Search

This study presents the Angular Particle Swarm Optimization(APSO) algorism which is an optimization technique, in order to reconfigure micro-grids. Micro-grids are concepts of distribution system that unifies directly with customers and distributed generations(DGs). It could supply the electric power to customers and do the power transaction using a power market by operating the economic dispatch through several DGs of diverse cost function. If there are a large number of micro-grids in one distribution system, it needs to adjust the configuration of many micro-grids in order to supply the electric power with the minimum generation cost to all customers who are under the distribution system. So this study offers the APSO algorism which applies to the optimization technique, the algorism has multidimensional vectors that consist of magnitudes and phase angles. more...

Electric power systems are extremely complex. Therefore, system operators and planners are faced with difficult problems, which are uncertainty of power system. Also, they have to obtain best efficiency with least cost of investment. Transmission network expansion planning (TNEP) vases on reliability, and considers economic aspect. This paper presents well-being method and cost-optimization method to solve the transmission expansion planning problem. Basic principle of cost-optimization is similar to fundamental principle of economics. When practical use of resources increases, it means that must endure more risk. Well-being method can briefly estimation state probability by capability and calculate reliability in system. Methods: first, calculate cost-optimization method, and obtain optimal system capability of present system. Second, use the optimal capability, well-being method shows system state probability. Finally, identify system probability, and determine future planning. To demonstrate the efficiency of the suggested methods, these methods are applied to IEEE-RTS 24 bus system. The result of these methods shows the reliable transmission expansion planning through IEEE-RTS 24 bus more...

As the electrical power industry is restructured, the electrical power exchange is becoming extended. One of the key information used to determine how much power can be transferred through the network is known as available transfer capability (ATC). To calculate ATC, traditional deterministic approach is based on the severest case, but the approach has the complexity of procedure. Therefore, novel approach for ATC calculation is proposed using cost-optimization method in this paper, and is compared with well-being method and risk-benefit method. This paper proposes the optimal transfer capability of HVDC system between mainland and a separated island in Korea through these three methods. These methods will consider production cost, wheeling charge through HVDC system and outage cost with one depth (N-1 contingency), {"references":["North American Electric Reliability Council (NERC), \"Available Transfer\nCapability -Definitions and Determinations\", NERC Report, June 1996.","H.I.Son, D.J.Shin, J.O.Kim, \"Evaluation if Optimal Transfer Capability in\nHaenam-Jeju HVDC system Based on Cost optimization.\", KIEE\nInternational Transactions on Power Engineering. Vol. 5-A. No.3 pp.9-15.\nSep. 2005","S.B.Choi, D.K.Kim, S.H.Jeon, H.S.Ryu, \"Evaluation of the Customer\nInterruption Cost taking into consideration Macro Economic Approach in\nLPREA\", Power System Technology, 2002. Proceedings. PowerCon 2002.\nInternational Conference on, Vol.4, pp.2358-2362, 2002.","Final Report, \"Composite-System Reliability Evaluation: Phase 1 - Scoping\nStudy\", Tech. report EPRI EL-5290, Project 2581-1, December 1987.","Billinton, R. and Allan, R. N., Reliability Evaluation of Power System,\nLongman, 1984","R. Billiton, S. Aboreshaid, M. Fotuhi-Firuzbad, \"Well-being Analysis For\nHVDC Transmission System\", IEEE Transactions on Power System, Vol.\n12, No. 2, May. 1997.","K.Audomvongseree, and A.Yokoyama, \"Consideration of an Appropriate\nTTC by Probabilistic Approach.\" IEEE Transactions on Power Systems,\nVol. 19, No.1. Feb. 2004"]} more...

By development of renewable energy and high-efficient faculties under the environment of deregulated electricity market, the operation cost of distributed generation(DG) becomes more competitive. Also, international environmental regulations of the leaking carbon become effective to keep pace with the global efforts for low-carbon paradigm. These contribute to spread out the business of DG. Therefore, the operator of DG is able to supply electric power to customers who are connected directly to DG as well as loads that are connected to entire network. In this situation, community energy system(CES) having DGs is recently a new participant in the energy market. DG's purchase price from the market is different from the DG's sales price to the market due to the transmission service charges and etc. Therefore, CES who owns DGs has to control the produced electric power per hourly period in order to maximize the profit. Considering the international environment regulation, CE newly will be an important element to decide the marginal cost of generators as well as the classified fuel unit cost and unit's efficiency. This paper introduces the optimal operation of CES's DG connected to the distribution network considering CE. The purpose of optimization is to maximize the profit of CES and Particle Swarm Optimization (PSO) will be used to solve this problem. The optimal operation of DG represented in this paper would guide to CES and system operator for determining the decision making criteria. more...

