bluuebunny/crossref_metadata_2025_split huggingface dataset:
Development of an advanced voltage control technique to improve voltage and reactive power characteristics of a large‐scale power cable system
Authors: Michigami Tsutomu , Nakamura Keiji , Suzuki Takamitsu , Yamabe Chobei , Horii Kenji 
Published: July 2007

AbstractThe power supply system for a metropolitan area consists of multiple 275‐kV power cable systems to supply power to a large number of consumers. Each system has a large charging capacity (capacitive reactive power). When 275‐kV power cable systems experience a voltage drop, their charging capacity decreases. However, the reactive power losses increase in the 275‐kV overhead transmission lines, which supply large power to power cable systems, thus causing the performance of the power supply system to deteriorate.In this paper, the following three points are reported:

When the secondary power system of the trunk substation is a large‐scale power cable system, new techniques can greatly improve the voltage and reactive power characteristics by controlling the rise of the sending‐end voltage at the secondary side of the trunk substations and maintaining the voltage of power cable systems at a constant level.
In the use of this control technique, it has been demonstrated that controlling by the direct‐detecting method of a voltage drop in the primary power system is superior to one that controls by the indirect‐detecting method, which increases load power in the cable system.
The results of simulations obtained by using a 275‐kV cable system model and a performance power system model show that the use of this control technique can produce a good effect despite the allowances made for the opposite effect, i.e., a decrease in the capacity of power capacitors resulting from voltage drop at the tertiary voltage of a 500‐kV transformer.
This study is carried out to examine the possibility of lightning control using a photoionized plasma produced by a UV laser without an optical air breakdown. As the fundamental experiment, the characteristics of a laser‐triggered spark gap (LTSG) are examined, where a laser beam is not irradiated on the surface of the electrodes. In this experiment, the KrF excimer laser is very effective in increasing the plasma density ne and the reduction ratio p of 50 percent breakdown voltage against the self‐breakdown voltage. The relation between ne and p is increased by generating a long and high‐density plasma parallel to the discharge axis.On the other hand, the abnormal discharge process in triggered lightning using a rocket is examined, and it is indicated that the most important condition to trigger a lightning discharge is the production of a plasma channel of length 200 m and density about 1019 m−3. It is suggested that such a plasma channel could be produced by a KrF excimer laser with an energy of only about 3.67 J.
Evaluation of photovoltaic modules considering spectral solar radiation
Authors: Hirata Youichi , Tani Tatsuo 
Published: July 2007

AbstractFor the optimum design of photovoltaic power systems, it is very important to estimate their annual maximum amount of output. In general, the annual maximum amount of output has been calculated by using photovoltaic module efficiency under irradiance of 1 kW/m2 at AM 1.5 with solar cell temperature of 25°C. Since the spectral distribution of solar radiation changes with weather, season and time, the efficiency of solar cells is not always constant.This paper describes a method evaluating the maximum amount of output in photovoltaic modules, ‘the spectral method,’ by using the measured annual spectral solar radiation and the spectral response of various photovoltaic modules.The calculated values using the spectral method agreed well with the measured values for amorphous silicon photovoltaic modules from March 1991 to February 1992. The spectral method proved most effective for optimum design of amorphous silicon photovoltaic power systems.
An algorithm for linguistic risk assessment of uncertain factors in generation planning
Authors: Tanabe Ryuya , Yasuda Keiichiro , Yokoyama Ryuichi 
Published: July 2007

