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Load Conditions (load + condition)
Selected AbstractsA critical path method for the estimation of service restoration time in power distribution systemsEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 4 2008C. Lakshminarayana Abstract Distribution systems (DSs) are invariably subjected to various types of faults, causing power blackouts to occur. Distribution Engineers have the main responsibility to minimizing the duration of these power blackouts. This minimization can be achieved by the detailed study of pre-fault load condition of the DS, isolating the faulted section, and restoring the supply to healthy sections of the DS. Hence the estimation of service restoration time (SRT) is very important in electrical distribution systems (EDS). The estimation of SRT requires detailed knowledge of the commencement time of the emergency diesel generator (EDG) in EDS and also the operating time of the various relays in EDS. This paper introduces a new concept of optimistic time (OT), pessimistic time (PT), and most likely time (MT) of starting of the EDGs in addition to the OT, PT, and MT of the operation of the relays. The proposed concept is tested on 14-bus, 17-bus, and 29-bus distribution networks. The results reveal that it is highly suitable technique for the estimation of SRT under abnormal conditions. Hence this technique can easily be improved in distribution automation/service restoration algorithms. Copyright © 2007 John Wiley & Sons, Ltd. [source] Stability analysis and simulation of a single-phase voltage source UPS inverter with two-stage cascade output filterEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 1 2008Jawad Faiz Abstract The primary role of an uninterruptible power supply (UPS) systems is to produce sinusoidal output voltage with minimum total harmonic distortion (THD) and fast dynamic response. This paper investigates the performance of two-stage cascade output filter for single-phase voltage source UPS inverter and it is compared with an LC output filter. The simulation result shows harmonic reduction of output voltage of the inverter due to using multiple-filter. Both THD of the low output voltage and good voltage utilization can be achieved by the proposed filter scheme. The THD of the output voltage in various load condition are all less than 4%. A good agreement between the simulation and experimental results is achieved. Copyright © 2007 John Wiley & Sons, Ltd. [source] Analytical comparison of reversed nested Miller frequency compensation techniquesINTERNATIONAL JOURNAL OF CIRCUIT THEORY AND APPLICATIONS, Issue 7 2010Alfio Dario Grasso Abstract In this paper, novel and previously proposed reversed nested Miller compensation (RNMC) networks are analyzed and compared, and their design equations are also presented. Hence, this paper is the natural extension of a previous paper by the authors (Int. J. Circ. Theor. Appl. 2008; 36(1):53,80), where only the nested Miller compensation topologies were treated. In particular, a coherent and comprehensive analytical comparison of the RNMC topologies, including two new networks presented for the first time, is performed by means of the figure of merit that expresses a trade-off among gain-bandwidth product, load capacitance and total transconductance, for equal values of phase margin (Int. J. Circ. Theor. Appl. 2008; 36(1):53,80). The analysis shows that there is no unique optimal solution among the RNMC topologies, as this depends on the load condition as well as on the relative transconductance magnitude of each amplifier stage. From this point of view, the proposed comparison also outlines useful design guidelines for the optimization of large-signal and small-signal performance. Simulations confirming the effectiveness of the proposed design methodology and analytical comparison are also included. Copyright © 2009 John Wiley & Sons, Ltd. [source] A discussion on the performance of impedance matched antenna system and considerations for a better performanceMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 2 2008Adnan Kaya Abstract Impedance matching networks are used extensively in radio communications. In this study, ,-matching circuit has been used as a matching network. The return loss level of several impedance matched microstrip antennas are compared as a function of matching techniques. The ,-matching device is used to construct the antenna tuning units, which is only used to match the front module and the antenna. This circuit impedance region has been investigated analytically under the variable load condition. When the mismatch is occurred, the result is an increase in the energy consumption or transmission quality deterioration. In addition, the input module in antenna system could be damaged if reflection of the signal levels is excessively high. This is interesting application because antennas cannot be considered alone as component with changing electromagnetic properties. The rectangular microstrip antenna was designed at 2.5 GHz frequency by using microstrip feed line. Better return loss level which is ,16.86 dB has been obtained for this antenna using ,-matching circuit. It is shown that theoretical, simulation, and laboratory results are good agreement. