bluuebunny/crossref_metadata_2025 huggingface dataset:
Basic characteristics of high‐Tc superconductor as a current‐limiting element
Authors: Nakamura Koichi , Ito Yasukazu , Kawashima Takao
Published: July 2007

This paper shows the basic characteristics of a current‐limiting element for the power system using y‐type high‐Tc superconductor. (1) A YBa2Cu3Ox‐type superconductor was produced. Its size was 4.7 × 1.5 × 47 mm. (2) Current I and voltage V were measured under the low temperature of 50 to 100 K. (3) The flow resistance and the resistance of the element were defined and evaluated from the I ‐ V characteristics obtained under the conditions of lower temperature than the critical value Tc, and larger current density than the critical value Jc. (4) The resistance value change due to temperature rise also was evaluated under the larger current than the critical current. (5) A schematic calculation was tried for practical use in some system condition.
Surge analysis of the tank of a gas‐insulated line using lumped constant circuits
Authors: Nagaoka Naoto , Ueno Shintaro , Sugahara Keishi
Published: July 2007

Surge voltages evaluated by a digital analysis method, for example, electromagnetic transients program (EMTP) and by an analog analysis method (transient network analyzer: TNA) are compared with experimental results on a scaled model of a gas insulated line. From the results, it is confirmed that the analog analysis method has a satisfactory accuracy and its computing speed is quite high. The error caused by the lumped element modeling of the gas insulated line is comparatively small, and the line is not necessary to be treated as a distributed parameter line. The lumped element model is advantageous to understand the mechanism of the transient characteristic of the induced transient voltage. A simple equivalent circuit of the gas insulated line is proposed and its accuracy is confirmed by a comparison with the calculated result obtained by an accurate line method. The transient overvoltages of the tank and across the insulated flange can be analytically calculated using the equivalent model.
Performance analysis and circuit design of high‐frequency resonant inverter using a single reverse‐conducting device
Authors: Ogiwara Hiroyuki , Nakaoka Mutsuo
Published: July 2007

This paper is concerned mainly with a performance analysis and a design method of a newly developed zero‐current switching quasi‐resonant high‐frequency inverter (ZCS‐QRI) using a single reverse‐blocking power device (high‐frequency GATT). As a matter of fact, GATT is replaced by the latest MOS‐gate power semiconductor devices, MOSFET, IGBT, MCT and Bi‐MOS · GTO thyristor.

The frequency‐modulated single‐ended inverter circuit, which incorporates an auxiliary diode and large reactor cascade branch in parallel with a resonant capacitor connected into the transformer‐link series‐resonant tuned tank load circuit can stably and efficiently operate in the frequency range from 20 kHz up to 50 kHz or so. It is proved that the ZCS‐QRI is more suitable for several kilowatt induction‐heating and melting power supplies and high‐intensity ultrasonic generator, and switched‐mode dc‐dc converters.

This simple high‐frequency ZCS‐QRI for induction‐heating load model is analyzed introducing normalized resonant and load circuit parameters and control variable on the basis of computer‐aided simulation. The load and frequency regulation characteristics of ZCS‐QRI and ZCS operating range are illustrated with a normalized expression in addition to voltage and current peak values and stresses of the power semiconductor device. The practical computer‐aided design procedure using the inverter characteristics in steady‐state expressed in the normalized technique is demonstrated and discussed including a design example. The simulation results of ZCS‐QRI are illustrated and compared with the experimental results in trial‐produced breadboard.
Optimization of 3‐D nonlinear magnetic circuit by using the magnetization integral equation method
Authors: Takahashi Norio , Nakata Takayoshi , Uchiyama Noriyuki
Published: July 2007

To design optimal electrical machines, it is necessary to develop an optimal design method for determining the shapes, sizes, positions of the cores, permanent magnets and windings which produce such specified values as flux distributions and torques.

In this paper, a design method for determining the optimal sizes of cores taking into account the nonlinearity of the core has been developed by using the nonlinear programming method and the magnetization integral equation method. The pole shape of an electromagnet which produces the uniform flux distribution is determined by using the design method for determining the optimal sizes of cores. The effectiveness of the method is shown by designing the pole piece of the permanent magnet‐type MRI device.
PI architecture functionally distributed system for power network supervisory control
Authors: Kunugi Masahiko , Yohda Masahiko , Tamura Shinsuke , Kishida Yukio , Hayashi Tatsuo , Hasegawa Tsuguo
Published: July 2007

In recent years, the sizes of Energy Management Systems (EMS) and Supervisory Control and Data Acquisition (SCADA) systems have grown to huge proportions for two reasons:

The power systems to which they are applied have grown in size and complexity; and

Their own functions have become more diverse and sophisticated.

This raises the following problems: degradation of response time; decreased reliability; limited expandability; less maintainability; and increased costs.

A functionally distributed system that is characterized by parallel processing and independent subsystems (parallel‐independent architecture) will solve these problems.

