Power Engineering Research Papers - Academia.edu (original) (raw)

An aging workforce and the need to modernize the electric power system are significant challenges facing many nations, and in particular the United States. This complex problem requires a multi-faceted solution that starts with outreach to pre-university students. The aim of these outreach programs is to introduce students to power engineering concepts and to encourage them to choose power engineering as an area of future study and vocation. Outreach activities may also be targeted at guidance counselors, teachers, parents and the general public to the increase the awareness and image of the power engineering profession. This paper identifies pre-university power engineering outreach resources. Funding sources and organizations involved with engineering outreach are also identified. Specific on-line multimedia and in-person, experiential learning lesson plans and activities are discussed. These resources are intended to be used by power engineering faculty and other interested individuals.

- by
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- Engineering Education, Experiential Learning, Organizations, United States

In this paper, an advanced control system for the optimal operation and management of isolated power systems with increased renewable power integration is presented. The control system minimises the production costs through on-line optimal scheduling of the power units, taking into account short-term forecasts of the load and the renewable resources. The power system security is supervised via on-line security assessment modules, which emulate the power system frequency changes caused by pre-selected disturbances. For each of the above functions, a number of techniques have been applied, both conventional and AI based. The system has been installed in the dispatch center of Crete since June 1999, and is under evaluation

- by Johnny Lopes
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- Power System, Control system, Power System Security, Power Engineering

The demand for credit is increasing constantly. Banks are looking for various methods of credit evaluation that provide the most accurate results in a shorter period in order to minimize their rising risks. This study focuses on various methods that enable the banks to increase their asset quality without market loss regarding the credit allocation process. These methods enable the automatic evaluation of loan applications in line with the sector practices, and enable determination of credit policies/strategies based on actual needs. Within the scope of this study, the relationship between the predetermined attributes and the credit limit outputs are analyzed by using a sample data set of consumer loans. Random forest (RF), sequential minimal optimization (SMO), PART, decision table (DT), J48, multilayer perceptron (MP), JRip, naïve Bayes (NB), one rule (OneR) and zero rule (ZeroR) algorithms were used in this process. As a result of this analysis, SMO, PART and random forest algorithms are the top three approaches for determining customer credit limits.

A knowledge of the structure of the boundary of solutions of the power flow problem is important when analyzing the robustness of operating points. This paper proposes a predictor-corrector technique to assist in exploring that structure. Points on the solution boundary satisfy the power flow equations together with an equation which forces the power flow Jacobian to be singular. Curves of such points result from freeing two parameters of the system. The proposed technique follows those curves. A simple example is used to illustrate the complex nature of the power flow solution space.

- by Ian Hiskens
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- Stability, Power Engineering, Robustness, Boolean Satisfiability

Coronavirus disease (COVID-19) altered the way of caregiving and the new pandemic forced the health systems to adopt new treatment protocols in which remote follow-up is essential. This paper introduces a proposed system to link a remote healthcare unit as it is inside the hospital. Two different network protocols; a global system for mobile communication (GSM) and Wi-Fi were used to simulate the heath data transfer from the two different geographical locations, using Raspberry Pi development board and Microcontroller units. Message queuing telemetry transport (MQTT) protocol was employed to transfer the measured data from the healthcare unit to the hospital's Gateway. The gateway is used to route the aggregated health data from healthcare units to the hospital server, doctors' dashboards, and the further processing. The system was successfully implemented and tested, where the experimental tests show that the remote healthcare units using a GSM network consumed about 900 mWh. A high percentage of success data packets transfer was recorded within the network framework as it reaches 99.89% with an average round trip time (RTT) of 7.5 milliseconds and a data transfer rate up to 12.3 kbps.

Face recognition is one of the important biometric authentication research areas for security purposes in many fields such as pattern recognition and image processing. However, the human face recognitions have the major problem in machine learning and deep learning techniques, since input images vary with poses of people, different lighting conditions, various expressions, ages as well as illumination conditions and it makes the face recognition process poor in accuracy. In the present research, the resolution of the image patches is reduced by the max pooling layer in convolutional neural network (CNN) and also used to make the model robust than other traditional feature extraction technique called local multiple pattern (LMP). The extracted features are fed into the linear collaborative discriminant regression classification (LCDRC) for final face recognition. Due to optimization using CNN in LCDRC, the distance ratio between the classes has maximized and the distance of the featu...

