06 Electrical power supply and utilization (scientific, technical)

charging and gassing. The modelled results were compared with the actual measurements. The model is given as a semi-empirical equation in closed form. With this equation, the response surface is displayed graphically to visualize the effect of changes in critical variables. The results of the investigation will help determine the best charging conditions for the regular and float charging modes in order to deliver the maximum charge without excessive gassing.

99103727 A new approach to identification of transient power quality problems using linear combiners Dash, P. K. er al. Electric Power Systems Research, 1999, 51, (l), l-11. In this paper, a new approach to identify transient power quality disturbances using linear combiners and a fuzzy decision support system is presented. The key idea underlying the approach is to obtain the amulitude and the slooe of the oeak fundamental component of a voltage wa;eform using adapt&e linear combiners, along with non-linear least mean squares (LMS) algorithm. Fuzzy logic is then used to identify the class to which the waveform belongs by a set of heuristic rules and an uncertainty index. Detailed digital simulation results involving various types of transient power quality disturbances are presented to prove the ability of the new approach in classifying these disturbances.

99103720 A new approach to the design of robust load- frequency controller for large scale power systems Ray, G. er al. Electric Power Systems Research, 1999, 51, (1) 13-22. A new method is presented for derivation of a robust controller for the load frequency controller of interconnected power systems with uncertain parameters. A combination of ‘Matching conditions’ and Lyapunov stability theory is adopted to implement a robust stabilizing controller. The stability analysis of the closed-loop interconnected systems for all admissible uncertainties is considered. The application of the proposed robust control scheme is considered through simulation studies of two-area power system model. Performance robustness of the proposed scheme is compared with the recent work of Wang et al. (1993, IEE Proc. C Vol. 140, pp. 11-16). and found to be very good.

99103729 New materials for polymer electrolyte membrane fuel cell current collectors Hentall. P. L. et al. J. Power Sources, 1999, 80, (l/2), 235-241. For application in automobiles, polymer electrolyte’ membrane fuel cells need to have high power density and be inexpensive and robust to compete effectively with the internal combustion engine. Development of mem- branes and new electrodes and catalysts have increased power significantly, but further improvements may be achieved by the use of new materials and construction techniques in the manufacture of the bipolar plates. To show this, a variety of materials have been fabricated into flow field plates, both metallic and graphitic and single fuel cell tests were conducted to determine the performance of each material. Maximum power was obtained with materials which had lowest contact resistance and good electrical conductivity. The performance of the best material was characterized as a function of cell compression and flow field geometry.

99lO3730 A novel approach to conventional power system stabilizer design using iabu search Abido. M. A. Electrical Power and Energy Systems. 1999, 21, (6), 443-454. A tab; search (TS) based power system stabilizer (PSS) is presented in this article. The orooosed aooroach uses the TS alnorithm to search for the optimal settings’of conv%tional lead-lag poweysystem stabilizer (CPSS) parameters. Incorporation of the TS algorithm in the PSS design significantly reduces the time consumed in the design process. One of the main advantages of the proposed approach is the fact that the TS algorithm leads to the outimal solution reeardless of the initial euess. The performance of the proposed PSS undoer different disturbances and loading conditions is investigated for single machine infinite bus and multimachine power systems. The eigenvalue-analysis and simulation results show the effectiveness of the proposed PSSs to damp out the local and the inter-area modes of oscillations and work effectively over a wide range of loading conditions and system parameter variations.

99103731 A novel framework for the process control of the restoration of electrical industrial systems Fountas. N. A. et al. Elec. Power Sysr. Res., 1999, 50, (3), 163-167. A technical process is the controlled flow of matter, energy or information. This work concentrates on event-related control rather than the widely investigated continuous control. Special attention has been given to the complex multi-variable problem of large-scale power systems restoration following a widespread outage. Processes taken place and related process control can be effectively described by states and transitions, which form the basis of a novel methodology using the Petri Net (PN) framework. Since PNs are a rieid mathematical tool. thev can be used as a very general

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approach to event-related process’ conirol in simulating, checking and providing a quantitative as well as qualitative understanding of the underlying processes.

