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Volume 120, Issue 5
Displaying 1-18 of 18 articles from this issue
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Isao Iyoda2000 Volume 120 Issue 5 Pages 651-654
Published: May 01, 2000
Released on J-STAGE: December 19, 2008
JOURNAL FREE ACCESSDownload PDF (4240K) -
Toshiyuki Ishii, Goro Shirai, Goro Fujita2000 Volume 120 Issue 5 Pages 655-664
Published: May 01, 2000
Released on J-STAGE: December 19, 2008
JOURNAL FREE ACCESSThis paper presents a decentralized load frequency control (LFC) based on H∞ optimal control theory with observer. A few LFC schemes have been proposed based on the optimal control theory, but they have not considered the change of system parameters in the operation and the characteristics of load disturbances in a target system. In this paper, H∞ robust control is introduced to address such problems. From the practical merit, the proposed control scheme is a decentralized LFC. Employing observer theory, the proposed method requires only frequency and tie-line power deviation in each area. The numerical simulations are shown to demonstrate the effectiveness of the proposed method. H∞ control was proven to show greater effectiveness of damping disturbance over the conventional optimal control by the design of control systems aimed at restricting the H∞ norm of its transfer function. Particularly, when a decentralized LFC is applied, by reducing the system size H∞ norm is easier to dampen, thus H∞ control is more effective in the decentralized control. Future research topics include the design of H∞ control system with a weight on frequency response.View full abstractDownload PDF (1310K) -
Katsunori Mizuno, Nobuhisa Hayashi, Yasuyuki Goto, Kazuto Yukita, Kats ...2000 Volume 120 Issue 5 Pages 665-671
Published: May 01, 2000
Released on J-STAGE: December 19, 2008
JOURNAL FREE ACCESSThis paper describes an application of a neural network for estimating the ground rainfall from radar echo data. A neural network system for this purpose is developed through a case study on a dam for hydro-power plant located the upper district of the Ooi River in Central Japan. We use the neural network comprised of three layers; an input layer, a hidden layer and output layer. The input data to the neural network are any numebr of radar echo amount observed in each radar mesh and x-y-z coordinates showing its location.
The four types of neural networks with different number of input units are proposed and discussed the relative importance of the number of input data. It is found that the estimating system using the most simple neural network yields good results for rainfall distribution.View full abstractDownload PDF (1546K) -
Koichi Nara, Yasuhiro Hayashi, Bin Deng, Kazushige Ikeda, Tomoo Ashiza ...2000 Volume 120 Issue 5 Pages 672-677
Published: May 01, 2000
Released on J-STAGE: December 19, 2008
JOURNAL FREE ACCESSDispersed generators (DG) such as fuel cells and solar cells etc. are going to be installed in demand side of power systems. The dispersed facilities can reduce distribution system loss by the appropriate allocation. So far, planning and operation of distribution system with the dispersed facilities have been discussed. In this paper, the authors discuss about how much the distribution system loss minimization can be reduced if DGs are optimally allocated at the demand side of the distribution system. In order to determine the optimal allocation and size of DG for minimizing the distribution system loss, an algorithm based on tabu search is employed. The proposed algorithm consists of the repetition of nested use of the tabu search algorithm. Namely, in the proposed algorithm, in one computational iteration, after the location of DG is temporarily determined by tabu search, the size of DG is also determined by tabu search so as to minimize the distribution system loss for the temporarily determined allocation. Numerical simulations are carried out for two system models in order to examine the validity of the algorithm.View full abstractDownload PDF (1756K) -
Chikashi Nakazawa, Yosuke Nakanishi2000 Volume 120 Issue 5 Pages 678-685
Published: May 01, 2000
Released on J-STAGE: December 19, 2008
JOURNAL FREE ACCESSIslanding of induction generators for wind power generation systems can cause a variety of problems and must be prevented islanding. In Japan, Ministry of International Trade and Industry (MITI) revised “technical requirements for distributed generators on distribution systems” in 1998. The technical requirements do not require islanding detection systems for wind power generation systems consist of induction generators. However, if reactive power of induction generators and capacitors of distribution systems are closely matched, the islanding detection by ordinary relays becomes difficult because of self-excited of induction generators. In this paper, frequency of induction generators after theirs disconnection from grids, so called the self-excited frequency, is studied by analytical procedures. The analytical procedures and related simulations, using the Electro-Magnetic Transients Program (EMTP) and Transient Network Simulator (TNS), are described. The analytical results are presented and compared with the corresponding obtained simulation results.View full abstractDownload PDF (1233K) -
