bluuebunny/crossref_metadata_2025 huggingface dataset:
Storage and growth of denitrifiers in aerobic granules: Part I. model development
Authors: Ni Bing‐Jie , Yu Han‐Qing
Published: July 2007

A mathematical model, based on the Activated Sludge Model No.3 (ASM3), is developed to describe the storage and growth activities of denitrifiers in aerobic granules under anoxic conditions. In this model, mass transfer, hydrolysis, simultaneous anoxic storage and growth, anoxic maintenance, and endogenous decay are all taken into account. The model established is implemented in the well‐established AQUASIM simulation software. A combination of completely mixed reactor and biofilm reactor compartments provided by AQUASIM is used to simulate the mass transport and conversion processes occurring in both bulk liquid and granules. The modeling results explicitly show that the external substrate is immediately utilized for storage and growth at feast phase. More external substrates are diverted to storage process than the primary biomass production process. The model simulation indicates that the nitrate utilization rate (NUR) of granules‐based denitrification process includes four linear phases of nitrate reduction. Furthermore, the methodology for determining the most important parameter in this model, that is, anoxic reduction factor, is established. Biotechnol. Bioeng. 2008;99: 314–323. © 2007 Wiley Periodicals, Inc.
Methylene blue protection against hypoxic injury in primary cultures of rat hepatocyte monolayers
Authors: Muratsubaki Haruhiro , Yajima Nozomi , Yoneda Hitomi , Enomoto Keiichiro , Tezuka Toshiharu
Published: July 2007

Mitochondrial respiration is inhibited in cells exposed to hypoxia, and the oxidation of NADH to NAD+ is blocked. As a result, oxidation reactions requiring NAD+ are blocked, disrupting cellular metabolism. We studied the influence of methylene blue, which oxidizes NADH, on hypoxic damage to primary cultures of rat hepatocyte monolayers. During hypoxic treatment of hepatocytes, aspartate aminotransferase leaked out of the cells into the culture medium. However, addition of methylene blue to the medium repressed the hypoxic leakage of the enzyme. The exposure of hepatocytes to hypoxia decreased the acetoacetate/β‐hydroxybutyrate ratio which reflects the redox state of the cell. The level of the acetoacetate/β‐hydroxybutyrate ratio in hypoxic cells was increased by the addition of methylene blue. These results suggest that methylene blue protects against hypoxic injury due to its oxidation of NADH. Copyright © 2007 John Wiley & Sons, Ltd.
Electronic and Optical Properties of Ladder‐Type Heteraborins
Authors: Agou Tomohiro , Kobayashi Junji , Kawashima Takayuki
Published: July 2007

Ladder‐type π‐conjugated molecules bearing heteraborin (azaborine or thiaborin) units were synthesized, and X‐ray crystallographic analysis of pentacene‐type molecules showed that these molecules have rigid and planar structures. UV‐visible spectroscopy and theoretical calculations revealed the enhancement of electronic interaction between heteraborin units, the decrease in HOMO–LUMO energy gaps, and the strong effect of the bridging main‐group elements (nitrogen or sulfur) on the electronic states. The ladder‐type molecules emitted strong fluorescence both in solution and in the solid state, and the emission‐band shapes were different from each other, indicating the existence of intermolecular interactions in the solid state. Complex formation of the ladder molecules with fluoride ion was monitored by UV‐visible spectroscopy, which revealed that the Lewis acidity of these molecules can be controlled by the elongation of π systems and the change of the bridging main‐group elements.
Sugar derived hexacoordinated phosphates: Chiral anionic auxiliaries with general asymmetric efficiency
Authors: Pérollier Céline , Bernardinelli Gérald , Lacour Jérôme
Published: July 2007

Mannose‐derived hexacoordinated phosphate anions, prepared in as few as two steps from methyl‐α‐D‐mannopyranoside and tris(dimethylamino)phosphine, are chiral anionic auxiliaries with broad asymmetric efficiency. These chemically robust anions are effective NMR chiral solvating agents and efficient asymmetry‐inducers, able to control the configuration of conformationally labile C2‐symmetric monomethinium cations (organic, helical, charge 1+, P or M enantiomers) and D3‐symmetric iron(II) trisdiimine complexes (metallo‐organic, octahedral, charge 2+, Δ or Λ enantiomers). Diastereomeric control with often unmatched selective levels was achieved with the help of mannopyranoside backbone of the anions and the substituents on the [1,3]dioxane ring that play a key role in the recognition process, something not obvious at first sight. Chirality, 2008. © 2007 Wiley‐Liss, Inc.
Supramolecular tilt chirality in crystals of steroids and alkaloids
Authors: Hisaki Ichiro , Tohnai Norimitsu , Miyata Mikiji
Published: July 2007

The concept of supramolecular chirality has assumed increasing importance in association with the development of supramolecular chemistry over the last two decades. In chiral crystals, 21 helical molecular assemblies are frequently observed as key motifs. Helical handedness of the 21 assemblies, however, has not been determined from the mathematical or crystallographical viewpoints. In this context, we have proposed two new concepts, three‐axial chirality and tilt chirality. On the basis of the concepts, we describe supramolecular chirality and determine the handedness of 21 assemblies that are composed of relatively complicated molecules with multiple stereogenic centers such as brucine, bile acids, and cinchona alkaloids as well as those of simple molecules. Chirality, 2008. © 2007 Wiley‐Liss, Inc.
Analysis of prognostic factors in 146 patients with anterior skull base sarcoma: An international collaborative study
Authors: Gil Ziv , Patel Snehal G. , Singh Bhuvanesh , Cantu Giulio , Fliss Dan M. , Kowalski Luiz P. , Kraus Dennis H. , Snyderman Carl , Shah Jatin P. ,   for the International Collaborative Study Group
Published: July 2007

BACKGROUND.

