bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reduction of higher harmonic sequences in terminal voltage of an AC exciting synchronous generator using magnetically anisotropic slot wedges
Authors: Ide Kazumasa , Watanabe Masatoshi , Sato Masaki , Takahashi Miyoshi , Takahash Noriyoshi 
Published: July 2007

AbstractThis paper describes relationships between characteristics of a magnetically anisotropic slot wedge and voltage higher harmonics in an ac exciting synchronous generator terminal due to permeance ripple caused by an open‐slot‐type rotor. From the relationships obtained, practical guidelines were formulated for machine designs applying the magnetically anisotropic slot wedge. The results are as follows.

(1) Equivalent permeability of the magnetically anisotropic slot wedge became isotropic wedge permeability for air‐gap flux ripple.
(2) Two ways were identified to reduce voltage‐higher harmonics by using the slot wedges.
(3) The level of leakage flux passing through the anisotropic slot wedge was determined only by its permeability in the width direction.
(4) Effectiveness of the magnetic anisotropic slot wedges inserted into the stator slots was verified from experimental results using a model machine of the open‐ slot‐type rotor.
A novel islanding protection system for photovoltaic inverters
Authors: Okado Chihiro , Kimoto Kenichi , Shinohara Hirofumi , Ichinose Takashi 
Published: July 2007

AbstractIt is very difficult to detect an islanding condition of a power distribution line with conventional voltage or frequency relays while the output power and the load power of utility interactive PV inverter units are in nearly balanced state in both active power and reactive power. This is because a sufficiently large voltage or frequency change cannot be expected at such a balanced state.Many studies have been reported so far to complement dead bands in combination of active and passive methods to prevent the islanding, but none of them has been successful.This paper presents the principle of a new active method called slip mode frequency shift (SMS). With this method the reactive power between the inverter and the load is made unbalanced intentionally to cause the frequency to shift as if it slips down a slide. The performance when the dead bands are eliminated effectively in the range of practical use has been examined through simulation and experiments.
A zero‐current‐switching based three‐phase pulse width modulation inverter
Authors: Fujita Hideaki , Akagi Hirofumi 
Published: July 2007

AbstractWith the remarkable progress of switching devices, the switching frequency of a voltage‐source PWM inverter has become higher and higher. A high‐frequency PWM inverter gives great benefits in the reduction of current ripples and acoustic noises. However, high‐frequency hard switching causes the increase of switching losses and EMI to be solved.The authors propose a zero‐current‐switching based three‐phase PWM inverter which has small resonant circuits on the ac side. The current flowing in a switching device is a sum of the resonant current and the load current. Since the switching device is turned on and off at zero current, the switching losses and electromagnetic noises are greatly reduced. This paper described the principle of the zero current switching operation, the design of the resonant circuits and the control scheme for the new soft switching inverter. Moreover, it shows interesting experimental results obtained by the zero‐current‐switching PWM inverter which drives an induction motor of 2.2 kW.
Development of automatic fault point locating and sectional isolating system for power distribution line
Authors: Kakimoto Hitoshi , Hayashi Takehiro , Handa Hirosi , Yukihira Kenzi , Okamura Yukio , Odaka Naotaka 
Published: July 2007

AbstractThis paper describes the development of the Automatic Fault Point Locating and Sectional Isolating System. This system locates a single‐line‐to‐ground fault point at each pole by using ground‐current sensors, and isolates the faulted section by controlling pole switches with no outage of unfaulted sections.The ground‐current sensor is connected to the line between allied ground terminals of pole devices and grounded conductor. It detects a ground fault current of more than 0.64 amperes that is determined so as to avoid an unexpected operation by stray current, but to detect the fault current accurately, and sends out an emergency signal with time delay of 0.1 s.Sectional isolation starts when both the emergency signal from the sensor and relay operation signals from a substation are received and ends within a feeder circuit‐breaker tripping time of 1.5 s.
Modeling by petri net with place invariants for sequential control systems
Authors: Cai Yigang , Nishii Ikuya , Sekiguchi Takashi 
Published: July 2007