AbstractThis paper presents an efficient computational algorithm for evaluating the risks of uncertain factors in generation planning. Uncertainty in a multiobjective risk assessment problem can be divided into (a) uncertainty of the possible conditions to be evaluated; (b) uncertainty in multiobjective decision making; and (c) uncertainty in risk which is obtained using imprecise information.The proposed method basically consists of two phases: (1) the aggregation of risks with respect to all of the objectives for each uncertain factor; and (2) the linguistic expression of the aggregated risk of each uncertain factor. In the first phase, uncertainty in possible conditions is treated as fuzziness in planning parameters, and uncertainty in multiobjective decision making is also treated as fuzziness in decision making.Furthermore, the statistical trend of risk with respect to an objective for each uncertain factor can be extracted from uncertain risks obtained using imprecise information. In this method, both classes of fuzziness and the statistical trend of risk for each uncertain factor can be integrated into the risk of each uncertain factor, and then the risks of each uncertain factor with respect to all the objectives can be aggregated by extension principle in fuzzy sets theory. In the second phase based on the linguistic approximation technique, the aggregated risk of each uncertain factor can be represented by natural language. The proposed method can realize an effective and flexible decision support for evaluating the risks of uncertain factors in generation planning. The effectiveness and feasibility of the proposed method are demonstrated on a typical power system model.
Nb3Sn single‐phase targets for fiber‐reinforced‐superconductors and technique of preparing superconducting films without post annealing
Authors: Arai Kazuaki , Tateishi Hiroshi , Agatsuma Ko , Saito Takashi , Sadakata Nobuyuki , Nakagawa Mikio 
Published: July 2007

AbstractA new type of superconductor is being developed for the application of high‐field pulsed superconducting magnets, which are called fiber‐reinforced‐superconductors (FRS). A filament of FRS consists of a reinforcement fiber with high elastic modulus and a superconducting layer around it. The strain can be reduced against electromagnetic force because of highelastic modulus fibers. If Nb3Sn target is utilized, the preparation process of FRSs is shortened and there is the possibility to produce Nb3Sn layer which leads to high current density because of its uniform stoichiometric Nb3Sn layer.This paper presents first a technique of preparing a single‐phase target of Nb3Sn to produce superconducting layers on reinforcement fibers of FRSs.Mixture of niobium and tin powder was reacted in a furnace filled with argon gas to be Nb3Sn, and then it was broken and cast into a stoichiometric target with a diameter of 77 mm. The critical temperature of the target itself was 17.5 K. The thin film deposited with the target showed no superconductivity without post annealing, but it had critical temperature from 14.5 K to 12.5 K after heat treatment. Second, a new target containing rich tin was prepared and the film deposited with it had superconductivity without post annealing.
Development of fault detector for 33‐kV ungrounded power line
Authors: Yamamoto Minoru , Ifukube Atsuchi , Murata Yoshikazu , Hashimoto Makoto 
Published: July 2007

AbstractA fault section detection system is being developed for 33‐kV ungrounded power line. The fault section is obtained from the relation of two point zero‐phase currents on power line. This fault detector is composed of optical current sensors and the processing unit and solar battery system. The optical current sensor consists of a Faraday cell and a porcelain bushing. Zero phase current on the processing unit is obtained through a three‐phase composer with auto gain control and residual current eliminator.This fault detector has the ability of 0.15 A zero‐phase current detection fault factory test; in field tests, this fault detector detects ground fault.
Accurate measurement method of the position of a buried line
Authors: Takao Toshiharu , Hara Kazuhiro 
Published: July 2007

AbstractA conventional method to measure the position of a buried line has been used. This method is based on the measurements of magnetic field around a line which conducts a current. However, the pitfall is that the magnetic field generated by an induced current in a secondary line allows considerable measurement errors.This paper describes a novel method to exclude such errors caused by the induced current. While the magnetic field generated by the current in the primary line is in phase with the current, that generated by the induced current delays more than 90° compared to that of the current in the primary line because of a reluctance component of the secondary line. Hence, the 90° component of the magnetic field results from the induced current. This component is measured by a solenoid coil and a lock‐in amplifier; the 0° component is measured also and corrected by using the 90° component. Thus, the net magnetic field generated by the current in the primary line is calculated. It is used to determine the correct position of the primary line. The new method is tested by using two buriéd lines and is proved to be useful.
Daily electric load forecasting using artificial neural network
Authors: Ishida Takaharu , Tamura Shigeru 
Published: July 2007

