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Power capacitors are highly reliable due to their completely enclosed configuration. They are relatively trouble-free over the long term. However, their dielectric strength can be reduced due to some stresses, including overvoltage application or thermal degradation of the insulation material during long periods of operation; these events can result in dielectric breakdown of capacitors in extreme cases. Since almost all power capacitors with oil-impregnated paper have been operated for more than twenty years, some kind of failure should be expected. To prevent these incipient accidents, it is important to examine the insulation deterioration mechanism and evaluate the degree of deterioration before capacitor breakdown. To establish a diagnostic method of deterioration of the capacitors with oil-impregnated paper, we have conducted thermally and electrically accelerated deterioration tests and investigated the changes of their characteristics. Based on the experimental results we obtained, it can be concluded that the behavior of the oil-dissolved gases can be used as a useful index to diagnose the insulator deterioration of these capacitors. [ABSTRACT FROM AUTHOR]

A multiagent system (MAS) has recently gained public attention as a technique to solve competition and cooperation in distributed systems. However, MAS's vulnerability due to the propagation of failures prevents its application to a large-scale system. This paper proposes a general composition technique to improve its reliability easily applied to the existent MAS. The proposed system monitors messages between agents to detect undesirable behaviors (failures). Collecting related information, the system generates global information of interdependence between agents and expresses it in a graph. This interdependence graph enables us to detect or predict undesirable behaviors. This paper also shows that the system can optimize performance of MAS and improve adaptively its reliability under complicated and dynamic environment by applying the global information acquired from analysis of the interdependence graph to a replication system. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(1): 62–68, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20517 [ABSTRACT FROM AUTHOR]

In optimal design of a permanent magnet (PM) motor, many design variables are required to consider some device properties. These variables are, for example, the shape of core and magnet, the tooth length, the number of turns, and the winding radius. Moreover, many restrictions must be considered in practical PM motor design. These restrictions are, for example, the slot space factor and the cogging torque. However, the optimization problem, which has many design variables by the finite element method (FEM), has not been reported. In this paper, the efficiency of PM motor under the considerations given above is optimized by using FEM and optimization algorithm. In this problem, an objective function has many local minima and it is difficult to calculate its gradient. For these reasons, the genetic algorithm (GA) and simulated annealing method (SA), which are stochastic methods, are used for optimization method, because of the possibility of global range search and because gradient calculation is not required. Adding to both optimization methods, in this paper, SA combined with GA is used for one of the optimization methods. It is found that the solutions optimized by these methods are reasonable from an engineering point of view. © 2001 Scripta Technica, Electr Eng Jpn, 138(3): 72–79, 2002 [ABSTRACT FROM AUTHOR]

This paper proposes an approach to one-day-through seven-day-ahead electrical load forecasting based on a realistic problem formulation which should contribute to more reliable and economic weekly power stations operation. Generally, the load forecasting has the following problems. (1) although the load is affected by various factors, such as temperatures, in the load forecasting, it is impossible to consider all of them; (2) the relationships between the load and some factors are not clear, and often vary with time; and (3) uncertainties in forecasts of the temperatures sometimes make the results of load forecasting worse. They are very influential in the power station operation. While a number of methods have been proposed to solve the problems (1) and (2), there have been few attempts to solve the problem (3). The following approach is proposed in this paper, taking these problems into consideration. First, concerning the problem (1), the focus is on such factors that have major influence on the load and whose values are obtainable as stochastic and are not included in the forecasting model. Second, regarding the problem (2), a self-organizing approach is used where the algorithm itself finds the optimal model structure or the optimal set of factors to be included in the model day by day. Finally, addressing the problem (3), a new performance index of model structures is proposed which can measure the balance between: i) improvement of the load-forecasting accuracy due to inclusion of a factor in the model; and ii) degradation caused by uncertainty or error in the factor included. Using this index, a model is constructed which does not yield a large error in spite of errors in the temperature forecasts. Examples show that this approach improves the forecasted results when erroneous temperature forecasts are fed into the model, and verifies its effectiveness. [ABSTRACT FROM AUTHOR]

