bluuebunny/crossref_metadata_2025 huggingface dataset:
Impulse breakdown voltages of triggered multistage vacuum gap
Authors: Itagaki Koichi , Ali Md. Mortuza , Kitamura Hiroshi , Maruyama Takeo
Published: July 2007

Several sealed‐off triggered vacuum gaps are connected in series to improve hold‐off voltage. The characteristics of impulse breakdown voltage of these series‐connected gaps are investigated experimentally. The sum hold‐off voltage of series‐connected gaps decreases to a unit hold‐off voltage when the maximum value of voltage division ratio across the gaps increases to unity.

Self‐breakdown probability of the series‐connected gaps is always higher than that of a single gap under the same conditions. Hence, stage efficiency of the multistage gap decreases with increasing number of stages. Its value is 90 percent with 2‐stage gap and 75 percent with 5‐stage gap, respectively, under the same voltage division ratio and the same gap length (2.0 mm) in each stage.

Triggered breakdown voltage of 2‐ or 3‐ stage gap is several hundred volts when all gaps are triggered simultaneously at the peak of the main impulse wave and a working voltage range is nearly 100 percent in this case. The working voltage range decreases with number of stages. Its value is 45 percent with 3‐stage gap and 15 percent with 5‐stage gap, respectively, when one triggered gap is fired for switching.
Reduction of AC flashover strength by the attachment of insulating strings on the insulator surfaces
Authors: Yamano Yoshiaki , Ishikawa Emi , Takahashi Yuzo , Kobayashi Shigeo
Published: July 2007

AC flashover voltage in air (ACFOV) decreases when nylon string is attached on the PMMA insulator surface which has a backside electrode. The decrease in ACFOV by the attachment is explained by the generation and the propagation of the negative surface leader along the string. When the contact angle between the HV electrode and the insulator surface is in a range from 90° to 120°, some of the negative surface leaders generated proceed along the string to the grounded counterelectrode. The magnitude of the negative leader along the string is stronger than that of the leader on the insulator without a string. In the range of the contact angle from 120° to 180°, the negative surface leader which does not appear on the insulator without a string is generated along the string by the attachment. In both ranges of the contact angle, the negative leader along the string promotes the flashover.
A novel technique for a DC brushless motor without position sensors
Authors: Kaku Kazunori , Yamamura Naoki , Tsunehiro Yuzuru
Published: July 2007

A dc brushless motor is a kind of synchronous motor driven by an inverter and requires sensors to detect the rotor position. As one of the methods, the induced voltages of a brushless motor have been utilized in practice. However, there are some problems in this method, e.g., the motor can obtain insufficient torque due to the low induced voltages in a low‐speed range.

This paper proposes a new method which controls the inverter angular frequency ω1 by using inherent characteristics wherein the torque current ir is almost proportional to the internal phase angle φ where the primary flux of a synchronous motor is controlled to be constant.

If the parameters of a motor are given exactly, the speed regulation is quite small and the transient characteristics with high response and high starting torque are obtained. Furthermore, it is possible to operate a synchronous motor in the field‐weakening range.

Here, the principle of the control method and the performance characteristics of a dc brushless motor having no position sensors are discussed. The simulation and the experimental results of the tested machine show that the proposed method is very useful for practical applications.
Relationship between the energy distribution of electrostatic field change and lightning activity
Authors: Miyazaki Tadaomi , Nishida Yasushi , Kokubu Satomi , Kawamata Shuichiro
Published: July 2007

A lightning strength parameter α (denoted as LSP or LAIDO), which is used for characterizing the phenomena of lightning activity, has been proposed, where α is defined by the characteristic energy obtained from the energy distribution of a radiated field component E in the electrostatic field changes produced by lightning discharge. Here, it is observed that the energy distribution of Eγ components is Maxwellian type.

To prove more clearly the forementioned assumption from another viewpoint, changes of the amplitudes of the electrostatic field component ES were measured and their distribution functions constructed.

In the cloud‐to‐ground lightning discharges, the ES components have a positive sign in the changes. However, those changes in the intercloud discharges are observed with either a negative or positive change depending on the distance between the striking point and the observation site. Therefore it is necessary to sum the numbers of occurrences of both positive and negative components for constructing an energy distribution of the ES component.

A fieldmill and a pair of doughnut‐shaped electrostatic antennas are used in measuring the changes of the ES component. As a result it is found that the changes of the amplitudes of the ES components have a Maxwelliantype energy distribution. A characteristic energy β is defined which is obtained from the component of the electrostatic fields as a measure of LSP.

Based on comparison of α and β it is clarified that β has the same characteristic nature with α. The lightning activity could be estimated from β.
Probability evaluation of low‐voltage distribution equipment lightning failures due to AC arc
Authors: Imai Yasutomo , Nagayama Katsuya , Matsuoka Masanori , Sadakata Takashi
Published: July 2007

To construct low‐voltage power distribution systems, it is important to have correct information on the probability of failures by lightning to meet the requirement for high reliability of these systems.