As the electrical power industry is restructured, the electrical power exchange is becoming extended. One of the key information used to determine how much power can be transferred through the network is known as available transfer capability (ATC). To calculate ATC, traditional deterministic approach is based on the severest case, but the approach has the complexity of procedure. Therefore, novel approach for ATC calculation is proposed using cost-optimization method in this paper, and is compared with well-being method and risk-benefit method. This paper proposes the optimal transfer capability of HVDC system between mainland and a separated island in Korea through these three methods. These methods will consider production cost, wheeling charge through HVDC system and outage cost with one depth (N-1 contingency). more...

The power system need to sustain high reliability due to its complexity and security. The reliability prediction method is usually based on independent failure. However, the common cause failure affects many components simultaneously in a system, and it turns out the system collapse seriously in a wide range. Therefore, to improve the reliability of the power system practically, the analysis using the common cause failure is required. This paper describes the common cause failure modeling combined with independent failure. Using the dynamic fault tree, the incorporated independent failure and common cause failure are proposed and analyzed, and it is applied to the power substation in order to examine the method. more...

This paper explains the concept of dynamic line rating (DLR) and suggests the method to forecast the thermal rating. The weather parameters are modeled corresponding to each transmission line, and thermal overload probability (TOP) is estimated using the predicted weather models and the present DLR value. In particular, a statistical wind speed model is developed using time series with compensation. In the case study, it is confirmed that the predicted TOP should be utilized as the criterion that decides forecast rating (FR) in order to operate the transmission line reasonably. The proposed method would be useful to enhance security and reliability of the transmission line. Moreover, this study could provide a better insight into the system operation and control, especially now a days when deregulation and liberalization of transmission systems are introduced. Copyright © 2009 John Wiley & Sons, Ltd. more...

The paper describes a theoretical and experimental study pertaining to torsional stress wave motion in an axisymmetric waveguide whose cross-sectional area varies periodically as a function of the axial coordinate. Dispersion relations for the phase speed are obtained for both nonresonant and resonant conditions, using perturbation techniques for small amplitude, sinusoidal modulation. Resonant conditions exist when the modulation wave number is proportional to the sum or difference of wave numbers corresponding to various modes of the torsional stress wave. The experiments consist of measuring the stress wave speed in waveguides with threaded surfaces. The experimental observations verify the general trends predicted by the theory. more...

A refined calculation of V(z) and V(z, x0) curves is presented for a line-focus acoustic microscope and for a specimen which contains a discontinuity normal to its free surface. In the context of a Fourier integral approach, more accurate expressions are employed for: (1) the angular spectrum of the field produced by the lens; (2) the voltage response of the transducer; and (3) the reflection coefficient of the object. In addition, the usual “thin” lens theory has been extended to “thick” lens theory. For V(z, x0) details are given for the case of a surface-breaking crack, and the inverse problem of determining the Rayleigh-wave reflection coefficient of a crack has been solved in an approximate manner. Comparisons between theoretical and experimental results are presented fpr the case that the discontinuity is the edge of the specimen. The reflection coefficient calculated from experimental results agrees well with the theoretical value. more...

The effects of an adjacent fluid’s viscosity and density on the characteristics of torsional stress waves transmitted in a waveguide with a circular cross section are studied theoretically and experimentally. Expressions for the torsional wave speed, dispersion relations, and attenuation are obtained as functions of the adjacent fluid’s viscosity and density. The theoretical results are compared with experimental observations. It is demonstrated that a device similar to the one described herein can be used as a rugged, real-time, on-line sensor for measuring the viscosity of a fluid with a known density. Such a sensor can measure the viscosity of fluids with a density viscosity product (ρfμ) greater than 100 kg2/m4 s to a precision of 1% or better. more...

A system called demand response programs (DRP) is being introduced among various countries owing to the lack of new generation capacity and the higher fuel generation cost. It is a program which provides for the end-users to select their consumption of electricity by recognizing the value of their consumption in real time. That is, Demand Response can be defined as the changes in electric usage by end-use customers from their normal consumption patterns in response to changes in the price of electricity or other signals. It is expected that the effects of DRP are preventing price spike, improving supply reliability and social welfare and increasing option of customers. Considering the customerpsilas thermal comfort zone, this paper determines the most profitable combination of optimal incentives and amounts of load reduction for a retailer to maximize profits according to predicted outdoor temperatures while implementing DRP. more...