The load of a dc railway has very large peaks while the average power is low. This makes the capacity of wayside power equipment larger. Recently, the ratio of peak power to average power has become even higher because of the introduction of a large number of electric multiple units with a regenerative brake system. This has also made the contact system unreceptiveness of the regenerated energy a significant problem. To solve these problems, researchers arc attempting to add intelligence to the power system. This paper describes a novel method of intelligently controlling the traction power of trains. In this system the trains reduce their accelerating power to cut current peaks in wayside substations. With the proposed method the load peaks can be reduced by up to 31 percent, which means that the characteristics of the railway load have been changed drastically. The delays of the trains involved are negligible. Also, the unreceptiveness of the regenerated power can almost be eliminated. In the first part of this paper, the idea of traction power control is described. Then a description is given of how the idea is applied to wayside substation load peak suppression or receptiveness improvement, with some simulation results to prove the method. Finally, the possibility is discussed of further improvement of the system by adding communication capability between trains and wayside equipment. [ABSTRACT FROM AUTHOR]

New technologies such as synchronized switching and power electronics will make it possible to change the configuration of a transmission network in future electric power systems, It is called VIPS (Variable Impedance Power System) by the authors who have been studying the effects of those technologies on power system stabilities. This paper consider the improvement of transient stability by means of switching-over control of transmission lines- It is clear that in some power systems, the simultaneous energization of the line de-energized in the normal state with the fault clearing better improves first-swing stability than the pre- and post-fault energization of the line. The energy function-based index to select such a transmission line is derived- In addition, this paper shows that multiple switching of a transmission line improves damping of post-fault conditions, where minimization of time derivative of energy functions is used The switching-over control is applied to multimachine power systems and its effectiveness is demonstrated. [ABSTRACT FROM AUTHOR]

This paper present 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 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 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. [ABSTRACT FROM AUTHOR]

This paper describes the development of three-dimensional electric field analysis by using the so-called segment method which enables the electric field to be calculated with high accuracy and with enhanced efficiency, for high-voltage apparatus. In the segment method, electrode configuration of high-voltage apparatus is simulated by small components which are called segments and by the arrangement of several kinds of such segments. In this calculation, the charge simulation method is used which is suitable for segment application. As basic segments, spherical, cylindrical and ring segments are used and in addition to these, as subsegments, discs and elbow segments are adopted for good simulation of the total electrode configuration. In this paper, the fundamental construction and arrangement parameter of segments were discussed. Moreover, the segment method was applied to an actual high-voltage apparatus and the calculation accuracy was discussed. It was clarified that the segment method has sufficient calculation accuracy and is a very efficient means for three-dimensional electric field analysis. [ABSTRACT FROM AUTHOR]

This paper deals with static var compensators using self-commutated inverters (which is so-called SVG) compared with conventional SVC and Rotary Condenser. Improvement of power system stability is explained by using simple system model and checked by dynamic digital simulation. In the latter part of this paper, system outline, basic specifications and control diagram of the SVG rated 154 kV, ±80 MVA, which has been installed at INUYAMA Switching Station, are briefly presented. Field tests at INUYAMA verify that power swing is effectively damped and transmission capacity is increased. [ABSTRACT FROM AUTHOR]

This paper describes a brushless de 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 de motors. In this paper, two sensorless position detecting methods, i.e., an "indirect method" suited for the lower-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-sensorless PLL control is proposed in applying the principle of the direct method. Experimental results obtained from a prorotype brushless de 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. [ABSTRACT FROM AUTHOR]

The electromagnetic quantities of the magnetic bodies and conductors are calculated by the Finite Element Method with Integral Equation and it is not necessary to divide the free air space. The field at an arbitrary point in the free air is obtained from the Integral Equation after the FEM-IEM analysis. In this paper, the magnetization is written in the terms of the unknown total scalar potential Ω, and the current vector potential T is added in the conductors. In order to calculate the unknowns defined in only the substances by FEM, it necessary to establish the boundary condition by IEM. Then the calculation of the boundary conditions on the surface of magnetic body requires high technical skills, so that formulation presented in this paper is improved by integration of parts. Results of the standard models specified by the I.E.E. of Japan suggest the validity of our method. [ABSTRACT FROM AUTHOR]

This paper analyzes a hydroelectric power system which collects electric power from many medium and small generators located along rivers. Finally, it transmits a large amount of electricity over a long distance to an area of customers. Thus, this system also implicitly possesses a problem of stability related to power swings which are described in the foregoing. This paper assumes a model system of hydroelectric power systems. First, we analyzed the instability phenomenon of the power swing. Next, we examine a stability control using a superconductor magnetic energy storage system (SMES) which has attracted attention as a new system of stabilizers. [ABSTRACT FROM AUTHOR]