Luonan Chen, Hideki Suzuki, Tsunehisa Wachi, Yukihiro Shimura2000 Volume 120 Issue 5 Pages 686-693
Published: May 01, 2000
Released on J-STAGE: December 19, 2008
JOURNAL FREE ACCESSThis paper proposes a methodology directly to link each concerned factors to the nodal prices, i.e., we break down each nodal price into a variety of parts corresponding to different factors, such as generations, transmission congestion, voltage limitations and other constraints. These detail information for nodal prices can be used not only to improve the efficient usage of power grid, energy resources and congestion management, but also to provide economic signals for generation or transmission investment. Several numerical simulations have been used to demonstrate our approach.View full abstractDownload PDF (1807K) -
Takeshi Hikosaka, Mitsunori Iwata, Kazuo Onda, Kohei Ito, Susumu Nagat ...2000 Volume 120 Issue 5 Pages 694-703
Published: May 01, 2000
Released on J-STAGE: December 19, 2008
JOURNAL FREE ACCESSA simulation model of solid oxide electrolysis cell (SOEC) was made to calculate the electrical efficiency of high-temperature water electrolysis system considering various kinds of realistic losses. High temperature helium heated by some external heat sources is circulated through SOEC stacks to give the entropy heat for water electrolysis. The voltage-current density characteristics of SOEC with uniform temperature are nearly equal to those of SOEC which takes account of temperature and current density variations in a cell when the temperature difference between supplied helium and water vapor is small such as 50°C. When some external heat sources such as solar heat can be utilized to give the water electrolysis heat, the electrical efficiency as high as 122% is obtained in a case for average current density of 300 mA/cm2.View full abstractDownload PDF (1329K) -
Shigemitsu Okabe, Masanori Koto, Tadashi Koshizuka, Susumu Nishiwaki, ...2000 Volume 120 Issue 5 Pages 704-710
Published: May 01, 2000
Released on J-STAGE: December 19, 2008
JOURNAL FREE ACCESSIn the underground sub-stations connected with transmission cables, lightning high overvoltages don't appear. So, it is very important to investigate well switching overvoltages to achieve the rational insulation coordination for apparatus installed in such underground substations. This paper discusses occurrence of steep front at the transient recovery voltages (TRV) which appear at circuit breakers when the inrush current of the transformers are interrupted. Caused by the steep front at the TRV, reignitions should occur at the circuit breakers resulting in generation of high overvoltages of high frequency. The overvoltages would be one of the highest switching overvoltages which would appear at the terminal of the transformers.
The authors clarified the mechanism of the generation of the steep front of the TRV by conducting EMTP analysis as well as by carrying out testing at high power laboratory.View full abstractDownload PDF (1808K) -
Masaru Ogawa, Isamu Morotomi, Kiyosh Tsuru, Yasumasa Morita, Toshihiro ...2000 Volume 120 Issue 5 Pages 711-718
Published: May 01, 2000
Released on J-STAGE: December 19, 2008
JOURNAL FREE ACCESSVariation in operation temperatures of catalyst tubes of a multi-tubular dispersed-use reformer for multi-megawatt fuel cell applications has crucial effects on its performance and efficiency. To reduce the temperature variation, thermal radiation media disposed so as to envelope each of catalyst tubes had been employed. Based upon pretests on a small scale device and extensive simulation analysis. A partial model reformer having a capacity equivalent to 500 kW was constructed and put into long term tests, thereby verifying the thermal radiation media proved to be much effective in improving the variation of catalyst tube temperature.View full abstractDownload PDF (3709K) -
Toru Fujisawa, Tatsuo Tani2000 Volume 120 Issue 5 Pages 719-724
Published: May 01, 2000
Released on J-STAGE: December 19, 2008
JOURNAL FREE ACCESSSide-by-side system, PVT hybrid system, and side-by-side PVT hybrid system can be designed for a self-sufficing system as a residential binary solar energy utilization. We designed and did annual simulation of the performance of three systems-PV with flat plate collector (PV/FPC), photovoltaic-thermal hybrid (PVT), and PV with photovoltaic-thermal hybrid (PV/PVT)-with auxiliary electrical heat pump. In this paper, Solar Energy Fraction (SEF) or Auxiliary Exergy Fraction (AUX) is adopted as a figure of merit of the system evaluation. We clarified the characteristics that these indexes are affected by AUX's COP and by the ratio of DHW (domestic hot water) load: annual synthetic load.