Single‐institutional studies lack sufficient power to assess the role of surgery and radiotherapy in the management of sarcomas involving the anterior skull base. For this study, an international collaborative study group analyzed a large cohort of patients who underwent surgery for the treatment of skull base tumors.

METHODS.

A subset of 146 patients who had a histologic diagnosis of skull base sarcoma (SBS) formed the basis of this report. Most patients were aged ≥21 years (77%) and had stage IV disease (56%). Adjuvant radiotherapy was received by 35% of patients, and chemotherapy was received by 10% of patients.

RESULTS.

Orbital involvement was encountered in 53% of patients, involvement of the orbital wall was encountered in 46% of patients, and intracranial extension was encountered in 28% of patients. Positive microscopic margins were reported in 43% of patients (51 of 118 patients). Treatment‐related complications were reported in 27% of patients, and postoperative mortality was reported in 1.4% of patients. With a median follow‐up of 34 months, the 5‐year overall, disease‐specific, and recurrence‐free survival rates were 62%, 64%, and 57%, respectively. Tumor grade and adjuvant radiotherapy were not significant predictors of survival. Prior radiotherapy, intraorbital extension, positive margins, and postoperative complications were significant predictors of reduced disease‐specific survival on univariate analysis. The presence of positive/close margins, however, was the only independent predictor of poor overall, recurrence‐free, and disease‐specific survival on multivariate analysis (relative risk, 2.4; P = .006). The 5‐year disease‐specific survival rate was 77%, 43%, and 36% for patients with negative, close, and positive margins, respectively.

CONCLUSIONS.

The current results indicated that wide craniofacial resection with negative margins is an independent prognostic predictor of better outcome. Patients with positive margins have a high risk for tumor recurrence independent of tumor grade. Cancer 2007. © 2007 American Cancer Society.
Increased bone marrow iron stores is an independent risk factor for invasive aspergillosis in patients with high‐risk hematologic malignancies and recipients of allogeneic hematopoietic stem cell transplantation
Authors: Kontoyiannis Dimitrios P. , Chamilos Georgios , Lewis Russell E. , Giralt Sergio , Cortes Jorge , Raad Issam I. , Manning John T. , Han Xin
Published: July 2007

BACKGROUND.

Invasive aspergillosis (IA) is a leading cause of death in patients with leukemia and those who have undergone hematopoietic stem cell transplantation. Laboratory studies have demonstrated that iron is essential for Aspergillus growth and virulence.

METHODS.

In the current study, the authors retrospectively evaluated the bone marrow iron stores (BMIS) in patients with leukemia as well as recipients of allogeneic hematopoietic stem cell transplantation with IA (n = 33) and those without fungal infections (n = 33). The first available bone marrow biopsy specimens prior to the IA diagnosis or date of hospitalization (control group) were assessed in a blinded fashion using a standardized scoring system (0–4). Both groups were comparable with regard to clinical characteristics and classic risk factors for IA.

RESULTS.

The majority of patients with IA (70%) were found to have increased BMIS (score ≥3) compared with the control patients (16%) (P < .0001). Increased BMIS was found to be an independent risk factor for IA on multivariate analysis (P < .0001).

CONCLUSIONS.

The prospective validation of BMIS for risk stratification in patients with leukemia or those who undergo allogeneic hematopoietic stem cell transplantation is needed. Cancer 2007. © 2007 American Cancer Society.
Sub‐Picosecond Mid‐Infrared Spectroscopy of Phytochrome Agp1 from Agrobacterium tumefaciens
Authors: Schumann Christian , Groß Ruth , Michael Norbert , Lamparter Tilman , Diller Rolf
Published: July 2007

The photoinduced primary reaction of the biliverdin binding phytochrome Agp1 (Agp1‐BV) from Agrobacterium tumefaciens was investigated by sub‐picosecond time‐resolved Vis pump–IR probe spectroscopy. Three time constants of τ1=0.7±0.05 ps, τ2=3.3±0.2 ps and τ3=33.3±1.5 ps could be isolated from the dynamics of structurally specific marker bands of the BV chromophore. These results together with those of accompanying sub‐picosecond Vis pump–Vis probe spectroscopy allow the extension of the reaction scheme for the primary process by a vibrationally excited electronic ground state. The isomerization at the C15C16 bond occurs within the lifetime of the excited electronic state. A quantum yield of 0.094 for the primary reaction is determined, suggesting that the quantum yield of formation of the Pfr far‐red‐absorbing form is already established in the primary photoreaction of the Pr (red‐absorbing) form.
A calculation method of the mutual and self‐inductances generated by currents on a cylinder
Authors: Yoda Kiyoshi
Published: July 2007

Conventional calculation methods of aircore inductance utilized Neumann's equation for solenoidal coils and Fourier series for saddle coils. However, inductance formulas for arbitrarily shaped coils on a cylinder have not been well known.

