Voltage stability has become a very important issue of power systems analysis. This paper discusses some important aspects related to voltage stability indices in electric power systems. Some techniques previously studied in the literature are analyzed and a comparison of the performance of several indices is presented. The effectiveness of the analyzed methods are demonstrated through numerical studies in IEEE 14 busbar test system, using several different scenarios of load increase

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.

3D Virtual Labs are the support of learning, a tool of education in the future. Learning in a 3D environment allows greater interaction with contents in a unique way as students perceive it as being really there. Simulations are being designed, a combination of real-world environment with the information supplied by devices, where measurements can be replicated and data analyzed. This study presents a virtual scenario of a Measurements and Instrumentation laboratory.Electrical Engineering courses aim to train students to succeed in meeting the challenges within competitive and everchanging professional contexts. In order to prepare undergraduate students for ongoing success, the courses must provide effective training in the application and development of practices, typically implemented in large projects and organizations. Developing high quality engineering course units is definitely a challenging task. Courses can be provided remotely, but careful planning is required to design quality course units because problems may occur in meeting quality targets. The developments in information and communication technologies (ICT), including multimedia and internet-based education platforms, facilitate the creation of reliable solutions to these challenges. Studies show that a smart application of multimedia technologies and webbased education platforms can provide great results towards better quality of engineering courses. Many challenges on how to suitably approach the educational process have already been put forward. Higher Education institutions use multiple approaches to teaching and learning, combining a range of methods, including e-learning, videoconferencing, face-to-face teaching and hard-copy resources in course delivery. The authors present a software model for engineering, which is based mainly on the Wirefusion ^® software, and a virtualreality platform called VEMA. The project intends to improve the quality of teaching and learning in higher education through effective application of information technologies and the sciences of learning. 3D virtual learning environments arise as solutions to the extent that, in addition to offering features associated with communication and information sharing, they promote flexible learning spaces and moments. At the level of higher education, and in accordance with the paradigm of Bologna, virtual environments acquire special importance to allow learning beyond the classroom time and space.

Promoting equity, equal opportunities to all and social inclusion of people with disabilities is a concern of modern societies at large and a key topic in the agenda of European Higher Education. Despite all the progress, we cannot ignore the fact that the conditions provided by the society for the deaf are still far from being perfect. The communication with deaf by means of written text is not as efficient as it might seem at first. In fact, there is a very deep gap between sign language and spoken/written language. The vocabulary, the sentence construction and the grammatical rules are quite different among these two worlds. These facts bring significant difficulties in reading and understanding the meaning of text for deaf people and, on the other hand, make it quite difficult for people with no hearing disabilities to understand sign language. The deployment of tools to assist the daily communication, in schools, in public services, in museums and other, between deaf people and the rest may be a significant contribution to the social inclusion of the deaf community. The work described in this paper addresses the development of a bidirectional translator between Portuguese Sign Language and Portuguese text. The translator from sign language to text resorts to two devices, namely the Microsoft Kinect and 5DT Sensor Gloves in order to gather data about the motion and shape of the hands. The hands configurations are classified using Support Vector Machines. The classification of the movement and orientation of the hands are achieved through the use of Dynamic Time Warping algorithm. The translator exhibits a precision higher than 90%. In the other direction, the translation of Portuguese text to Portuguese Sign Language is supported by a 3D avatar which interprets the entered text and performs the corresponding animations.

Over the last years, there has been an increase in hearing-impaired students who use sign language as their main form of communication attending higher education institutions around the world. The knowledge that their comprehension of texts is reduced due to sentence structure differences causes a need for more solutions to improve communication and support students in environments where they are unable to be accompanied by sign interpreters. This article details the improvements and current structure of the VirtualSign platform, a bidirectional sign language to text translation tool that has been in development since 2015. The platform is divided into two main parts, sign to text and text to sign, and both components are described and explained. The solution has received positive feedback on several tests and a pilot experiment, and is being developed with partnerships with sign interpreters from six different European countries. Some planned improvements and future functionalities for the tool are also mentioned and detailed.

Virtual labs are more likely to offer a user friendly environment as well as greater flexibility, allowing students to carry out experiments and repeat them as often as necessary. Nevertheless, they do not discard the need for a conventional system as traditional labs are a valuable asset. In this context, the student is the centre of the whole process, taking on the main role and is responsible for his/her own learning process, although there may be an extra support through in-class sessions in order to keep him/her in contact with the system, to offer guidance and motivation for the challenges ahead. One of the advantages of virtual experimentation is the opportunity of using a lab in situations which might be impossible otherwise, allowing students to take part in lab sessions; another one is related with its use to improve learning results. Virtual experimentation labs create flexible learning environments suitable for different types of learners, allowing the interactive and systematic development of competences in the various areas of learning and can be used to complement the conventional type of lectures. VEMA is a practical asynchronous software tool devised to meet the needs of students who can't be present in regular lab classes in the Electrical Engineering Department of ISEC (Instituto Superior de Engenharia de Coimbra).