This paper presents a failure analysis of traction power systems. The electric railway consists of traction power systems, various vehicles, operating equipment, track, overhead line and electric equipment. It is a fundamental function of traction power systems that they supply customers with acceptable reliability and high quality power. Perhaps the most commonly used reliability assessment for railway systems has been the failure analysis of the traction signal system. The reliability assessment of traction power systems has also been an indispensable issue for reliability assessment. This paper deals with the classification of railway accidents caused by electrification problems, the estimation of failure rate in power equipments and failure analysis using fault trees. In study cases, the fault tree method for failure analysis is applied to railway substations in South Korea. more...

The electricity demand in Korea has rapidly increased along with a steady economic growth since 1970s. Therefore Korea has positively propelled not only SSM (Supply‐Side Management) but also DSM (Demand‐Side Management) activities to reduce investment cost of generating units and to save supply costs of electricity through the enhancement of whole national energy utilization efficiency. However study for rebate, which have influence on success or failure on DSM program, is not sufficient. This paper executed to modeling mathematically expanded Bass model considering rebates, which have influence on penetration amounts for DSM program. To reflect rebate effect more preciously, the pricing function using in expanded Bass model directly reflects response of potential participants for rebate level. more...

This paper suggests the method that forecasts Dynamic Line Rating (DLR). Thermal Overload Risk (TOR) of the next time is forecasted based on the present weather condition and DLR value by Monte Carlo Simulation (MCS). To model weather elements of transmission line for MCS, this paper will propose the use of statistical weather models that time series law is applied. Also, through the case study, it is confirmed that the forecasted TOR probability can be utilized as criterion that decides DLR of next time. In short, proposed method may be used usefully to keep security and reliability of transmission line by forecasting transmission capacity of the next time. more...

By environmental and technical reasons, the amount of distributed generation will considerably increase in the future power system. As a large number of distributed resources with diverse characteristics have been installed in the distribution system, concerns in the aspect of engineering and operation are focused on the development of new control approaches. This paper discusses how to operate these distributed resources to achieve the maximum benifit. While the output of thermal units is controlled voluntarily by the owner of distributed resources, the power from PV system fluctuates according to the insolation and the atmospheric temperature. Therefore, in order to solve these complications, the optimal model for the operation of mixed distributed resources, such as photovoltaic, diesel and CHP, is proposed in this paper. The customer demands are compared with the resources output to find optimal point of system operation, and in addition, the methodology in this paper can be used for evaluation of economic profit by distributed resources. (5 pages) more...

The distance relay is the most widely relay used in transmission line protection because it is applicable not only as main protection but also as back-up protection. However, the protection range of the distance relay is always fixed in the unchangeable operating range while the power system varies and therefore the distance relay is the one that is the most highly influenced by the power system changes. In this regard, this paper describes an approach to minimize the maloperation of the distance relay due to the power system changes through changing protection range of the distance relay into optimal condition in response to the load variation and power system condition. Also malfunction of the distance relay in case of high resistance ground faults could be minimized through modeling the protection range into a quadratic function. more...

The purpose of this paper is to assess experimentally system stability of the 154 kV transmission systems due to the current of the forthcoming ac high-speed railway (HSR) era. It introduces a simple method to evaluate the system stability. The proposed method shows the relationship between stability and power losses, and the stability indices made by the numerical process is used to assess whether a system can be stabilized or not. This paper also presents the improvement of the stability via loss reduction using STATCOM. Reactive power compensation is often the most effective way to improve both power transfer capability and system stability. The suitable modeling of the traction power system should be applicable to the PSS/E. In the case study, the proposed method is tested on a practical system of the Korea Electric Power Corporation (KEPCO) which is expected to accommodate the heavy HSR load. Furthermore, it proves that the compensation of voltage drop and its by-product, loss reduction is closely related to improvement of system stability. more...

This paper presents the vibration characteristics of the radial mode in spherical piezoelectric transducers. The differential equations of piezoelectric radial motion have been derived in terms of radial displacement and electric potential. Applying mechanical and electrical boundary conditions yielded a characteristic equation for radial vibration. Theoretical calculations of the fundamental natural frequency have been compared with numerical and experimental results for transducers of several sizes, and have shown a good agreement. This paper discusses the dependence of natural frequencies on the radius and thickness of the piezoelectric spheres and the difference between piezoelectric and elastic resonances. From the results it has been concluded that the natural frequency was not affected for the first radial mode but was reduced by the piezoelectric phenomenon. It has also been concluded that the natural frequency of the first radial mode depended mostly on the radius rather than on the thickness of the sphere whereas the natural frequency of the second radial mode depended mostly on the thickness rather than the radius. more...

