Geraldo Caixeta Guimarães

Analysis and Evaluation of Residential Air Conditioners for Power System Studies

Air conditioners deserve special attention because they represent a significant part of the power system load, mainly in high temperature regions. This work takes into account conventional and variable-speed types, as the latter one presents two possible arrangements, i.e., with and without undervoltage protection. The modeling of equipments is analyzed for simulation purposes, as a novel representation of variable-speed units with undervoltage protection is introduced. The behavior of each air conditioner is verified in steady state operation considering typical power quality and voltage disturbances that occur in power systems such as voltage sags and interruptions. Furthermore, the influence of the aforementioned equipment on the power system is analyzed within the context of a distribution network

Methodology for control and analysis of a series multiterminal DC system

The DC electric energy transmission has shown to be an attractive solution for many applications. In the last few years, the multiterminal arrangement has assumed a relevant position facing die growing necessity of the main grid. Although a great deal of development has been made for parallel schemes, there is not much information and experience in literature concerning series multiterminal DC transmission systems. Thus, this paper aims to present the results of studies to establish a control strategy for such systems, as well as die implementation into a transient stability program. Study results using a typical system are presented and discussed in order to verify the proposed model performance.

A Comparative Performance Analysis of a Controlled D.C. and A.C. Motor Which Emulates Wind Turbines for Teaching and Research Purposes

The growth of wind farms has motivated the development of computational and experimental approaches which supplement needs related to teaching and research in the field of engineering. Even though there have already been recognized advances made in the field of computational modeling, the development of viable means through experiment to clarify the operation of wind farm complexes has become relevant to this area. In light of these facts, this study focuses on a comparative evaluation of two strategies which emulate wind turbines: one based on d.c. motors, the other on three-phase induction motors. In both cases, the apparatus is modeled on time-domain representation techniques and motor driving structures are proposed, allowing for the reproduction of features typically found in wind turbines. Lastly, experiments are realized and the results discussed for the confirmation of potentialities, along with the efficiency of the strategies used.

Steam Turbines Under Abnormal Frequency Conditions in Distributed Generation Systems

Considerable efforts have been developed to encourage the installation of independent electricity producers in distribution systems. Obvious example of such efforts is demonstrated by the attempt to standardize their interconnection and protection requirements. However, this standardization can be difficult due to variations in the design of distribution circuits, the various types of generators coupled to the network and the particular requirements of each utility. However, a series of questions points to the development of further studies to ensure the quality of electric power, the system transient stabilty and lifetime of the blades of steam turbines (Moura et al.,2011).

Maximization of variable speed wind turbine power including the inertia effect

In recent decades wind energy has gained great prominence in various parts of the world, resulting in the emergence of new technologies to improve its efficiency. Thus, this paper presents a technique for maximizing the power extracted from the wind by a variable speed wind turbine through measurements of voltage and current at the three-phase rectifier terminals, establishing its rotor speed control by changing the duty cycle of the boost converter. Hence, the proposed algorithm enables the maintenance of the maximum value of the turbine power coefficient even before a significant variation of wind speed and considering the inertia effect. The effectiveness and versatility of the suggested method is verified through computer simulations using the software ATP.

The dynamic interaction of independent power producer synchronous machines connected to a distribution network in ATP-EMTP

The main task in this paper is to present a performance analysis of a distribution network in the presence of two synchronous generators in parallel, with its speed and voltage regulators modeled with TACS - Transient Analysis of Control Systems, for distributed generation studies. This type of configuration is common in systems where renewable fuels are used as sugar cane bagasse or straw. Must be highlighted that these generators are driven by steam turbines, and the whole system with regulators and the equivalent of the power authority system in the point of connection (CCP - Common Coupling Point) are modeled in the “ATP-EMTP - Alternative Transients Program”. Technical questions studied here refer to steady-state voltage profile, voltage stability, voltage dip due to a balanced three-phase fault, load rejection, distribution line outage and the behavior of machine regulators facing the aforementioned contingencies. Results show that, in some cases, the independent power producer (IPP) can be a risk to the physical integrity of the system and in other cases can be very beneficial to the distribution system in the point of connection.

Influence of Load in Performance of the Static Excitation Control of Synchronous Generator

This paper has as its prime objective to analyze the performance of a static excitation system in function of the type of load applied to the synchronous generator. This is seen through how the magnitude, the power factor and the load variation rate influence the working of the excitation system in the restoration of the generators terminal voltage. Also shown is the influence of the non-linear load in this type of excitation system.

Comparative Study of TACS/DBM and MODELS of ATP-EMTP Applied to Power Systems Computer Simulation

The ATP-EMTP has become a reference program for electromagnetic transients computer simulations. Due to the contributions of its officers users groups spread around the world, several improvements were made and additional resources have been developed to facilitate and expand its application. Tools, like ATPDraw, PlotXY, TACS, DBM and MODELS, can drive and enable excelent research studies which may result in internationally renowned scientific papers in the field of Electrical Systems. It is then presented in this paper an additional user guide for these tools with procedures tested in practice and often not covered by official manuals, combined with an analysis of the use of TACS/DBM and MODELS through the computational implementation of a speed governor. The purpose is to identify the potentiality as well as the advantages and disadvantages of TACS/DBM and MODELS. Thus, any user interested in the correct and effective use of these tools may determine the one most suitable to accomplish the computer simulation.

Two-Wire Distribution System for Power Supply to Three-Phase Rural Facilities

Nowadays, the electric power supply to rural facilities is commonly composed by single-phase medium voltage grids. Eventually, some of these rural facilities require the use of more significant driving loads, making necessary the replacing of the single-phase networks by a new medium voltage three-phase network. Thus, despite the fact it is a new or an existing facility, the construction costs related to a new medium voltage three-phase grid, which may have some miles long, could cripple investment to be made by the farmer as well as increase utility tariffs due to higher costs of the three-phase distribution networks in rural areas. In this context, this paper presents an innovative and low cost power supply to attend three-phase rural facilities through a new two-wire distribution system.

Modeling and performance analysis of special permanent magnetic excitation six-phase synchronous generators for wind farm application

This paper presents a proposal for the mathematical modeling and computational analysis of special permanent magnetic excitation six-phase synchronous generators, as required by variable wind farm application. The strategy uses time domain techniques so as to highlight the transient, dynamic and steady state operational conditions. Having completed the representation and the computational implementation of these special machines, the representation is implemented in the ATP platform and performance analyses are carried out to highlight the main operational characteristics of the special generator.