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
This article covers a rather innovative and powerful technology that enables the creation of a 3D interactive laboratory for WEB applications based on open standard VRML format for 3D multimedia and the subsequent distribution of this virtual laboratory on the Internet. The project develops an environment, called "interactive technology of a 3D Internet Laboratory" to create various types of 3D laboratory experiments as well as their application via the Internet. The application produced is the creation of a 3D virtual laboratory for measurements and instrumentation. The description of the laboratory, fonts and data are also provided. The various steps for creating a 3D virtual laboratory are presented. Lastly, the application of the "interactive technology laboratory 3D" is displayed and can be considered as a step forward in the development of innovative technologies for distance learning. © 2011 University of Maribor.

Abstract
Electrical utilities are confronted daily with unpredictable events in their grids, which may lead to severe security level repercussions in the system, far exceeding all the security principles used for operation and consequently jeopardizing the essential service to the consumers. Incidents are unpredictable disturbances and recent experiences prove that severe contingencies happen. Given these facts, the need to evaluate harsher contingencies arose and such analysis must be rigorous and exhaustive. The security principles used for planning and system operation determine that, given an incident in the Electrical Power System (EPS) which involves the breakdown of any grid element or the simultaneous failure of a double circuit overhead line or the failure of the largest generator in service the supply interruption shall never take place (excluding single-feeding points without alternative) or permanent overloads. To analyse the steady-state security of an EPS it is required too, accurately and efficiently identify the critical contingencies set, i.e., those that when occur may endanger the system's security. The steady-state simulations of the Portuguese Transmission System (PTS) were made in PSS/E software from Siemens PTI using snapshots that represent pictures of the real system. All these security studies produce a large amount of data and information. Recently, the Rough Sets Theory (RST) has been used successfully to handle efficiently problems where large amounts of data are produced. RST constitute a framework for inducing minimal decision rules. These rules in turn can be used to perform a classification task. The main goal of the rough set analysis is to search large databases for meaningful decision rules and finally acquire new knowledge. This approach is based on four main topics: Indiscernibility, Approximation, Reducts and Decision rules. A reduct is a minimal set of attributes from the whole attributes set that preserves the partitioning of the finite set of objects and therefore the original classes. It means that if the redundant attributes are eliminated the reducts are found. Decision rules extracted knowledge, can be used when classifying new objects not in the original information system. In this paper it is proposed an efficient study and contingency analysis in the PTS using the RST. The developed methodology produces a system operation classification, distinguishing in four possible states: normal, alert, emergency I and emergency II. These different operating states correspond to a four levels of security. The four states can be classified horizontally as secure, in normal state and insecure for the remaining ones. The computer programs SecurMining2.0 developed, were applied to the Portuguese test power network.

Abstract
In this paper it is presented a methodology to assess the dynamic voltage stability of an electric power system using trajectory sensitivity analysis. Trajectory sensitivity analysis can provide valuable insights into the security of an electric power system. In this study it was simulated a significant disturbance in two test power network. The Automatic Voltage Regulator of the generating units, the Under Load Tap Changer and loads models were taken into account. The simulation results were obtained using EUROSTAG program and post-processing module developed using the Matlab software package. © 2011 INESC Coimbra.

Abstract
State estimator is vital for on-line power system monitoring, analysis and control. With the increasing use of synchronized phasor measurement units (PMU) in power grids, how to utilize phasor measurements to improve the precision of state estimator becomes imperative. In this paper, a state estimator including voltage phasors, injected current phasors and traditional measurements is proposed. 14 IEEE bus system and 30 IEEE bus system are used as test systems and the simulation results demonstrate that the presented state estimation algorithm combining traditional SCADA measurements with PMU (Phasor Measurement Unit) measurements for power system state estimation improves the precision greatly. © 2011 INESC Coimbra.

Abstract