AbstractIt is more difficult to model a discrete system than a continuous system. Recently, a great number of applications of Petri nets to the design and the analysis of discrete systems has been reported. However, a common problem in its applications is that the required computer memories and the computation times increase explosively in accordance with the increase in the number of systems components. Some methods to divide or to reduce Petri nets have been proposed to solve this problem. Although the liveness and boundedness of Petri nets are held in the divided or reduced Petri nets, the reachability problem cannot be solved by these methods.This paper proposes another method to model discrete systems by Petri nets with place invariants. A sequential control system will be described as a typical kind of discrete system, and its structural characteristics will be used in modeling. Each component of a sequential control system will be modeled by a sub‐Petri net with place invariants. There are many components in one sequential control system, but not each one is necessarily complicated. Most sub‐Petri nets do not have so many places or transitions. It is also well known that a Petri net with place invariants is bounded and can be live by placing sufficient tokens into its initial marking. Besides, the reachability problem is not so difficult to solve in a small sub‐Petri net. Further, an activating relation to combine two or more sub‐Petri nets is defined, and some rules to reduce conflicts among enabled transitions will be described for simulations.
Improvement of dielectric strength on transformer winding using new aramid paper
Authors: Endoo Kaoru , Uwano Yoshito , Hiraishi Kiyoto , Oonuma Toshiyuki , Uemura Ryuuji 
Published: July 2007

AbstractLarge power transformers using perfluorocarbon liquid have advantages of high dielectric strength, excellent cooling ability, and nonflammability.To make the transformer more compact, it is very important to improve the insulation material.Recently, the authors succeeded in developing a new type of aramid insulation paper which has no fluff on its surface to avoid field concentration.In this study, an outline of the developed paper and the experimental results of the insulation strength on turn‐to‐turn and intercoil models are described.It was found that the new aramid paper increases the insulation strength 1.2 (turn‐to‐case) to 1.7 (intercoil case) times that of the existing insulating paper.
Magnetic‐shield type superconducting fault current limiter with high Tc superconductors
Authors: Kajikawa Kazuhiro , Kaiho Katsuyuki , Tamada Noriharu , Onishi Toshitada 
Published: July 2007

AbstractThe continuous development of electric power utilities has led to the increase in problems concerning fault currents. The use of fault current limiters, which suppress fault currents below a certain level, has been examined widely. The authors have studied a superconducting fault current limiter that is based on the magnetic shielding characteristics of superconductors.In this paper, three kinds of fault current limiters with high Tc superconductors and their results tested at liquid nitrogen temperature are presented. The experimental results show that the impedances of limiters in the fault condition became higher than those in the normal condition but were lower than the anticipated ones.Next, a numerical calculation model to analyze the experimental results is presented. The calculation results with this model agreed with the aforementioned experimental ones very well.From these studies it is concluded that it is necessary for the sudden transition from the superconducting state to the fully resistive state to be caused by suitable means.
A new self‐excitation scheme for three‐phase synchronous generators
Authors: Fukami Tadashi , Miyamoto Toshio , Shibata Fukuo , Taka Koji 
Published: July 2007

AbstractA new self‐excitation scheme has been developed for three‐phase synchronous generators. The generator that uses this scheme behaves as a flat‐compound machine without automatic voltage regulators. The stator of the generator is provided with an armature winding that generates the fundamental and 2nd‐harmonic mmfs. The rotor is equipped with a field winding and a harmonic winding. The harmonic winding is magnetically coupled to the 2nd‐harmonic mmf produced by the armature winding. The current flows in the stator armature winding by way of a three‐phase set of capacitors connected across its three‐phase terminals and the ac voltage is induced in the rotor harmonic winding due to the armature 2nd‐harmonic mmf. By connecting the harmonic winding to the field winding through a rectifier circuit, self‐excitation of the generator is obtained. This excitation scheme is both self‐excited and brushless, and no exciter is required. Additionally, voltage regulation due to load variation can be improved by connecting suitable capacitors.In this paper the operating principle and circuit configuration of the generator are explained and the experimental results using a 1‐kVA prototype machine are shown. The generator characteristics are theoretically clarified by approximate analysis, and appropriateness of the theory and the usefulness of the proposed scheme are experimentally confirmed.
An experimental investigation of the electrical breakdown phenomena of interface insulation in prefabricated‐type joints
Authors: Takahashi Yoshihisa , Hara Makoto 
Published: July 2007