The system is comprised of a group of functional units, each of which runs in parallel, independently and asynchronously. Copies of some programs and power system status data are stored in the relevant functional units, and data‐driven architecture is adopted, which eliminates the need for a centralized control mechanism.

The feasibility of a functionally distributed system was tested through construction of a prototype. The results were satisfactory.
A feasibility study of a direct‐mapping parallel processing method to solve linear equations in load‐flow calculation
Authors: Inayoshi Hiroaki , Homma Takuya , Ohsawa Yasuharu
Published: July 2007

With the growing size and complexity of power systems, system analysis—such as transients calculation—takes much time. Hence, fast calculation methods are required. Although parallel processing is a hopeful method, there have been difficulties in the parallel solution of linear equations which appear in power‐flow calculations by the Newton‐Raphson method.

This paper aims at the fast calculation of the power‐flow problem by means of parallel processing. In order to improve the suitability to the parallel solution of the differential equation in transients calculation, we assume the use of a direct‐mapping parallel processing machine to map directly the network of a power system onto a network of processors. Under this assumption, we propose a new parallel‐processing‐oriented method in which the linear equation is solved by linear iterations between nodes with Aitken acceleration. We simulate the method on three model power systems and compare this Parallel Iterative Method (PIN) with a Parallel Direct Method (PDM) which uses the banded matrix according to the number of operations required. As a result, we can expect that PIM may solve linear equations faster than PDM with m processors, although the PIM might be inferior to the PDM with m × m processors, where m denotes the half‐band width of the banded matrix.
New power consolidation‐inversion‐control system for faraday MHD generator
Authors: Inui Yoshitaka , Kato Mitsuhide , Morimoto Kenji , Ishikawa Motoo , Umoto Juro
Published: July 2007

The authors propose a new power consolidation‐inversion‐control system for the Faraday MHD generator using the voltage source PWM inverters. The dc output power for each electrodes pair of the MHD generator is at first inverted into three‐phase ac power by a voltage source PWM inverter, and then the ac powers are consolidated by transformers. The proposed system does not need such expensive equipment as an ac filter or phase modifier and can independently and simultaneously control the active and reactive powers provided to the electric power system. Numerical simulations of the whole system, including the Faraday MHD generator, the proposed power consolidation‐inversion‐control system, and the electric power system, show that the proposed system can stably and steadily transmit and control the electric power from the MHD generator to the electric power system. It is also confirmed that the proposed system can independently and simultaneously control the active and reactive powers and can be used as a fast power controller.
High‐field conduction and carrier traps in polyethylene copolymerized with various monomers
Authors: Ishino Iwao , Hikita Masayuki , Suzuoki Yasuo , Mizutani Teruyoshi , Ieda Masayuki
Published: July 2007

The electrical breakdown and electrical conduction of ethylene copolymers have been studied. The electric strength of ethylene copolymers containing an optimum content of halogen moieties such as bromophenyl and fluoroethylene groups was found to be higher than that of LDPE over the wide temperature range from −196°C to 90°C. Also, conduction currents in the copolymers were suppressed at high electric fields. X‐ray‐induced thermally stimulated currents (TSC) revealed that halogen comonomers act as carrier traps with a depth of about 0.4 eV. Consequently, the introduction of comonomer‐containing halogen groups into polyethylene suppresses electron acceleration as a result of an increase in trapping and scattering of conduction electrons. This leads to an increase in electric strength which is determined by the electron avalanche breakdown.
Study of space‐charge characteristics in polyethylene for power cable insulation by laser‐induced pressure‐pulse technique
Authors: Yoshifuji Naohisa , Suzuoki Yasuo , Han Sangok , Matsukawa Youji , Furuta Tetsuya , Yamada Hironori , Mizutani Teruyoshi , Ieda Masayuki
Published: July 2007

By utilizing the laser induced pressure‐pulse (LIPP) technique, the behavior of space charge in low‐density polyethylene (LDPE) and crosslinked polyethylene (XLPE) films in contact with metal or carbon‐loaded semiconducting layers was studied quantitatively to clarify the space‐charge characteristics in power cables.

Negative heterospace charge near the anode and positive space charge in the bulk were observed in unoxidized LDPE under the fields above 120 kV/mm. The amount of negative space charge increased with applied field, while positive space charge in the bulk disappeared with increasing applied field. This indicates that electron injection and ionization are enhanced by applied field.

Prominent negative homospace charge was formed near the cathode in oxidized LDPE, which indicates that oxidation enhanced electron injection. The depth of charge centroid from the cathode became larger with increasing temperature. This indicates that the effective electron mobility increases with temperature.

