Marcus Vinícius Alves Nunes

Planned islanding for Brazilian system reliability

This paper presents an impact study case of a new operational strategy regarding planned islanding operation of distributed generation. Traditionally, interconnection standards avoid islanding operation of distributed generation due to the concerns of equipment failure and safety issues. However, allowing the islanded operation of distributed generation may enhance reliability to final consumers and decrease outage cost by providing an alternative power source when there is an interruption in the upstream network. This paper performs dynamic studies in a Brazilian system which operates in the islanded mode during fault to supply critical loads. The analysis presented in this paper includes the behavior of the islanded system under load following and load rejection, faults, the load-frequency control and varying short-circuit level. The results show that this operational strategy can potentially bring many benefits to the distributed generator owner and customers.

Simultaneous Fault Section Estimation and Protective Device Failure Detection Using Percentage Values of the Protective Devices Alarms

This paper proposes a new approach to fault diagnosis in electrical power systems, which presents an aspect little explored in the literature that is the protective device failure detection together with the fault section estimation, since the majority of the methodologies so far proposed to fault diagnosis are limited to the fault section estimation alone. The proposed methodology makes use of operation states of protective devices as well as information related to the protection philosophy. Initially, these data undergo a preprocessing step to convert the format of 0 and 1 to percentage values. The conversion to percentage values allows the use of artificial neural networks, whose numbers of inputs do not depend on the number of alarms of the protection philosophy, or the type of bus arrangement or the number of circuit breakers. This allows the same set of neural networks to be trained and applied in different power systems with different protection schemes and bus arrangements. The proposed system has five neural networks, each containing few neurons and requiring 30 μs to perform fault diagnosis. The proposed system was trained considering the IEEE 57-bus system, containing different selective protection schemes, and subsequently tested in the IEEE 14-bus, 30-bus, and 118-bus systems, and Eletronorte 230-kV real power system.

A 3D learning tool for a hydroelectric unit

This paper presents a new learning system for a hydroelectric unit of energy (HUE) by using desktop virtual reality (VR) techniques. The software offers the possibility to understand the relation between the physical structures of a UHE, through computer simulations, graphical outputs, and animations. Three learning courses are offered. Educative is the first course that allows familiarizes the student with the structure and with the constituent pieces of a HUE, as well its general and technical information. The second course, maintenance, uses the learning approach based on practice and offers different learning levels, divided into three modes: automatic, guided, and exploratory, in which these modes are accessed according to the acquired degree of knowledge by the user in relation to maintenance procedures. The last course, operation learning, allows the student to visualize the operation of HUE during a certain event as the electromechanical dynamics of the turbine‐generator assemblage in the virtual world by the visualization of several requisite conditions before the startup procedure of HUE. Finally, it was made a performance comparison between the Electrical Engineering students which used the learning module with the case where that was not adopted.

Impact of distributed generation in steady state, voltage and transient stability — Real case

This paper investigates the influence of a synchronous distributed generation on a Brazilian real network. The distributed generation represents a small hydro power plant with total capacity of 30MW. The model of the network is developed in a professional computer software package. Simulations are carried out considering voltage dependency of static loads and different DG penetration levels. The technical aspects analyzed are steady-state voltage profile, electrical power losses, voltage and transient stability. Also, some adequacy aspects are analyzed, related to national and international standards. It was found that the distributed generation enhanced the overall system performance.

Reactive power control of direct drive synchronous wind generators to enhance the Low Voltage Ride-Through capability

This paper explores the performance of alternative voltage control strategy applied to direct drive synchronous wind generators, more specifically with permanent magnetic (PMSG). The reactive power control of the grid-side converter is investigated for voltage control purposes. In Brazil, the Grid National Operator (ONS) requires that wind turbines stay connected to the grid during voltage dips, but does not stipulate yet the need of reactive power injection during faults in the electric grid. It just specifies the Low Voltage Ride-Through (LVRT) capability curve for voltage dips that the wind generators should follow to avoid the trip of the under-voltage relay. Criteria of the synchronous wind generators protection are evaluated starting from short-circuit simulations in a test grid with adoption of the Brazilian grid code, without reactive power injection, being compared with those of other countries that adopt reactive power injection curves.