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 410,415, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23101 [source] Procrastination as self-regulation failure of performance: effects of cognitive load, self-awareness, and time limits on ,working best under pressure'EUROPEAN JOURNAL OF PERSONALITY, Issue 5 2001Joseph R. Ferrari Effects of cognitive load, objective self-awareness and time limits on the self-regulation of performance speed and accuracy were investigated between procrastinators and non-procrastinators. In experiment 1 chronic procrastinators completed fewer items (slow speed) and made more errors (less accuracy) than non-procrastinators under high but not low cognitive load conditions when the time span was limited and brief. In experiment 2 chronic procrastinators performed slower than non-procrastinators under a 2 second, but not under no limit, 1 second, or 4 second time limit conditions. Chronic procrastinators compared to non-procrastinators also performed more slowly and made more performance errors under objective self-awareness conditions regardless of the length of time. These experiments indicate that chronic procrastinators regulate ineffectively their performance speed and accuracy when they ,work under pressure' (defined by high cognitive load, objective self-awareness, and imposed time limitations). Copyright © 2001 John Wiley & Sons, Ltd. [source] Optimal production cost of the power producers with linear ramp model using FDR PSO algorithmEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 2 2010M. Anitha Abstract In practice, the power producers have to be rescheduled for power generation beyond their power limits to meet vulnerable situations like credible contingency and increase in load conditions. During this process, the ramping cost is incurred if they violate their permissible elastic limits. In this paper, optimal production costs of the power producers are computed with ramping cost considering stepwise and piecewise linear ramp rate limits using fitness distance ratio particle swarm optimization (FDR PSO) algorithm. Transient stability constraints are also considered while formulating the optimal power flow (OPF) problem as additional rotor angle inequality constraints. The proposed algorithm is demonstrated on a practical 39 bus New England and 62 bus Indian Utility system with different case studies. Copyright © 2008 John Wiley & Sons, Ltd. [source] Review: Durability and Degradation Issues of PEM Fuel Cell ComponentsFUEL CELLS, Issue 1 2008F. A. de Bruijn Abstract Besides cost reduction, durability is the most important issue to be solved before commercialisation of PEM Fuel Cells can be successful. For a fuel cell operating under constant load conditions, at a relative humidity close to 100% and at a temperature of maximum 75,°C, using optimal stack and flow design, the voltage degradation can be as low as 1,2,,V·h. However, the degradation rates can increase by orders of magnitude when conditions include some of the following, i.e. load cycling, start,stop cycles, low humidification or humidification cycling, temperatures of 90,°C or higher and fuel starvation. This review paper aims at assessing the degradation mechanisms of membranes, electrodes, bipolar plates and seals. By collecting long-term experiments as well, the relative importance of these degradation mechanisms and the operating conditions become apparent. [source] Architecture design, performance analysis and VLSI implementation of a reconfigurable shared buffer for high-speed switch/router,INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 2 2009Ling Wu Abstract Modern switches and routers require massive storage space to buffer packets. This becomes more significant as link speed increases and switch size grows. From the memory technology perspective, while DRAM is a good choice to meet capacity requirement, the access time causes problems for high-speed applications. On the other hand, though SRAM is faster, it is more costly and does not have high storage density. The SRAM/DRAM hybrid architecture provides a good solution to meet both capacity and speed requirements. From the switch design and network traffic perspective, to minimize packet loss, the buffering space allocated for each switch port is normally based on the worst-case scenario, which is usually huge. However, under normal traffic load conditions, the buffer utilization for such configuration is very low. Therefore, we propose a reconfigurable buffer-sharing scheme that can dynamically adjust the buffering space for each port according to the traffic patterns and buffer saturation status. The target is to achieve high performance and improve buffer utilization, while not posing much constraint on the buffer speed. In this paper, we study the performance of the proposed buffer-sharing scheme by both a numerical model and extensive simulations under uniform and non-uniform traffic conditions. We also present the architecture design and VLSI implementation of the proposed reconfigurable shared buffer using the 0.18 µm CMOS technology. Our results manifest that the proposed architecture can always achieve high performance and provide much flexibility for the high-speed packet switches to adapt to various traffic patterns. Furthermore, it can be easily integrated into the functionality of port controllers of modern switches and routers. Copyright © 2008 John Wiley & Sons, Ltd. [source] A distributed adaptive guard channel reservation scheme for cellular networksINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 9 2007H.K. Pati Abstract In this paper, a distributed adaptive guard channel reservation (DAGCR) scheme is proposed to give priority to handoff calls. This scheme is built upon the concept of guard channels and it uses an adaptive algorithm to search automatically the optimal number of guard channels to be