Lia Toledo Moreira Mota

An Analytical Method for Analysis of Large-Disturbance Stability of Induction Generators

This paper presents an analytical method for analysis of large-disturbance stability of squirrel-cage rotor induction generators. The proposed analytical method is based on the steady-state equivalent circuit of the induction generator and on the concepts of stable and unstable electrical-mechanical equilibrium points, which are calculated in the electrical and mechanical torque versus rotor speed space. This analytical approach sheds light on theoretical issues related to the stability of induction generators. Moreover, this method can be used as a guide to significantly reduce the simulation efforts necessary to assess the large-disturbance stability of induction generators. The method has been validated by comparing the results obtained by the analytical method with those determined by extensive dynamic simulation results through a sensitivity study. In the dynamic simulations, the induction generators are represented by a fourth-order algebraic-differential model. In addition, a simple approach is proposed for assessing the fault ride-through capability of induction generators.

Visualization of Power System Restoration Plans Using CPM/PERT Graphs

The risk of blackouts is inherent in complex power systems, despite all efforts to prevent their occurrences. To mitigate the consequences of major blackouts, better restoration plans have been demanded. Commonly, these plans consist of a set of actions textually described. In order to enhance the operating staff comprehension about the restoration plan, this paper proposes a methodology, based on CPM/PERT graph theory, that allows power system restoration plans to be graphically visualized. This approach permits to clearly see the precedence relations among activities and to graphically follow the restoration process during its execution. The methodology can also take advantage of calculations involved with CPM/PERT methods to evaluate the restoration duration and the plan critical path. The application of the proposed approach is illustrated using the IEEE 30-bus network and the restoration plan developed for a portion of the Brazilian interconnected power system.

Teaching power engineering basics using advanced web technologies and problem-based learning environment

This paper describes the experience of teaching power systems basics to undergraduate engineering students using a pedagogical approach that is based upon computer-mediated and problem-based learning in an integrated way. In this approach, an interactive learning environment based on web technologies replaces the traditional lectures. The pedagogical project behind this approach is focused on the problem-based learning paradigm, where the students are instigated to construct the knowledge required to solve the problem (constructivist learning). The paper addresses the technological aspects, such as how to create simulators using Java applets and animation, as well as the pedagogical aspects, such as student performance and knowledge acquisition. The experience of using this approach at the State University of Campinas, Brazil, during the years 2001/2002 is described in detail. Advantages and disadvantages of this approach are also addressed and finally the students point of view are presented based on surveys.

PREDICTING BATTERY CHARGE DEPLETION IN WIRELESS SENSOR NETWORKS USING RECEIVED SIGNAL STRENGTH INDICATOR

This article aims to identify an adequate mathemati cal model to predict battery power depletion at the nodes of a Wireless Sensor Network (WSN), by analyzing the Received Signal Strength Indicator (RSSI). Six general models were tested, the simplest Average model, Linear Regression model, Autoregressive (AR) models and Autoregressive Moving Average (ARMA) models.The selected model (AR) presented a low absolute mean residue and adequately represents the charge depletion process, permitting to predict it s behavior and to detect the best moment to replace b atteries in the WSN nodes.

Dynamic evaluation of reenergization times during power systems restoration

CPM/PERT graphs can be successfully used as a computational model representation for power system restoration plans. They constitute an adequate container to decompose the plans into a logical interdependent sequence of activities and stages. This work describes a computational methodology that could be adopted in order to efficiently estimate the duration of restoration activities using CPM/PERT graphs, during the electric network reenergization. The methodology is based on object-oriented modeling and heuristic search approaches. Some issues about graphical representation of restoration plans and alarm generation for operators are also addressed. Test results of the proposed methodology, conducted on the IEEE-30 buses network, are presented.