Genetic algorithms and treatment of multiple objectives in the allocation of capacitor banks in an electric power distribution system

Genetic Algorithm (GA) is a non-parametric optimization technique that is frequently used in problems of combinatory nature with discrete or continuous variables. Depending on the evaluation function used this optimization technique may be applied to solve problems containing more than one objective. In treating with multi-objective evaluation functions it is important to have an adequate methodology to solve the multiple objectives problem so that each partial objective composing the evaluation function is adequately treated in the overall optimal solution. In this paper the multi-objective optimization problem is treated in details and a typical example concerning the allocation of capacitor banks in a real distribution grid is presented. The allocation of capacitor banks corresponds to one of the most important problems related to the planning of electrical distribution networks. This problem consists of determining, with the smallest possible cost, the placement and the dimension of each capacitor bank to be installed in the electrical distribution grid with the additional objectives of minimizing the voltage deviations and power losses. As many other problems of planning electrical distribution networks, the allocation of capacitor banks is characterized by the high complexity in the search of the optimum solution. In this context, the GA comes as a viable tool to obtaining practical solutions to this problem. Simulation results obtained with a real electrical distribution grid are presented and demonstrate the effectiveness of the methodology used.

New Fuzzy Control Strategies Applied to the DFIG Converter in Wind Generation Systems

This paper presents new fuzzy control strategies which may be applied to the converter connected to the rotor of doubly fed induction generators (DFIG) composing a variable speed wind generation system connected to a real electrical grid. The fuzzy control proposed strategies are of the type supervised “look-up-table”. The performance of these intelligent controllers are compare with the fixed parameters PI controllers for fault ocurrence in the power system. The fuzzy controllers are supposed to better the transient performance of the electrical power system as compared with the conventional PI controllers. The obtained results from simulation studies have of the fuzzy controllers. To formulate the simulation studies an equivalent mathematical model of a significant number of wind turbines was implemented using the MATLABTM software packcage.

New solution for resolution of the Economic Load Dispatch by different mathematical optimization methods, turning off the less efficient generators

The Economic Load Dispatch (ELD) is one of the most important tasks of optimization and operational decision for the in power systems. Traditional materials and methods have been developed to solve the economic dispatch. They allow you to determine the ideal combination of the output power of each generating unit, in order to meet the desired demand, without violating the restrictions. Traditional methodologies underutilize the capacity of the power plant by leaving all generators connected, in cases where demand is less than the total generation capacity of the plant, increasing total fuel costs. The objective of this work is to perform a comparison of several mathematical optimization methods (Lambda Iteration, Newtons Method and Quadratic Programming) in solving the ELD problem, considering the traditional methodology and the proposed methodology that includes turning off the less efficient generators.

Analysis of electromagnetic-mechanical stresses on the winding of a transformer under inrush currents conditions

The main objective of this paper is to assist in the investigation of electromagnetic forces, structural deformation, stresses, and Safety factor when energizing unloaded transformers. The methodology is based on modeling of a single-phase 50 MVA transformer subjected to inrush currents through finite element method (FEM). In this perspective, the conditions of inrush currents are used to estimate the magnetic field density dispersion in the transformer and to find the values of forces in axial and radial directions. These components are distributed along the energized windings for observing the loads in high- voltage windings. Thus, this article will contributes with the investigations of a structural Analysis on transformers when subjected to inrush current.

Security-Constrained Optimal Dispatch of Combined Natural Gas and Electricity Networks Using Genetic Algorithms

This paper proposes a method based on genetic algorithm (GA) for the security-constrained 11 optimal dispatch of integrated natural gas and electricity networks, considering operating scenarios 12 in both energy systems. The mathematical formulation of the optimization problem consists of a 13 multi-objective function which aims to minimize both cost of thermal generation (diesel and natural 14 gas) as well as the production and transportation of natural gas. The joint gas-electricity system is 15 modeled by two separate groups of nonlinear equation, which are solved by the combination of 16 Newtons method with the GA. The applicability of the proposed method is tested in the Belgian gas 17 network integrated with the IEEE 14-bus test system and a 15-node natural gas network integrated 18 with the IEEE 118-bus test system. The results demonstrate that the proposed method provides 19 efficient and secure solutions for different operating scenarios in both energy systems. 20 21