Determining and classifying pathological human sounds are still an interesting area of research in the field of speech processing. This paper explores different methods of voice features extraction, namely: Mel frequency cepstral coefficients (MFCCs), zero-crossing rate (ZCR) and discrete wavelet transform (DWT). A comparison is made between these methods in order to identify their ability in classifying any input sound as a normal or pathological voices using support vector machine (SVM). Firstly, the voice signal is processed and filtered, then vocal features are extracted using the proposed methods and finally six groups of features are used to classify the voice data as healthy, hyperkinetic dysphonia, hypokinetic dysphonia, or reflux laryngitis using separate classification processes. The classification results reach 100% accuracy using the MFCC and kurtosis feature group. While the other classification accuracies range between~60% to~97%. The Wavelet features provide very good classification results in comparison with other common voice features like MFCC and ZCR features. This paper aims to improve the diagnosis of voice disorders without the need for surgical interventions and endoscopic procedures which consumes time and burden the patients. Also, the comparison between the proposed feature extraction methods offers a good reference for further researches in the voice classification area.

This work describes the structure and regulation of transmission-related activities in Brazil, and assesses their effectiveness/limitations when addressing issues such as network expansion, locational pricing, transmission financial rights, and others. The paper also discusses the cross-border energy trading between Brazil and neighbor countries, and the perspectives of an integrated regional electricity market.

The aim of this work is to solve the unit commitment (UC) problem in power systems by calculating minimum production cost for the power generation and finding the best distribution of the generation among the units (units scheduling) using binary grey wolf optimizer based on particle swarm optimization (BGWOPSO) algorithm. The minimum production cost calculating is based on using the quadratic programming method and represents the global solution that must be arriving by the BGWOPSO algorithm then appearing units status (on or off). The suggested method was applied on "39 bus IEEE test systems", the simulation results show the effectiveness of the suggested method over other algorithms in terms of minimizing of production cost and suggesting excellent scheduling of units.

This paper describes the optimal power flow (OPF) architecture implemented in MATPOWER, an open-source Matlab power system simulation package. It utilizes an extensible architecture that allows the user to easily add new variables, constraints and costs to the standard OPF problem formulation while preserving the structure needed to use pre-compiled solvers. A software object is used to encapsulate the definition of the problem formulation, manage the corresponding named sets of variables, constraints and costs, and handle all of the tedious index maintenance tasks. The software design has the advantage of minimizing the coupling between variables, constraints and costs, making it possible, for example, to add variables to an existing model without having to explicitly modify existing constraints or costs to accommodate them. The example of adding joint co-optimization of reserves to the OPF, based on fixed zonal reserve requirements, is used to illustrate the capabilities of MATPOWER's extensible OPF architecture.

- by Ray Zimmerman
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- Computer Architecture, Software Engineering, Power Systems, Software Maintenance

The next generation for mobile communication is new radio (NR) that supporting air interface which referred to the fifth generation or 5G. Long term evolution (LTE), universal mobile telecommunications system (UMTS), and global system for mobile communication (GSM) are 5G NR predecessors, also referred to as fourth generation (4G), third generation (3G) and second generation (2G) technologies. Pseudo-noise (PN) code length and modulation technique used in the 5G technology affect the output spectrum and the payload of DL-FRC specification, in this paper quadrature phase shift keying (QPSK), 16 QAM modulation approaches tested under additive white Gaussian noise (AWGN) in term of bit error rate (BER) which used with 5G technology system implemented with MATLAB-Simulink and programing and, resulting of 1672, 12296 bit/slot payload at frequency range FR1 from 450 MHz-6 GHz and 4424, 20496 bit/slot payload at frequency range FR2 from 24.25 GHz-52.6 GHz, also determining subcarrier spacing, allocated source block, duplex mode, payload bit/slot, RBW (KHz), sampling rate (MHz), the gain and the bandwidth of main, side loop where illustrated.