As a result, the best figure has achieved by the side-by-side PV/PVT hybrid system. Using PVT with PV leads to the improvement of the PVT alone system's SEF or AEF. It is found that glazing is indispensable for PV/PVT system with AUX's COP of 1, and is unnecessary for PV/PVT system with higher COP.View full abstractDownload PDF (1705K) -
Takaharu Takeshita, Yuji Hayashi, Nobuyuki Matsui, Hideki Fujita2000 Volume 120 Issue 5 Pages 725-732
Published: May 01, 2000
Released on J-STAGE: December 19, 2008
JOURNAL FREE ACCESSThis paper presents the amplitude control and unbalance compensation of load voltage using a seriesshunt power converter. The series power converter works to obtain the constant balanced sinusoidal load voltage. The shunt converter regulates the dc link voltage and compensates for the reactive current of the source within the rated current of the converter. To design the required capacity of the series-shunt power converter, the relations between the converter capacity and the load power factor under the constant compensation voltage are introduced. The required capacity of the series-shunt power converter is reduced to less than 50% compared with that of the conventional series power converter. The effectiveness of the proposed load voltage compensation using the series-shunt power converter has verified by experiments.View full abstractDownload PDF (1758K) -
Sadayuki Machida, Tatsuo Tani2000 Volume 120 Issue 5 Pages 733-738
Published: May 01, 2000
Released on J-STAGE: December 19, 2008
JOURNAL FREE ACCESSPhotovoltaic (PV) power generation has increased as the institutions to subsidize and purchase surplus electricity have been introduced. Environmental awareness has also played a part. To increase this trend there is a need to reduce installation costs. Consequently there is a need for standardization of system components.
In our country manufacturers have been developing mainly domestic and small industrial sized units. Inverters of 4 kW for small units and 10 kW with master-slave function for large units are being produced on a large scale. This means that installation costs are being reduced for these specific unit sizes but not for the other sizes. In Europe, AC module that integrates inverter has been developed. It can then be added to produce a generation plant of any required size.
In this paper, we have calculated annual power output and power generation costs of these different inverter systems. PV modules, PV arrays and inverters of various sizes have all been compared in an attempt to determine the most cost-effective system. The results revealed that the power output of AC modules system is sufficiently high as well as providing the cheapest generating cost.View full abstractDownload PDF (2500K) -
Hideyuki Ohno, Tomio Tange, Hiroshi Ito, Katsuhiko Naito, Yasunobu Yok ...2000 Volume 120 Issue 5 Pages 739-745
Published: May 01, 2000
Released on J-STAGE: December 19, 2008
JOURNAL FREE ACCESSExperimental investigations were performed on electron density of an arc around nozzle throat and the dependence of the arc interrupting capability on the electron density at current zero in a flat-type air-blast quenching chamber. The inlet width W of the orifice nozzle and the axial distance D between the nozzle throat and the tip of upstream electrode were varied. The electron density measured at the current zero has lower magnitude at the nozzle throat than that at other two axial positions for the same W and D. For D=15mm, the electron density at the nozzle throat decreases from 4.2×1019 to 3.5×1019m-3 with a rise in W from 15 to 25mm while growing to 3.8×1019m-3 with W to 34mm. For W=25mm, the electron density at the nozzle throat increases from 3.5×1019 to 4.6×1019m-3 with D from 15 to 25mm. The interruption tests showed the dependence of the failure rate of an arc interruption on W and D same as that of the electron density at the nozzle throat on W and D. The measurement results of the electron density and the failure rate revealed that the failure rate increases linearly with electron density at the nozzle throat at the current zero.View full abstractDownload PDF (2196K) -
Yoshiki Susaki, Toshio Matsumura, Takamu Genji, Jun-ichi Inoue, Kinji ...2000 Volume 120 Issue 5 Pages 746-752
Published: May 01, 2000
Released on J-STAGE: December 19, 2008
JOURNAL FREE ACCESSCertain orders of harmonic currents are generated when many non-linear loads are used in the electrical distribution systems. Then the generated harmonic currents are amplified due to the resonance between the system impedance and the static capacitors under the leading power factor conditions. As a result, the voltage distortion grows up.