AbstractA multilayered‐type neural network is attractive for daily electric load forecasting because the neural network can acquire a nonlinear relationship among the electric load data and their factors (weather, temperature, etc.) automatically. This paper discusses first some essential issues to be considered in neural network applications. One is difficulty of obtaining sufficient effective training data, another is the influence of abnormal learning data, and one more is the inevitable outerpolation. For these issues, the following three methods are developed in order to forecast more accurately: (1) a structure of the neural networks for insufficient training data; (2) detection and diminishing the influence of abnormal data; (3) employment of interpolation network and outerpolation network with additional data for outerpolation. Furthermore, to increase the sensitivity between electric loads and factors, (4) removal of base load is developed. Those methods work effectively to decrease the average absolute errors of peak‐load forecasting and 24‐hour load forecasting to 1.78 percent and 2.73 percent, respectively.
Transient stability limit issues at three‐phase short‐circuit in parallel running of both a superconducting generator and a conventional one
Authors: Nitta Tanzo , Shirai Yasuyuki , Kawauchi Toshikazu , Okada Takao , Ogawa Yoshihiro 
Published: July 2007

AbstractExperimental studies using20‐kVA superconducting generators (SCG) have been performed in an attempt to understand some of the characteristics of SCG in power systems. It is necessary to investigate the characteristics for the parallel operations of both an SCG and a conventional generator (CG) when an SCG is installed in a present power station. Some of the results of the authors' studies on parallel running of the 20‐kVA SCG and the 20‐kVA CG are described in this paper. In the experimental system, the SCG is connected to a regional power system (infinite bus) through reactors (artificial transmission lines) and the CG is connected to the terminal of the SCG. Using experiments and computer simulations, the transient characteristics at three‐phase short‐circuit faults are investigated: 1) when the CG is not disconnected; and 2) when the CG is disconnected after reclosing the line with the fault cleared. Two kinds of stable limit curves are obtained for output power at three‐phase short‐circuit fault for the aforementioned two cases.
Diagnosis method for live‐wire insulation of high‐voltage XLPE cables by DC superimposition
Authors: Shinmoto Takashi , Kimura Chiaki , Yamamoto Ken , Ninomiya Nobuo , Umeda Susumu 
Published: July 2007

AbstractRecent preventive maintenance for equipment has grown to include diagnosis of the insulation of cables under hot‐line conduction. Much of the equipment constructed during the high‐growth period in the 1960s has become obsolete. Recent circumstances make it difficult to obtain a longer service interruption time.Results of a study of the method that measures the live‐wire insulation resistance by superimposing dc 50 V to a high‐voltage busbar through GPT and forms a bridge with the resistance of a cable insulation are discussed. It is clarified that this live‐wire insulation diagnostic method is highly effective at detecting degradation of a cable insulation resistance and is, therefore, suitable for so‐called trend monitoring as well.
Fundamental characteristics of overhead transmission line galloping determined by simulating calculation using equivalent single‐conductor method
Authors: Yamaoka Masaru , Hasegawa Jun 
Published: July 2007

AbstractTheoretical study and phenomenal examination have been ongoing for many years; however, some electric power companies still have instantaneous power failure due to galloping. This study differs from others in that nonlinear three‐dimensional simultaneous equations of conductor movement can be solved directly using numerical calculation. Fundamental characteristics of galloping can be ascertained by changing calculation parameters variously. This time, a method is used in which bundle conductors are changed equivalently to single conductor. It is also clarified that unstable domain becomes wider when rotational movement of conductor occurs.
Development of a new two‐input PSS to control low‐frequency oscillation in interconnecting power systems and the study of a low‐frequency oscillation model
Authors: Michigami Tsutomu 
Published: July 2007

AbstractIn Japan, large and small power systems were interconnected over time and thus ultimately grew into a large‐scale national power system. A highly important stability problem arising from large‐scale power system interconnections is low‐frequency oscillation (about 0.3 Hz to 0.5 Hz) of interconnected systems. The ΔP‐type PSS has been applied to all generators in trunk power systems as a measure to improve the damping of local mode oscillation (about 1 Hz). However, it is difficult for this PSS to improve the damping of low‐frequency oscillation because of the hardware and the design of PSS control constants. Therefore it has become necessary to develop a new two‐input PSS.This paper explains the development of this two‐input PSS and the study of a low‐frequency oscillation model. This paper can be summarized as follows:

(1) The effect of control over low‐frequency oscillation is affected by the kinds of PSS detecting signals. The Δω‐type or Δf‐type detecting signals used for lead‐phase compensation are suitable for this purpose.
(2) It is possible to cause low‐frequency oscillation studies in a one‐machine infinite‐bus power system model with medium loads.
(3) According to the simulation of a three‐machine and actual large‐power system models, dynamic stability was largely increased by this two‐input PSS used for generators.
Influence of charged droplet cloud on flashover of air gaps for lightning impulse voltage
Authors: Sugimoto Toshiyuki , Higashiyama Yoshio , Asano Kazutoshi 
Published: July 2007

AbstractTransmission lines passing through a mountainous region often are struck by winter lightning. As a result, numerous double‐circuit faults occur. Space charge might be responsible for this phenomena. Several investigations on flashover characteristics have been performed focusing on reduction of flashover voltage due to ionic space charge formed by corona discharge.In this paper, flashover characteristics of an air gap within a charged droplet cloud ejected from an airless nozzle using an induction charging method are discussed. The droplets are charged in the range ‐200 to 200 μC/kg, forming the space‐charge density of approximately 13 μC/m3. The flashover voltage and the time lag to flashover were measured when 1.2 × 50 μs lightning impulse voltage applied to a rod‐sphere gap is placed within the charged cloud. Flashover voltage for a positive rod increased markedly within a positive charged cloud by increasing the charge‐to‐mass ratio. The increase of flashover voltage was up to 80 percent in comparison with uncharged droplets. Flashover voltage for the negative rod decreased about 20 percent in the cloud of either polarity. The results show that the presence of charged droplets in the air gaps affects the discharge process significantly.
Fast‐switching‐speed, low‐forward‐voltage‐drop static induction (SI) thyristor
Authors: Maeda Mitsuhide , Keno Takuji , Suzuki Yuji , Abe Toshiro 
Published: July 2007

AbstractA static induction (SI) thyristor using a normally‐off planar‐gate structure in a low power class has been developed to be used as a power switching device in a three‐phase inverter circuit. A 600 V‐15 A class SI thyristor with very fast switching time (tgt, tgq) and low forward voltage drop (VTM) was designed and created. This design was performed with a reasonable wafer structure (n−/n/p+), an n− base carrier concentration and thickness, and a gate structure (gate diffusion length and gate‐gate pitch). Microscopic processing was used to obtain this SI thyristor. The performance trade‐off between turn‐off time and forward voltage drop is controlled by a lifetime control process using proton irradiation that results in a very fast switching time with tgt of 500 ns and tgq of 500 ns with VTM of 1.5 V (at IT= 18 A). At a current level of IT = 18 A, the current density in the active area becomes 200 A/cm2, which indicates that the performance of the SI thyristor is superior to that of conventional IGBTs and MOSFETs.
Suspension of soft magnetic materials using high Tc superconductors
Authors: Tsutsui Yukio , Higuchi Toshiro 
Published: July 2007

AbstractThis paper describes a novel suspension technique using high Tc superconductors and magnetic materials. It was found for a field‐cooled superconductor and an adjacent magnetic material that the usual inverse relationship between the attractive magnetic force and gap distance reverts to a direct relationship for small gap length. Thus, stable, noncontact suspension is possible within a certain gap range. This phenomenon was found for even a soft magnetic material possessing minimal coercive force. Since remarkable reversals were observed for magnetic materials with diameters much smaller than that of the pinned area, it is considered that some of the pinned flux is subject to a gathering effect in the magnetic material. Stable, contactless suspension of a 180 g carbon steel weight under a high Tc superconductor was achieved using this technique.
Change of characteristics of desulfurization and denitrification by combustion flue gas composition and electrode configuration under pulsed corona discharge
Authors: Kato Ken , Kasuga Yasuhiro , Fujiwara Masanori , Onda Kazuo 
Published: July 2007

