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
The significant increase of production of energy from renewable sources led to the necessity of developing new ways of exploration of the power systems. The evaluation of the intermittent of the renewable generation, which characterizes some of the renewable sources, such as wind power, becomes very important to assess its impact on the generation reliability of power systems. This paper studies and analyses the reliability impact of a Portuguese wind farm in the power system using a computer model which represents the Portuguese wind farm by a Markov process. The probabilistic model combines the stochastic characteristics of wind speed with the characteristics of the wind turbines. The transition between the operative and failed states of the wind turbines, characterized by failure and repair rates, are combined with wind behaviour to allow the calculation of some performance indices used on the analysis of the wind power output expectation of the Portuguese wind farm. Some results obtained with the model applied to a Portuguese wind farm are presented. The results show the modelling of the mind form in reliability studies and the use of the model to evaluate the generation states and their probabilities, allied to several reliability indices.

Abstract
This paper presents a study of the application of artificial neural network (ANN) to the evaluation of the distance to the voltage collapse point. Voltage stability has been of the major concern in power system operation. To prevent these problems, technical staff evaluates frequently the distance of the operation state to the voltage collapse point. This distance normally is calculated with power flow equations. This classic technique is very slow for electric power systems with large dimension. In abnormal exploration situations it may introduce serious limitation in the voltage stability analysis process. So, the application of a fast and reliable evaluation technique is very important to diminish the evaluation time. This paper also presents the method FSQV (Full sum dQ/dV) for the detection of the collapse point.

Abstract
Wind energy is the renewable energy source with a higher growth rate in the last decades. The huge proliferation of wind farms across the world has arisen as an alternative to the traditional power generation and also as a result of economic issues which necessitate monitoring systems in order to optimize availability and profits. Tools to detect the onset of mechanical and electrical faults in wind turbines at a sufficiently early stage are very important for maintenance actions to be well planned, because these actions can reduce the outage time and can prevent bigger faults that may lead to machine stoppage. The set of measurements obtained from the wind turbines are enormous and as such the use of neural networks may be beneficial in understanding if there is any important information that may help the prevention of big failures. © 2011 IEEE.

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
In this paper it is studied and analyzed the impact of different security performance indices on a contingency screening and ranking algorithm. The proposed filtering technique consists of three modules, with different complexity levels. The contingencies are ranked in accordance with severity indices that allow assessing the influence of the overloads and voltage limit violations in the power network. The developed software package was applied to the IEEE 118 Test Power System. The simulation results that were produced using two different sets of security indices were compared, showing a satisfactory agreement The simulation was carried out considering a monotonous increase of the load level as well as a random one. For the different solutions the computing times were also obtained. Finally, some conclusions that provide a valuable contribution to the understanding of the Electric Power System security analysis are pointed out. © 2003 IEEE.