reserved at each base station. The quality-of-service (QoS) parameters used are the new and handoff call blockings. Simulation studies are performed to compare the present algorithm with the static guard channel policy. Simulation results show that this proposed algorithm guarantees the handoff call blocking probability to remain below the targeted threshold up to a substantially high offered load with a minimal blocking to new calls up to a moderate offered load and also shows significantly high channel utilization in all offered load conditions. This scheme is examined over a wide range of offered load. Thus, it seems the proposed scheme is very useful in controlling the blocking performances in wireless cellular networks. Copyright © 2006 John Wiley & Sons, Ltd. [source] An experimental investigation on manifold-injected hydrogen as a dual fuel for diesel engine system with different injection durationINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 15 2009N. Saravanan Abstract Stringent emission norms and rapid depletion of petroleum resources have resulted in a continuous effort to search for alternative fuels. Hydrogen is one of the best alternatives for conventional fuels. Hydrogen has both the benefits and limitation to be used as a fuel in an automotive engine system. In the present investigation, hydrogen was injected into the intake manifold by using a hydrogen gas injector and diesel was introduced in the conventional, mode which also acts as an ignition source for hydrogen combustion. The flow rate of hydrogen was set at 5.5,l,min,1 at all the load conditions. The injection timing was kept constant at top dead center (TDC) and injection duration was adjusted to find the optimized injection condition. Experiments were conducted on a single cylinder, four stroke, water-cooled, direct injection diesel engine coupled to an electrical generator. At 75% load the maximum brake thermal efficiency for hydrogen operation at injection timing of TDC and with injection duration of 30°CA is 25.66% compared with 21.59% for diesel. The oxides of nitrogen (NOX) emission are 21.7,g,kWh,1 for hydrogen compared with diesel of 17.9,g,k,Wh,1. Smoke emissions reduced to 1 Bosch smoke number (BSN) in hydrogen compared with diesel of 2.2 BSN. Hydrogen operation in the dual fuel mode with diesel exhibits a better performance and reduction in emissions compared with diesel in the entire load spectra. Copyright © 2009 John Wiley & Sons, Ltd. [source] Influence of high rates of supplemental cooled EGR on NOx and PM emissions of an automotive HSDI diesel engine using an LP EGR loopINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 15 2008A. Maiboom Abstract Previous experimental studies on diesel engine have demonstrated the potential of exhaust gas recirculation (EGR) as an in-cylinder NOx control method. Although an increase in EGR at constant boost pressure (substitution EGR) is accompanied with an increase in particulate matter (PM) emissions in the conventional diesel high-temperature combustion (HTC), the recirculation of exhaust gases supplementary to air inlet gas (supplemental EGR) by increasing the boost pressure has been suggested as a way to reduce NOx emissions while limiting the negative impact of EGR on PM emissions. In the present work, a low-pressure (LP) EGR loop is implemented on a standard 2.0 l automotive high-speed direct injection (HSDI) turbocharged diesel engine to study the influence of high rates of supplemental cooled EGR on NOx and PM emissions. Contrary to initial high-pressure (HP) EGR loop, the gas flow through the turbine is unchanged while varying the EGR rate. Thus, by closing the variable geometry turbine (VGT) vanes, higher boost pressure can be reached, allowing the use of high rates of supplemental EGR. Furthermore, recirculated exhaust gases are cooled under 50°C and water vapour is condensed and taken off from the recirculated gases. An increase in the boost pressure at a given inlet temperature and dilution ratio (DR) results in most cases an increase in NOx emissions and a decrease in PM emissions. The result of NOx,PM trade-off, while varying the EGR rate at fixed inlet temperature and boost pressure depends on the operating point: it deteriorates at low load conditions, but improves at higher loads. Further improvement can be obtained by increasing the injection pressure. A decrease by approximately 50% of NOx emissions while maintaining PM emission level, and brake specific fuel consumption can be obtained with supplemental cooled EGR owing to an LP EGR loop, compared with the initial engine configuration (HP moderately cooled EGR). Copyright © 2008 John Wiley & Sons, Ltd. [source] Influence of the heat recovery steam generator design parameters on the thermoeconomic performances of combined cycle gas turbine power plantsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 14 2004Manuel Valdés Abstract This paper proposes a methodology to identify the most relevant design parameters that impact on the thermal efficiency and the economic results of combined cycle gas turbine power plants. The analysis focuses on the heat recovery steam generator (HRSG) design and more specifically on those operating parameters that have a direct influence on the economic results of the power plant. These results are obtained both at full and part load conditions using a dedicated code capable of simulating a wide number of different plant configurations. Two different thermoeconomic models aimed to select the best design point are proposed and compared: the first one analyzes the