Dynamic characteristics of the digital distance relay and PCM current differential relay are described in this paper. It is difficult to achieve various fault simulation using conventional static type tests, while RTDS can handle not only various fault modeling but also dynamic characteristic test modeling because it is a full digital and real time simulator. Thus, this paper describes a test procedure, using RTDS, to verify the high possibility of malfunction cases for the distance relay and PCM current differential relay. In this paper, test modeling is established and then simulation for this test model is performed with RTDS. The results are compared with the ones calculated by PSS/E and by hand calculation. more...

This paper describes a Neural-Tabu algorithm approach to the optimal reconfiguration of distribution network. The optimal routing of distribution network should provide electricity to customers with quality, and this paper shows that optimal routing of distribution network can be obtained by a neural-Tabu algorithm while keeping constraints such as line power capacity, voltage drop and reliability indices. The neural-Tabu algorithm is a Tabu algorithm combined with neural network to find neighborhood solutions. This paper shows that not only the loss cost but also the reliability cost should be considered in distribution network reconfiguration to achieve the optimal routing. This paper also presents the advantages of the neural-Tabu algorithm against using the neural network algorithm only. more...

A novel experimental technique for studying the characteristics of the interface between the fibers and the matrix in both undamaged and damaged fiber-reinforced composite materials is described. The experimental technique involves the transmission of stress waves in one or more fibers of the composite. The characteristics of the stress waves, such as speed, dispersion, and attenuation, are measured. These measured variables can be correlated with the characteristics of the bonding between the fiber and the matrix. more...

The determination of elastic constants of bulk specimens and anisotropic films deposited on anisotropic substrates from V(z) measurements obtained by using a line-focus acoustic microscope is discussed. The procedure has three essential components: (1) V(z) curve measurement as a function of direction of wave mode propagation in the sample at fixed frequency and/or as a function of the frequency or film thickness for a fixed direction, (2) use of a measurement model for parametric studies of V(z) curves, and (3) determination of elastic constants by systematically comparing wave-mode velocities obtained from the measurement model and the V(z) measurement. Some examples are presented for transition metal nitride films used as hard protective coatings of softer surfaces. Attention is also directed to certain advantages of using multiple modes. It is shown that multiple-mode results reduce the region in a plane of material constants for which a deviation function between theoretical and experimental results has prescribed small values. Finally a brief discussion is presented of some recent results obtained at much lower frequencies by time resolved acoustic microscopy. more...

Thin film materials are widely used as hard, protective coatings for softer surfaces. It is known that fracture strength and hardness are related to the elastic and plastic properties [1]. The elastic constants of the film deposited on a substrate are, however, difficult to measure. By a technique which was recently discussed [2] the elastic constants of amorphous (isotropic) films and single-crystal (anisotropic) films can be obtained by measuring the velocities of surface acoustic waves (SAWs) propagating over a thin-film/ substrate specimen by the use of a line-focus acoustic microscope. more...

This paper discusses a method to determine the elastic constants of solid materials from the measured velocities of leaky surface acoustic waves (SAWs), and it explores the feasibility of determining the mass density from attenuation data. For an anisotropic solid such as a cubic crystal, the direction-dependent velocity of a leaky SAW has been measured by line-focus acoustic microscopy (LFAM) for various propagation-directions. A set of elastic constants has then been determined by inverting the velocity data. For an isotropic solid, the elastic moduli have been determined from the leaky Rayleigh wave velocity measured by LFAM and a longitudinal wave velocity measured by a pulse-echo transit-time technique. In addition to determining the elastic constants, it has been attempted to use the leaky SAW attenuation data measured by LFAM to determine the mass density more...

Acoustic microscopy can be used for very localized measurements of the velocity and attenuation of surface waves, and hence is a possible technique for nondestructive evaluation of near surface damage due to fatigue, machining, friction, wear, etc. Because the frequency of operation of an acoustic microscope is high, usually above 100 MHz, the wavelength of the surface wave is relatively small, and thus the roughness of the specimen may affect the wave velocity. In most cases the specimens must be polished to a metallurgical level to ensure that the true Rayleigh wave velocity, i.e., the one for a smooth surface will be measured. For some cases the specimens should, however, not be polished. For example, for the prediction of fatigue life, the roughness may increase during the fatigue test. Usually there remains a certain amount of roughness on the surface after friction, wear or machining. Polishing or any other surface preparation process may destroy the true surface condition of the specimen. Therefore, measurements should often be made for specimens with rough surfaces and it is then important to know the effect of surface roughness on the surface wave velocity in order that roughness effects can be distinguished from the effects that are of actual interest in the measurement. more...

