are more exposed to the action of external factors which cause most of the grid incidents. An accurate characterization of each incident's cause, an analysis of their occurrence and of the intrinsic characteristics of the Portuguese territory is presented in reference [3], including geographical and meteorological data, which are a crucial part of the inputs for the risk assessment methodology. This paper aims to describe the key issues of the calculation of the circuit-part of overhead lines contingencies probability, as part of the risk assessment methodology (figure 1), which is being developed and has as main purpose to support control room operators in their continuous task.

Abstract
Nowadays most of the transmission systems' operating conditions are more stressed due to the introduction of a competitive environment in the power system industry and the regulatory changes causing the unbundling of generation, transmission and distribution, the environmental concerns, which limit the construction of new transmission lines and generation capacity, and the strong incentives to the generation through renewable energy sources. The use of methodologies that take advantage of the actual real-time conditions in combination with past knowledge is extremely interesting in the system operation's environment, because it gives a more accurate overview to the control room operators allowing them to prevent harmful situations. Obviously, this type of methodologies has received even more interest after the large disturbances which occurred in recent years, because they increase the awareness about the risk of unpredictable disturbances. Recent international data show that the frequency of large blackouts has increased and also that simple initiating faults can have very severe consequences. References [1-4] present a few examples of severe disturbances, which occurred in the recent past. Despite all the efforts being done regarding supervisory practices, operation strategies and protection and control systems' improvements, it is technically and economically impossible to eradicate major disturbances and blackouts. They will be a permanent threat to the electrical power systems, making incident analysis a crucial activity. The risk assessment methodology that is being developed is composed of two parts: probability of occurrence and severity for all contingencies under analysis. This paper aims to present the complete probabilistic model used to calculate the probability of occurrence of contingencies, including overhead lines, transformers and busbars. N-2 common cause contingencies are also considered for faults caused by lightning and forest fires.