The burn‐out of low‐voltage distribution equipment is triggered by flashover due to lightning overvoltage followed by the arc discharge current at the commercial frequency voltage. The arc characteristics were investigated by superimposing the lightning impulse voltage across terminals of the low‐voltage distribution equipment connected to the commercial frequency power supply to reproduce these events on an experimental basis. As a result, it was found that the arc characteristics were affected by a number of factors.

The probability of flashover occurrence on low‐voltage distribution equipment is determined based on the frequency distribution data of lightning overvoltage occurrence obtained by monitoring the surge counters on actual distribution lines. Then the probability distribution of arc currents is established by application of the forementioned experimental equation on arc characteristics. Finally, the method for evaluating damages by lightning to low‐voltage distribution equipment on actual lines was investigated with the frequency of lightning strokes and the configuration of low‐voltage distribution systems taken into consideration.
Development of a pumped‐storage power station model for power system stability study
Authors: Taniguchi Haruhito , Nagao Taiji , Higasa Hiromasa
Published: July 2007

Since a pumped‐storage power station generally is located far from the load center, it frequently encounters problems of power system stability, especially at the pumping operation mode. Capacity of units constructed in recent years is as large as a few hundred megawatts, and water head is as high as 500 m. The period of water pressure oscillation of such a high head station becomes longer and closer to power system swing.

Under such condition the output is affected by the conduit system dynamics and becomes different from analytical results using the classical model which assumes constant torque or output during power system disturbance at the pumping operation mode.

This paper describes the newly developed simplified pumped‐storage plant model based on the elastic theory of the conduit system and the complete characteristics of the turbine, which has necessary accuracy to be analyzed because it is connected to bulk power system. Comparison with the real plant test result verifies the validity of the developed model. The interaction with power system is examined by linearized analysis and simulation study.
Development of an expert system for analyzing faults in power systems based on waveform recognition by artificial neural networks
Authors: Fukuyama Yoshikazu , Ueki Yoshiteru , Kaneko Kazuhiro
Published: July 2007

In restoration of a power system, appropriate steps need to be taken in early stages to avoid damage to the public caused by insufficient power supply. The first step in the restoration is the analysis of the fault that has produced the power failure.

Today, a large amount of data will be available at the occurrence of a fault due to the use of advanced communication systems using digital relays and optical fibers. Such systems are intended to obtain data from the relays and circuit breakers (CBs) under operation and the voltage and current during operation and the prefault and postfault periods.

This paper presents a hybrid fault analyzing expert system using data based on protective devices and phasor measurement. This system is a combination of an artificial neural network (ANN) and an expert system (ES). The ANN is used to simplify the analysis of current and voltage waveforms, which is considered difficult due to the presence of a fault resistance and the line impedance. Since a fault waveforms contains various ambiguous factors depending on the nature of the fault resistance, load current and other system parameters, the use of ANN is effective making such determinations.
Constant frequency and constant voltage control of induction generator
Authors: Kuge Katsutaro
Published: July 2007

A doubly fed induction generator is useful for a local‐use water power plant. Setting it in nonconstant water flow, we can use it as a constant‐frequency power generator. This paper shows how to control this generator system.

This paper has two important points. One is that this generator system is always excited at primary winding. Another is that the control target in this study is secondary q axis current to obtain a constant voltage of primary generated power.
Thrust control of a linear induction motor using magnetic field detection
Authors: Onoki Takashi , Numata Hiroyuki , Yamamura Tsugio
Published: July 2007

A two‐dimensional hybrid finite‐element method is used to analyze the thrust response of a linear motor system in terms of vector control, using the air‐gap flux as the input signal. A novel control scheme is used, in which the supply current leads the flux vector by 45°, obviating the need for circuit analysis that arises in the usual vector control scheme. The flux detection method is compared with the conventional average thrust control method and its effectiveness is evaluated.
A novel control scheme of magnetic lift and guidance
Authors: Kwon Byung Il , Masada Eisuke
Published: July 2007

The electromagnetic suspension system, which is a kind of magnetic levitation, can be divided into two groups: separate lift and guidance system; and combined lift and guidance system. This paper considers the latter system, in which lift and guidance forces are generated by a pair of staggered magnets with the inverted U‐shaped rail. Although the forementioned arrangement provides the lift and the guidance simultaneously, a separate control scheme over them is desirable.

In this paper, a quasi‐decoupled control method is presented which reduces the coupling between guidance and lift over a substantially wide range of lateral displacement. Simulation showed that the lift control has a small effect on the guidance but the guidance control has a considerable effect on the lift. Therefore a parallel complimentary controller on the lift controller is proposed to reduce the sensitivity for parameter variation and force disturbance.