AbstractLaboratory‐scale and parametric experiments of SO2 and NOx removal from the simulated combustion gas by pulsed corona discharge have been performed by changing the combustion gas composition and temperature, the electrode configuration of plasma reactor, and the polarity of high‐voltage electrode. The following results are obtained: 1) the higher the concentration of H2O and O2, the higher the efficiency of desulfurization and denitrification at the same specific input; 2) the pulsed corona discharge with a voltage pulsewidth as short as 200 ns of negative polarity shows the possibility to attain almost 90 percent deSOx and deNOx efficiency at the specific discharge input of 20 J/g, which is almost the same as the specific input in the electron‐beam process; 3) the deNOx characteristics show a little temperature dependence in the range of 70 to 130°C, but the deSOx efficiency increases rapidly in the temperature region below 100°C suggesting the thermochemical dependence of deSOx reaction; 4) when desulfurization and denitrification proceed, the white dendritic powder deposits on the plasma reactor whose composition is identified to be 49 mol% (NH4)2SO4 and 47 mol% of 2NH4NO3 · (NH4)2SO4, and the ratio of SO2, NO and NH3 of the deposit is almost equal to that of supplied gas.
Development of the DC superimposition bridge method for the measurement of high insulation resistance of medium voltage XLPE cables in operations
Authors: Shinmoto Takashi , Kimura Chiaki , Yamamoto Ken , Umeda Susumu 
Published: July 2007

AbstractThe method for measuring insulation resistance by superimposing the dc voltage has potential for detecting the deterioration of cable insulations. The deterioration of cable insulations can be detected by measuring current which flows through a grounded shielding wire. However, the earth current also flows from the cable sheath into the grounding wire as noise. Thus, to assess the deterioration properly, it is necessary to separate the earth current from the total current. On the other hand, to improve detection sensitivity, it is desirable to superimpose the highest possible dc voltage. In this case, provision must be made so that there are no adverse effects on the GPT.The authors, placing special emphasis on the method of measuring high insulation resistance by configuring the bridge, have conducted an investigation on how to detect the insulation deterioration with high accuracy and sensitivity without impairing the functions of the GPT. The following issues were investigated and the results are reported in this paper:(1) It is possible to measure insulation resistance as high as 100,000 MΩ by superimposing 50‐V dc through the GPT after cancelling the earth‐current and by configuring a bridge for determining insulation resistance from voltage ratio.(2) Even if 50‐V dc is superimposed through the GPT, it is possible to prevent the magnetic saturation of GPT if the current injected by such superimposition is limited (i.e., below max. 5 mA).(3) In lieu of a variable resistor, a variable dc voltage supply is employed in the bridge. The variable dc voltage supply requires no mechanically driven part, thus making it possible to realize a fully automatic monitoring system.
Selection of the best siting of static var compensators for effective damping
Authors: Okamoto Hiroshi , Kurita Atsushi , Kobayashi Naoki , Sekine Yasuji 
Published: July 2007

AbstractA static Var compensator (SVC) can improve the steady‐state stability (or the small signal stability), if it is located appropriately. The present paper proposes a method for selecting the best siting of SVC in large‐scale power systems for damping effectively.Conventionally, it is thought that SVC improves steady‐state stability by its voltage regulating ability. From this point of view, the stability can be improved significantly if SVC is located at the bus which has a large voltage fluctuation due to the lightly damped power swing mode. In contrast to the conventional viewpoint, the present paper makes it clear that the steady‐state stability deteriorates by the conventional voltage regulating control of SVC in some cases. Therefore, the voltage fluctuation is not an appropriate index for effective damping.This paper explains the mechanism of improvement of steady‐state stability by SVC in terms of modal analysis. On the basis of modal analysis, an index for determining the location of SVC is derived. The index is called LIED (Location Index for Effective Damping) by the authors. Digital simulations are conducted for an 8‐machine longitudinal system and a 29‐machine looped system to demonstrate the validity of the proposed index.