99103732 Novel modeling for the prediction of aged transformer oil characteristics Wahab, M. A. A. et al. Elec. Power Syst. Res., 1999, 51, (1). 61-70. The effect of ageing on transformer oil physical, chemical and electrical properties has been studied using the international testing methods for the evaluation of transformer oil quality. The study has been carried out on 12 transformers in the field and for monitoring periods up to eight years. The orooerties which are stronelv time-deoendent have been soecified and ihose which have a great imsact on the’transformer oil breakdown voltage have been defined. Mathematical models for the breakdown voltage, total acidity and water content as a function of service periods have been given. The validity and applicability of these models for future prediction of these properties have been verified by the good agreement between the measured end predicted values. A multiple linear regression model for each transformer oil breakdown voltage as a function of its water content, total acidity and service period has been introduced and its adequacy has been illustrated by statistical analysis. Another multiple linear regression model has been developed by combining the results of a group of transformers into that of a single equivalent transformer. This model has been validated by predicting the properties of some other transformers and comparing them with the measured values. The comparison showed a good agreement for the results of transformers which have either been used or not in the derivation of the model.

99103733 Operation of solid oxide fuel cells at reduced temperatures Sahibzada, M. er al. Fuel, 1999, 78, (6). 639-643. For intermediate temperature operation, the fuel cell arrangement La,, $jro 4Co,, zFe,, sOT,CeogGd,, 10,.ss/Ni-YSZ, incorporating a dense film (5-10 pm) ofthe Ce~:~Gdu.iOi.~s electrolyte tape cast onto ?he supporting anode was investigated. Open circuit voltages of 0.75-0.8 V were obtained at 550-65o”C, using moist hydrogen as fuel. These open circuit voltages were consistent with theoretical predictions taking into account the electronic/ionic leakage of the electrolyte film. Power outputs in excess of 125 mW/cm2 were obtained at 650°C and the cell resistance was approximately 1 R.cm’. Most of the cell resistance was derived from the cathode according to ac impedance measurements and a great deal of effort was spent in testing a double layer cathode structure and a lead-promoted cathode. Hence oower outouts in excess of 150 mW/cm2 were obtained at 65O”C, although greater improvements were anticipated. Experiments were also carried out at 600°C using direct methanol fuels at the anode; the maximum power output was approximately half of that obtained with hydrogen.

99103734 Optimal multistage modernization of power system subject to reliability and capacity requirements Levitin, G. and Lisnianski, A. Elec. Power Sysl. Res., 1999, 50, (3) 183- 190. Addressed in this paper is the multistage modernization problem for power systems with series-parallel structure. The study period is divided into several stages according to demand forecast. At each stage the consumer demand distribution is predicted in the form of a cumulative load curve. Different actions, such as modifying existing equipment, changing main- tenance policy or adding new elements, may be undertaken in any system component at any stage to increase the total system capacity and/or reliability. The objective is to minimize the sum of costs of system modernization actions over the study period, while satisfying reliability constraints at each stage. In order to solve the problem, a genetic algorithm is used as an optimization tool. The solution encoding technique developed allows the genetic algorithm to manipulate integer strings representing multi-stage system modernization planes. A solution quality index is comprised of both reliability and cost estimations. The procedure based on the universal generating function is used for evaluation of the availability of multi-state series-parallel power systems. This technique allows one to estimate the effect on the entire system availability when both capacity and availability of system elements are varied. An illustrative example is presented in which the optimal expansion plan is found for a coal transportation system of a power station.

99103735 Organic fuels: composition and formation enthalpy. Part l-wood derivatives, related carbohydrates, exudates and rosin Meyerriecks, W. .I. Pyrofech., 1998, (8) l-17. The use of free energy minimization computer programs, for selection of fuels for pyrotechnic applications is among the topics addressed in this paper. Although data on the formation enthalpies of common compounds can be readily available in handbooks, complex organic compounds or poorly characterized mixtures may not have the required data available in a directly usable form. A variety of organic fuels used in pyrotechnics were evaluated based on establishing useful chemical formulas and formation enthalpies. Fuels discussed include wood and wood derivatives, carbohy- drates, oligosaccharides, cellulose ami cellulose derivatives, hemicellulose, hydroxyethyl cellulose, CM-cellulose, starch, gums and resins, gum arabic, gum tragacanth, guar gum and rosin.

Fuel and Energy Abstracts November 1999 393