As a result, the lift system has robustness to parameter variation and force disturbance, while the guidance system is independently controllable with respect to the lift system. Hence it is possible to obtain adequate guidance force and to meet the ride quality standard related to the guidance of levitation vehicles.
Principle and operation of a new type motor consisting of piezoelectric device and strain wave gearing
Authors: Ishida Muneaki , Hori Takamasa , Hamaguchi Junichi
Published: July 2007

The authors have developed a new type of motor consisting of a piezoelectric device and strain wave gearing, and is called a piezoelectric motor. This is a first step in realizing a low‐speed, small‐size and lightweight motor. The principle of the motor is that the traveling wave is produced by piezoelectric devices and displacement conversion devices without mechanical resonance, and the torque to rotate the motor is generated by a mechanism of strain wave gearing (circular spline and flexspline) without using friction. The motor is operated at variable frequency and its rotational position (angle) is controlled in open‐loop because it is basically a synchronous motor.

In this paper, the structure and principle of the proposed motor are explained and the driving method and the mechanical characteristics of an experimental motor also are described.

The results are as follows:

The realizability of the proposed piezoelectric motor is verified experimentally. The experimental motor operates at 2920 steps per revolution, and its speed range is 0 to 960 pps [or 0 to 20 (rpms)].

The torque characteristics are clarified qualitatively.

The generated torque of the experimental motor is small (less than 0.03 Nm) and therefore the improvement of the torque is an important subject hereafter.

It is possible to construct the motor with nonmetallic material. This fact is considered to facilitate obtaining a means to lighten the weight of the motor in the future.
Finite‐element analysis of electromagnetic force based on permeance
Authors: Kimura Akio , Matsuzaka Tomoyuki , Kagawa Yjkio
Published: July 2007

The permeance coefficient of actuators and motors with permanent magnets depends primarily on the effective magnetic flux density and the magnetomotive force. A finite‐element technique is used to calculate the torque and electromagnetic force from the permeance based on the magnetic flux density distribution. The calculation results are consistent with measurements and with calculated values obtained by other methods. The permeance coefficient at the operating point, which is a performance characteristic of actuators, is estimated.
Investigation of space‐charge effect on the AC treeing mechanism in an LDPE film by tsc and TSSP measurement
Authors: Fukuzawa Masahiro , Iwamoto Mitsumasa
Published: July 2007

When an ac voltage is applied to a low‐density polyethylene (LDPE) film placed under a needle‐plane electrode system, there is a possibility of the formation of the space‐charge field in the vicinity of the needle electrode by electrons (or holes) injected from the needle electrode. In this paper we investigated the properties of the space charge, e.g., the total amount of trapped charge formed in the vicinity of the needle electrode by using electrical measurements of thermally stimulated current (TSC) and thermally stimulated surface potential (TSSP).

From the investigation, it was concluded that a space‐charge field is formed in an LDPE film by the application of the ac voltage, and that the total amount of trapped charge by the application of the ac voltage is less than that by the application of the dc voltage, etc. Finally, on the basis of the present experimental results, we studied the space‐charge effect on the ac treeing mechanism.
Investigation of a new extinguishing principle for a gas circuit breaker
Authors: Hamano Suenobu , Sasao Hiroyuki , Wada Yuuichi , Hasegawa Hiroshi , Kobayashi Noboru
Published: July 2007

A self‐extinguishing principle of a gas circuit breaker (GCB) without puffer action (autopuffer GCB) using an external magnetic field was investigated to improve the interrupting capability in the small current region (several kA). Properties of the rotating speed of an arc, the arc voltage, and the gas pressure rise in an expansion space under the external magnetic field were studied experimentally. The relation between the interrupting capability and the radial magnetic flux density in the autopuffer GCB with a permanent magnet (magnet‐assisted autopuffer GCB) was obtained experimentally and also analyzed numerically. The results are summarized as follows.

The arc column is driven in the azimuthal direction by the radial component of the external magnetic field.

The rotating speed of the arc driven by the radial magnetic field of a permanent magnet remains constant in the arc current range below several kA, and it decreases with an increasing current in the current above several kA.

Since the arc rotation raises the arc voltage and gas pressure in the expansion space, the gas flow from the expansion space to the arc increases in the vicinity of current zero. The interrupting capability is then improved in the small current region.

It is confirmed that the magnet‐assisted auto‐puffer GCB has a good interrupting capability not only for the large current region but also for the small current region.
Development and characteristics of superconductor for 70‐MW class high‐response excitation superconducting generator
Authors: Yamaguchi Mitsugi , Nakanishi Kazuo , Ohmatsu Kazuya , Meguro Shinichiro , Kobayashi Yoshio
Published: July 2007

The superconducting field winding of the 70‐MW classhigh‐response excitation superconducting generator requires a maximum operation current of 4.5 kA at the field of 6 T and needs to allow the field change of 10 T/s. In addition, superconductors have to meet the requirements of saddle‐shape winding in the rotor slot and require the mechanical strength withstanding the centrifugal force as well as electromagnetic force.

