06 Electrical power supply and utilization (scientific, technical) 04/02790 A novel scheme of local protection against voltage collapse based on the apparent-power losses Verbi, G. and Gubina, F. International Journal of Electrical Power & Energy Systems, 2004, 26, (5), 341-347. A new algorithm for protection against voltage collapse is proposed using local phasors' magnitudes and angles. A change in apparent power line flow in a time interval is exploited for computation of the voltage collapse criterion. The criterion is based on the fact that the line losses in the vicinity of voltage collapse increase faster than delivery of the apparent power and at the voltage collapse point the losses take all the increase. The selected criterion equals zero when a voltage collapse occurs, which gives the relay an opportunity to react earlier with an appropriate setting. The proposed algorithm could be easily implemented in a numerical relay. The algorithm is simple and computationally very fast. An on-line protection scheme could be applied at the end of an endangered line. The algorithm was tested on various test systems including New England 39-bus test system.
04•02791 A polymer electrolyte membrane fuel cell system for powering portable computers Tiiber, K. et al. Journal of Power Sources, 2003, 122, (1), 1 8. The Fraunhofer Institute for Solar Energy Systems has developed a fuel cell system to power a portable computer. The components are a four-cell polymer electrolyte membrane fuel cell (PEMFC) system, a six-phase DC/DC-converter, an air pump, two cylindrical metal hydride storage tanks, a valve and a pressure sensor to adjust the hydrogen flow [national patent applied, DE 101 19 339, 03 (2001)] and a control unit for the management of the whole system. Prominent characteristics of the system are a flat design of the fuel cell stack and the integrated DC/ DC-converter [national patent granted, DE 198 10 556 C1, 11 (1999)]. The system provides a nominal power output of about 42 W at 12 V. Extensive physical investigations of different flow field combinations as well as the system design are presented.
04102792 A VRLA battery simulation model Pascoe, P. E. and Anbuky, A. H. Energy Conversion and Management, 2004, 45, (7-8), 1015 1041. A valve regulated lead acid (VRLA) battery simulation model is an invaluable tool for the standby power system engineer. The obvious use for such a model is to allow the assessment of battery performance. This may involve determining the influence of cells suffering from state of health (SOH) degradation on the performance of the entire string, or the running of test scenarios to ascertain the most suitable battery size for the application. In addition, it enables the engineer to assess the performance of the overall power system. This includes, for example, running test scenarios to determine the benefits of various load shedding schemes. It also allows the assessment of other power system components, either for determining their requirements and/or vulnerabilities. Finally, a VRLA battery simulation model is vital as a stand-alone tool for educational purposes. Despite the fundamentals of the V R L A battery having been established for over 100 years, its operating behaviour is often poorly understood. An accurate simulation model enables the engineer to gain a better understanding of VRLA battery behaviour. A system level multipurpose VRLA battery simulation model is presented. It allows an arbitrary battery (capacity, SOH, number of cells and number of strings) to be simulated under arbitrary operating conditions (discharge rate, ambient temperature, end voltage, charge rate and initial state of charge). The model accurately reflects the VRLA battery discharge and recharge behaviour. This includes the complex start of discharge region known as the coup de fouet.
discharge heat by condensing steam. Moreover, hydrogen can be burned with oxygen to produce steam and to generate power in hightemperature steam cycles. These considerations suggest that an integration of the processes could result in a very high efficiency of conversion. It could allow to start immediately to convert efficiently fossil fuels to power and clean hydrogen. Some theoretical evaluations are carried out which show that an improvement of efficiency could be reached with respect to separate plants. However, it is necessary to investigate each specific case in order to evaluate the real advantage obtained.
04/02795 Control-oriented nonlinear modelling of molten carbonate fuel cells Shen, C. et al. International Journal of Energy Research, 2004, 28, (5), 403-410. Performance and availability of molten carbonate fuel ceils (MCFC) stack are greatly dependent on its operating temperature. Control of the operating temperature within a specified range and reduction of its temperature fluctuation are highly desirable. The models of MCFC stack existing are too complicated to be suitable for design of a controller because of its lack of clear input-output relations. In this paper, according to the demands of control design, a quantitative relations model of control-oriented MCFC between the temperatures of the stack and flowrates of the input gases is developed, based on conservation laws. It is an affine non-linear model with multi-input and multi-output, the flowrates of fuel and oxidant gases as the manipulated vector and the temperatures of MCFC electrodeelectrolyte plates, separator plates as the controlled vector. The modelling and simulation procedures are given in detail. The simulation tests reveal that the model developed is accurate and it is suitable to be used as a model in designing a controller of MCFC stack.