G A A b st ra ct s loss of stool” as their sole reason, contradicting their answer on the e-PAQ -PF. The most frequently cited reasons for not discussing FI were “other health problems more important to discuss”(n=9), “able to manage symptoms on my own”(n=7), and “thought leakage was a normal part of aging”(n=4). 17 women indicated a most important reason; “other health problems more important”(n=4) and “normal part of aging”(n=3) were the most frequently chosen. No one chose embarrassment as the most important reason. Conclusion: Consistent with other reports, participants who had discussed FI in the past had more severe FI than those who had not. Some women who indicated FI in the past 4 weeks, did not consider themselves to have the problem for unclear reasons. Higher prioritization of other health problems, perception that they are able to manage FI on their own, and belief that FI is a normal part of aging were the most common reasons for not discussing FI with clinicians. more...

We developed a 2.0 inch, QCIF (160×128×RGB), a-Si:H TFT-LCD with a low noise gate driver integrated on glass substrate. By simulation and measurement, the proposed gate driver was found to be noise-free compared to conventional one. A new gate driver can make it possible to perform operation regardless of the voltage coupling from other voltage sources. more...

This paper presents the radial vibration characteristics of piezoelectric cylindrical transducers and the application of the transducers to the generation and detection of axisymmetric longitudinal waves in a pipe. Dynamic differential equations of piezoelectric radial motion derived in terms of radial displacement and electric potential and mechanical and electric boundary conditions have yielded a characteristic equation for radial vibration of the radially polarized piezoelectric cylinder. Theoretical calculations of the fundamental natural frequency have been compared with numerical and experimental results for transducers of several sizes, and have shown a good agreement. It has been shown that the piezoelectric natural frequency of the fundamental mode for radial vibration in a cylindrical transducer depends mostly on the radius rather than on the thickness of the cylinder. Experiments have been performed in empty and water‐filled pipes equipped with the transducers that were used for transmitting a... more...

A novel LTPS method called MICC (metal-induced crystallization using a cap) is introduced. The role of cap layer on a-Si is the control of the nickel concentration for inducing crystallization as well as the passivation of the surface during thermal process for crystallization. Circular grain growth can be seen, due to lateral grain growth from a seed. Polycrystalline silicon with large grain and smooth surface can be achieved by MICC. We fabricated a AMLCD with high aperture ratio of 80 % using silicon-based spin-on low-K dielectrics as a planarization layer. more...

The authors comment sequentially on several statements in the paper by M. Mendik, S. Sathish, A. Kulik, G. Gremaud, and P. Wachter, J. Appl. Phys. 71, 2830 (1992) and suggest a more reliable technique to determine the elastic constants of a {100}‐oriented cubic crystal. more...

The speed of a torsional stress wave transmitted in a solid waveguide, which has a noncircular cross section and is submerged in a liquid, is inversely proportional to the density of the liquid. Thus, by measuring the speed of the torsional stress wave, information can be obtained about the density of the liquid or density‐related characteristics such as liquid level and the mass composition of biphase mixtures. A predictive theory is developed to correlate the speed of the wave with the density of the liquid and the shape of the waveguide’s cross section. The theory is used to optimize the waveguide’s geometry so as to increase sensor sensitivity. The theoretical results are compared and found to favorably agree with experimental observations. more...

The speed of torsional stress waves transmitted in solid waveguides submerged in a liquid depends, among other things, on the liquid’s density and viscosity and the waveguides’ cross‐sectional geometry. By measuring the speed of torsional stress waves in two waveguides of different cross‐sectional geometries, one can obtain both the liquid’s density and viscosity. An on‐line, real‐time sensor for the simultaneous measurement of density and viscosity is described. The article details the sensor’s principles of operation and reports experimental results conducted using viscosity standard calibration liquids with well‐known thermophysical properties. For fluids with density ρf >1×103 kg/m3, it is estimated that the instrument can measure density with a precision better than 0.5%. For fluids with the product shear viscosity (μ) and density, ρfμ>100 kg2/(m4 s), it can measure the shear viscosity with a precision better than 1%. more...