The developed conductor has the configuration of double stranded cable, consisting of NbTi, Cu and CuNi. An optimization was made, taking into account the requirement of low ac loss and high current density. The critical current of 13.6 kA was achieved at the field of 6 T and the ac loss was 6.9 kW/m3. The developed low‐loss high‐current density superconductor will be able to be applied to the field winding of the 70‐MW class high‐response excitation superconducting generator.
Line fault test of model power system with three‐phase superconducting fault current‐limiting reactors
Authors: Kado Hiroyuki , Uriu Yoshihisa , Ishigooka Takeshi
Published: July 2007

A novel three‐phase conducting fault current limiting reactor (SCFCLR) is fabricated. The SCFCLR has three superconducting windings with the same number of turns wound on an iron core. The rating of SCFCLR is 200 V, 10 A. Two SCFCLRs are inserted in the sending and the receiving ends of the model power‐transmission line. The line fault test of a model power system with two SCFCLRs is undertaken. The fundamental behavior of this reactor is confirmed. In the case of single‐line‐to‐ground fault, the fault current is limited to a very small value by the large zero‐phase sequence reactance of the SCFCLR without quench. In the case of a three‐phase short circuit, the SCFCLR quenches, and the short‐circuit current is limited by the normal conducting resitance of the winding. It is confirmed that the transient stability of the system during line faults is greatly improved by the insertion of SCFCLRs.
Conditions for existence of optimal solution in the synthesis of a multivariable control problem for power systems by using optimization problem
Authors: Kaizu Hiroyuki
Published: July 2007

This paper considers the synthesis of a multivariable control problem for power systems by using the optimization method. The power system dynamics based on the usual assumptions can be formulated as a class of nonlinear dynamic systems which contain the sinusoidal functions associated with the power torque‐angle curve of the ac generator. Then, an optimal control law, which retains the principal nonlinearity of the power system, is derived by using the optimization techniques in the linear optimal control theory. The feedback gain matrices are obtained by solving matrix equations which appear in the optimization procedure.

In this paper, the conditions for the existence of an optimal solution of these matrix equations are derived by using Anderson's theorem. The stability criterion for the control system is discussed from the viewpoint of a Lur'ye‐type Lyapunov function. Thus, the optimal control law can be applied to a class of nonlinear dynamical systems represented by the ordinary differential equations divided into linear and nonlinear terms.
Radial flux type hysteresis motor with rotor ring of copper‐sprayed surface layer
Authors: Wakui Genjiro , Kurihara Kazumi , Kubota Tomotsugu
Published: July 2007

This paper describes a new form of radial flux type hysteresis motor having large output, high efficiency, and high power factor. The rotor has a copper‐sprayed surface layer on the rotor ring, which is made of Fe‐Cr‐Co magnet steel and has magnetic anisotropy and slits. The new configuration has two features. First, it is designed to give a combined hysteresis and reluctance‐motor action effectively, particularly at a synchronous speed. Second, it is designed to give a combined hysteresis torque and large torque due to eddy current in asynchronous conditions, particularly at starting.

To analyze motor performance at synchronous and asynchronous operations, the finite‐element method is used. In this paper, magnetic hysteresis is considered by using complex permeability. The agreement between predicted and measured values of motor performance characteristics is good.
Characteristics of superconducting generator at high response excitation
Authors: Nitta Tanzo , Tanaka Shoichi , Okada Takao
Published: July 2007

Superconducting generators have many advantages, one of which is their ability to improve the stability of power systems because of their low synchronous impedances. The advantage may be increased by adoption of high‐response excitation. The first 100 kVA high‐response excitation superconducting generator has now been built. One of the problems in the design of such generators involves the characteristics of the field circuit, i.e., the field armature winding, losses in the component materials, and loss in the superconducting field winding. In this paper, a 2‐dimensional electromagnetic field analysis of field circuit characteristics is presented.
Transient sheath voltage characteristics of a crossbonded cable installed within a tunnel
Authors: Nagaoka Naoto , Ametani Akihiro , Yoshida Kyoto , Karasaki Takashi
Published: July 2007

The wave‐propagation characteristics of a cable installed within a tunnel has been investigated. The transient characteristic of this cable system differs from that of a cable system in which the cables are buried without tunnels. The transient characteristic is heavily dependent on both the distance from the cable to the tunnel wall and the physical parameters of the tunnel. A modeling method of the cable system installed within a tunnel is proposed based on investigation.

A field measurement of transient sheath voltages on a 275 kV crossbonded cable system is made. Numerical results obtained using the proposed model agree well with field test results; thus the accuracy of the modeling method proposed in this paper is confirmed.