In this paper, mutual and self‐inductances generated by any currents on a cylinder are expressed using Fourier‐Bessel expansion of the vector potential. An experiment shows the validity of the proposed formulas.
Annealing effect on a boundary layer between oxide superconducting films and a substrate
Authors: Fuchino Shuichiro , Agatsuma Ko , Ohara Takeshi , Kaiho Katsuyuki , Tateishi Hiroshi
Published: July 2007

Since the discovery of the new high Tc superconductor, various kinds of film growth techniques have been reported on fabrication of an oxide superconducting film, especially YBCO and BSCCO above liquid nitrogen temperature. All these techniques require the so‐called post‐growth heat treatment or a heating of the substrate during the deposition to grow an adequate polycrystal which can realize the superconducting state in the oxide. Such a heating process, however, yields some intermediate products at a boundary layer between the starting materials and the substrate, and the products result in degradation of the superconducting property.

In this paper, the annealing effect on the growth of YBCO or BSCCO oxide superconducting film and the substrate is investigated by using EDX analysis and SEM examination. To enhance the annealing effect, relatively thin YBCO and BSCCO films are fabricated with the starting materials pasted on substrates, and rather than sputtered thin films used for the analysis. MgO, Al2O3, SrTiO3, 5 or 8 percent Y stabilized ZrO2 (YTZ or YSZ), and so on, are chosen as a substrate.

The results show that the heat treatment yields Ba compounds between YBCO and the substrates and Sr and Bi compounds between BSCCO and the substrates. Since the product boundary layer of the intermediate product is the thinnest, MgO substrate can be recommended for YBCO film, and SrTiO3 substrate for BSCCO film.
Development of advanced generator excitation control regulator (PSVR) for improving voltage stability of a bulk power transmission system
Authors: Michigami Tsutomu , Onizuka Naganori , Kitamura Satoshi
Published: July 2007

Earlier generator excitation control systems were based on AVR control of generator terminal voltage. This system cannot accommodate reactive power up to the facility limit even when the power system voltage decreases to the limit for stable operation. An attempt was made to develop an advanced excitation control system (PSVR) to achieve higher constant sending end voltage of power stations. The intent was to apply the system to the generator connected to a 500‐kV system which contributes most effectively to the voltage stability of a bulk power transmission system. This PSVR produces higher control gains than the AVR, and the following functions were adopted: (1) AVR gain reduction circuit; (2) phase compensation circuit; and (3) damping improvement by enlarging the limiter of the PSS. In addition, various functions were provided, e.g., voltage slope characteristics to balance the reactive power of adjacent generators and PSVR output and terminal voltage limiter to stabilize the generator operation. Before application to a real system, a transient response test was performed by combining the PSVR and a generator simulator to verify the damping improvement and stability of the voltage control.
Experiments on dependency of metal mixing ratio in Ag‐Pd alloy contacts on breaking arc duration, metal erosion and transfer
Authors: Ishida Hiroyuki , Sone Hideaki , Takagi Tasuku
Published: July 2007

Breaking arc durations and the differences between the mass of a contact before and after an experiment which is a quantity of metal erosion and transfer (QMET) were measured in Ag‐Pd alloy contacts. The experiments were performed in air under particular combinations of voltage, current, and opening speed. The effects produced on arc duration and QMET by different proportions of metals were investigated.

In a practical Ag 40 wt% contact, the arc duration was not especially longer and the metal loss was not more than the other ratios. In an Ag 90 wt% contact, the arc duration had a large tendency to become longer under certain conditions and the metal loss was large. The arc duration of Ag 20 wt% had a tendency to become long with the number of operations. The characteristics of arc durations and QMET were different due to two ways of fixing a columnar contact from one side to a holder and from two sides. The curves of QMET were zero‐crossed and the mixing ratio for QMET became zero for one of the two electrodes.