Negative space charge also was formed in the bulk in XLPE films with metal electrodes, which indicates that crosslinking enhanced electron injection. XLPE films with a carbon‐loaded semiconducting layer showed both negative and positive homospace charges near the semiconducting layers, which indicates that both electrons and holes were injected from the semiconducting layer.
Development of a new detection method of partial discharge for EHV long‐distance active cable line
Authors: Katsuta Ginzo , Toya Atsushi , Endoh Takeshi , Suzuki Hiroshi , Sekii Yasuo
Published: July 2007

A new method was used to measure the characteristics of partial discharge (PD) for an active 9.5‐km long‐distance 275‐kV XLPE cable line with insulating joints. It was found that the detection of PD and the calibration of detection sensitivity were carried out safely and easily. The proposed method includes:

detection of PDs and injection of calibration pulses using two pairs of metal electrodes placed on PVC jackets with anti‐corrosion layers separated by a joint sleeve sectionalizing insulator;

measurement of detection sensitivity with distance using calibration pulses injected from an adjacent insulating joint;

detection of PDs with a high S/N ratio measured at a frequency corresponding to the lowest noise level; and

usage of rf cores attached at cross‐bonding leads and wires for sheath current limiters to reduce the crosstalk of signal and noise through these lines at insulating joints.

Using a combination of these techniques, the highest detection sensitivity was 1 pC in the vicinity of an insulating joint, and 15 pC at 617 m from the adjacent joint. The sensitivity obtained by the conventional PD measurement using a low‐frequency method was at most 1000 pC.
Piezoelectric ceramics of (Bi1/2Na1/2)TiO3‐PbTiO3‐BaTiO3 system
Authors: Takenaka Tadashi , Naitou Yuichi , Sakata Koichiro
Published: July 2007

Piezoelectric and ferroelectric properties of bismuth sodium titanate, (Bi1/2Na1/2)TiO3(BNT)‐based solid solution, that is, (Bi1/2Na1/2)(1‐x)(Pba Bab)xTiO3(a + b = 1) [BNPB(100x‐100a/100b)], are studied from the viewpoint of a new group of lead‐free or low‐lead content piezo‐electric ceramics with a rhombohedral(Fa‐tetragonal (Fβ) morphotropic phase boundary (MPB). It is evident that the MPB seems to be remarkably efficacious in promoting piezoelectric and pyroelectric activities by electrical poling.

X‐ray diffraction data, dielectric properties and D‐E hysteresis loops show that the MPB exist near (Bi1/2Na1/2)TiO3[BNT] at x = 0.13–0.14, 0.08–0.09 and 0.06–0.07 in the case of b = 0, b = 0.5 and b = 1, respectively. BNPB ceramics are superior for piezoelectric ceramics in high‐frequency ultrasonic uses, or special piezoelectric actuator materials with a lower free permittivity ε33Tε0, and a high electromechanical coupling factor k33, along with a high mechanical strength.
Equivalent circuit analysis for magnetostatic wave devices
Authors: Koike Takuro , Ohba Masafumi
Published: July 2007

Magnetostatic wave (MSW) devices are potentially very promising for carrying out signal processing directly at microwave frequencies, and recently have been receiving much attention. Although the development of a general design theory is essential for significant progress in the signal processing capabilities of the MSW devices, relatively few design theories have been discussed in the past.

This paper extends and improves the general equivalent circuit approach to the magnetostatic wave devices proposed and discussed earlier. Based on the definitions of the purely magnetostatic terminal parameters and the magnetostatic characteristic impedance, the electromagnetostatic energy conversion is discussed and the appropriate general equivalent circuit models for the MSW devices are developed. Calculated insertion losses for various MSW devices are in excellent agreement with experimental results.
On the design of a single‐sided linear induction motor for urban transit
Authors: Nonaka Sakutaro , Higuchi Tsuyoshi
Published: July 2007

Single‐sided linear induction motor (SLIM) propulsion and wheel‐on‐rail support and guidance for urban transit has been developed in Canada and Japan. The maximum speed for urban transit is about 70 km/h, with the trains repeatedly performing powering, coasting, and braking operations within relatively short distances between stations. In the design of SLIM's operating under such conditions, we must take into account energy consumption as well as motor weight, input KVA, and performance characteristics. In this paper, we conduct a theoretical examination of such a SLIM design, estimating its performance characteristics in using space harmonic analysis. Energy consumption is reduced by decreasing the mechanical clearance. The flux density, then, should be a low value of from 0.5 T to 0.6 T. A motor length of from 2 to 2.5 m and pole pitch of about 300 mm are advisable.
Characteristics of lead‐plastic laminate tape for water‐impervious XLPE cable
Authors: Fukuda Teruo , Uematsu Tadayuki
Published: July 2007

To take full advantage of combined effects of metal and plastic materials, a composite tape combining lead foil which lacks mechanical strength with plastic film which imparts strength has been developed. This composite tape is designed to serve the purpose of a water‐impervious layer in an XLPE cable. Evaluation of its properties such as corrosion resistance, fatigue, expansion and shrinkage was made. The results of tests indicate that the combination of lead foil with plastic film is more effective in several ways than either alone. As one of its applications, the lead laminate tape was used as a water‐impervious layer in an XLPE cable. This composite material may be used not only in XLPE cable applications but also in many other various fields of industry.
Dynamic preventive control for power system using transient stability assessment based on pattern recognition
Authors: Kita Hiroyuki , Nishiya Ken‐Ichi , Hasegawa Jun , Mizuno Takahiro
Published: July 2007

To maintain power system security, the authors are developing an integrated security monitoring and control (ISMAC) system which consists of the three main functions: security monitoring, preventive control and emergency control. This paper focuses on the dynamic preventive control which deals with the transient stability immediately after the contingency has occurred. The proposed method is based on the transient stability assessment using the pattern recognition with two‐dimensional feature space. Therefore, a preventive control strategy can be obtained rapidly. An index which represents the severity of the contingency quantitatively (security index) is defined by the distance from a linear decision surface which divides a feature plane into a stable and an unstable region. Further, this method has also the advantage that it is possible to consider the effect of the control devices or damping to some extent and specify the operator demand for stabilization flexibly.