AbstractTo establish the reliability of the insulating performance of prefabricated‐type joints (PJs), dielectric breakdown characteristics of interface insulation were studied.Using two types of electrodes, which simulate the interface configuration in an actual 275‐kV PJ, ac and impulse BDSs, together with long‐term performance of the interface, were evaluated under various conditions. Among the many factors which would influence the insulating characteristics of the interface, the effect of the silicone oil layer, as well as the applied external pressure, were examined. It was determined that the BDSs were influenced greatly by silicone oil application, by the applied interface pressure, and by the pretreatment of the surface of XLPE insulation. On the basis of the result of experiments, the functions of the silicone oil layer in the insulation interface of the PJ were examined.The authors concluded that the thinner silicone oil layer in the insulation interface is favorable for the establishment of the insulation interface of the PJ.
Analysis of primary‐on‐slider ultrasonic piezoelectric actuators and experiments on multidegree of motion freedom plane actuator
Authors: Hoshi Nobukazu , Kawamura Atsuo 
Published: July 2007

AbstractRecently, various machines and tools have been miniaturized, and with this trend, the size of an actuator becomes a very important factor. An ultrasonic actuator is different from other actuators using electromagnet force in the driving principle. The structures of an ultrasonic piezoelectric actuator is simple. An ultrasonic actuator converts the ultrasonic mechanical energy to mechanical thrust force by a friction force. Based on this idea, various ultrasonic actuators have been proposed and experimentally constructed.In this paper, the basic characteristics of a piezoelectric actuator are analyzed theoretically. The relationship between the thrust force and the weight force is clarified and verified by experiments. Various prototypes of plane ultrasonic piezoelectric actuators are constructed experimentally, and the fundamental characteristics are measured.
Inertia moment identification in the average speed‐type instantaneous speed observer
Authors: Okamura Yusaku , Chun Yeonghan , Hori Yoichi 
Published: July 2007

AbstractIn recent servomotor control systems using highspeed microprocessors, it is difficult to obtain accurate speed information by using a low‐resolution shaft encoder because encoder pulses are very sparse in the low‐speed range. To overcome this problem, the instantaneous speed observer is proposed, system stability is improved, and strong disturbance rejection control is realized. However, when the inertia moment changes, the estimated instantaneous speed has error because the observer uses the nominal value of the inertia moment to calculate the instantaneous speed. For this reason, the identification method of the inertia moment for the “position input‐type” speed observer is proposed but it operated at about 50 rpm speed command. This paper proposes some novel identification methods for the “average speed‐input type” instantaneous speed observer and identifies the inertia moment in the very low speed range below 1 rpm.
Research on synchronous type and induction type levitated rotating motor
Authors: Ohishi Tetsuo , Shimura Seiji , Okada Yohji 
Published: July 2007

AbstractA general solution of levitation control applicable to PM synchronous and induction type rotating motor is presented. It is intended for a single rotor to have both magnetic bearing and rotating motor. The rotational control is achieved with the traditional P pole magnetic flux, while the radial force is controlled with either P + 2 or P ‐ 2 pole magnetic flux in the stator. In the previous work, the proposed general theory of levitated motor is successfully confirmed with no load experiments.In this paper, the load capability of the levitated motor is tested using a horizontal‐type experimental setup. The stator has eight concentrated wound electromagnets, each of which is controlled individually by a DSP and power amplifier. The radial load is the gravity of the rotor, while the produced rotating torque is measured with a variable torque load system. The results obtained are discussed in detail.
Stabilization of inter‐area and/or oscillatory modes in large‐scale power system by voltage impedance power system (VIPS) apparatus based on decentralized control scheme
Authors: Nagata Masaki , Yokoyama Akihiko , Sekine Yasuji 
Published: July 2007