The downlink multiuser precoding of the multiple-input multiple-output (MIMO) method includes optimal channel state information at the base station and a variety of linear precoding (LP) schemes. Maximum ratio transmission (MRT) is among the common precoding schemes but does not provide good performance with massive MIMO, such as high bit error rate (BER) and low throughput. The orthogonal frequency division multiplexing (OFDM) and precoding schemes used in 5G have a flaw in high-speed environments. Given that the Doppler effect induces frequency changes, orthogonality between OFDM subcarriers is disrupted and their throughput output is decreased and BER is decreased. This study focuses on solving this problem by improving the performance of a 5G system with MRT, specifically by using a new design that includes weighted overlap and add (WOLA) with MRT. The current research also compares the standard system MRT with OFDM with the proposed design (WOLA-MRT) to find the best performance on throughput and BER. Improved system results show outstanding performance enhancement over a standard system, and numerous improvements with massive MIMO, such as best BER and throughput. Its approximately 60% more throughput than the traditional systems. Lastly, the proposed system improves BER by approximately 2% compared with the traditional system.

The basis of comprehension of power-flow problems obtained from lectures, lecture slides and subject book. Circuit built and simulated in the Power World program, and then the analytical solution obtained using the theoretical knowledge. Finally, both answers were compared with each other and the difference in the figures were deducted and discussed elaborately.

Coronavirus disease (COVID-19) altered the way of caregiving and the new pandemic forced the health systems to adopt new treatment protocols in which remote follow-up is essential. This paper introduces a proposed system to link a remote healthcare unit as it is inside the hospital. Two different network protocols; a global system for mobile communication (GSM) and Wi-Fi were used to simulate the heath data transfer from the two different geographical locations, using Raspberry Pi development board and Microcontroller units. Message queuing telemetry transport (MQTT) protocol was employed to transfer the measured data from the healthcare unit to the hospital’s Gateway. The gateway is used to route the aggregated health data from healthcare units to the hospital server, doctors’ dashboards, and the further processing. The system was successfully implemented and tested, where the experimental tests show that the remote healthcare units using a GSM network consumed about 900 mWh. A hig...

- by Bilal Mubdir
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- Information Technology, Technology, Control Engineering, Computer Networks

This paper constitutes the final report of the IEEE Task Force on Generator Model Validation Testing, which was created in 2002 and served under the Power System Stability Subcommittee. The objective of the TF was to provide technical guidance to utilities undertaking testing and modeling of generation facilities. This paper outlines accepted industry methods for establishing dynamic models for generators and their control systems. Index Terms-generator modeling, model validation, field testing of power plants

- by L. Hajagos and +2
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- Power Engineering

Reliability centered maintenance (RCM) has a key role in the quality system of thermal power plants. Electricity production is definitely not only production of a product, but also becomes a customer service. Reliability is the top quality tier of this service. Incorporation in the Integrated energy system means fast transformations of organization on all levels. The reliability of modern generation components basically influences the efficiency and capacity of a power plant as a whole. This paper presents the results of RCM practice on Unit Two of The Thermal Power Plant ″Nikola Tesla -B″, 2x600 MW, Yugoslavia. RCM implementation on current problems during exploitation emphasized problems with the boiler tubing system. The methodological approach included outages analyses, marking of the most significant ones, determination of main causes of damage (determination of the material exhaustion state based on expert analyses), application of adequate remaining life assessment methodology and finally the recommendations. Based on these analyses, certain technical solutions were performed and as a result, the mean time between failures of the plant increased, as well as its reliability. According to cost efficiency, RCM methodology presented the most effective cost-benefit method for reliability upgrade.