Research papers on failure forecasting of electronic circuits have been published, presenting analyses of the distribution of malfunctions over circuit life, and failure rates and patterns based on statistical analysis. However, we are not aware of technical discussions on the forecasting of failure of individual electronic circuits, although physical analysis of malfunctions have been made with the scanning electron microscope and with X-ray devices and ion analyzers, and numerical models of failure mechanisms have been used to obtain qualitative and quantitative results. But such analyses do not deal with degradation phenomenon appearing before failure occurs. Thus, the electronic circuit testing methods now in use involve the analysis of malfunctions after they have occurred. This paper presents a method of degradation diagnosis method which detects the degradation symptoms in the electronic cards earlier and with higher sensitivity than in previous techniques. [ABSTRACT FROM AUTHOR]

We conducted a study for the conceptual designs of superconducting magnetic energy storage systems for each temperature level. For this study we assumed that superconductors will be realized at each of the liquid nitrogen, liquid hydrogen and room temperatures. The Nb-Ti superconductor is close to the level of perfection by the present technology, and is used widely through mass production. For a lower limit of the expected cost of realization of future high-temperature superconductors, we used the cost of the present Nb-Ti superconductors as a reference level. This paper presents the results of the study of conceptual design in section 2 for a 5 GWh SMES at the liquid helium temperature. Section 3 presents the results of conceptual designs assuming possible applications of superconductors at liquid hydrogen, liquid nitrogen and room temperatures based on the results of section, and makes a comparative analysis. Due to space limitations, some parts of detailed examination processes have been omitted. The estimated construction cost represents trial calculations for a theoretical paper and it is not the estimated construction cost assuming a concrete construction. [ABSTRACT FROM AUTHOR]

This paper proposes a control system which improves OPU (Optical Pick Up) control performance in an optical disk system. This system can be realized by adding a correction pulse control block which is based on a position error signal onto a conventional position control loop composed of the PID control rule. Using this function, the position error resulting from a physical distortion and acceleration disturbance to the disk can be decreased sharply. Furthermore, this system can decrease the deviation caused by the shock disturbance which cannot be controlled by the PID control rule. In addition, it becomes possible to decrease the overshoot in the impulse response sharply, and realize stable capture of a target position. Since this system can be created with a simple algorithm, it is possible to use it in a wide range of applications. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(2): 53–67, 2007; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/eej.20570 [ABSTRACT FROM AUTHOR]

The unevenness of contact lines is one of the factors that considerably influences the dynamic characteristics of current collection systems. In order to analyze the influence of the contact line unevenness on the fluctuation of the contact force between contact line and pantograph, an instrument was devised to measure the unevenness of contact lines accurately and continuously. The instrument consists of two pairs of laser sensors for the purpose of reducing measurement errors by vertical vibration of the measurement vehicle. This paper describes the measuring method of contact line unevenness, reports some examples of the measurement of real lines, and proposes a method to evaluate the conditions of overhead equipment. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(2): 77–85, 2007; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/eej.20209 [ABSTRACT FROM AUTHOR]

It has been pointed out that if the social configuration of the three relations (market, communal, and obligatory relations) is not balanced, a market-based society as a total system fails. Using multiagent simulations, this paper shows that a sustainable society is formed when all three relations are integrated and function appropriately. When agent trades are based on the market mechanism (i.e., agents act in their own interest and thus only market relations exist), weak agents who cannot perform transactions die. If a compulsory tax is imposed to enable all weak agents to survive (i.e., obligatory relations exist), then the fiscal deficit increases. On the other hand, if agents who have excess income undertake the unselfish action of distributing their surplus to the weak agents (i.e., communal relations exist), then the trade volume increases. It is shown that the existence of unselfish agents is necessary for the realization of a sustainable society. The survival of all agents, however, is difficult in a communal society. In an artificial society, for all agents to survive and fiscal balance to be maintained, all three social relations must be fully integrated. These results show that adjusting the balance of the three social relations will lead to the realization of a sustainable society. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(1): 38–46, 2006; Published online in Wiley InterScience (http://www.interscience.wiley.com). DOI 10.1002/eej.20368 [ABSTRACT FROM AUTHOR]

