Abstract
In this work is discussed the importance of the renewable production forecast in an island environment. A probabilistic forecast based on kernel density estimators is proposed. The aggregation of these forecasts, allows the determination of thermal generation amount needed to schedule and operating a power grid of an island with high penetration of renewable generation. A case study based on electric system of S. Miguel Island is presented. The results show that the forecast techniques are an imperative tool help the grid management.

Abstract
One of the major problems of voltage stability is the reactive power limit of the system. Improving the system's reactive power handling capacity via Flexible AC transmission System (FACTS) devices is a solution for prevention of voltage instability. In this paper it is studied the influence of Static Synchronous Compensators (STATCOM) and Static Var Compensators (SVC) in dynamic Voltage Stability during Low Voltage Ride Through (LVRT), in wind farms. The wind turbines are equipped with pitch control coupled with a Fixed Speed Induction Generator (FSIG). Due to the nature of asynchronous operation, system voltage instability of wind farms based on FSIG is largely caused by the excessive reactive power absorption by FSIG after a fault due to the large rotor slip gained during fault. Wind farm models based on FSIG and equipped with either STATCOM or SVC are developed in EUROSTAG. The Automatic Voltage Regulators (AVR) of the generating units and the turbine speed governors were modeled in detail. Different load models were used and the Under Load Tap Changers (ULTC) were also taken into account. Finally, some conclusions that provide a better understanding of the dynamic voltage stability of a system with FSIG model during LVRT, using various capacities of STATCOM and SVC are pointed out.

Abstract
This paper discusses the effective contribution of a Learning Object (LO) to teach circuit theory based on research conducted with students of higher education, and their interaction with a teacher of Electronics. From the results of such research, it is pointed out which features one wants in the LO so that it successfully promotes learning. It is in this perspective that this work was conceived having as goal the development of LO, admitting that this may be a possible alternative to represent models of interactions, which occur within the area, thereby improving understanding of physical concepts, in particular those involved with the subject of electrical circuits. It has also as objective to characterize the learning process through a series of situations that are replicated leading to a set of behaviors from the students. It is assumed that the use of this tool can lead to acquiring a specific set of skills, a better practice and meaningful learning.

Abstract
With the development of synchronized phasor measurement technology in recent years, it gains great interest the use of PMU measurements to improve state estimation performances due to their synchronized characteristics and high data transmission speedThe ability of the Phasor Measurement Units (PMU) to directly measure the system state is a key over SCADA measurement system. PMU measurements are superior to the conventional SCADA measurements in terms of resolution and accuracy. Since the majority of measurements in existing estimators are from conventional SCADA measurement system, it is hard to be fully replaced by PMUs in the near future so state estimators including both phasor and conventional SCADA measurements are being consideredIn this paper, a mixed measurement (SCADA and PMU measurements) state estimator is proposedSeveral useful measures for evaluating various aspects of the performance of the mixed measurement state estimator are proposed and explainedState Estimator validity, performance and characteristics of the results on IEEE 14 bus test system and IEEE 30 bus test system are presented. © ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING.

Abstract
The voltage stability security is a very important and relevant issue in the modern power networks. The voltage instability can drive the system to a blackout. One of the methodologies to deal with this problem is analysing the trajectory sensitivity of the system. The STATCOM is an important hardware that is used to improve the voltage stability of an electric power network. The main objective of this paper is to analyse the results of different studies that were realized in a power system with wind farms. The wind farms were modelled considering that the wind turbines were equipped with pitch control coupled with a Permanent Magnet Synchronous Generator. The EUROSTAG program was used to obtain the simulation results. The Matlab software package was used for the post-processing module developed.

Abstract
In this paper it is applied a Rough Setapproach that takes into account an incomplete information system to study the steady-state security of an electric power system. The Rough Set Theory has been conceived as a tool to conceptualize, organize and analyze various types of data, in particular, to deal with inexact, uncertainor vague knowledge. The knowledge acquisition process is a complex task, since the experts have difficulty to explain how to solve a specified problem. So, an incomplete set of relevant information may arise. The study presents a systematicapproach to transform examples in a reduced set of rules. These rules can be used successfully to avoid security problems and provides a deeper insight into the influence of parameters on the steady-state system performance. © Springer Science+Business Media Dordrecht 2014.