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00388 Molten carbonate fuel cells for power generation from high-ash Indian coals
06
Electrical power supply and utilization (scientific, technical)
this purpose were determined. Controller gains, droop slopes, reference voltages and compensator ratings were found for maintaining the load nude voltages constant irrespective of system loadabilities to values which lead to voltage instabilities. Finally, the influence of system equivalent impedances on these parameters is discussed. Evaluation of the critical load increase direction in 98/00381 voltage collapse studies Bompard, E. et al. Electric Power Systems Research, 1997, 43, (1) 61-67. The problem of assessing the direction of minimum distance (MD) from the current operating point to the static critical boundary, describing the maximum loading conditions in the steady-state voltage collapse analysis. A high computational effort is needed to determine the exact calculation of the MD. Fast approximated criteria, based on computing the maximum sensitivities of total reactive generation or total losses with respect to the load increase factor, are illustrated and compared in the paper. The theoretical bases of these criteria are given in the case of a simple two-node system, discussing the possibility of approximating the critical load increase direction, especially when the operating point becomes close to the critical boundary. The authors discuss extending the above criteria to the analysis of larger power systems and applied to the standard IEEE 30-bus test system. An expert system for power system voltage stabi98100382 lity improvement Thukaram, B. D. and Parthasarathy, K. Electrical Power and Energy Systems, 1997, 19, (6) 385-392. A prototype system for monitoring and improving steady state voltage stability in power systems is introduced, based on the L-index of load buses (Kessel and Glavitsch, IEEE Transactions, 1986, PWRD-I, (3), 346-354). This index uses information on a normal load flow and is in the range from 0 (no load on the system) to 1 (voltage collapse). To protect against voltage collapse, the system reduces the magnitude of the L-indices of the critical nodes for a given system operating condition based on heuristic criteria. The control variables considered are switchable VAR compensators, OLTC transformers and generators excitation. The proposed expert system technique has been tested under simulated conditions on a few practical Indian power systems. The expert system has been compared with conventional optimization technique and was found to be suitable for online application in an energy control centre for voltage stability improvement as the solution is obtained quickly, with a minimum of numerical computations. The system is illustrated with results from a 24.node EHV Indian power network and a modified IEEE 30-bus system. High power factor correction circuits with space 98lOO383 vector and hysteresis control methods Lin, B.-R. and Wu, D-P. Elec. Power Syst. Res., 1997, 43, (3), 207-214. A new topology of the three-phase a.c. to d.c. converter is presented. Only three a.c. switches are required to perform the power factor correction. The series connection of the two output capacitors is adapted to employ the high dc. output voltage. A space vector modulation strategy is used to control two of the three a.c. switches at any time, hence the switching numbers can be reduced. The addition of a hysteresis current control technique can simplify the hardware circuit and reduce the cost. Furthermore the input current can be made to follow any desired waveform. Finally, simulation and experimental results are presented to verify the characteristics of unity power factor and sinusoidal input current. Influence of internal resistance on fuel cell perfor98100384 mance by equivalent electrical circuit Murakami, K. et al. Mem. Fat. Eng., Miyazaki Univ., 1997, 26, 109-115. (In Japanese) Fuel cells offer high conversion efficiency of fuel energy to electricity, high efficiency under partial load, very low emission levels and a wide range of operating fuels from natural gases to coal-derived fuel gases. The performance of a fuel cell is much affected by a internal resistance, however, so it is important to improve the performance by simulation model. An equivalent electrical circuit of multiple type cell which had nine unit cells on the same plane was developed in order to examine influences of cell performance by their internal resistances. In the case of no parallel resistance, the model was simplified and it is easy to calculate the cell performance by the ohmic raw. The cell voltage distribution and power output are much affected by the internal resistance change, when there are parallel resistances. Intelligent tap changer duty cycle control for load 98lOO385 voltage improvement Chang, C. S. and Huang, J. S. Electric Power Systems Research, 1997, 43, (I), l-10. Load characteristics and voltage control devices such as on-load tapchanging (OLTC) transformers affect the voltage stability of a power system. This paper discusses the need for enhancing the OLTC operation and identifies five control requirements for intelligent control of the OLTC duty cycle. An adaptive fuzzy logic controller (AFLC) developed for satisfying these requirements is also described. By simulations on a six-bus study system the ALFC is shown to be an effective means of enhancing the OLTC operation. By preventing the reverse actions suppressing voltage transients reducing control errors and ensuring fast response and robustness, the five control requirements are fulfilled.