The effects of the circuit parameters, such as inductance of the sheath bonding wire and the equivalent capacitance of the sheath protection arrester, are studied.
A sensorless brushless dc motor system
Authors: Ogasawara Satoshi , Suzuki Kazuto , Akagi Hirofumi
Published: July 2007

This paper describes a brushless dc motor system without position or speed sensor. The brushless motor consists of a permanent magnet synchronous motor and a voltage‐source inverter capable of controlling the amplitude and frequency of voltage. The rectangular‐shaped stator current with a conducting interval of 120° (electrical) is controlled to be in phase with the trapezoidal back electromotive force. This results in producing maximum torque. Variable speed is achieved by adjusting the average motor voltage similarly to chopper control of dc motors.

In this paper, two sensorless position detecting methods, i.e., an “indirect method” suited for the lower‐speed range and a “direct method” suited for the higher‐speed range are proposed. The combination of the two makes it possible to detect the rotor position over a wide‐speed range. Furthermore, a speed‐sen‐sorless PLL control is proposed in applying the principle of the direct method. Experimental results obtained from a prototype brushless dc motor are shown to confirm the validity of the sensorless drive. The starting procedure of the motor also is discussed because it is impossible to detect the rotor position at a standstill.
Flashover phenomena in positive rod‐to‐plane air gaps under impulse and DC voltages
Authors: Tsuneyasu Itaru , Nisijima Kiyoto , Izawa Yasuji
Published: July 2007

Discharge phenomena in positive rod‐to‐plane air gaps under lightning impulse and dc voltages were investigated.

Under impulse voltages, the 50 percent flashover voltages agree with the 50 percent corona inception voltages only in a gap shorter than a certain value dc which increases with the rod diameter φ. The 50 percent flashover voltage at dc rises at a rate of about 14 kV/cm with dc in the range of dc < 2.8 cm (φ ⩽ 1.5 cm), and then it rises at a rate of about 5 kV/cm. Experimental results show that the flashover process in the former region (termed the Gp process) is different from that in the latter region (the Lp process).

Under dc voltages, the critical gap length, at which the first corona may lead to flashover without any succeeding streamer corona, corresponds to dc under impulse voltage. In a gap shorter than dc flashover occurs through the Gp process (φ ⩽ 1 cm) or Lp process (φ ≥ 2 cm), but in gap longer than dc flashover may occur through another process which cannot be seen under impulse voltages.

In this paper, those flashover characteristics and processes are described on the basis of experimental results and photographic observations with an image converter camera.
Distributed architecture for energy management D‐structure
Authors: Kokai Yutaka , Fukuhara Akira , Morita Ken'Ichi , Kanke Tatsunori , Kata Mamoru , Hayashi Tatsuo , Takenuki Toru
Published: July 2007

Electric power systems are expanding in size and complexity, and the requirement for the energy management system (EMS) is becoming more important. In this computer control system, a single control computer is used mainly as the primary computer and its software is very complicated because of its hugh number of small, quick tasks to obtain high response speed. Therefore, much effort is needed to develop and modify the programs, and the responsiveness of this centralized architecture varies greatly when many faults occur in the power system.

This paper describes a new distributed architecture for the EMS. Distributed processors execute the functions cooperatively with periodic access to the common bulletin board database in which information about the power system exist. This architecture facilitates the software development and maintenance, and it also enhances the performance by the parallel processing of the distributed functions.
Development of three‐dimensional electric field computation system by surface charge method
Authors: Hanai Etsuyo , Oyama Mitsutoshi , Aoyagi Hirokuni , Murase Hiroshi , Oshima Iwao
Published: July 2007

This paper describes development of three‐dimensional electric field computation system by surface charge method. Using this system, both potential and electric field in the case which includes resistance or true electric charge can be calculated. And this system is able to be connected to the pre‐post processors, which is useful for us to make arbitrary shape and to display results of analysis.
Comparisons of direct‐current breakdown characteristics in dry air and SF6 gaps using a parallel‐plane arrangement with variable height protrusion
Authors: Nishijima Kiyoto , Tsuneyasu Itaru
Published: July 2007

Breakdown voltages in uniform and quasi‐uniform field gaps are sensitive to the presence of small protrusion on the electrode surface in SF6 at high pressures. The aim of the present work is to study direct breakdown and corona stabilized breakdown for the transitive region from uniform to nonuniform gap in dry air and SF6 at low pressures up to a critical pressure when direct breakdown takes place by a leader discharge crossing the gap in SF6. In a parallel‐plane gap with a variable‐height protrusion subjected to the dc voltage, corona onset voltage is remarkably controlled by the protrusion height. The present electrode arrangement has the advantage of directly measuring the minimum critical guiding field strength for the propagation of a streamer discharge at corona onset.