Feasibility of Desktop Virtualization Per Software Services and Local Hardware Based on the Network Throughput

In recent years, virtualization computing has become a worldwide reality present in datacenters servers of most organizations. The motivations for the use of this solution are focused primarily on cost reduction and increases in availability, integrity and security of data. Based on these benefits, recently it was started the use of this technology for personal computers as well. That is, for desktops, giving birth to the so-called desktop virtualization. Given the technical advantages of the approach, its growth has been so significant that, before 2014, it is expected to be present in over 90% of organizations. However, this new method is completely based on a physical client-server architecture, which increases the importance of the communication network that makes this technique possible. Therefore, analyzing the network in order to investigate the effects according to the environment implemented becomes crucial. In this study it’s varied the local’s client hardware and the application, i.e., the service used. The purpose was to detail their effects on computer networks in a Quality of Service (QoS) parameter, throughput. Secondarily are outlined perceptions regarding the Quality of Experience (QoE)? This culminated in an assessment that traces the feasibility for applying this technology.

Restoration building blocks identification using a heuristic search approach

The restoration process can be defined as the control actions sequence necessary to reenergize power lines and loads in a rapid and safe way, after a disturbance in power supply. In this work, a methodology to identify restoration building blocks (nuclear elements of the restoration process) is proposed. This method is based on the numerical inspection of a nodal matrix associated to heuristic search techniques in different stages, taking into account load priority levels and the identified RBBs (restoration building blocks) interconnection. Operational costs and electrical feasibility of suggested configurations are also considered in the problem formulation. The proposed method was tested using IEEE14 and IEEE30 networks

Simulation and analysis of restoration plans using fuzzy rule-based systems

A methodology for virtual simulation of restoration plans is desirable because it can save costs and resources during the initial restoration planning stage or before the plans evaluation through drills and exercises. Analyzing the Brazilian power system restoration plans, it is possible to detect the regular occurrence of three elements: the usage of a standard linguistic variables basis, the presence of decisory processes and the existence of prerequisite conditions and restrictions that must be attended before the reenergization can proceed. These facts suggest the use of fuzzy rule-based systems in order to simulate the plans activities coordination and logical precedence. In this work, a fuzzy rule based approach is proposed for the plans virtual simulation, taking advantage of the tabular format of the restoration operative instructions defined, for the Brazilian systems restoration, by the National System Operator (NSO).

Decision Making Support in Telecommunications Networks Management with Matrix Analysis of Fuzzy Rule-based Systems

This paper presents a new general method for Fuzzy analysis, based on mathematical operations between arrays, which allow the development of simple and fast computational algorithms, for applications to support decision making in different processes of the telecommunications network management. The approach is generic enough to be applied at the operational, tactical and strategic levels of management. To validate the method, prospective scenarios are analyzed in the period of 2012-2020 for Wire line services in Brazil, developed through exploratory research, based upon data from official bodies such as Anatel (National Telecommunications Agency), IBGE (Brazilian Institute of Geography and Statistics) and the Ministry of Communications

Non-Destructive Current Sensing for Energy Efficiency Monitoring in Buildings with Environmental Certification

Nowadays, buildings environmental certifications encourage the implementation of initiatives aiming to increase energy efficiency in buildings. In these certification systems, increased energy efficiency arising from such initiatives must be demonstrated. Thus, a challenge to be faced is how to check the increase in energy efficiency related to each of the employed initiatives without a considerable building retrofit. In this context, this work presents a non-destructive method for electric current sensing to assess implemented initiatives to increase energy efficiency in buildings with environmental certification. This method proposes the use of a sensor that can be installed directly in the low voltage electrical circuit conductors that are powering the initiative under evaluation, without the need for reforms that result in significant costs, repair, and maintenance. The proposed sensor consists of three elements: an air-core transformer current sensor, an amplifying/filtering stage, and a microprocessor. A prototype of the proposed sensor was developed and tests were performed to validate this sensor. Based on laboratory tests, it was possible to characterize the proposed current sensor with respect to the number of turns and cross-sectional area of the primary and secondary coils. Furthermore, using the Least Squares Method, it was possible to determine the efficiency of the air core transformer current sensor (the best efficiency found, considering different test conditions, was 2%), which leads to a linear output response.