- by Milos Djukic
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- Materials Engineering, Materials Science, Quality Management, Materials Chemistry

In precision farming, identifying weeds is an essential first step in planning an integrated pest management program in cereals. By knowing the species present, we can learn about the types of herbicides to use to control them, especially in non-weeding crops where mechanical methods that are not effective (tillage, hand weeding, and hoeing and mowing). Therefore, using the deep learning based on convolutional neural network (CNN) will help to automatically identify weeds and then an intelligent system comes to achieve a localized spraying of the herbicides avoiding their large-scale use, preserving the environment. In this article we propose a smart system based on object detection models, implemented on a Raspberry, seek to identify the presence of relevant objects (weeds) in an area (wheat crop) in real time and classify those objects for decision support including spot spray with a chosen herbicide in accordance to the weed detected.

- by Sergej Oboroc
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- Hydrogen, Fuel Cells, Power Engineering, Nuclear Reactors

This article presents a resonant DC-DC converter topology suitable for ultra-low power and low voltage applications. The presented topology is dedicated to energy harvesting sources in general and especially for Radio-Frequency RF sources. Main advantage of this converter is its autonomy, i.e., it operates from low voltage levels without the need of an external energy source or any other startup assistance. Theoretical modelling of the converter is used together with circuit simulations in order to make an optimal design based on the requirements of a low power rectifying antenna (rectenna). A discrete prototype was fabricated and tested. Low voltage and ultra-low power as lows as 100mV and 3.7µW respectively were achieved. The input low voltage is boosted to a usable level allowing to power wirelessly and autonomously low power circuits as wireless sensors.

Hybrid electric vehicle (HEV) has much lower emissions compared to conventional gasoline powered vehicles. Permanent magnet synchronous machines are known as a good candidate for hybrid electric vehicles due to their unique merits. In this research paper an optimal design of a permanent magnet machine is presented. A reduction of permanent magnet material for a constant torque and an extension in speed and torque ranges are chosen as the optimization aims. As the high field strength of neodymium-iron-boron (NdFeB) magnets become commercially available with affordable prices, PMSMs are receiving increasing attention due to their high speed, high power density and high efficiency. In this research paper, 50 kW, 3000 r.p.m permanent magnet synchronous motor is designed.

- by IRE Journals
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- Power Engineering

The aim of this paper is to provide methods and techniques used for wireless monitoring of the parameters of a widely-used induction motor through interfacing of Arduino UNO (for wired communication) and Node Micro Controller Unit (NodeMCU) Wi-Fi module (for wireless communication) with MATLAB (Matrix Laboratory) software. The parameters which can be monitored through the techniques discussed in this paper are current waveform, voltage waveform, temperature (Celsius), rms value of voltage and current, peak to peak values of current and voltage, power factor, magnitude spectrum of induction motor. Technique of carrying out Motor Current Signature Analysis (MCSA) has also been discussed in this paper for health monitoring of the motor.

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- by chandrasekhar guluru
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- Power Electronics, Power Engineering, IEE

Solar power generation had been used as a renewable energy since years ago. Residential that uses solar power as their alternative power supply will bring benefits to them. The main objective of this project is to develop an automatic solar tracking system which will keep the solar panels aligned with the Sun in order to maximize in harvesting solar power. The system tracks the maximum intensity of light. When the intensity of light is decreasing, this system automatically changes its direction to get maximum intensity of light. LDR light detector is used to trace the coordinate of the Sun. While to rotate the appropriate position of the panel, a DC geared motor is used. The system is controlled by two relays as a driver and a microcontroller as a main processor. This project is covered for a single axis and is designed for residential usage. Finally, the project is able to track and follow the Sun intensity in order to get maximum power at the output regardless motor speed.

- by asmarashid ponniran
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- Renewable Energy, Microcontrollers, renewable Energy sources, Sensors

Nano-optics is the study of optical phenomena and techniques on the nanometer scale, that is, near or beyond the diffraction limit of light. It is an emerging field of study, motivated by the rapid advance of nanoscience and nanotechnology which require adequate tools and strategies for fabrication, manipulation and characterization at this scale.

- by hajar moradi
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- Electrical Engineering, Genetic Algorithms, Genetic Algorithm, Microgrid

The losses in European Union distribution transformers are estimated at about 33 TW · h/year, whereas reactive power and harmonic losses add a further 5 TW · h/year. The reduction of distribution transformer no-load loss is particularly important as the ratio of no-load to load losses is nearly three. In this paper, the no load operation of wound-core transformers under sinusoidal and distorted supply-voltage conditions is investigated. For that purpose, a 2-D nonlinear transient finite-element analysis taking into account hysteresis has been developed. The hysteresis model is based on a modified Jiles–Atherton representation, and the proposed analysis is compared to experimental data.