generating cost of the energy while the second one analyzes the annual cash flow of the plant. Their objective is to determine whether an increase in the investment in order to improve the thermal efficiency is worth from an economic point of view. Both models and the different HRSG configurations analysed are compared in the results section. Some parametric analysis show how the design parameters might be varied in order to improve the power plant efficiency or the economic results. Copyright © 2004 John Wiley & Sons, Ltd. [source] Stability analysis of an adaptive packet access scheme for mobile communication systems with high propagation delaysINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 2 2003Giovanni Giambene Abstract In this paper, we investigate a packet access scheme that is able to support mixed traffics in the presence of high propagation delays. Referring to a Time-Code Division Multiple Access air interface, we propose a Medium Access Control (MAC) protocol based on a random access scheme. A successful attempt grants the use of a slot-code resource. This protocol is named Adaptive Time Code-Packet Reservation Multiple Access (ATC-PRMA), since the access parameters are changed, depending on the traffic load conditions, so as to fulfil Quality of Service requirements. Numerical examples are carried out for the Low Earth Orbit (LEO)- Mobile Satellite System (MSS) scenario, but all these considerations could be applied to High-Altitude Platform Stations (HAPSs) as well. In both cases, high propagation delays prevent an immediate feedback to users. An analytical approach is proposed to study the stability of our MAC scheme. Accordingly, we define a criterion for optimizing system performance. The predicted ATC-PRMA behaviour is supported by simulation results. Finally, we show the performance improvement of ATC-PRMA with respect to a MAC protocol not employing adaptive parameters. Copyright © 2003 John Wiley & Sons, Ltd. [source] Transfer of metallic debris from the metal surface of an acetabular cup to artificial femoral heads by scraping: Comparison between alumina and cobalt,chrome headsJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2008Chong Bum Chang Abstract We aimed to investigate the transfer of metal to both ceramic (alumina) and metal (cobalt,chrome) heads that were scraped by a titanium alloy surface under different load conditions. The ceramic and metal heads for total hip arthroplasties were scraped by an acetabular metal shell under various loads using a creep tester. Microstructural changes in the scraped area were visualized with a scanning electron microscope, and chemical element changes were assessed using an energy dispersive X-ray spectrometry. Changes in the roughness of the scraped surface were evaluated by a three-dimensional surface profiling system. Metal transfer to the ceramic and metal heads began to be detectable at a 10 kg load, which could be exerted by one-handed force. The surface roughness values significantly increased with increasing test loads in both heads. When the contact force increased, scratching of the head surface occurred in addition to the transfer of metal. The results documented that metallic debris was transferred from the titanium alloy acetabular shell to both ceramic and metal heads by minor scraping. This study suggests that the greatest possible effort should be made to protect femoral heads, regardless of material, from contact with metallic surfaces during total hip arthroplasty. © 2007 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2008 [source] The Relationship Between Multiple Scratch Tests and Wear Behavior of Hot-Pressed Silicon Nitride Ceramics with Various Rare-Earth Additive SystemsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2008Hideki Hyuga The wear behavior of Si3N4 ceramics sintered with various rare earth additives was studied for nonlubricated sliding under different conditions, and scratch tests carried out in an attempt to correlate the wear behavior. When multiple scratch testing is used the results can be used to indicate the initial wear behavior under fracture-dominated wear of the materials. The additive system used in the sintering of the Si3N4 ceramics affected the specific wear rate under nonlubricated sliding conditions, and under high load conditions, where fracture is dominant, the specific wear rate was shown to increase in samples sintered with lutetium as a consequence of a strong bonding strength between the grains and grain boundary resulting in a higher degree of brittle fracture. [source] Measurement and analysis of vibration levels for truck transport in Spain as a function of payload, suspension and speedPACKAGING TECHNOLOGY AND SCIENCE, Issue 8 2008Manuel-Alfredo Garcia-Romeu-Martinez Abstract The vibration levels that occur during transportation in vehicles are complex and play a significant role in the level of damage experienced by products when shipped. In the past decade, technology has allowed packaging engineers to measure and analyse the vibration levels in commercial shipments. Recent studies have measured vibration in shipping environments on a global basis to allow packaging designers to develop packaging to meet worldwide distribution challenges. The purpose of this study was to measure and develop simulation methods for truck transport in Spain. The study quantifies vibration characteristics in trucks as a function of speed, payload and suspension type. The shipments were instrumented with vibration data recorders to measure the vibration levels and a global position