The authors have proposed the resin molded type of voltage–current sensor for the real-time observation of the power factor. The sensor has been designed and implemented based on the FEM; however, the current waveform and practical power distribution system includes harmonic components due to the inverter-fed power apparatuses in households and factories. Therefore, it is necessary to apply not the conventional jω method but the finite-difference approximation to the time derivative term in a transient electromagnetic field analysis using FEM. In the paper, the authors will show the result of electromagnetic field analysis of the sensor adopting the finite-difference approximation. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(1): 1–9, 2006; Published online in Wiley InterScience (http://www.interscience.wiley.com). DOI 10.1002/eej.20294 [ABSTRACT FROM AUTHOR]

Superconducting magnetically levitated vehicles have guidance coils that produce vehicle guidance forces using a null flux coil connection. However, the resulting forces do not have sufficient damping forces to suppress lateral vibration of the vehicle. Even though the experimental system has some magnitude of damping, it is still unsatisfactory. Moreover, since the guidance forces are very weak at low speeds, the minimum levitating speed is limited. The paper proposes a guidance method using LSM armature coil currents. When the currents are decomposed into the dq frame variables so that the d-axis is assigned to the field axis, the d-axis component of the currents generates lateral forces. The lateral forces of the vehicle are formulated, and the guidance force coefficient is defined. In addition, the author presents a design formula for a guidance regulator system that employs a dynamic compensator using a feedback signal of lateral displacement. The calculated results show that the guidance regulator system works as intended. © 2001 Scripta Technica, Electr Eng Jpn, 137(2): 44–51, 2001 [ABSTRACT FROM AUTHOR]

This paper describes single-sided linear induction motors (LIMs) with a short primary member. In these machines a solid-plate conductor is usually used for the secondary. We here propose the partial adoption of wound secondary members in LIMs. The characteristics of such machines are summarized as follows. 1. Basic characteristics: The wound secondary shortens the magnetic clearance and makes the characteristics of the machine superior to those of the solid-plate conductor version. In addition, we can improve the thrust and efficiency characteristics by applying the proportional shifting method. 2. Primary and secondary winding scheme: Parallel connection is appropriate for the primary and independently shorted-circuit scheme in order to obtain stable performance. 3. Transient phenomena at the boundary between the wound secondary and the solid-plate secondary: Undesirable phenomena develop at the boundary, especially at the end of the solid-plate conductor. Thus, we propose a novel boundary structure that yields stable transient performance. © 2001 Scripta Technica, Electr Eng Jpn, 135(3): 48–55, 2001 [ABSTRACT FROM AUTHOR]

In this paper we propose an optimal slip ratio estimation method based on fuzzy inference. One of the major advantages of electric vehicles is the quick and precise torque response of the electric motor, which realizes a novel traction control system. To prevent skidding, optimal slip ratio control has been successfully developed. It maintains the slip ratio at the optimum value that gives the maximum driving force. The remaining problem is how to generate the optimal slip ratio command sent to the controller. First we show that effective estimation of the optimal slip ratio is difficult to perform by the simple gradient method, which is a well-known optimization method. But various experimentally obtained data can be easily incorporated into fuzzy inference, and therefore its estimation performance can be easily improved by the accumulation of human experience. This is a major advantage in the nonlinear estimation of real road-tire characteristics. The effectiveness of the proposed estimation and control methods is confirmed by numerical simulation. © 2001 Scripta Technica, Electr Eng Jpn, 135(3): 56–63, 2001 [ABSTRACT FROM AUTHOR]

Among various variable speed drives, switched reluctance motors (SRMs) have been found to be competitive with traditional ac and dc motors because of their simple construction and drive electronics. However, the necessity of using a shaft-mounted position sensor is one of the drawbacks of the SRM from the standpoint of cost, size, and reliability. Position sensorless SRM drives are expected to solve these problems. This paper presents a method of position sensorless control based on a simple fuzzy model of nonlinear position-dependent magnetizing curves. The sensors needed for the drive are one voltage sensor and one current sensor. Experimental studies using a 1.5-kW, 5400-rpm SRM with a 6/4 tooth configuration show that the maximum error of rotor position estimation is less than three mechanical degrees in the 1:20 speed range under any load conditions. © 2001 Scripta Technica, Electr Eng Jpn, 135(2): 60–68, 2001 [ABSTRACT FROM AUTHOR]

