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A Proposed Voltage Ride Through Compensators for Improving Power System Performance
Hamed H. H. Aly,
Mahdi M. El-Arini,
M. T. Youssef
Issue:
Volume 2, Issue 2, April 2013
Pages:
29-36
Abstract: Power quality is one of the most common problems now and in the near future especially after the increas-ing penetration of renewable energy in the power system grid. The abnormal operating conditions (such as heavy load-ing conditions, frequently starting of large induction motors and transmission system faults…) in electric system utility are considered as the main reasons of power quality problems. In this paper, the various main reasons of voltage sag problem are studied. The obtained results of the used simulation program (Electromagnetic Transient Programs ETAP and ATP) show the magnitude and duration of the voltage sag arising from the faults is more severe than that of the other causes, especially in the heavily loaded network. Also, three types of compensators (shunt, series and a combined of shunt and series (Unified Power Flow Controller (UPFC)) are addressed. The obtained results of hundred runs of the simulation program show the performance of the overall system before and after using different types of compensators. The proposed Unified Power Flow Controller (UPFC) gives better performance over the shunt and the series compensators. The most effective buses or lines (best location of compensators) also determined using the proposed system performance indices.
Abstract: Power quality is one of the most common problems now and in the near future especially after the increas-ing penetration of renewable energy in the power system grid. The abnormal operating conditions (such as heavy load-ing conditions, frequently starting of large induction motors and transmission system faults…) in electric system utility are con...
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A Novel Numerical Scheme for a Scale-Invariant Form of Equation of Motion: Development of Solver and Application to Engineering Flow Problems
Bo Wan,
F.-K. Benra,
H. J. Dohmen
Issue:
Volume 2, Issue 2, April 2013
Pages:
37-45
Abstract: The goal of the current paper is to describe an in-depth study of a numerical implementation of the modified equation of fluid motion for incompressible flow. The applications of the developed solver are discussed for both laminar and turbulent flow problems. The results are evaluated by comparing them with those obtained by other methods, including the numerical results obtained by the Navier–Stokes solver measurement data. Then, the computational effort and accuracy of the solver are emphasized. The comparisons indicate that the developed solver, which is based on the modified equation of fluid motion, requires less computation time than the Navier–Stokes solver, and it produces physically reasonable results validated by measurement data
Abstract: The goal of the current paper is to describe an in-depth study of a numerical implementation of the modified equation of fluid motion for incompressible flow. The applications of the developed solver are discussed for both laminar and turbulent flow problems. The results are evaluated by comparing them with those obtained by other methods, includin...
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Transformer Inrush Current Mitigation Using Controlled Switching and Magnetic Flux Shunts
S. Jamali Arand,
M. Saeedi,
S. Masoudi
Issue:
Volume 2, Issue 2, April 2013
Pages:
46-53
Abstract: The inrush current is a transient current that results from a sudden change in the exciting voltage across a transformer’s windings. It may cause inadvertent operation of the protective relay system and necessitate strengthening of the transformer’s mechanical structure. Many methods were reported in the literatures for reduction and mitigation of transformer inrush currents. This paper represents a study of techniques that have been proposed for transformer inrush current mitigation. A new, simple and low cost technique to reduce inrush currents caused by transformer energization is presented here. In this method, a controlled switching approach with a grounding resistor connected to transformer neutral point and a magnetic flux shunt is used. By energizing each phase of the transformer in sequence, the neutral resistor behaves as a series-inserted resistor and thereby significantly reduces the inrush currents. The dimensions of the magnetic flux shunts are chosen such that the inrush current amplitude is further reduced. The proposed method has been tested by computer simulation using 2-D FEM (two-dimensional finite element method) by Maxwell software. The obtained results show that the proposed method is efficient in reduction of transformer inrush current and is much less expensive since there is only one resistor involved and the resistor carries only a small neutral current in steady-state.
Abstract: The inrush current is a transient current that results from a sudden change in the exciting voltage across a transformer’s windings. It may cause inadvertent operation of the protective relay system and necessitate strengthening of the transformer’s mechanical structure. Many methods were reported in the literatures for reduction and mitigation of ...
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Optimization of the Production of Biodiesel Assisted by Ultrasonic and Microwave
Ming-Chien Hsiao,
Chin-Chiuan Lin
Issue:
Volume 2, Issue 2, April 2013
Pages:
54-59
Abstract: The transesterification reaction of present study was assisted by ultrasonic mixing and microwave irradiation. Central composite design (CCD) was employed to optimize the transesterification reaction conditions of biodiesel production from soybean oil. A mathematical model predicted that the theoretical conversion rate of soybean oil of 102.19% could be obtained under the following reaction conditions: amount of catalyst used, 1.4wt%; reaction temperature, 57.89oC; and methanol/oil molar ratio, 8.11:1, assisted by 1-min ultrasonic mixing and 2-min microwave irradiation. This result indicated that there are a wide range of reaction conditions to obtain conversion rate approach 100% assisted by ultrasonic mixing and microwave irradiation. Combined the ultrasonic mixing and microwave irradiation are very efficiency process to produce biodiesel. The total reaction time was shorter than those obtained in previous studies
Abstract: The transesterification reaction of present study was assisted by ultrasonic mixing and microwave irradiation. Central composite design (CCD) was employed to optimize the transesterification reaction conditions of biodiesel production from soybean oil. A mathematical model predicted that the theoretical conversion rate of soybean oil of 102.19% cou...