This paper possibly suggests some way to design electrodes for heat produced in the Ag‐Pd alloy contact, and the possibility of zero QMET.
Development of a knowledge‐based system for voltage/reactive power operation planning
Authors: Kono Yoshiyuki , Doi Atsushi , Omichi Yuichi
Published: July 2007

Voltage/reactive power planning is a tremendous process which requires a planner to have intellectual expertise. This paper presents a large knowledge‐based system that can make voltage/reactive power planning. The knowledge acquisition has been completed on the basis of interview and protocol analysis methods. The result shows that the voltage/reactive power planning is composed of three phases: the first is reactive power adjustment where overall reactive power balance is investigated; the second is voltage adjustment where all bus voltages are tuned within the permissible operational range; and the third is voltage adjustment with a single fault of all major lines. The knowledge base is coded by about 700 production rules. It can succeed in making a voltage/reactive power plan for a very large power system.
Development of extruded ethylene propylene rubber insulated superconducting cable
Authors: Kosaki Masamitsu , Nagao Masayuki , Mizuno Yukio , Shimizu Noriyuki , Horii Kenji
Published: July 2007

A superconducting power cable is one of the promising ways of underground transmission of huge electric power in the future. The authors have long proposed the idea of the extruded polymer insulation for superconducting cables. The prominent features of the design are to exploit the excellent electrical properties of polymer in the cryogenic temperatures and to separate the helium coolant from the electrical insulation. Although the extruded cross‐linked polyethylene cable has proved ability at the liquid nitrogen temperature, the cable insulation cracked due to mechanical stress during cooling to the liquid helium temperature.

To overcome this problem, ethylene propylene rubber (EPR) was selected as a new insulating material considering the good results of mechanical and electrical tests of EPR samples at cryogenic temperatures. An extruded EPR insulated superconducting cable 15 m in length was fabricated and a cooling test down to the liquid helium temperature and a voltage test at the liquid helium temperature were carried out with fair success. This is a breakthrough in terms of the electrical insulation design of cryogenic cables.
DSP‐based real time output waveform synthesis for three‐phase PWM inverter
Authors: Ishihara Kiyoshi , Kawamura Atsuo
Published: July 2007

A new digital control technique is proposed to synthesize an arbitrary three‐phase PWM inverter output. Sensing two line‐to‐line voltages, the required pulse patterns for deadbeat response are computed in a real time manner based on the predicted voltage by an observer at 18‐kHz sampling frequency. When used for the uninterruptible power supply, this closed‐loop voltage control inherently results in a very low THD and a very quick transient response with less filter capacity. Also, with the repetitive compensator, the proposed scheme has advantages in improving the output waveform for nonlinear load. This paper describes the modeling technique, theoretical analysis, simulations and experimental results.
Fundamental characteristics of a brushless and self‐excited sinusoidal‐wave single‐phase synchronous generator having a two‐phase field winding excited by a half‐wave rectified current
Authors: Shibata Fukuo , Naoe Nobuyuki
Published: July 2007

It is desired from the viewpoints of maintenance and construction to make single‐phase synchronous generators of brushless and self‐excited types.

A novel brushless and self‐excited single‐phase synchronous generator was devised by one of the authors. The stator exciting current is made to flow simultaneously with the load current in the armature winding. Thus, the iron core for the magnetic circuit can be both for the synchronous generator itself and for the exciter.

Experimental studies of the brushless and self‐excited single‐phase synchronous generator of which the rotor winding is used as a rotor exciting winding and a field winding are described in this paper.

In the proposed generator, the rotor is provided with a balanced two‐phase field winding to improve the voltage wave distortion. The terminal voltage of this generator can be kept constant in spite of the load variation. Therefore, the proposed synchronous generator can be expected to be used widely.
On‐line preventive control for power system transient stability based on the energy function method
Authors: Kita Hirokuyi , Nishiya Ken‐Ichi , Hasegawa Jun
Published: July 2007

For the purpose of maintaining the power system security, an integrated security monitoring and control (ISMAC) system, is being developed in which both preventive and emergency control have important roles. Static security control strategies which deal with the steady state after the contingency is cleared, have been studied by various researchers including the authors. However, the basic research on dynamic security control which deals with the transient state immediately after the contingency has occurred is seldom found.

This paper presents a method of dynamic preventive control for the transient stability considering plural contingencies and coordinating in a flexible way the requirements of both security and economy.

In the preventive control for transient stability, it is necessary to judge the transient behaviors properly and also to evaluate the security quantitatively for a postulated contingency. The authors define a security index which represents absorbing capacity of post‐fault kinetic energy based on the energy function method. The index has these advantages: it is possible to calculate values rapidly; and physical meanings are easily understood. The effectiveness of the proposed method is ascertained through numerical examples for model power systems.
Direct calculation of voltage‐stability limit of electric power systems
Authors: Suzuki Mamoru , Masegi Ken
Published: July 2007

On‐line monitoring of voltage‐stability conditions is a new requirement for the energy management systems of the electric power industry. Preferred by the utility engineers and dispatchers is an index which represents explicitly the margins to a voltage‐stability limit (collapse point) expressed in a physical unit ordinarily used. For example, such indices are the system load and voltage‐voltage‐stability‐margins (SVVSM) between the present operating point and a voltage collapse point. However, long computer time is required to calculate accurately the voltage collapse point by the conventional method because many multiple load‐flow solutions are required.