The experimental observations have been explained qualitatively on the basis of a streamer model and precise electric field calculations of gap.
Evaluation of a cogeneration system treating and utilizing municipal refuse cleanly and efficiently for district heating and cooling
Authors: Pak Pyong Sik , Nakamura Kenichi , Suzuki Yutaka
Published: July 2007

This paper is a comprehensive analysis of the characteristics and economics of systems which treat municipal refuse and utilize its contained energy as the energy source to generate not only electric energy but also the heat energy for district heating and cooling. The following two systems are investigated: (1) System A which is composed of a plant to incinerate municipal refuse and a cogeneration system with a bleeder/condensate turbine power generation unit; and (2) System B which is the system proposed here and is composed of a pyrolysis furnace for treating municipal refuse, a two‐stage‐cleaning process for refining generated pyrolysis gas, and a cogeneration system constructed by a combined cycle power generation unit using cleaned pyrolysis gas as its fuel gas. It was estimated that the maximum net power‐generating efficiency of System B is 24.8 percent, and is higher by 63 percent compared to that of System A.

Economics of the systems have also been investigated, and it was shown that System A if the extra electric energy of the systems can be supplied directly to various facilities, which is different from the case where it should be sold only to electric companies. Effects of changes in major social and technological factors which affect the economics of the two systems are also analyzed, and it was shown that the possibility is considered to be high that the economics of System B will become more advantageous than that of System A in the future.
Sliding mode control with adaptive vss observer
Authors: Chen Yi‐Feng , Mita Tsutomu
Published: July 2007

The conventional sliding mode control or variable structure control (VSC) of a nonlinear uncertain system is well known for its robust property and simplicity of control law. However, the use of either is permitted only on the assumption that the upper bound of parameter variation or nonlinearity is known and that the complete information about the state is available. Although the former has recently been solved with adaptive robust control theory, the latter does not appear to be solved.

This paper attempted to solve this problem using the technique of VSS adaptive robust control theory. That is, a VSS adaptive observer and a sliding mode control incorporated with this observer was proposed. The robust stability of the closed system can be proved applying Lyapunov's second method.
A magnetic semiconductor protective device with built‐in multifunction sensors
Authors: Seki Kyoshiro , Osada Hiroshi , Chiba Shigeki , Shida Jun‐Ichi , Murakami Koichi
Published: July 2007

This paper describes protectors and multisensors using ferrite‐magnetic semiconductor (FMS). Useful FMS devices with Curie temperature from −15° to 300°C, in which the ferromagnetic properties below are retained below the Curie temperature, can be produced.

The magnetic and electrical properties of FMS depend on temperature, humility, and gas concentration and can perform a switching function. The magnetic reluctance increases with temperature and approaches a maximum at the Curie temperature, but is independent of humidity or the concentration of combustible gases. The semiconducting resistance decreases from 225 to 170 kω as the humidity changes from 50 to 90 percent The FMS's specific dielectric constant above 900 is dependent on temperature, humidity, and the concentrations of combustible gases, including acetone, methanol, and ammonia In methanol, the capacitance increases from 0.18 to 0.5 nF as the concentration rises from 0 to 850 ppm. Bidirectional switching characteristics appear at voltages above 250 V. These characteristics should have practical applications in protective and measuring instruments. An overheating/overvoltage protector with temperatwe/humidity/gas concentration sensors composed of two annular FMSs is described.
Analysis of terminal voltage waveform of AC exciting synchronous generators
Authors: Ide Kazumasa , Takahashi Miyoshi , Ito Motoya , Tsuji Eiji , Yasaka Yasuhiro , Fujimoto Takashi
Published: July 2007

Recently, adjustable speed hydroelectric power systems have been developed. In those power systems, ac exciting synchronous generators are used instead of the ordinary salient‐pole‐type synchronous machines. However, some higher harmonic sequences are included in the distribution of air‐gap magnetic flux density and in the terminal voltage waveform of the ac exciting synchronous machines because these machines have open winding slots. To develop better machines without terminal voltage waveform distortions, an evaluation method of the terminal voltage harmonics has been needed.

This paper describes the mechanism of higher harmonics generation qualitatively and proposes an analytical method of no‐load terminal voltage waveforms on the basis of two‐dimensional magnetic field analysis considering movement of the rotor for quantitative higher harmonics analysis. The analytical results of higher harmonics show good agreement with the experimental ones.
A saturable reactor‐assisted soft switching PWM DC‐DC converter
Authors: Hamada Satoshi , Ogino Yasumasa , Nakaoka Mutsuo
Published: July 2007

Owing to the demand to increase the power density of switched‐mode power converters, resonant topologies have attracted much attention because of their low switching losses and low EMI. However, they require relatively large resonant components and necessitate high current or voltage ratings at semiconductor devices.

This paper describes a new soft‐switching PWM full‐bridge DC‐DC converter which can overcome these drawbacks by utilizing a small saturable reactor. The principles of operation and the steady‐state characteristics are illustrated and the role of the saturable reactor is discussed. Moreover, the voltage and current stresses for active and passive components are also presented.