AbstractNew technologies such as power electronics have made it possible to change continuously the impedance of a power system not only to control power flow but also to enhance stability. A power system incorporating a variable impedance apparatus such as a variable series capacitor (VSrC) and high‐speed phase shifter (HSPS) is called VIPS (Variable Impedance Power System) by the authors.This paper proposes a novel control method of VIPS apparatus such as VSrC and HSPS installed at an interconnecting point for stabilizing inter‐area unstable and/or oscillatory modes. The proposed design method of the control system is a kind of hierarchical decentralized control method of a large‐scale power system based on a Lyapunov function.Under the proposed control scheme, each subsystem can be stabilized independently by local controllers such as AVR, speed governor and PSS, and then the whole interconnected system can be stabilized by VIPS apparatus taking into account interactions between subsystems. The effectiveness and robustness of the VIPS apparatus control are shown by numerical examples with model systems including a large‐scale power system.
An analysis of generation mechanisms of transitional peak current in sense‐emitter current for IGBTs with current sense and techniques to remove it
Authors: Hagino Hiroyasu , Yamada Tomihisa , Uenishi Akio , Tomomatsu Yoshifumi 
Published: July 2007

AbstractIt is important to remove the transitional peak current in sense‐emitter current which is due to dynamic current‐sharing during turn‐on for a design of IGBTs with current‐sense used protection against overcurrent and short circuit. But this analysis has been scarcely investigated.This paper clarifies generation mechanisms of the transitional peak current by simulations and experiments using a parallel operation model and reports on techniques to remove it.The following results were obtained.(1) In the two paralleling devices model which consists of a sense cell and main cells, the transitional peak current occurs during turn‐on when a sense cell turns on faster than main cells. In this case, the main parameters that effect dynamic currents imbalance are gate resistance (Rg) and gate threshold voltage (Vth).(2) In dynamic currents imbalance based on individual Rg and Vth among main cells, it may be treated as a two‐paralleling devices model which consists of a sense cell with Rgs and Vths, and main cells with average values Rgm and Vthm.(3) The transitional peak current can be removed by the design of Rgs and Vths in a sense cell are larger than average values of Rgm and Vthm in main cells.(4) On trial IGBTs with current sense Vths in a sense cell is different from the average‐value Vthm in main cells to change impurity concentrations of each channel. It was confirmed that the transitional peak current in sense‐emitter current can be removed by the design that Vths in a sense cell is larger than average value Vthm in main cells.
Substation simulation system using virtual reality technology
Authors: Mizukami Yuichi , Morita Shigeru , Asano Kunihiro , Kamiji Noboru 
Published: July 2007

AbstractAn indoor distribution substation simulation system based on virtual reality technology has been developed. The system is designed to give the user the feeling of actually touring a substation for routine inspection. Various states of the substation facilities, such as the opening and closing of the doors and the disconnectors as well as the relocation and extension of the installations, can be simulated. In the event the user approaches the energized components of the equipment and fails to keep the specified insulation distance from them, the system first sounds an alarm, and then a flashing red light on the display warns of passage beyond the safety point and that the operation has suffered an electric shock. Validation of equipment operating procedures, training of unskilled workers and work‐schedule preparation can be upgraded by using this system.
The principle and fundamental characteristics of brushless three‐phase synchronous induction motor with two stators
Authors: Inoue Kenji , Ohnogo Yukio , Yamashita Hideo 
Published: July 2007