To scale up the capacity of an SMES for a practical application, it is necessary to adopt a high-voltage system, a large current system or a modular system. The first system is difficult because of the very low withstanding voltage of a superconducting coil and the second also involves difficulties such as multiple connections of many convertors on the dc side and large current conductors in the superconducting coil. The third system, composed of several modules with small-scale convertor units and element coils, might be a solution of the above difficulties. In this modular system, the module coils have magnetic linkage with one another. In this paper, the influence of magnetic linkage between coils of a modular SMES is investigated by computer simulation. The magnetic linkage varies with the number of modules and the type of connection of the coils. By the effect of this magnetic linkage, each module's coil current is different at the same power. The current and energy transfer characteristics are determined for discharge from one or more of 6 modules, consisting of 18 coils. The discussion deals with the case in which there is an unused module when quenching occurs. The transfer with the same current in all modules is shown by control of convertor power of the current feedback. © 1997 Scripta Technica, Inc. Electr Eng Jpn. 118 (4): 1–9, 1997 [ABSTRACT FROM AUTHOR]

An ideal inverter should have sinusoidal voltage and current outputs. Generally, output voltages of a voltage-source PWM inverter contain high-level switching frequency harmonies due to the PWM operation, while output currents are kept nearly sinusoidal. High-level harmonics contained in output voltages of a voltage-source inverter cause acoustic noises, iron losses and electromagnetic interferences. An LC filter was used to suppress the switching frequency harmonics; however, there is a danger of resonance in the LC filter. Accordingly, to remove harmonics of the LC filter resonance frequency, the authors add a voltage feedback loop. A conventional system can operate without difficulty within 50 Hz. However, with accompanying increases in the output frequency, output voltages are largely delayed and reduced by a high-pass filter inserted in the feedback loop. These problems are caused by a high-pass filter inserted in the feedback loop. Accompanied by the inverter output frequency, a high-pass filter cannot remove the fundamental component perfectly. As a result, a small fundamental component is fed back, which causes a delay and decrease in output voltage. This paper proposes the application of coordinate transformation to a high-pass filter inserted in the feedback loop. As a result, the proposed system realizes an ideal filter which can suppress fundamental frequency components perfectly, and improves the characteristics of the inverter with sinusoidal voltage outputs greatly. Theoretical analyses, simulations and experiments showed satisfactory results. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 118 (4): 94–102, 1997 [ABSTRACT FROM AUTHOR]

This paper proposes a new method of optimizing the operation of a power transmission system, based on a structured neural network. Because the structured neural network is built by prewiring, the network construction time is very short. Simulations of transmission loss of reduction have been carried out. It is shown that the optimization performance of the proposed method is satisfactory in practice. © 1997 Scripta Technica, Inc. Electr Eng Jpn. 118 (4): 27–34, 1997 [ABSTRACT FROM AUTHOR]

Since a three-phase circuit has phase interference, control/modulation in three-phase converters becomes very complicated as compared with single-phase converters. The phase interference problem has not been discussed in depth in any published work. As the primary objective, this paper describes an analysis of phase interference in a three-phase voltage-fed converter circuit and the resultant phase-decoupled equivalent circuits expressed with local-averaging value (or averaging value in a control/modulation period). A simplification of a predictive instantaneous-current control for a voltage-fed high-power-factor converter is then introduced as the secondary objective. By combining the proposed techniques, a simple control/modulation scheme for three-phase high-power-factor converters is obtained. A controller/modulator for experimental setup is introduced to demonstrate the simplicity achieved by the proposed theories. The pulse area modulation scheme, employed in the modulator to compensate modulation errors caused by ripples of the output voltage, is also introduced. To show the validity and applicability of the proposed theory, experimental results obtained from a 2-kW setup are shown. Finally, the author draws conclusions from the work. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 118 (4): 70–83, 1997 [ABSTRACT FROM AUTHOR]