The effectiveness of the proposed method is ascertained through numerical examples for model power systems.
A method of fault diagnosis in adaptive control systems by using fuzzy inference
Authors: Kumararu Kousuke
Published: July 2007

An on‐line fault diagnosis scheme for adaptive controlled systems designed by a self‐tuning approach is proposed. A physical parameter change in the controlled system can effectively be detected by using Kullback Discrimination Information (KDI) as an index for model discrimination. In the adaptive controlled system, parameter changes may occur under the normal operation, as well as under a failed situation. In order to decide whether the detected system parameter change really means a fault occurrence or not, a fuzzy inference approach to fault diagnosis is considered. Some appropriate membership functions which describe fuzzy events of the fault are constructed to implement the fuzzy inference. In this way, useful knowledge about fault modes obtained from, e.g., experts, can be introduced into the model‐based diagnosis technique. Simulation studies on a second order damped oscillator have been carried out to demonstrate the effectiveness of the method.
Magnetic properties of melt‐spun Nd‐Pr‐Fe‐Co‐B‐V system alloys and their bonded magnets
Authors: Yamamoto Hiroshi , Kodama Iwao
Published: July 2007

Melt‐spun ribbons of Nd‐Pr‐Fe‐Co‐B‐V system alloys were prepared by the single‐roller rapidquenching method. The effects of composition, wheel velocity and heat treatment on the magnetic properties were investigated. The magnetic properties of their isotropic compression bonded magnets prepared from optimally annealed ribbons also were measured. Remanence (Br) was found to increase with decreasing rare‐earth content, and a maximum value of more than 1.0 T was obtained. A maximum energy product of 164.0 kJ/m3 was obtained for (Nd0.5 Pr0.5)9Fe4Co8B7.5 V1.5 alloy ribbon prepared at a wheel velocity of 17.1 m/s.

From TEM observation, the particle size of these ribbons was determined to be between 20 to 30 nm. It is conjectured that the high remanence is obtained by the interaction of these fine particles. The amorphous (Nd0.5Pr0.5)9Fe74Co8 B7.5V1.5 ribbons prepared at a wheel velocity of 20.7 m/s were crystallized by heat treatment, and the optimum annealing condition was found to be at 650°C for 20 min. Its corresponding value of (BH)max was 146.2 kJ/m3. A maximum energy product of 86.4 kJ/m3 was achieved with (Nd0.5Pr0.5)9Fe74Co8 B7.5V1.5 bonded magnets made from the optimally prepared ribbons.
Separately frequency modulated single‐ended type quasi‐current resonant DC/DC converter with high‐frequency‐link incorporating forward and flyback hybrid transformer
Authors: Lu Ding , Nakaoka Mutsuo
Published: July 2007

This paper considers an improved bidirectional zero‐current switching (ZCS) quasi‐resonant‐type single‐ended soft‐switching mode dc/dc converter with an HF center‐tapped transformer link and ZCS commutated diode rectifier which is capable of minimizing switching losses of a power device, its electrical stresses and electromagnetic interference (EMI/RFI) noises. This converter topology can operate efficiently under a simple frequency‐regulation strategy in the ultrasonic frequency ranges.

The advanced exact computer‐aided simulating analysis of the new converter circuit is presented introducing the normalized frequency variable and circuit system parameters. The open‐loop/closed‐loop steady‐state voltage regulation characteristics in a variable frequency‐modulation mode are illustrated and discussed in the normalized general‐purpose expressions in addition to the load variation performance.

The feasible high‐power density SMPS breadboard with a full‐wave quasi‐current resonant switch assembly using a single MOS‐gate switching power semiconductor device is originally developed and investigated, and is optimally designed for a distributed low‐voltage large‐current power supply system. Its experimental results in the PFM control implementation are demonstrated compared with the exact simulation ones from a practical viewpoint.
Characteristics of a brushless and exciterless three‐phase synchronous generator with DC exciting system
Authors: Shibata Fukuo , Naoe Nobuyuki
Published: July 2007

From the viewpoint of maintenances and constructions, it is desirable that brushless and exciterless type three‐phase synchronous generators be made.

To meet this requirement, one of the authors devised a brushless and exciterless synchronous generator in which exciting currents flow simultaneously with load currents in armature windings. Thus, generators can be used both as the generators themselves and as the exciters. A generator system has already been reported by one of the authors. In it, the dc stator exciting current flows between the middle points per phase of the double‐star armature winding through the rectifiers. However, the winding connection between the armature winding and the rectifiers are complicated. Three sets of rectifiers are needed by the stator excitation.