AbstractBrushless three‐phase synchronous motor involving a rotating ac exciter on the same shaft as the motor and with the windings linked through a shaft‐mounted rectifier is widely used as medium and large capacity machines. However, the motor needs to fit with damping windings for self‐starting outside of the field winding in the rotor and needs to equip discharge resistance with complex electronic device to dispose of electromagnetic force induced in the field winding at starting. Therefore, the rotor structure is very complex, and there are disadvantages, especially for the robust and highly reliable motor that is desired.To solve the problem found in traditional motors, the authors proposed a brushless three‐phase synchronous induction motor with two stators and one wound rotor. This problem is solved because the proposed motor is of two‐stators structure: the rotor winding operates as a secondary winding of induction motor at starting and as the field winding at synchronous operation.The motor can self‐start as a wound‐rotor induction motor without external secondary resistance. Therefore, discharge resistance is not necessary; the starting equipment is very simple and the rotor structure is robust. It is possible to start with high torque.In this paper, the basic constitution of the proposed motor and the principles of operation are described in detail. The experimental results at starting and pulling into synchronism are shown for confirming the principles of operation and the experimental and numerical results of the starting characteristics. The load ones and the generating ones are shown and then the practical use of the proposed motor is confirmed.
A new method for discrimination of ground faults causes in distribution lines
Authors: Watanabe Makoto , Kotanishi Kazuji , Nakamura Osamu , Kurioka Hideaki , Hukui Sukenori , Tuji Katunori 
Published: July 2007

AbstractSince most problems in distribution lines are ground faults, the technology to distinguish the causes in the distribution lines will be very useful in preventing faults beforehand or, at least finding any problems at an early stage.The waveforms of ground faults which were collected from data concerning problems in the distribution lines and ground fault experiment are analyzed. The technology which could predict classified groups drawn from the scale of I0 (the waveform of ground fault current) and V0 (the waveform of ground fault voltage), and both of them in the ground faults is studied.The results demonstrated that I0 could be classified into three groups, that is, leaking ground faults are sine curve shaped, gap discharge ground faults are triangular, and intermittent discharge ground faults are needle shaped.Also, simulated equivalent impedance of the causes of ground faults by EMTP is calculated. Furthermore, the influence caused by the condition of the distribution lines is investigated. With these results, a technique is proposed which could predict the cause of problems in ground faults.
Optimization of failure diagnosis procedure based on diagnosis error loss
Authors: Kohda Takehisa , Inoue Koichi 
Published: July 2007

AbstractBased on the results of its inspection items, the failure diagnosis system identifies the cause of system failure. The role of failure diagnosis is to identify the system state correctly. However, diagnosis errors may be caused by sensor failure or operator errors, which lead to serious damage or unnecessary protective actions. The effect of an error depends on the system condition. In the design of a failure diagnosis procedure, not only diagnosis error probabilities, but also the effect of diagnosis error on the system must be considered.This paper proposes the optimization of failure diagnosis procedures based on diagnosis error loss. The optimal procedure that minimizes the expected loss caused by inspection errors is developed for two cases: one where all results of inspection items are given simultaneously, and one where an inspection item is examined sequentially. In the former case the optimal failure diagnosis logic is obtained, while in the latter case the optimal test sequence is developed. Illustrative examples show the merits and details of the proposed method.
The development of bi‐based high‐temperature superconductor and coil
Authors: Ogiwara Hiroyasu , Horigami Osamu , Yamada Yutaka , Satou Masako , Kitamura Tasuku , Hasegawa Takayo 
Published: July 2007

AbstractAg‐sheathed Bi‐2223 superconducting oxide conductors with a critical current density of 66,000 A/cm2 at 77 K and coils that have generated magnetic fields of approximately 1.5 Tesla at 4.2 K have been successfully developed. The conductors consist of piled‐up bundles of four to six sheets of element tapes with transport currents of approximately 200 Amps. The core size limit (CSL) prevented the production of single conductors that had the capacity to transport a current as high as 200 Amps at 4.2 K. Until now, it was difficult to develop a conductor having both high critical current density and the capability of transporting a large amount of current simultaneously. The role of CSL in large scale applications of high temperature superconducting oxides is discussed.