This paper presents a peak lord forecasting system using multilayer neural networks and fuzzy theory, Electric load forecasting in power systems is a very important task from the perspective of reliability and economic operation. Daily peak load forecasting is one of the basic operations of generation scheduling for the following day. Therefore, many statistical methods have been developed and used for such forecasting even though it has been difficult to construct a proper functional model. The developed system is applied by neural network and fuzzy theory to forecast for daily, weekly and monthly peak load. The system consists of an engineering workstation (EWS) and a personal computer (PC). The EWS is for learning and data-bases, and the PC is for man-machine interface such as forecasting operation. The system has been used since June 1993. The result evaluated with an absolute mean error is 1.63 percent for 10 months. From the results shown here, the system applied by neural network and fuzzy theory has high validity. [ABSTRACT FROM AUTHOR]

It is difficult to determine the subtransient (transient) reactance and subtransient (transient) short-circuit time constants of medium and large synchronous machines by the sudden three-phase short-circuit test because large-capacity equipment is required. This paper describes a new method of measuring these constants by means of a simple test using a small dc power supply. The key points of this method are as follows. (1) A dc voltage is applied to the armature winding (two terminals with the third one open) of a stationary synchronous machine through a resistance. When the two terminals are closed, the winding is short-circuited and the current in the armature winding decays. The whole process of decaying current is recorded. (2) The value of the transient phenomena of the winding calculated from circuit equations (armature, field winding and damper winding circuits) is compared with actual data, and the unknown equivalent circuit constants are identified by the least squares method. (3) Transient phenomena of the sudden three-phase short-circuit are calculated by the two-reaction theory using identified constants, and, hence, these constants are calculated. The transient constants of synchronous machines obtained by the new method agree closely with the observed values. [ABSTRACT FROM AUTHOR]

Based 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. [ABSTRACT FROM AUTHOR]

A new motor (ADTR-motor: Anti-Directional Twin Rotary Motor) for electric vehicle drive is proposed. A stator in a conventional motor is reformed to be movable, and the stator (outer rotor) and the rotor (inner rotor) rotate in anti-directions. The IM-type ADTR-motor and the SM-type ADTR-motor are considered, and in this paper a prototype of the IM-type ADTR-motor is constructed experimentally. When the ADTR-motor is used for an EV drive, the direction of one of the rotors should be reversed. Both rotors, when rotated in the same direction, propel the two wheels of EV. The torque of the wheels can be balanced without differential gear. The fundamental characteristics of ADTR-motor are clarified. The characteristics are the structure of ADTR-motor, the equivalent circuit parameters, the torque balance theory, the torque-speed characteristics, the rotor speed transient characteristics, and the transient response under the speed sensorless torque control. [ABSTRACT FROM AUTHOR]

A new type of actuator with both magnetic levitation and linear drive is proposed. The actuator, called magnet wheel, has a rotating magnetic field obtained by revolving permanent magnets with high coercivity mechanically. The induction repulsive-type magnetic lift force with self-stabilization can be obtained by linking the rotating flux to a conducting plate. The induced simultaneous drag torque, which causes power loss, is used to obtain thrust in two proposed ways. These are called "tilt type" and "partial overlap type," respectively. In the tilt type, the magnet wheel is tilted against the surface of a conducting plate. In the partial overlap type, the magnet wheel operates near the edge of a conducting plate. In this paper, the fundamentals of the structure of proposed magnet wheels are described. The basic characteristics at parallel to the conductor are shown by using a numerical three-dimensional electromagnetic analysis and measured results. The generation of both lift force and thrust in tilt type and partial overlap type magnet wheel are proved by experiments, respectively. [ABSTRACT FROM AUTHOR]

This paper presents a fuzzy-based method for determining a flexible generator maintenance scheduling by means of subjective relaxation of constraints imposed on the maintenance scheduling problem. The constraints are divided into hard (crisp) constraint set and soft (fuzzy) constraint set according to reflecting conditions which surround power systems. The problem is formulated as a fuzzy mathematical programming problem and solved with the fuzzy branch-and-bound method using Bellman-Zadeh maximizing decision. The proposed approach provides not only a new flexible concept of planning problems in power systems, but also natural expansion of conventional approaches based on crisp set theory. The effectiveness and feasibility of the proposed approach are demonstrated on two typical power system models which consist of 15 generators and 60 generators, respectively. [ABSTRACT FROM AUTHOR]