32
Fuel and Energy Abstracts
January 1998
98lOO388 Load representation for steady-state voltage stability studies El-Sadek, M. Z. et al. Elec. Power Syst. Res., 1997, 43, (3). 187-195. New models for representation of different load types in steady-state voltage stability studies are introduced. The models are derived from the available measured characteristics of the power system loads. Special attention is paid to the induction motor load, with different mechanical loading as well as for special large loads such as aluminium smelter plants and arc furnaces loads. Results from the known models and those from developed models were compared and the need for use of these developed models is stated. It is also proved that erroneous results will be obtained using known available models of these loads. 98100387 A method for calculating a load curve using average values of load over time intervals Dubinsky, A. and Elperin, T. Electrical Power and Energy Systems, 1997, 19, (6), 393-395.
The curve of time-dependent instantaneous load using average values of load over time periods can be calculated and the average values determined for the load over shorter time intervals using this method. It can be used in the procedures for load forecasting and for processing real time data on the power load. 98100388 Molten carbonate fuel cells for power generation from high-ash Indian coals Perumal, R. et al. Proc. Intersoc. Energy Convers. Eng. Conf., 1997, 32, 811-816. The first phase of the study on MCFC at TERI has recently been completed. It entailed the development of a laboratory-scale MCFC single cell, testing its performance with simulated coal-gas mixtures and the development of a mathematical model for estimating the material and energy requirements of an integrated coal gasification-MCFC (IG-MCFC) system. The results obtained from the monocell indicate that the drop in performance while using simulated coal gas as compared to that using pure hydrogen as the fuel is nominal. Furthermore, the efficiency levels predicted by the model indicate that, as over 60% of the power generation in India is coal-based, IG-MCFC systems would be attractive for the Indian power sector. The second phase of this work, currently underway and scheduled for completion in mid-1998, involves the development of a kilowatt level MCFC stack for continued testing with simulated coal gas. The third phase will comprise of field demonstration of a 5-10 kW MCFC stack coupled to an experimental gasifier. 98lOO389 Neural-net based coordinated control of capacitors and ULTC transformer in daily operation of radial distribution systems Sari, A. et al. Elec. Power Syst. Res., 1997, 43, (3) 169-177. The coordinated VARiVOLT control problem of general radial distribution systems with lateral branches, in daily operations is addressed. The investigation uses mechanically switched shunt capacitors and under-load tap-changing (ULTC) source transformers, feeding the radial network. Control variables are switchable, fixed or regulated capacitors and tap positions of the ULTC transformer, assuming the no-load tap-changing (NLTC) transformers within the network remain in fixed tap positions. Firstly, the training patterns required for the neural-net supervised learning process are generated by using a decoupled model for the co-ordinated VAR/VOLT control. The corresponding optimal daily schedules are used in the second stage, within the unsupervised/supervised concept, to synthesize complex mapping relating input load and source-voltage data to control variables. If discrepancy between forecasted and measured variables is greater than the pre-specified tolerance threshold, the iterative decoupled algorithm for co-ordinated VARiVOLT control is initiated to perform the correction of the schedule. The effectiveness of the proposed method is verified on the real 110 kVi35 kV/lO kV distribution system with 53 nodes. This case study demonstrates that the proposed approach preserves the optimization accuracy provided by the decoupled model for co-ordinated VARiVOLT control. It also avoids the unnecessary calculations used for similar load profiles. 98100390 Nonaqueous electrolyte lithium secondary battery and manufacture of graphite anode Otsuka, A. et al. Jpn. Kokai Tokkyo Koho JP 09,199,126 [97,199,126] (Cl. ROlM4/58), 31 Jul 1997, Appl. 9617,063, 19 Jan 1996, 6 pp. (In Japanese) The graphite anode is fabricated via the following process. The mesophase microparticles having B-resin 12 and I5 wt% are graphitized to give graphite having average diameter 3-25 I’m and specific surface area >I.0 and 8.0 m’ig. Coal-tar pitch is melted at 350-430°C isolating mesophase microparticles having average diameter 3-25 ,rm from the pitch matrix, adjusting the J-resin of the mesophase microparticles to >2 and I5 wt%. Carbonization of the mesophase microparticles at SOO-1300°C is followed by graphitization at 2400-3000°C. The battery exhibits high energy density, high charging-discharging efficiency, and resistance to storage in high temperature.