The authors present a generator system by which the electric connection of between the stator armature winding and the rectifier can be simplified, and the number of the rectifiers can be reduced. In this system, the stator is provided with a double‐star armature winding having two neutral points.

In this paper, first, a circuit constitution and the principle for the brushless and exciterless three‐phase synchronous generator are described, and second, the characteristics are elucidated by means of characteristic analysis. Further, the results of the experiments for the generator conducted on the test machine of 2.0 kW are shown.
Fundamental electromagnetic characteristics of magnetically anisotropic damper‐wedges
Authors: Takahashi Miyoshi , Watanabe Masatoshi , Arai Keizi , Takahashi Noriyoshi
Published: July 2007

A magnetically anisotropic conductor was applied to the damper‐wedge which acts as a slot wedge and damper bar in electrical rotating machinery. This conductor is composed of copper‐clad steel wires of 1.6 mm diameter aligned in the same radial direction. This means permeability in the direction of the wires, i.e., the thickness direction of the damper‐wedge, is larger than the permeability perpendicular to this direction, and electrical conductivity is good.

To evaluate the electromagnetic characteristics, a trial damper‐wedge, 1.2 m in length and with a steel space factor of 40 percent to total volume, was manufactured and maintained in a standstill model iron core. Test results were as follows when the magnetically anisotropic damper‐wedge was employed.

(1) As the magnetic flux flowed well in the radial direction, the flux distribution at the core slot portion was flattened. Consequently, the ripple amplitude became small and the average flux density increased compared with cases when the nonmagnetic or magnetic isotropic conductor is used.

(2) The damper‐wedge had a smaller skin effect for ac current than a conventional copper damper bar. The losses concentration for the damper system was relieved so that better machine performance under heavy load condition would be obtained.
Fast parallel algorithm on sparse matrix for power system analysis
Authors: Oyama Tsutomu , Karube Takafumi
Published: July 2007

Power system analysis is the basis of operation and planning. Since power systems are very large and complex, however, it takes a long computation time for the analysis. It is desired to develop a fast method especially for transient stability analysis. In this paper, a parallel algorithm for sparse matrix factorization, forward substitution, and backward substitution is discussed. The algorithm is made operational on the actual transputer network. The computation time using the algorithm is measured and compared with that of the ordinary (single processor) algorithm. Finally, the parallel transient stability program is developed and evaluated.
Compensation for parameter variation of induction motor improved torque control characteristics in low‐ and high‐speed regions
Authors: Yamada Tetsuo , Yamamoto Yasuhiro , Ichioka Tadashi , Niwa Tohru
Published: July 2007

In the vector control system using the slip frequency control method, the rotor resistance of an induction motor is used to calculate a slip frequency. Thus the change in temperature of the rotor resistance causes the deterioration of the torque control characteristic.

This paper presents a new method of compensating for the rotor resistance change which is robust for the stator resistance change. A current control loop is composed of the λ‐δ axes in which the λ axis is coincident to the stator current. In this method, the stator voltage error on the δ axis which is directly obtainable from this current control loop was used. The change in the stator voltage was able to be detected accurately, therefore the torque control accuracy was improved, particularly in the low‐speed region. The experimental results of the current response and the compensation for the rotor resistance deviation also are shown.

Moreover, although the mutual inductance has been treated as an invariable value, the value does change by a frequency and an exciting command. In this control method, an initial tuning of the equivalent mutual inductance was achieved by detecting the deviation component of the stator voltage on the δ axis at the no‐load running condition. Furthermore, in the region with the constant power where the field weakening control was achieved, the excellent experimental results of the compensation for the deviation of the equivalent mutual inductance are shown.
Novel control strategies for HVDC system with self‐contained converter
Authors: Tokiwa Yukio , Ichikawa Fumitoshi , Suzuki Kenichi , Inokuchi Haruhisa , Hirose Syunichi , Kimura Kazuaki
Published: July 2007

This paper discusses newly developed control strategies of a self‐commutated converter applied to the HVDC system. An upper and lower power‐limited dc voltage control establishes high performance in a two‐terminal HVDC system. A voltage margin method to reverse dc transmission power also is introduced. Even when the communication system is shut down, if required, dc transmission power can be changed with the authors' proposed controls applied to the terminal control. Furthermore, the dc voltage control scheme with two‐stage voltage control characteristic is presented for multiterminal HVDC system use. When one terminal is collapsed, the multiterminal HVDC system can be operated because of the proposed control characteristics.

Simulator studies were carried out to verify the proposed control performance in the two‐terminal HVDC system and successful test results such as power reversal and a terminal start‐up during other terminal operations are shown.
A vector control system using a neutral‐point‐clamped voltage‐source pwm inverter
Authors: Ogasawara Satoshi , Sawada Tadashi , Abe Keiichi , Akagi Hirofumi
Published: July 2007

This paper describes a vector control system of an induction machine using a neutral‐point‐clamped voltage‐source inverter (NPC‐VSI) that is one of the double series‐connected inverters.