04•02796 Effect of anode electrocataiyst for direct hydrazine fuel cell using proton exchange membrane Yamada, K. et al. Journal of Power Sources, 2003, 122, (2), 132-137. Hydrazine was examined as a fuel in a direct-liquid-fueled fuel cell that uses proton exchange membrane (PEM) such as Nafion ®. Different kinds of noble metals were examined as anode electrocatalysts for direct hydrazine fuel cells (DHFCs). In DHFC using platinum or palladium as the anode electrocatalyst, more than 1 V of cell voltage was obtained in the low-current density region. The F V characteristics changed drastically depending on the kind of anode electrocatalyst used. Compositions of the exhaust materials from each electrode were analysed to investigate the reaction occurring at the electrodes. The analysis revealed that the catalytic decomposition reaction of hydrazine proceeded further than the electro-oxidation reaction on the anode side using rhodium or ruthenium.
04/02797 Effects of unbalances and harmonics on optimal capacitor placement in distribution system Ghose, T. and Goswami, S. K. Electric" Power Systems Research, 2004, 68, (2), 167-173. A method comprising of heuristic search technique and simulated annealing (SA) has been proposed for solving the problem of optimal capacitor placement in radial distribution system and the effects of network and load unbalances, supply harmonics and load nonlinearities have been studied. The effect of network unbalances is most severe and can be incorporated very easily. But a new formulation of the problem is needed to include the effects of load unbalances, supply harmonics and load non-linearities as these are uncertain in nature.
04/02793 Application of VTB in design and testing of satellite electrical power systems
04/02798 Electrochemical capacitance of self-ordered mesoporous carbon
Jiang, Z. et aI. Journal of Power Sources, 2003, 122, (1), 95-108. Satellite electrical power systems (SEPS) are strongly interdisciplinary, exhibit complex non-linear behaviour, and operate over a wide range of power levels. The Virtual Test Bed (VTB) provides a unified computational environment that allows rapid modelling, simulation and virtual-prototyping of such complex systems. VTB handles modelling in a comprehensive and efficient way by using both topological and mathematical descriptions. The VTB is also endowed with mechanisms to import models and to co-simulate with other standard software. This paper presents a study of two representative SEPSs to demonstrate design and testing of such systems in the VTB. The performances of Li-ion and Ni-H2 batteries are compared in a particular system.
Zhou, H. et al. Journal of Power Sources, 2003, 122, (2), 219-223. The capacitance properties of the self-ordered mesoporous carbons (CMK-3), from a template of hexagonal self-ordered mesoporous SiO2 (SBA15) using sucrose as the carbon source, have been investigated. The pore distribution was narrow with a diameter of 3.90 nm and a surface area of 900 m2/g. Rectangular shape of the cyclic voltammetry was observed even if the scan rate is increased to about 5 x 10 -2 V/s. Self-ordered mesoporous carbon exhibited a electrochemical doublelayer capacitance of 60-90 F/g in scan rate from 5 x 10- 4 to 5 x 10 2 V/s between 1.5 and 3.4 V (Li/Li+). The specific capacitance of 10 F/cm z was similar to that of the typical value of EDLC. After the 100th cycle, the capacity decreased 20% in comparing with that of the first one.
04/02794 Cogeneration of power and hydrogen with integrated fuel processor counterpressure steam cycles Spazzafumo, G. International Journal of Hydrogen Energy, 2004, 29, (11), 1147-1150. The concept of cogeneration of power and hydrogen plants is introduced with specific regard to the fossil fuels. Fossil fuels require steam to be converted to hydrogen, while powerplants usually
Fuel and Energy Abstracts
04/02799 Exergy analysis of a PEM fuel cell at variable operating conditions Kazim, A. Energy Conversion and Management, 2004, 45, (11-12), I949-1961. This paper presents a comprehensive exergy analysis of a 10 kW PEM fuel cell at variable operating temperatures, pressures, eel1 voltages and air stoichiometrics. The calculations of the physical and chemical exergies, mass flow rates and exergetic efficiency are performed at