Electrical power supply and utilization (scientific, technical)
this purpose were determined. Controller gains, droop slopes, reference voltages and compensator ratings were found for maintaining the load nude voltages constant irrespective of system loadabilities to values which lead to voltage instabilities. Finally, the influence of system equivalent impedances on these parameters is discussed. Evaluation of the critical load increase direction in 98/00381 voltage collapse studies Bompard, E. et al. Electric Power Systems Research, 1997, 43, (1) 61-67. The problem of assessing the direction of minimum distance (MD) from the current operating point to the static critical boundary, describing the maximum loading conditions in the steady-state voltage collapse analysis. A high computational effort is needed to determine the exact calculation of the MD. Fast approximated criteria, based on computing the maximum sensitivities of total reactive generation or total losses with respect to the load increase factor, are illustrated and compared in the paper. The theoretical bases of these criteria are given in the case of a simple two-node system, discussing the possibility of approximating the critical load increase direction, especially when the operating point becomes close to the critical boundary. The authors discuss extending the above criteria to the analysis of larger power systems and applied to the standard IEEE 30-bus test system. An expert system for power system voltage stabi98100382 lity improvement Thukaram, B. D. and Parthasarathy, K. Electrical Power and Energy Systems, 1997, 19, (6) 385-392. A prototype system for monitoring and improving steady state voltage stability in power systems is introduced, based on the L-index of load buses (Kessel and Glavitsch, IEEE Transactions, 1986, PWRD-I, (3), 346-354). This index uses information on a normal load flow and is in the range from 0 (no load on the system) to 1 (voltage collapse). To protect against voltage collapse, the system reduces the magnitude of the L-indices of the critical nodes for a given system operating condition based on heuristic criteria. The control variables considered are switchable VAR compensators, OLTC transformers and generators excitation. The proposed expert system technique has been tested under simulated conditions on a few practical Indian power systems. The expert system has been compared with conventional optimization technique and was found to be suitable for online application in an energy control centre for voltage stability improvement as the solution is obtained quickly, with a minimum of numerical computations. The system is illustrated with results from a 24.node EHV Indian power network and a modified IEEE 30-bus system. High power factor correction circuits with space 98lOO383 vector and hysteresis control methods Lin, B.-R. and Wu, D-P. Elec. Power Syst. Res., 1997, 43, (3), 207-214. A new topology of the three-phase a.c. to d.c. converter is presented. Only three a.c. switches are required to perform the power factor correction. The series connection of the two output capacitors is adapted to employ the high dc. output voltage. A space vector modulation strategy is used to control two of the three a.c. switches at any time, hence the switching numbers can be reduced. The addition of a hysteresis current control technique can simplify the hardware circuit and reduce the cost. Furthermore the input current can be made to follow any desired waveform. Finally, simulation and experimental results are presented to verify the characteristics of unity power factor and sinusoidal input current. Influence of internal resistance on fuel cell perfor98100384 mance by equivalent electrical circuit Murakami, K. et al. Mem. Fat. Eng., Miyazaki Univ., 1997, 26, 109-115. (In Japanese) Fuel cells offer high conversion efficiency of fuel energy to electricity, high efficiency under partial load, very low emission levels and a wide range of operating fuels from natural gases to coal-derived fuel gases. The performance of a fuel cell is much affected by a internal resistance, however, so it is important to improve the performance by simulation model. An equivalent electrical circuit of multiple type cell which had nine unit cells on the same plane was developed in order to examine influences of cell performance by their internal resistances. In the case of no parallel resistance, the model was simplified and it is easy to calculate the cell performance by the ohmic raw. The cell voltage distribution and power output are much affected by the internal resistance change, when there are parallel resistances. Intelligent tap changer duty cycle control for load 98lOO385 voltage improvement Chang, C. S. and Huang, J. S. Electric Power Systems Research, 1997, 43, (I), l-10. Load characteristics and voltage control devices such as on-load tapchanging (OLTC) transformers affect the voltage stability of a power system. This paper discusses the need for enhancing the OLTC operation and identifies five control requirements for intelligent control of the OLTC duty cycle. An adaptive fuzzy logic controller (AFLC) developed for satisfying these requirements is also described. By simulations on a six-bus study system the ALFC is shown to be an effective means of enhancing the OLTC operation. By preventing the reverse actions suppressing voltage transients reducing control errors and ensuring fast response and robustness, the five control requirements are fulfilled.