The NPC‐VSI is able to output five‐level step‐shaped line‐to‐line voltage without output transformers or reactors, and it may reduce harmonic currents corresponding to torque ripples. However, the NPC‐VSI has a problem in that excessive high voltage is applied to switching devices when a neutral point of two dc capacitors of the NPC‐VSI varies from the center of the dc link voltage, because the neutral point is floating.

This paper proposes also a current controller to which the space vector theory is applied. This can reduce harmonic currents to one‐fourth those of a conventional voltage‐source inverter using six switching devices, and regulate the neutral point potential within a preset range. To simplify the current controller, information about voltage space vectors is given from the vector controller to the current controller. The validity of the current controller is confirmed by a prototype using an induction machine of 2.2 kW.
Magnetic noise caused by output waveform harmonics of voltage‐source inverters
Authors: Iida Shoji , Okuma Yasuhiro , Masukawa Shigeo
Published: July 2007

Harmonic components included in the output waveforms of inverter circuits cause magnetic noise, that is, audio noise, from the output transformers or load motors. To estimate the magnetic noise due to the harmonic components, we have already proposed the equivalent noise voltage Es and current Is.

In this paper, by applying the aforementioned Es, we compare quantitatively the magnetic noise in the various ordinary voltage‐source inverters, both PWM inverters with multipulse waveforms and PAM inverters with multistep waveforms. Then, to reduce the magnetic noise, the output waveforms of the PWM inverters are improved by applying Es into the idea of harmonic elimination. Moreover, by employing PAM system as voltage regulation in the aforementioned method, the more improved output waveforms can be obtained with lower noise and also lower distortion.
The vector potential revisited
Authors: Adachi Toshimi , Sasabe Shigeru , Inagaki Toshio , Ozaki Masao
Published: July 2007

The vector potential in electrodynamics is investigated through the decomposition of its form to the following two parts: 1) the so‐called transverse part represented by a divergenceless vector; and 2) the longitudinal part represented by an irrotational vector. The decomposition can be done by the Helmholtz theorem in the vector analysis because the conditions which should be required when the Helmholtz theorem is used are satisfied for the almost vector potentials of physically interesting problems.

As an example of such interesting problems, the Aharonov‐Bohm effect is chosen here. As for the Aharonov‐Bohm effect, the vector potential given in the original paper of Aharonov and Bohm has the singularities along the z‐axis. It is shown that even for such a singular potential the Helmholtz theorem is held provided that the concept of the distribution is introduced in it. Generally, the transverse part of the vector potential obtained through such a decomposition is determined uniquely by the magnetic field and does not alter by a gauge transformation. On the other hand, the longitudinal part depends on the choice of special gauge. It is shown that the Aharonov‐Bohm effect is due to the contribution of the transverse part of the vector potential and therefore should not be influenced by any gauge transformations.
Mechanical characteristics related to fault currents in bundle conductors
Authors: Hanamura Makoto , Kobayashi Takayuki , Yoshida Kouji , Serizawa Yasuo
Published: July 2007

The flow of fault currents in bundled conductors induces an electromagnetic attraction between subconductors and thereby the bus conductor system to an extremely high level of tension. This tension, which is the most important factor in designing the mechanical strength of the system, is determined by a large number of parameters—the magnitude of the fault current, the size and number of the subconductors, spacer interval, the spring of the structure, and so on.

Full‐scale 63‐kA class fault current tests were carried out on eight types of bus conductors used in 275‐and 500‐kV subconductors, and measurements of fluctuation in tension were used to clarify the relationship between the various parameters and maximum tension at fault time.

A method also was devised for calculating maximum tension at fault time on the basis of the various parameters, and it has been applied in the mechanical strength design of the bus conductor system.
Verification and expansion of a method of transient analysis of voltage collapse based on the induction motor load model
Authors: Ohtsuki Hiroshi , Yokoyama Akihiko , Sekine Yasuji
Published: July 2007

Voltage instability is now under intensive study in Japan, and some dynamic methods for analyzing voltage collapse have already been presented. However, the suitability of load models used in the methods and the generality of the results have not been verified.

In this paper, useful voltage collapse data acquired in real power systems are presented. The measured data are compared with the result of dynamic digital simulation to verify the suitability of an induction motor load model.

In the latter half of this paper, dynamic simulations of voltage collapse with consideration of generator dynamics are carried out. An interconnected power model system with 10 nodes is analyzed. The generality of basic characteristics concerning voltage collapse which have already been obtained without considering generator dynamics is verified by such simulations.
Soft switching based on analysis of transient and steady‐state characteristics: Application to a single‐ended high‐frequency inverter
Authors: Hatanaka Yoshihiro , Mutsuo Nakaoka
Published: July 2007

A single‐ended resonant‐type high‐frequency inverter using a static induction transistor (SIT) described in this paper can be performed as a zero current switching (ZCS) operation without dc reactor.