This paper presents a new algorithm to calculate directly, exactly, and rapidly the voltage‐stability limit. The algorithm uses the load‐flow equations and the explicit expressions of the voltage collapse root conditions are expressed as dR/dV = 0, where R is active or reactive power node injection, and modifying the conventional N‐R load‐flow program, and is not affected numerically by singular Jacobians. The proposed algorithm is verified through calculating the voltage stability limit of a 176‐node power system.
Fault location for transmission lines using inference model neural network
Authors: Kanoh Hitoshi , Kaneta Masahisa , Kanemaru Kimaharu
Published: July 2007

The authors propose a new fault location method that uses a neural network to analyze the distribution pattern of the ground wire current along the power line. This method is able to locate the fault section even for secondary power lines with complicated configurations. The method is based on the inference process, i.e., human experts will analyze the distribution pattern of the current amplitude and phase angle. In locating fault sections, higher precision than ordinary three‐layer neural network or the expert system of previous development can be obtained.

The proposed neural network comprises three sets of three‐layer neural networks which follow the back‐propagation learning procedure. The 1st and 2nd neural networks calculate the candidate‐1 and candidate‐2 for the fault section using current amplitude and phase angle distribution patterns, respectively. The 3rd neural network then performs final fault location using these candidates and a current amplitude distribution pattern. The results evaluated with all possible fault causes indicate that the new method is precise to as high as 98.4 percent even when the measured values differ by 30 percent from predicted ones with EMTP.
Three‐phase voltage‐fed type PWM power converter via power factor control
Authors: Ohnishi Tokuo
Published: July 2007

Recently, the voltage‐fed type PWM converters have been investigated for their ideal and inherent properties as a dc power source. However, the current control system generally used may be somewhat complicated due to dc voltage detection.

We propose here a simple control system of the PWM converter using the power factor control in which dc voltage detection is not always needed. In this system, the dc voltage is given by the line voltage and the modulating index of the PWM converter.

The principle of the PWM control system is shown at first. From the simplified circuit model and its phasor diagrams, some basic relations of the PWM converter system are obtained and some fundamental characteristics are shown. From these investigations, it is seen that the phase control region is restricted to a certain angle, which depends on the setting power factor, the modulating bypass index of the PWM and the load. Under the operating condition of unity power factor, it is given by ±π/4 for both the converting and inverting operations. The system can be operated over the all‐control range of the modulating index by restricting the angle to this critical value for the angle over this control range.

The ideal operating characteristics as a dc power source can be verified by some experimental results, including the operating waveforms of line current, the steady state characteristics and the transient response between both operations of the converter and inverter.

In this system it is simple to construct the control circuit; it also has some inherent and excellent characteristics as a voltage fed type dc power source.

This control system may be applicable to any types of PWM converter used today.
Examination of simple analytical method for calculating 60‐Hz magnetic field in power substations
Authors: Hayashi Noriyuki , Katsuo Isaka , Yokoi Yoshihide
Published: July 2007

In the last decade, increasing attention has been paid to ELF (Extremely Low Frequency) electromagnetic environments in work areas as well as in and near homes, regarding their interaction both with electric apparatus such as CRT's and with biological systems. Experimental and theoretical analyses are presented of 60 Hz magnetic field (B‐field) characteristics at and near ground level in both 187/66‐kV EHV and 66/6.6‐kV HV power substations.

Experimental results of B‐field profiles along horizontal paths as well as harmonic contents in B‐field waveforms at several positions are shown and discussed.

Furthermore, analytical B‐field profiles calculated by using a B‐field approximation method based on Biot‐Savart law are shown and compared with the measured ones. The comparisons verify that the assumptions employed are applicable to the substation B‐field calculation, and that the B‐field calculation method employed can estimate B‐field in EHV and HV power substation to significant accuracy, except for areas where localized B‐field sources, such as power transformers and underground power cables, exist. The analytical profiles of three orthogonal components of B‐field are also described in terms of equiflux contour maps, which show 3‐D characteristics of B‐field in power substations.
Optimal scheduling of hydraulically coupled power plants with runoff prediction
Authors: Yamashiro Susumu , Nakamura Kouichi , Hiraki Toshiyuki , Tatekoji Takashi
Published: July 2007

This paper discusses an optimal short‐range scheduling of multireservoir hydrothermal power systems considering runoff prediction. Using Prasad's rainfall‐runoff model and the Kalman filter‐based, second‐order filtering technique, the hour‐by‐hour characteristic is estimated for a given short‐range forecasted rainfall pattern. Unlike the usual hydroscheduling problem in which a single‐reservoir operating condition is specified at the end of the scheduling period, various end point conditions are examined to deal with the predicted runoff characteristic and to avoid possible water spillages from reservoirs.

Dynamic Programming Successive Approximations are applied successfully to obtain optimum operating strategies for many end point conditions at a time. A rapid convergence characteristic coupled with a simple computation algorithm makes the proposed method one of the attractive approaches for scheduling of complicated multireservoir hydrothermal systems considering runoff prediction.
An algorithm for discrete optimal power flow
Authors: Fan Mingtian , Aoki Kenichi , Nishikori Akimine , Nara Koichi
Published: July 2007

This paper presents a new algorithm to solve an optimal power flow problem which can take into consideration the discrete nature of some facilities in power systems. The optimal power flow problem is formulated as a nonlinear mixed‐integer programming problem in which the number of transformer taps and the number of shunt capacitor units and reactor units are treated as discrete variables.