To solve this problem, an active filter is developed for distribution system and its field test results are presented and discussed in this paper.View full abstractDownload PDF (2353K) -
Kazushi Mimura, Hirotaka Shimizu, Yasunobu Yokomizu, Toshiro Matsumura2000 Volume 120 Issue 5 Pages 753-759
Published: May 01, 2000
Released on J-STAGE: December 19, 2008
JOURNAL FREE ACCESSAs a equipment to limit the fault current in electric power system, superconducting fault current limiter (SC-FCL) is expected to be introduced. Since the SC-FCL was required to recover to superconducting state rapidly after current interruption, it is important to understand the recovery characteristics of SC-FCL. In this paper, the recovery characteristics of SC-FCL in a 6.6 kV distribution system were theoretically investigated. We computed the time variation of superconducting cable temperature after quench and the recovery time for the commutation type of SC-FCL having the superconducting element connected to limiting resistor in parallel. The calculations were carried out for different conditions of system impedance, limiting impedance of SC-FCL and length of superconducting cable, considering the time-current characteristics of protective relay. As a result, it is found that the recovery time decreases with an increase in system impedance and with a reduction in limiting impedance of SC-FCL. Furthermore, the decrease in length of superconducting cable causes the increase in the recovery time.View full abstractDownload PDF (1427K) -
Shogo Nishikawa2000 Volume 120 Issue 5 Pages 760-765
Published: May 01, 2000
Released on J-STAGE: December 19, 2008
JOURNAL FREE ACCESSThough photovoltaic power generation (PV) and wind power generation (WG) have advantages that they are clean and infinite energies, they have a disadvantage that electrical output energy is unstable. The disadvantage causes them to need big energy storage device such as a battery and to increase their construction cost. A PV and WG hybrid system may be effective for stabilizing output energy in strong wind sites. However, since the stability may relate to a ratio of PV output energy fluctuation to WG output energy fluctuation, it is very important to clear an optimum ratio. In this paper, the optimum ratio at strong wind sites is described. Moreover, it is cleared that how load profile or quantities of surplus power affect the optimum ratio and capacity of battery.View full abstractDownload PDF (1503K) -
Shigeto Fujita, Shoji Nakatsuka, Yoshikazu Shibuya2000 Volume 120 Issue 5 Pages 766-772
Published: May 01, 2000
Released on J-STAGE: December 19, 2008
JOURNAL FREE ACCESSVery Fast Transient Overvoltages (VFTO) comprising oscillating waveform generate a voltage oscillation in transformer windings. The behavior of the voltage oscillation has been shown experimentally using actual transformer windings. An interturn traveling wave is generated at either end of the coil and propagates along the winding. A resonance phenomenon is found, probably due to the superposition of the traveling waves.
In this paper, the voltage oscillation is thrown light on using simple 2- and 4-coil models. Effect of capacitive voltage distribution in the windings are discussed in relation to the traveling waves. The simulation of the voltage oscillation is performed using multi-conductor transmission line model in which the capacitive voltage distribution and the traveling waves are considered. A good agreement between the analysis and the experiment is shown in the interturn voltage at application of a pulse.View full abstractDownload PDF (3949K) -
Tatsuo Udo2000 Volume 120 Issue 5 Pages 773-777
Published: May 01, 2000
Released on J-STAGE: December 19, 2008
JOURNAL FREE ACCESSLightning location systems, such as UP and LPATS, cover the whole Japanese land at present, However, the winter lightning flash density measured by these systems are less than 0.3 times per km2 per one winter season, which are very small than the appropriate density. The author points out three reasons of this contrariety. (1) The velocity of winter lightning return stroke is less than one third of summer ones. (2) The average channel length of winter lightning discharge is less than one third of summer ones. (3) The attenuation of radiation field may be much larger in winter because the height of a discharge channel (the source of electro-magnetic field) is much lower in winter than in summer.View full abstractDownload PDF (1248K)
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