The SIT high‐frequency inverter is a low‐cost one which has no transformer and it would be developed for a high‐intensity ultrasonic power supply and dc‐dc converter. The circuit operation regions, not only ZCS but also ZCS‐ZVS (zero current switching and zero voltage switching), were elucidated in the normalized plane. The characteristics of the inverter including the power control by frequency regulation were discussed. Furthermore, the switching characteristics in the transient‐state were investigated. These characteristics were substantiated on the basis of the numerical analysis and experimental results.
Disturbance suppression control with preview action for a linear dc brushless motor
Authors: Egami Tadashi , Okabayashi Senri
Published: July 2007

This paper proposes a disturbance suppression control with preview action for a brushless and coreless‐type linear dc motor. The brushless and coreless‐type linear dc motor is coggingless and has long life. It is suitable for high speed and precise positioning control. Parameter variation and load change are regarded as an equivalent disturbance signal and the compensation action is applied by utilizing the estimated value of the equivalent disturbance inside the inner loop. Next, an optimal preview control system is synthesized including the disturbance suppression control system mentioned in the foregoing. Disturbance suppression, improving phase delay and lowering the input peak value are attained in this control system. These effects are confirmed by applying the linear dc motor.
Development of a partial discharge location method for power cables
Authors: Ohno Hironobu , Katsuta Ginzou , Sakaguchi Ryuji , Ebinuma Yasumitsu , Sakai Nobuhiro , Nagaoka Akira
Published: July 2007

Insulation deterioration of power cables can be measured by the method of partial discharge. If a large partial discharge is detected in a cable, the cable is considered to be defective and a partial discharge is located to find the position of the defect. However, partial discharge location methods are generally disadvantageous in that they require much skill for operation and have inferior sensitivity and accuracy.

To solve these problems, the authors developed a locating method using two‐phase cable and an automatic partial discharge locator which automatically localizes the generating site of discharge immediately after making partial discharge measurement by simple operations. Field measurements are made on SL (separately lead‐covered) cables and other cables with the locator to test its accuracy and reliability, and it was found that the device is effective and useful.
Development of a live‐line partial‐discharge detection method for XLPE‐insulated copper wire‐shielded cable using a “yoke coil”
Authors: Nakanishi Yutaka , Nakatani Youichi , Suzuki Hiroshi , Endoh Takeshi
Published: July 2007

This paper describes a new partial‐discharge detection method for an XLPE‐insulated copper wire‐shielded cable line using a “yoke coil.” Partial discharges are measured with the yoke coil which detects the azimuthal component of the current flowing through the copper wires wound on an outer semiconducting layer with a given angle against the axial direction of the cable.

The highest detection sensitivity of 2 pC has been achieved at a frequency range of 5 to 20 MHz using a 77‐kV 100‐mm2 model cable line (200 m in length). It was confirmed that the partial discharge caused by an artificial defect has successfully been detected using the proposed method.

In the PD measurement for an actual 77‐kV XLPE‐insulated live line, the detection sensitivity was 10 pC.
Partial discharge detection by AE sensors for prefabricated joints for xlpe cables
Authors: Nakanishi Yutaka , Nakatani Youichi , Iizumi Masahiro , Kasuya Masaharu
Published: July 2007

This paper describes detection by the AE (acoustic emission) sensor of partial discharge in a prefabricated joint, one of the accessories for XLPE cables which is composed of factory‐formed parts. Since the prefabricated joints can be installed in a short time, an increasing number of such joints has been used on power transmission lines. However, the interface between the parts of prefabricated joints tends to exhibit weak points because of a structure peculiar to this type of joint.

The AE sensor is provided for practicability in comparison with conventional electrical defect detection methods. In the course of the present study, a method for locating a defect using multiple signals from the AE sensors was developed and its validity was evaluated by the dielectric breakdown test.
Flux synthesizing linear induction motor with super multiphase switching
Authors: Koseki Takafumi , Morizane Toshimitsu , Masada Eisuke
Published: July 2007

A novel concept of structure and control of linear induction motors (LIMs) called “Flux Synthesizing Linear Induction Motors (FSLIMs),” is proposed where each slot has a conductor carrying an electric current whose amplitude and phase angle are controlled with super multiphase switching devices. It is well known that an LIM has the merits of direct drive and simple structure. However, a conventional LIM has low power factor and energy efficiency. The end effect is one of the significant reasons for the bad characteristics. Strategies against the effect have been limited by conventional three‐phase winding.