- by Themistoklis D. Kefalas
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- Engineering, Electrical Engineering, Harmonic Analysis, Electromagnetism

Systems focuses on systems utilizing FA+ F3CTS and helps understand monitor performance and disturbances. Also covered are network simulation techniques, transmission systems, AC load flow, faulted system, harmonic flow, and... more

- by Mark McGranaghan
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- Power Quality, Power Engineering, Economic evaluation

Field analysis in conjunction with circuit model has been used to predict the performance of a switched reluctance machine. This paper describes the procedure to model a 3 phase 12/16 Switched Reluctance (SR) machine. Its operation as a generator is analyzed. An accurate representation of machine requires good representation of its magnetic characteristics. With the advent of high speed computing, numerical method is used to take into account its nonlinear characteristics. In this research, a 2D Finite Element Method (FEM) is used to determine the magnetic characteristics of the machine. Results from FEM are used as Look Up LUT) for simulation using MATLAB/SIMULINK. Using the same machine parameters and current density, the influence of different phase winding polarity on the performance of an SR machine operating as a generator under single phase excitation is observed. Optimum performance/high efficiency can be achieved by using different phase winding polarity.

With the increasing use of distributed energy (DE) systems in industry and its technological advancement, it is becoming more important to understand the integration of these systems with the electric power systems. New markets and benefits for DE applications include the ability to provide ancillary services, improve energy efficiency, enhance power system reliability, and allow customer choice. Advanced power electronic (PE) interfaces will allow DE systems to provide increased functionality through improved power quality and voltage/volt-ampere reactive (VAR) support, increase electrical system compatibility by reducing the fault contributions, and flexibility in operations with various other DE sources, while reducing overall interconnection costs. This paper will examine the system integration issues associated with DE systems and show the benefits of using PE interfaces for such applications.

- by Marcelo Simoes
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- Power Electronics, Power Quality, Power System, System Integration
- by Zarafi Ahmad
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- Support Vector Machines, Energy Conversion, Modulation, Hysteresis

- by Gordana Bakic
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- Materials Engineering, Materials Science, Quality Management, Materials Chemistry
- by IJERT Journal
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- Engineering, Power Engineering

Abstrak-Termostat digital HX-W1209 merupakan jenis termostat yang umum digunakan pada inkubator tetas telur, menerapkan sistem pengendalian on-off. Dengan penerapan yang sama, saat ini terdapat teknologi yang sedang dikembangkan dan... more

- by Hadi Purwanto
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- Power Engineering

The purpose of this research is to create a smart system based on internet of things (IoT) application for a plant aquarium. This smart system helps users to maintain the environment's parameters of the plant aquarium. In this study, the parameters to be controlled by the system are light intensity and temperature. The hardware used to develop this system is the ESP32 as the microcontroller, BH1750FVI as the light sensor, high power led (HPL) lightemitting diodes (LED) lamp as the light source, DS18B20 as temperature sensor, the heater, and the 220 VAC fan that is used to raise and lower the temperature. In this study also developed an application that is used by the user to provide input to the system. The developed application is then installed on the user's smartphone and used to connect the user to the system via the internet. The ease of adding and removing devices used on the system is a capability that is also being developed in this smart system. The developed system can produce light intensity with accuracy rate of 96% and always manage to keep the temperature within the predetermined range.

This study presents the model, design, and construction of the Arduino based robotic arm, which functions across a distance as it is controlled through a mobile application. A six degree of freedom robotic arm has been designed and implemented for the purpose of this research. The design controlled by the Arduino platform receives orders from the user's mobile application through wireless controlling signals, that is Bluetooth. The arm is made up of five rotary joints and an end effector, where rotary motion is provided by the servomotor. Each link has been first designed using solid works and then printed by 3D printer. The assembly of the parts of the robot and the motor's mechanical shapes produce the final prototype of the arm. The Arduino has been programmed to provide rotation to each corresponding servo motor to the sliders in the designed mobile application for usage from distance.