To verify the results, experiments were performed with a 350 W, 500 kHz prototype converter. They demonstrated that the converter achieves soft switching in a wide load range with no substantial increase in voltage and current stresses on active and passive components.
Impulse insulation characteristics of a composite insulation system having a wedge gap in SF6 gas
Authors: Inui Akifumi , Yamada Shin , Murase Hiroshi , Teranishi Tsuneharu , Ohshima Iwao
Published: July 2007

Impulse insulation characteristics were investigated in a composite insulation system having a wedge gap in SF6 gas. The partial discharge inception voltages of wedge gaps with various types of film were measured and compared with the calculated breakdown voltages estimated from Paschen's curve of SF6 gas. Also discussed is how the charge accumulated on the film surface due to a partial discharge had an effect on the creepage breakdown voltage. Partial discharge inception voltages in wedge gaps were higher with higher SF6 gas pressures and with lower film permittivities.

Creepage breakdown voltages depended little on gas pressures or on creepage distances. The dependency of breakdown voltages on gas pressures and the effect of polarity on the breakdown voltage differed with the types of film. This may be partly because the charge on the film due to partial discharge had an effect on the discharge propagation, and that charging of the film differed with the types of film.
Digital input filters for measurement, control and protection in electric power systems
Authors: Kido Mitsuyasu , Chiba Tomio , Kudou Hiroyuki , Kawakami Junzou , Kawai Tadao
Published: July 2007

Power system control and protection equipment is subject to especially stringent sensitivity and operational reliability requirements.

Projected digital signal processing systems suitable for electric power systems fulfill these requirements by means of 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 spectra 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 a high resolution equivalent to 14‐bit conversion.

This paper describes the design concept and the operating characteristics and illustrates applications to current differential relays, distance relays and power system controllers.
Dynamics of an HVDC system in the presence of unbalanced AC transmission line faults and a stabilization scheme
Authors: Takasaki Masahiro , Takenaka Kiyoshi
Published: July 2007

The introduction of an HVDC system into the trunk power supply system requires transmitting as much dc power as possible for improving the whole ac/dc system stability. The continued operation scheme of an HVDC system which makes it possible to operate even under very low commutation bus voltage is adopted to cope with such system requirement. Further stability improvement can be achieved by adding damping control which modulates converter active and/or reactive power.

To take full advantage of these control effects, it is essential that the HVDC system can maintain stable operation during the ac system faults and reclosing. Particular attention should be given to a repetitive commutation failure following the unbalanced ac transmission line faults.

This paper discusses first the cause of the repetitive commutation failure when supplied with unbalanced ac system voltage based on an experiment using the CRIEPI AC‐DC Power System Simulator. Then a stabilization control scheme with an on‐line extinction angle estimation is proposed and the effect is verified by digital simulation.
An experimental study of the flux control characteristics of a magnetic fluid controlled by a parallel or orthogonal magnetic field
Authors: Oka Hideo
Published: July 2007

This paper presents experimental results of the flux control characteristic and the inductance control characteristic of magnetic fluid which is controlled by the permanent magnets. Two kinds of magnetic field, parallel and orthogonal, are discussed comparatively. The position between the magnetic fluid and the permanent magnet determines the magnetic field. The results are useful when employing magnetic fluid as a sensor or a control element.
Combined system of a series active filter and a shunt passive filter—an optimum design of the shunt passive filter
Authors: Fujita Hideaki , Akagi Hirofumi
Published: July 2007

The combined system of a series active filter and a shunt passive filter that is proposed by the authors has the ability to eliminate a major disadvantage of shunt passive filters, namely, harmonic amplification. The series active filter needs a much smaller kVA rating than a conventional shunt active filter, and as a result, the combined system has good filtering characteristics and high efficiency.

This paper presents an optimum design of the shunt passive filter that makes possible a great reduction in the required kVA rating of the series active filter. It can minimize the peak voltage across the series active filter and reduce the required kVA rating of the filter to 60 percent. A computer simulation geared to practical applications of large three‐phase. twelve‐pulse thyristor rectifiers is used to compare the compensation characteristics of the optimized system with those of a combined system that uses a conventional shunt passive filter. Experimental results obtained with a laboratory model of the filter corroborate the design approach.
A brushless three‐phase synchronous motor using the armature winding as both load and DC excitation winding
Authors: Shibata Fukuo , Fukami Tadashi
Published: July 2007

This paper presents a new brushless three‐phase synchronous motor which has no exciter. The technique applied to the motor provides an effective way for conventional brushless synchronous motors to simplify the system configuration. The stator of the motor is equipped with a double‐star connected armature winding which has two neutral points. The rotor is a cylindrical one, which is equipped with a two‐phase field winding. The field winding is connected with shaft‐mounted rectifiers.

A dc voltage is applied to the two neutral points of the armature winding to obtain the rotor excitation when the motor is operated at synchronous speed. At that time. the armature winding acts as a stator dc exciting winding while also acting as a load winding.