On the other hand, high‐speed power‐switching devices are available at a reasonable cost. A super multiphase drive enables more freedom for controls with the proposed structure of the FSLIM. Basic characteristics of a tubular test LIM with twelve slots have been measured and calculated to investigate an appropriate flux synthesis. As a result, an appropriate switching scheme which synthesizes sinusoidal distribution of the gap flux density, enables the end‐effects to be suppressed and, consequently, improves the energy efficiency. In addition, basic conditions for the field‐coordinated oriented control of a thrust force are satisfied by keeping the amplitude of the gap flux constant with the flux synthesis.
Characteristics of linear actuator with semiclosed magnetic circuit excited by discharge current of capacitor
Authors: Maeda Tsutomu , Fujita Hiroshi
Published: July 2007

The simple structured linear actuator considered in this paper is based on the model, called the single‐phase oscillating motor, proposed by Jayawant. Reports have already been made on the static and kinetic characteristics of the actuator of the model proposed by the authors for two cases considered and not considered the magnetic saturation when it was driven by an ac source. Although the theoretical procedure to calculate the characteristics is very simple, the calculated results in both cases have shown close agreement with the experimental ones.

To improve the actuator for practical use, some methods will be considered and one of them is to use a dc source instead of an ac source. Using the charged capacitor as a dc supply, an instantaneous large current flows easily in the exciting coil in comparison with the case of an ac supply.

In this paper, qualitative explanation of the ring motion and calculated results of the ring speed which have good agreement with experimental results are reported.
Power oscillation damping by superconducting magnetic energy (SMES) storage unit
Authors: Ogimoto Kazuhiko , Masuda Tatsuo , Inabe Hiroto , Komukai Toshihiko , Tsuruta Syunichi , Momotake Toyofumi
Published: July 2007

With the increase in the size and capacity of electric power systems and the growth of widespread interconnections, the problem of power oscillations due to the reduced system damping has become increasingly serious. Since a Superconducting Magnetic Energy Storage (SMES) unit with a self‐commutated converter is capable of controlling both the active (P) and reactive (Q) power simultaneously and quickly, increasing attention has been focused recently on power system stabilization by SMES control.

This paper describes the effects of SMES control on the damping of power oscillations. By examining the case of a single generator connected to an infinite bus through both theoretical analyses and experimental tests (performed with a SMES unit with maximum stored energy of 16 kJ and an artificial model system), the difference in the effects between P and Q control of SMES is clarified as follows:

In the case of P control, as the SMES unit is placed closer to the terminal of the generator, the power oscillations will decay more rapidly.

In the case of Q control, it is most effective to install the SMES unit near the midpoint of the system.

By comparing the P control with Q control, the former is more effective than the latter based on the conditions that the SMES unit location and the control gain are the same.
A control method for improving ac input current waveform of current‐type PWM rectifiers
Authors: Sato Yukihiko , Miyazawa Hideki , Kataoka Teruo
Published: July 2007

Recently, PWM rectifiers which realize high‐power factor and almost sinusoidal ac input current have been proposed and some of them have already been put into practice.

In many cases the PWM rectifiers are of current type, that is, they have a smoothing reactor on the dc side. In such rectifiers, anLCfilter has to be inserted on the ac side to reduce current harmonics due to the PWM operation. However, theLCfilter may cause waveform distortion and transient oscillation of the ac side current.

As a solution to this problem, a new control method is proposed introducing ac side current control by means of state feedback of theLCfilter. In this case, both the dc output current and the ac input current controls should be achieved by the PWM operation of the rectifier. Furthermore, to obtain sufficient controllability regardless of the operating condition, the dc output and ac input current controls should be done independently. To meet these requirements, existing control methods for PWM rectifiers are not directly applicable.

In this paper, a novel control circuit configuration and a method of generating a PWM pulse pattern suitable for the proposed control method are described in detail. From the viewpoint of stability, feedback coefficients and circuit parameters are investigated on the basis of root locus analysis.

Some experimental results also are shown to confirm the effectiveness of the proposed control method and the validity of the analytical results. Improvement of the ac side current waveform and the stability of the transient response are demonstrated by these experimental results.
A study on technical feasibility of applying tubular linear induction motor to vertical movement
Authors: Morizane Toshimitsu , Koseki Takafumi , Masada Eisuke
Published: July 2007

It is necessary for a linear induction motor (LIM) to have large thrust force in applications for the vertical movement. If it does not have sufficient thrust force, it cannot lift even itself. A ratio (thrust force/weight of motor), therefore, is the most important factor for the design of this motor.

In this paper, assuming the LIM has no slot‐effect and infinite length, a simple analytical model is introduced for steady‐state operation. By comparison with the results of detailed numerical analysis, it is verified to be applicable for basic evaluation of the motor. The design of the motor for vertical movement is carried out and the ratio is maximized. The basic dimensions of a feasible motor are given for such application.
Simulated power source based on output characteristics of solar cell
Authors: Tanaka Kunio , Sakoguchi Etsuo , Yamada Eiji
Published: July 2007

Numerous studies were performed to evaluate the performance of photovoltaic power systems (PV systems), including maximum power control of the solar cell, effects of the PV systems on distribution feeders, long‐term performance of the PV systems, etc. To estimate the performance of PV systems, the output characteristics of the solar cell should be taken into consideration.

This paper proposes a new method of the simulated power source (SPS) to analyze the PV system. The SPS is under the control of the 10 cm2 reference solar cell, hence, the output characteristics of the SPS are in proportion not only to the static output characteristics of the reference solar cell, but also the dynamic ones.