32
Fuel and Energy Abstracts
January 1998
98lOO388 Load representation for steady-state voltage stability studies El-Sadek, M. Z. et al. Elec. Power Syst. Res., 1997, 43, (3). 187-195. New models for representation of different load types in steady-state voltage stability studies are introduced. The models are derived from the available measured characteristics of the power system loads. Special attention is paid to the induction motor load, with different mechanical loading as well as for special large loads such as aluminium smelter plants and arc furnaces loads. Results from the known models and those from developed models were compared and the need for use of these developed models is stated. It is also proved that erroneous results will be obtained using known available models of these loads. 98100387 A method for calculating a load curve using average values of load over time intervals Dubinsky, A. and Elperin, T. Electrical Power and Energy Systems, 1997, 19, (6), 393-395.
The curve of time-dependent instantaneous load using average values of load over time periods can be calculated and the average values determined for the load over shorter time intervals using this method. It can be used in the procedures for load forecasting and for processing real time data on the power load. 98100388 Molten carbonate fuel cells for power generation from high-ash Indian coals Perumal, R. et al. Proc. Intersoc. Energy Convers. Eng. Conf., 1997, 32, 811-816. The first phase of the study on MCFC at TERI has recently been completed. It entailed the development of a laboratory-scale MCFC single cell, testing its performance with simulated coal-gas mixtures and the development of a mathematical model for estimating the material and energy requirements of an integrated coal gasification-MCFC (IG-MCFC) system. The results obtained from the monocell indicate that the drop in performance while using simulated coal gas as compared to that using pure hydrogen as the fuel is nominal. Furthermore, the efficiency levels predicted by the model indicate that, as over 60% of the power generation in India is coal-based, IG-MCFC systems would be attractive for the Indian power sector. The second phase of this work, currently underway and scheduled for completion in mid-1998, involves the development of a kilowatt level MCFC stack for continued testing with simulated coal gas. The third phase will comprise of field demonstration of a 5-10 kW MCFC stack coupled to an experimental gasifier. 98lOO389 Neural-net based coordinated control of capacitors and ULTC transformer in daily operation of radial distribution systems Sari, A. et al. Elec. Power Syst. Res., 1997, 43, (3) 169-177. The coordinated VARiVOLT control problem of general radial distribution systems with lateral branches, in daily operations is addressed. The investigation uses mechanically switched shunt capacitors and under-load tap-changing (ULTC) source transformers, feeding the radial network. Control variables are switchable, fixed or regulated capacitors and tap positions of the ULTC transformer, assuming the no-load tap-changing (NLTC) transformers within the network remain in fixed tap positions. Firstly, the training patterns required for the neural-net supervised learning process are generated by using a decoupled model for the co-ordinated VAR/VOLT control. The corresponding optimal daily schedules are used in the second stage, within the unsupervised/supervised concept, to synthesize complex mapping relating input load and source-voltage data to control variables. If discrepancy between forecasted and measured variables is greater than the pre-specified tolerance threshold, the iterative decoupled algorithm for co-ordinated VARiVOLT control is initiated to perform the correction of the schedule. The effectiveness of the proposed method is verified on the real 110 kVi35 kV/lO kV distribution system with 53 nodes. This case study demonstrates that the proposed approach preserves the optimization accuracy provided by the decoupled model for co-ordinated VARiVOLT control. It also avoids the unnecessary calculations used for similar load profiles. 98100390 Nonaqueous electrolyte lithium secondary battery and manufacture of graphite anode Otsuka, A. et al. Jpn. Kokai Tokkyo Koho JP 09,199,126 [97,199,126] (Cl. ROlM4/58), 31 Jul 1997, Appl. 9617,063, 19 Jan 1996, 6 pp. (In Japanese) The graphite anode is fabricated via the following process. The mesophase microparticles having B-resin 12 and I5 wt% are graphitized to give graphite having average diameter 3-25 I’m and specific surface area >I.0 and 8.0 m’ig. Coal-tar pitch is melted at 350-430°C isolating mesophase microparticles having average diameter 3-25 ,rm from the pitch matrix, adjusting the J-resin of the mesophase microparticles to >2 and I5 wt%. Carbonization of the mesophase microparticles at SOO-1300°C is followed by graphitization at 2400-3000°C. The battery exhibits high energy density, high charging-discharging efficiency, and resistance to storage in high temperature.