This paper attempts to solve such a large‐scale nonlinar mixed‐integer programming problem by some effective programming techniques. The optimization procedure of the algorithm is that the nonlinear mixed‐integer programming problem is linearized iteratively and solved by an approximation method for linear mixed‐integer programming.

A fundamental feature of the algorithm is that it can guarantee a solution which is discrete, feasible and near‐optimal. The validity and efficiency of the algorithm is demonstrated by the numerical results of real‐scale optimal power flow problems.
Power swing analysis in a future metropolitan electric power system on a contingent trip of cryogenic high‐power cables
Authors: Hayakawa Naoki , Kito Yukio , Matsumura Toshiro
Published: July 2007

A cryogenic power cable is expected to be capable of carrying bulk power as a main transmission line in a future metropolitan electric power system. It is important to establish a strategy of how to sustain power supply when such a highly densified power supply route trips from the network due to contingency.

It is proposed here that the bulk power transmitted by the cryogenic cable could be distributed into the parallel conventional transmission lines by suitable circuit breaker operations in the system. In this process, power‐flow routes are forced to be changed with a remarkable modification in the system configuration.

In this paper, the power swings associated with the large power‐flow change following contingent faults are analyzed by means of a transient network analyzer. It is found that the proposed system modification could be realized without any harmful power swing if the parameters in generators as well as in control devices have conventional magnitudes. It is shown also by simulations that the margin to occurrence in an unstable power swing is left sufficient even if the parameters deviate somewhat from the present magnitudes.
Fabrication and fundamental characteristics of a superconducting air‐core autotransformer
Authors: Ishigohka Takeshi , Okada Naotaka , Kamijo Hiroki , Yamamoto Mitsuyoshi
Published: July 2007

With the recent advent of high‐performance ac superconductors with very small ac loss and large current‐carrying capacity, the possibility of an air‐core superconducting transformer is being studied. Although the exciting current is very large, the air‐core transformer has the following merits: (1) no iron loss; (2) no insulation care of the core; (3) no harmonics, and no in rush current induced by iron saturation, etc. Thus, the authors fabricated and tested a small experimental transformer (2.5 kVA, 330/150 V). As easily predicted, the exciting current becomes very large. It occupies about 45 percent of the rated current. Meanwhile, the leakage reactance increase considerably. The %IX becomes about 28 percent. These experimental results show good agreement with the theoretical analysis based on an equivalent circuit.
Influence of AC‐DC parallel interconnection on voltage stability of AC systems
Authors: Tada Yasuyuki , Yokoyama Akihiko , Sekine Yasuji
Published: July 2007

The static and dynamic characteristics of power supply to each node in a hybrid ac‐dc power system are analyzed by means of static and transient P‐V curves. Three kinds of dc transmission control scheme are compared. DC transmission systems are more effective in delivering power to inverter nodes. The constant firing angle, constant current control techinque provides more power to inverter nodes than the conventional constant current, constant voltage and constant power, constant extinction angle techniques. Transient digital simulations indicate that dc interconnection improves voltage stability to both the opening of a dc interconnected line and one‐line opening of ac double‐circuit interconnected lines.
Three‐dimensional magnetic field analysis by T‐Ω method using the finite element method coupled with integral equations
Authors: Tanaka Yoshifumi
Published: July 2007

The electromagnetic quantities of the magnetic bodies and conductors are calculated by the Finite Element Method with Integral Equation and it is not necessary to divide the free air space. The field at an arbitrary point in the free air is obtained from the Integral Equation after the FEM‐IEM analysis. In this paper, the magnetization is written in the terms of the unknown total scalar potential Ω, and the current vector potential T is added in the conductors. In order to calculate the unknowns defined in only the substances by FEM, it is necessary to establish the boundary condition by IEM. Then the calculation of the boundary condition on the surface of magnetic body requires high technical skills, so the formulation presented in this paper is improved by integration of parts. Results of the standard models specified by the I.E.E. of Japan suggest the validity of our method.
Digital input filters for measurement, control and protection of electric power systems
Authors: Kido Mitsuyasu , Chiba Tomio , Kudo Hiroyuki , Kawakami Junzou , Kawai Tadao
Published: July 2007

Power system control and protection equipment has required higher sensitivity and operational reliability than conventional one.

Studies of digital signal processing suitable for electric power systems fulfill this objective using fast sampling and digital filtering by a 32‐bit floating point DSP (Digital Signal Processor). The sampling rate of 3 kHz is carefully selected in order to separate the power spectrums of the A‐D conversion output errors from the signal bandwidth. The new 12‐bit A‐D conversion unit equipped with a recursive‐type digital filter achieved the equivalent high resolution of 14‐bit conversion.

This paper describes the design concept and the characteristics showing applications to current differential relays, distance relays and power system controllers.
Analysis of moving magnet linear dc motor with two straight stators
Authors: Hanaoka Motoyasu , Miyaji Hiroshi , Kano Yoshio , Hasebe Shinya , Ohta Kenichiro
Published: July 2007

The thrust force of moving magnet‐type linear direct current motors (MM‐LDM) is analyzed in this study. A moving magnet‐type MM‐LDM consists of a stator and a carriage. The stator is composed of two stick shaped electromagnetics and the carriage consists of a movable permanent magnet that is located between the two electromagnets.