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Coupled Thermoelastic Analysis of Thick-Walled Pressurized Cylinders
Begüm Kanlıkama,
Ayşegül Abuşoğlu,
İbrahim H. Güzelbey
Issue:
Volume 2, Issue 2, April 2013
Pages:
60-68
Abstract: In the present study, the coupled thermoelastic analysis was carried out for determining the temperature, radial displacement, and radial and circumferential stress distributions of a classical cylinder, and later a reactor pressure vessel exposed to an inner moderator pressure and thermal loads. For the solution, a critical region is analyzed to imitate the effect of the outlet nozzles of the reactor pressure vessel. In order to certify our computational code, the temperature, radial displacement, radial stress, and circumferential stress distributions were also calculated using finite element (FE) method. It was concluded that the analytical results were in good agreement with the computational ones for the classic cylinder. The effect of thermomechanical loads on the temperature, displacement, and stress distributions was discussed in detail. This presented analysis proposes satisfactory results to design reactor pressure vessels.
Abstract: In the present study, the coupled thermoelastic analysis was carried out for determining the temperature, radial displacement, and radial and circumferential stress distributions of a classical cylinder, and later a reactor pressure vessel exposed to an inner moderator pressure and thermal loads. For the solution, a critical region is analyzed to i...
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Numerical Investigation of Flow in Generation IV Pebble Bed Gas Cooled Core Reactors
André A. C. Santos,
Franklin C. Costa,
Amir Z. Mesquita,
Hugo C. Rezende
Issue:
Volume 2, Issue 2, April 2013
Pages:
69-76
Received:
4 May 2013
Published:
30 May 2013
Abstract: This article presents a numerical investigation of thermal-fluid dynamics processes through the gaps of the spherical fuel elements (fuel pebbles) in the core of a Pebble Bed Reactor (PBR), using Computational Fluid Dynamics (CFD). The PBR is one of the most promising projects of the six classes of Generation IV Very High Temperature Reactor (VHTR). The results of two analyzes are presented. In the first case were evaluated two models of heat transfer to the spherical fuel. In this model is specified the volumetric heat generation, with thermal conduction in the fuel, and in the cladding. In the second model was specified a particular heat flux at the spherical fuel elements surface. In this analysis were performed simulations in two arrays of spheres i.e., the spheres into contact and spaced 2 mm. In the second analysis was also evaluated the influence of the spheres arrangement in the bed thermal-fluid dynamic behavior. The set of pebbles that constitute the core was modeled by representations of crystalline structure with different packing factors. The four simulations of the first analysis showed differences in flow and temperature profiles and maximum surface coating. There were also no significant differences in flow and heat transfer between the beads and the fluid in cases with different packing factors. These results show the importance of simulation of heat conduction inside the pebble fuel as well as the need to better assess the influence of the arrangement formed by pebbles fuel in PBR reactors thermal-fluid dynamics behavior.
Abstract: This article presents a numerical investigation of thermal-fluid dynamics processes through the gaps of the spherical fuel elements (fuel pebbles) in the core of a Pebble Bed Reactor (PBR), using Computational Fluid Dynamics (CFD). The PBR is one of the most promising projects of the six classes of Generation IV Very High Temperature Reactor (VHTR)...
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Comparative Investigation of Lean Effect of Stator Vane in Hydrogen-Fueled Combustion Turbine
Ryouta Nakamura,
Masaya Suzuki,
Makoto Yamamoto
Issue:
Volume 2, Issue 2, April 2013
Pages:
77-83
Received:
19 April 2013
Published:
30 June 2013
Abstract: In these years, a lot of environmental problems like air pollution and exhaustion of fossil fuels have been discussed intensively. In our laboratory, a hydrogen-fueled propulsion system has been researched as an alternative to conventional jet engine systems. A hydrogen-fueled propulsion system is expected to have higher power, lighter weight and lower emissions. However, for the practical use, there exist many problems that must be overcome. For example, there is little knowledge how the three-dimensional vane design affects on the flow characteristics and the aerodynamic performance of the hydrogen-fueled combustion turbine vane. The purpose of the present study is to clarify the influence of lean vanes, which is one of typical 3-dimensional design techniques, on the characteristics of the 3-dimensional flow field with hydrogen-fueled combustion within a turbine vane passage. The Reynolds-averaged compressible Navier-Stokes equations are solved with incorporating a k-ε turbulence and a reduced chemical mechanism models. Using the computational results for normal, compound lean and reverse compound lean vanes, the 3-dimensional turbulent flow fields with chemical reactions are visualized and investigated numerically. Through this study, it is confirmed that compound lean can suppress the excessively high temperature region on the endwall and reduce the total pressure loss.
Abstract: In these years, a lot of environmental problems like air pollution and exhaustion of fossil fuels have been discussed intensively. In our laboratory, a hydrogen-fueled propulsion system has been researched as an alternative to conventional jet engine systems. A hydrogen-fueled propulsion system is expected to have higher power, lighter weight and l...
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Stability Analysis of Power System with the Penetration of Photovoltaic Based Generation
Mohammed Masum Siraj Khan,
Md. Shamsul Arifin,
Ariful Haque,
Nahid-Al-Masood
Issue:
Volume 2, Issue 2, April 2013
Pages:
84-89
Received:
6 May 2013
Published:
10 June 2013
Abstract: As the recognition in renewable energy is increasing widely, the development of renewable energy can be major alternative energy resources in Bangladesh. This paper represents the impact of large-scale photovoltaic generation on Bangladesh power system stability. First, the model of PV based generator has been analyzed. Then system-loading margin is studied without and with PV based generator. The contribution of PV based generator on solving under voltage problem and improving bus voltage is studied in the paper. This paper will also show the solution of overloading problem of power transformers with solar PV generator. The transient voltage, angle and frequency stability with PV based generator is discussed also.
Abstract: As the recognition in renewable energy is increasing widely, the development of renewable energy can be major alternative energy resources in Bangladesh. This paper represents the impact of large-scale photovoltaic generation on Bangladesh power system stability. First, the model of PV based generator has been analyzed. Then system-loading margin i...
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