system to measure the truck speed. The recorders were mounted at the rear and front location of the trailer. Two different trucks, one with leaf spring suspension and the other with air ride suspension were studied using two different load conditions. The road surface was asphalt. The data is presented in the form of power spectral density that can be used to program electrohydraulic vibration tables using ASTM, ISTA and ISO vibration test methods. Results showed that the air ride vibration levels were lower than that of leaf spring suspension trailers. Overall, the vibration intensity was lower for both types of truck as compared with the levels measured in North America, China, India and Southeast Asia. Copyright © 2007 John Wiley & Sons, Ltd. [source] Predictive mechanical performance evaluation of consumer food cans using stereolithography modelsPACKAGING TECHNOLOGY AND SCIENCE, Issue 1 2003D. Karalekas Abstract The development of new metal food containers can be a technologically challenging and costly process. Understanding the interplay between the major design characteristics and requirements affecting the product's final structural capability is paramount to achieving an optimum design proposition. As a result, computer-based simulation has been employed by industry to assess a container's performance under a variety of load conditions, including axial load and panelling of cans. In this paper, the feasibility of a new approach for addressing the effects of design parameters on the structural performance of containers under development is investigated. The evaluation methodology is based on structural testing of stereolithography-built physical prototypes of a rigid metal container used for coffee packaging. It is shown that the experimentally obtained findings are in accordance to those resulting from computational simulation. This method can be used to support the development of existing and new metal containers. Copyright ©2003 John Wiley & Sons, Ltd. [source] Membrane reformer PEM cogeneration systems for residential applications,Part A: full load and partial load simulationASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2009Stefano Campanari Abstract This two-part paper investigates the performances and economic potential benefits of a fuel cell cogeneration system based on a membrane reformer (MREF), using polymer electrolyte membrane (PEM) fuel cells, applied to residential cogeneration. Part A of this work focuses on the thermodynamic analysis and simulation of the system at full and partial load conditions, discussing its performance by means of a sensitivity analysis carried out under different operating conditions. Part B presents the technoeconomic analysis of the proposed system integrated into a real residential application, dealing with the energy savings and the economic balances, and proposes a preliminary design of the cogeneration unit. The system is based upon a PEM fuel cell, integrated with a membrane reformer (MREF) to form a small-scale, highly efficient cogeneration unit, potentially suitable for application to distributed generation in the residential field. The high purity hydrogen fuel required by the PEM fuel cell is produced in the membrane reformer through hydrogen selective membranes based on a Pd-Ag alloy. The analysis is carried out aiming to define the system energy balances in all the conditions occurring under real operation, including the influence of ambient temperature and of the expected fuel cell efficiency decay with time. The discussion reveals the relevant potential advantages of the MREF solution with respect to fuel cell units based on steam reforming (SR) or auto-thermal reforming (ATR): when compared to these solutions, MREF exhibits a 10% points higher electrical efficiency and requires a much simpler plant layout. These results are the basis for the detailed system technoeconomic analysis carried out in Part B of the work. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Membrane reformer PEM cogeneration systems for residential applications,Part B: techno-economic analysis and system layoutASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2009Stefano Campanari Abstract This two-part paper investigates the performances and potential economic benefits of a membrane reformer (MREF)-based fuel cell cogeneration system, using polymer electrolyte membrane (PEM) fuel cells, applied to residential cogeneration. Part A of the work focuses on the thermodynamic analysis and simulation of the system at full and partial load conditions, discussing its performance by means of a sensitivity analysis carried out under different operating conditions. Part B presents the techno-economic analysis of the proposed system integrated into a real residential application, dealing with the energy savings and the economic balances, and proposes a preliminary design of the cogeneration unit. The higher electric efficiency of the innovative MREF system proposed in this work allows a yearly cost savings about 50% higher than cost savings allowed by fuel cell cogeneration units based on conventional fuel processors. Moreover, CO2 emissions savings, calculated for an average northern Italy single-family load, is about 1.6 tCO2/year. The paper also presents a proposed system layout, discussing the preliminary design of all the required components and analyzing with particular care the issues related to the heat recovery loop and to the arrangement of the system key component: the membrane reforming reactor. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||||||||