One of the methods for calculating the thrust force of an MM‐LDM is to analyze the energy gradient which is determined by the distribution of magnetic flux. However, this method is very difficult when used to calculate the thrust force of this kind of LDM. This type of MM‐LDM can be considered to be a transformer in which the magnet of the mover is assumed to be a one‐turn coil carrying a large current. The stored energy in the MM‐LDM can be obtained by measuring the self‐inductance and the mutual‐inductance of the equivalent circuit of the MM‐LDM. And this energy gradient gives the thrust force.

The calculation of the thrust force induced in this motor shows that the mutual inductance has a large influence on the generation of thrust force.
Analysis and improved control method of resonant DC link inverters
Authors: Sato Yukihiko , Matsumoto Yasushi , Kataoka Teruo
Published: July 2007

High performance power conversion requires high switching frequency power converters. Resonant dc link inverters, which are investigated in this paper, are suitable for this purpose because they cause no switching loss in principle. But in these inverters, loss of the resonant oscillation and occurrence of high peaks in the resonant capacitor voltage are serious problems. In this paper, we investigate a control method for resonant dc link inverters which can overcome these problems.

First of all, we summarize the basic control principle of an ideal resonant dc link inverter. Then we present an analyzing method for the practical resonant dc link inverter introducing two equivalent circuits in which the influence of the power losses in the resonant link and in the inverter load is considered. From these equivalent circuits, the problems of existing control methods are clarified. Based on the results of this analysis, we propose an optimum and keep the capacitor voltage at an allowable level. A simple compensation method for the influence of storage time of switching devices, which affects the implementation of the proposed control method, is described.

Some experimental results are included to confirm the validity of the analytical results and the effectiveness of the proposed control method.
Development of three‐dimensional electric field analysis by segment arrangement based on a charge simulation method
Authors: Okubo Hitoshi , Yanabu Satoru
Published: July 2007

This paper describes the development of three‐dimensional electric field analysis by using the so‐called segment method which enables the electric field to be calculated with high accuracy and with enhanced efficiency, for high‐voltage apparatus.

In the segment method, electrode configuration of high‐voltage apparatus is simulated by small components which are called segments and by the arrangement of several kinds of such segments.

In this calculation, the charge simulation method is used which is suitable for segment application. As basic segments, spherical, cylindrical and ring segments are used and in addition to these, as subsegments, disc and elbow segments are adopted for good simulation of the total electrode configuration.

In this paper, the fundamental construction and arrangement parameter of segments were discussed. Moreover, the segment method was applied to an actual high‐voltage apparatus and the calculation accuracy was discussed. It was clarified that the segment method has sufficient calculation accuracy and is a very efficient means for three‐dimensional electric field analysis.
Effect of surfactants on superstructure and dielectric breakdown strength of crosslinked polyethylene insulation
Authors: Ishida Masayoshi , Okamoto Tatsuki
Published: July 2007

This paper describes the influences of a surfactant on crosslinked polyethylene (XLPE) insulation. Several kinds of additives are mixed into the insulation in order to improve the dielectric breakdown strength of XLPE cables. It has been verified that the interfacial diffusion method, which modifies the interfacial region between the insulation and the semiconducting layer by a surfactant, is effective. The effects of the surfactant on the morphology in the XLPE insulation were studied with two kinds of specimens.

In the first kind of specimens, a mill was used to disperse the surfactant throughout the insulation material. Alternating current dielectric breakdown tests were performed on disk specimens. Their average breakdown strengths were improved, but the breakdown strengths were not increased at the low probabilities of the hazard function. In the other specimens, the surfactant was milled into the semiconducting layer, and later allowed to enter the insulation by diffusion during the high‐temperature crosslinking process. It was found that the average breakdown strengths were improved further. Moreover, the breakdown strengths were found to increase significantly at the low probabilities of the hazard function.

The two kinds of specimens were followed by material analysis using analytical methods, such as TEM, FT‐IR, etc. Results from the milled specimen indicated that the improvement in property was probably due to the increase in density of the amorphous portion, the increase in the lamella thickness, and the increase in spherulite radius created by the additive content. Therefore the insulation near the interface where a concentration gradient was established by diffusion from the semiconducting layer is considered to have similar morphological changes caused by the additive. In addition, the diffusion specimen was observed to have an absence of introduced microdefects that existed in the milled specimen.
Preventive control in an autonomous decentralized system
Authors: Kurihara Ikuo , Takahashi Kazuhiro
Published: July 2007

For more rational operation and control of future electric power systems which would continue to expand in size and complexity, an autonomous decentralized control system is proposed as one of the new control architectures. In the autonomous decentralized control system, each generating station and substation behaves independently and cooperatively without being controlled by the central station. Besides the inherent fault‐tolerant characteristics of the architecture, flexible and rapid control depending on the circumstances can be achieved.