The current lifestyle of humanity relies heavily on energy consumption, thus rendering it an inevitable need. An ever-increasing demand for energy has resulted from the increasing population. Most of this demand is met by the traditional sources that continuously deplete and raise significant environmental issues. The existing power structure of developing nations is aging, unstable, and unfeasible, further prolonging the problem. The existing electricity grid is unstable, vulnerable to blackouts and disruption, has high transmission losses, low quality of power, insufficient electricity supply, and discourages distributed energy sources from being incorporated. Mitigating these problems requires a complete redesign of the system of power distribution. The modernization of the electric grid, i.e., the smart grid, is an emerging combination of different technologies designed to bring about the electrical power grid that is changing dramatically. Demand side management (DSM) allow customers to be more involved in contributors to the power systems to achieve system goals by scheduling their shiftable load. Effective DSM systems require the participation of customers in the system that can be done in a fair system. This paper focuses primarily on techniques of DSM and demand responses (DR), including scheduling approaches and strategies for optimal savings.

Abstract: Improvement the efficiency of power energy production, modernization of industrial process in frame of ecological and industrial safety are one of the strategic problems for any country. Mongolia is same those countries with rich natural resource of coal fuel in energy balance, where coal is occupied the largest position in it and this situation will be kept in the future. The combustion process of untreated coal had many negative effects such as climate change, air pollution, environment and nature. Since Kioto’s protocol has been implemented the requirements on developing ecologically harmless for coal combustion. According to this situation humanity faced actual problems. One of the way to avoid from these problems is developing technology of stationer and circulation fluidized bed boiler with low temperature.
Fluidized bed combustion (FBC) technology has lot of advantage for burning solid fuels and recovering energy to produce steam. So we decide to confirm advantage of fluidized bed combustion technology by testing of our country's stationer and circulating fluidized bed steam generators.
The overall objective of the test is determining efficiency of stationery and circulation fluidized bed steam boilers with small and medium capacity in the thermal power plant of Mongolia. We tested and studied of steam boiler types DTH-11-10/350BD (Thermal plant of Zuun Haraa), НХ-35/3,82-450 (Uhaa Hudag Thermal Power Plant) and BKZ-75-39 (Darkhan Power Plant).

Equivalent circuits of electromagnetic devices are an efficient alternative to full transient EM analysis especially when phenomenon such as inrush currents are investigated. The time-constants in such cases generally, for a 50 Hz transformer, are in the order of several minutes hence rendering full transient EM simulation time consuming. On the circuit level, the simulation time involved is a fraction of the EM transient case. Furthermore, parametric analysis may take place in the circuit simulation allowing what-if scenarios to be tested e.g. effect of system impedance on inrush behaviour.This article shows the application of the CST EM STUDIO® (CST EMS) Magnetostatic solvers within the System and Assembly Modeling (SAM) framework to the emulation of two standard transformer tests for the extraction of T-equivalent circuit parameters at 50 Hz.

- by nishant kumar
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- English, Electrical Machines, Power Engineering, Non-linear

Coronavirus disease (COVID-19) altered the way of caregiving and the new pandemic forced the health systems to adopt new treatment protocols in which remote follow-up is essential. This paper introduces a proposed system to link a remote healthcare unit as it is inside the hospital. Two different network protocols; a global system for mobile communication (GSM) and Wi-Fi were used to simulate the heath data transfer from the two different geographical locations, using Raspberry Pi development board and Microcontroller units. Message queuing telemetry transport (MQTT) protocol was employed to transfer the measured data from the healthcare unit to the hospital’s Gateway. The gateway is used to route the aggregated health data from healthcare units to the hospital server, doctors’ dashboards, and the further processing. The system was successfully implemented and tested, where the experimental tests show that the remote healthcare units using a GSM network consumed about 900 mWh. A hig...