In this paper the principle and characteristics of the motor are described. and the experimental results are shown. It is confirmed that with a 2‐kW experimental machine, the proposed motor has good performance. For example, by adjusting the stator dc current, this motor power factor can easily be controlled within a wide range.
Levitation coil length optimization of a magnetically levitated train
Authors: Shibata Masayuki , Maki Naoki , Saito Toshio , Kobayashi Takashi
Published: July 2007

An experimental line of a magnetically levitated train (MAGLEV) using superconducting magnets (SCM) is now under construction in Yamanashi Prefecture. In the MAGLEV system, the levitation coils are mounted in the side walls. The induced current of the levitation coils generates magnetic flux that includes higher order harmonics. These harmonics generate eddy currents at the surface of the vacuum vessels of the SCM. Forces produced by interaction between the eddy current and the static magnetic field of the SCM cause evaporation of liquid helium, or SCM quenching in the worst case. The number of levitation coil layer is now restricted to one, but by removing the restriction, it is possible to reduce the amplitude of the harmonics of the magnetic flux. In this paper, the relationship of the flux amplitude to the levitation coil length is investigated; it is found that there is an optimum length at which the amplitude is minimized.
Effects of silicon content, thickness and heat treatment on iron loss properties of high silicon electrical steel sheets
Authors: Tanaka Yasushi , Namikawa Misao , Hiura Akira , Bi Xiao Fang , Takada Yoshikazu
Published: July 2007

The magnetic properties of high‐silicon steel sheets ranging in thickness from 0.35 to 0.03 mm and silicon content from 3 to 7.5 percent is investigated. The minimum iron losses are obtained with the silicon higher than 6.5 percent at the high‐frequency range over 30 kHz. The sheet thickness dependency index m is estimated. The heat treatment effects to soft magnetic properties also are studied.
Effect of dimension ratio on the magnetic properties of tape‐wound toroidal core with ac excitation
Authors: Saito Koichi , Shinya Kunihiro , Miyazawa Eijiro
Published: July 2007

Tape‐wound toroidal cores are used widely as magnetic devices of electronic equipment and instruments. In the design of equipment employing magnetic cores, it is necessary to know the relation between the magnetic properties of the core and the magnetic properties of the material. This paper describes the effect of the dimension ratio of the core on the magnetic properties for the sinusoidal flux waveform drive condition. In carrying out the analysis, a mode analysis in which the magnetization characteristics are approximated by a piecewise‐linear curve is adopted. From the results obtained by the numerical analysis, local flux waveforms and exciting current waveforms of the core are shown. As a result, the relation between iron loss and magnetizing apparent power of the core and the dimension ratio is derived. These results were confirmed by experiments.
Fault‐locating method using harmonic components of the arc‐voltage waveform
Authors: Okazaki Masayuki , Inaba Tsuginori
Published: July 2007

This paper describes a new type of the fault‐locating method by using voltage and current values measured in a substation or transmission lines. This method is based on the impedance method and consists of the following items: (1) analysis of harmonic components in voltage waveforms measured in the substation; (2) estimation of the arc fault voltage on the lines; (3) calculation of the line impedance voltage drop; and (4) determination of the fault‐locating distance.

The availability of this method was confirmed by arc fault tests on 6‐kV cable and overhead distribution lines. As a result, the fault‐locating error of this method was proved to be roughly less than 10 percent.
Dual voltage converter with improved power factor and enabling voltage control
Authors: Mashiko Tomomi , Kamatani Masahiko , Sato Noriaki
Published: July 2007

In this paper, a novel version of the dual voltage converter is presented with improved voltage regulation and enabling a wide range of voltage control by using self‐turn‐off devices (power transistors) instead of diodes. Further, this system operates with unity displacement factor. We have obtained the analytical expressions of this circuit. The results are, however, quite complex. We could calculate values of the voltage and current waveforms by using a computer. The calculated values are essentially in agreement with the experimental values.

Experimentally, an ideal load characteristic with null voltage regulation was obtained by the conduction angle control for power transistors. Further, a wide range of voltage from 220 V to 39 V was obtained.

A disadvantage for this system is the requirement for snubber circuits with a larger value of capacitor in order to suppress the surge voltages at turn‐off periods.
High‐frequency link‐type dc/ac converter for ups with a new voltage clamper
Authors: Tokunaga Norikazu , Yamato Ikuo , Matsuda Yasuo , Amano Hisao
Published: July 2007

This paper proposes a new type of high‐frequency dc/ac converter developed for flexible, compact and high‐efficiency uninterruptible power supply (UPS) systems. The proposed dc/ac converter consists of a high‐frequency inverter, a high‐frequency transformer and a cycloconverter with a new voltage clamper. This cycloconverter is capable of being operated by both source‐commutation and self‐commutation (commutation by turning off the switching device). Consequently, by choosing between the two commutating methods, based on consideration and the internal voltage drop caused by commutating reactance, a compact and efficient UPS can be realized. The voltage clamper effectively reduces power loss of the conversion system. Fabrication of a 10‐kVA high‐frequency link‐type dc/ac converter is described and its loss reduction effect is demonstrated.