In this paper, the fundamental logic of preventive control in an autonomous decentralized system is developed. It is based on the bidding method in which each station proposes its own output taking into consideration its own situation and cooperation with others. The economic load dispatch including preventive control can be performed, based on the bidding rule adopting the equivalent incremental generating cost curve in which the security constraints are incorporated. Application of the logic to a model system revealed satisfactory control performance for preventing the overload of transmission lines and the undervoltage.
A new combined system of active and passive filters to obtain harmonic compensation for large‐capacity thyristor converters
Authors: Tanaka Toshihiko , Akagi Hirofumi
Published: July 2007

Shunt passive filters, which are connected in parallel to harmonic‐producing loads, have been used widely for harmonics suppression in power systems because of low cost and high efficiency. However, they have such inherent problems as series and parallel resonance. On the other hand, shunt active filters, which are also placed in parallel, have such an inherent problem as initial and running costs are high compared with those of shunt passive filters. To solve these inherent problems in shunt passive and shunt active filters, the authors have proposed a combined system of a shunt passive filter and a small rated series‐active filter.

The purpose of this paper is to reduce the required rating of the series‐active filter, considering a practical application of the combined power filter to harmonic compensation for large‐capacity thyristor converters. The points are summarized as follows:

The required rating of the series‐active filter can be reduced less than one‐tenth by connecting a series‐resonant circuit in parallel to the secondary of current transformer.

It is clarified theoretically and verified experimentally that compensation characteristics of the new combined system are equivalent to those of the already‐proposed system with no series‐resonant circuit.
An AC voltage switching regulator with instantaneous output voltage control
Authors: Nomura Hiroshi , Kawasaki Naoya
Published: July 2007

This is the first attempt to control the instantaneous output of an ac/ac direct power converter. The ac chopper‐type regulator has the potential ability of quick response to the control command. However, detecting the mean or effective value of the ac output voltage, as is commonly done in the conventional closed‐loop ac regulators, greatly degrades the inherent fast response capability of the chopper circuit.

The proposed ac switching regulator adopts the Cuk converter for the main circuit and an instantaneous voltage control technique. A practical state feedback scheme together with the integral control was devised to stabilize the system and also minimize the steady‐state error. The response speed is so fast (about 300 μs with resistive load) that the converter can produce a sinusoidal output voltage even from a distorted source voltage. The four‐quadrant operation can handle any kind of ac load. A complete analytical description and relevant design data of this new regulator are provided with some experimental results.
Ac losses in superconducting coils
Authors: Akita Shirabe , Ishikawa Tadao , Tanaka Toshikatsu
Published: July 2007

AC superconducting wire is being developed for such electrical equipment as superconducting transformers and superconducting generators. AC loss reduction is of primary concern in the development of such high‐efficiency equipment. In reducing ac losses, it is necessary to develop assessment methods for ac loss in test samples which have shapes similar to the end‐product equipment.

This paper described a least squares calculation of ac losses of superconducting wire as a function of frequency and magnetic field strength measured in test coils.

Two sample solenoid coils were made to test the influence of different capacities and winding methods on ac losses in ac superconducting coils with rated capacities of 500 kVA and 20 kVA, and impregnated (epoxy resin) and nonimpregnated windings.

The ac losses in the superconducting coils were measured by a calorimetric method using the evaporating rates of liquid helium. Estimated ac losses in the superconducting wire of the two coils were compared with Joule losses of copper conductors at ambient temperature. As a result of this comparison, a low‐loss ac superconducting wire winding can be made for electrical equipment rather than employing conventional copper winding when used under low magnetic fields less than 0.5 T.
Optimal capacities of large‐ and small‐scale power plants in the face of uncertain demand
Authors: Matsuhashi Ryuji , Ishitani Hisashi , Hayashi Takehito , Kaya Yoichi
Published: July 2007

The future demand for electricity is uncertain and difficult to forecast, but it is necessary to do so in order to construct power plants. In that sense, a large‐scale power plant is disadvantageous because it takes a long time to construct. On the other hand, although it takes less time to construct, a small‐scale power plant is more expensive. Therefore large‐ and small‐scale power plants could complement the disadvantages of each other. This paper develops a stochastic dynamic programming model to investigate the possibility. The model determines the capacities of large‐ and small‐scale power plants in the face of uncertain demand to minimize the expected value of the total cost. Computed results have shown that small‐scale plants can play a significant role in this case even if they are more expensive than large‐scale plants.
Practical method for generation expansion planning based on dynamic programming
Authors: Tanabe Ryuya , Yasuda Keiichiro , Yokoyama Ryuichi
Published: July 2007

This paper presents an efficient method which provides the optimal generation mix and the optimal generation construction process. The approximation method in which the dynamic programming technique and gradient method are combined is applied to determine the optimal generation mix with hydropower generation technologies. The successive approximations dynamic programming (SADP) technique, which is very suitable for high‐dimensional multistage decision process problems, is used for obtaining the optimal generation construction process. The effectiveness and feasibility of the developed technique are demonstrated on a practical power system model which has five types of generation technologies including a hydropower generation technology.