- by Hassan Mohammed Ali
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- Information Technology, Technology, Control Engineering, Computer Networks

This paper presents a proposed design and analysis of a three-phase squirrel cage induction motor when changing of internal characteristic design for the three-phase induction motor. Two situations have been applied to enhancing the performance of the three-phase induction motor. The first situation has been implemented by changing the magnetic flux density (MFD) via the build of the six-phase for the same induction motor. The second situation has been implemented by changing core materials of the rotor part of the induction motor, like aluminum (AL) and cast iron (CI). The finite element method (FEM) has been used to analyze the rotor part, also to obtain the representation and simulation of the realty cylindrical rotor part of motor. The frequency domain (FD) analysis using to obtain the results within the environment of the COMSOL multiphysics 5.5 version.

- by Chul-Hwan Kim
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- Power Systems, Power System, Wavelet Transform, Wavelet Transforms

The paper presents the actual situation and the ongoing development concerning load participation to power system security in Italy. It is intended as a contribution to a panel session organized by the Fast-Acting Load Control for System... more

- by Marino Sforna
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- Power System, Power System Security, Power Engineering, Price Stability

0272-1724/00/$10.00©2000 IEEE IEEE Power Engineering Review, December 2000 ... 2001 Cigré International Symposium on Gas and Electricity Networks: Complementarity or Competition 3-6 December 2001, Iguaçu, Brazil ... Cigré and the... more

This study revealed the limitations of freelancers’ inability to perform portfolios and biographies, their performance ratings to a large community of customers. The difficulties were evident in searching for reliable, qualified and experienced freelancers from multi-channel information sources. These limitations might impact the ability of freelancers selected by customers to perform the required task to the customers’ satisfaction. This research focused on the case study of the freelance community for photography business in southern of Thailand. This aims to establish an online facility in which freelance photographers can publicize their services and performance to potential customers. The concepts entailed in web portals and e-services were the key elements in the development and ensured that its functions worked efficiently. The study employed qualitative methods were used to assess the current practices of web portal and thus determining the requirements for the e-service web...

- by Nattaporn Thongsri
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- Information Systems, Marketing, Information Technology, Technology

Catastrophic failures of power systems are phenomena which occur with some regularity throughout the world. It is recognized that these cannot be prevented, although with the use of newer developments in power engineering, in communication systems, and in computer engineering it would be possible to reduce their frequency and their impact on society. Analyses of many blackouts point to some salient features which are common to most such events: power systems under stress because of high load levels or outages of important facilities, some initiating event-usually a fault, often followed by cascading effects due to unwanted operation of some protection systems. In particular, the role of hidden failures (HFs) in protection systems in propagating power system disturbances has become clearer with some of the recent research reported in the literature. This paper explores further the issue of HFs of protection systems and possible countermeasures.

- by Lamine Mili
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- Logic, Biomedical Engineering, Power System, Risk

This paper introduces the power quality issues of wind power installations in a historic perspective, as the development from a few small wind turbines connected directly to the low voltage grid, to the present system with high penetration on the medium voltage distribution grids and two large offshore wind farms connected at transmission level. In this perspective, the power quality issues are divided into local issues particularly related to the voltage quality in the distribution systems and global issues related to the power system control and stability. Power quality characteristics of wind turbines and wind farms are described according to national and international standards, and measurements from wind farms are presented.

- by Troels Sorensen and +2
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- Power Quality, Distributed System, Wind Power, Wind turbine

This paper shows experimental results of longitudinal flux density and its harmonics at the limb, the yoke and the corner of a three phase, Si-Fe, five-legged wound transformer core. Results show that the flux density is nonuniform in the cores and there is high level of third harmonic component. Moreover, the lower flux values in the outer cores have been assessed and the simultaneous time variation of the flux in both outer cores has been demonstrated by measurements while the peak magnetic flux density values have been compared to FEM analysis. These findings enable a better understanding of the magnetic behavior of five legged wound transformer cores and their consideration is expected to achieve respective improvement of the design with respect to core losses and magnetostriction noise.

- by Themistoklis D. Kefalas
- •
- Engineering, Electrical Engineering, Numerical Simulations, Power Systems