This paper presents a new switching control scheme for static var compensator (SVC) using fuzzy logic control rules to enhance the overall stability of electric power systems. In addition, the coordination with power system stabilizers (PSS) is also considered to achieve a wider stable region. An SVC is set on one of the busbars in the transmission system, where the real power flow signal is utilized at the location of the SVC to determine the firing angle of the thyristor switch. The switching control scheme is simple so as not to require heavy computation on the microcomputer based switching controller. The PSSs are also set on the generators in the study system. Simulation results show the effectiveness of the proposed fuzzy logic switching control scheme for the SVC. The coordination between SVC and PSS is also effective to enlarge the stable region. [ABSTRACT FROM AUTHOR]

A 3000/6000V, 1000 kVA class superconducting transformer (SC-Tr) was developed for a Prospective Power Transmission Model System Integrated under Superconducting Environment (PROMISE). In this transformer, the core and superconducting windings are immersed in liquid helium and the major insulation is provided by the liquid helium. This paper describes both the design features and measured characteristics of the SC-Tr. Fundamental characteristics of the SC-Tr are obtained through no-load, short-circuit tests and quench experiments. The results of the no-load test have verified that the SC-Tr has the capability to withstand ac voltage of 3000/6000 V of 60 Hz without any partial discharge. The short-circuit tests have proved that the SC-Tr is capable of carrying ac current of 170 Arms without quench in the superconducting windings. Furthermore, in a real-load experiment with the PROMISE, electric power of 3800 V-460 kVA of 50 Hz in high-voltage side is transmitted through this SC-Tr. [ABSTRACT FROM AUTHOR]

This paper discusses optimal planning problems for dispersed generating sources so as to provide a guideline for their introduction to power systems. First, a recursive method is developed from the viewpoint of supplying electric power only where solutions for one unit are superposed. The computational loads are decreased by selecting alternatives of buses based on the so-called penalty factor. However, for effective utilization of dispersed generating sources, it is indispensable to consider their thermal merits in addition to electric power. After applying the Kuhn-Tucker theory to the optimal dispatching problem including boiler fuel costs, thermal values of the dispersed generating units are evaluated quantitatively. Finally, the above-mentioned technique for the optimal planning basically is also the proposed algorithms are demonstrated using a real-scale model system. [ABSTRACT FROM AUTHOR]

It 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. [ABSTRACT FROM AUTHOR]

Brushless 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 inductor 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. [ABSTRACT FROM AUTHOR]

New 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. [ABSTRACT FROM AUTHOR]

Since unstable phenomena that load bus voltages collapse rapidly after a large disturbance occurred in a bulk power system, it is becoming necessary to develop a fast and precise evaluation method of what is called transient voltage stability. Although many indices have so far been proposed for static voltage stability assessment, there are few evaluation methods, digital simulation analysis for example, for the transient voltage stability assessment that deals with the dynamic characteristics of generators, loads, etc. This paper presents the transient voltage stability evaluation system that consists of two artificial neural networks (NNs). The first NN judges whether the system is stable or not under a given operating condition, load composition and fault location from the viewpoint of the transient voltage stability. If it is judged to be unstable, the second NN estimates critical operating time of emergency control action as a severity index of the transient voltage instability. Here, closing of a bus tie that is switched off in the normal state is adopted as the emergency control for voltage stabilization. Numerical examples for a 26-bus model system are shown in order to check the effectiveness of the proposed evaluation system. [ABSTRACT FROM AUTHOR]

Electric power demand has increased rapidly and this is expected to continue. Undamped power swings with low frequency tend to occur in large power systems with complex configuration. Therefore, several stabilizing control schemes, e.g., a power system stabilizer (PSS), have already been investigated. On the other hand, superconducting magnetic energy storage (SMES) is expected to be an effective apparatus in power systems since any SMES located in power systems is capable of leveling load demand, compensating for load changes, maintaining bus voltages and stabilizing power swings. The effectiveness of each function, however, depends upon the location of the SMES in the power system because output power from the SMES is distributed according to the impedance ratio of the transmission line at the SMES location. Therefore, it is difficult for SMES to serve two different purposes simultaneously. This paper proposes a combination of SMES with a high-speed phase shifter (HSPS). The HSPS, which consists of a phase shift transformer and a set of power converters, is capable of controlling the power flow of the transmission line by adjusting the phase angle of a phase shift transformer. Therefore, it is expected that the combination of SMES and HSPS can realize a highly effective controller independent of its location. Numerical examples demonstrate that the proposed apparatus located far from a generator in a long distance bulk power transmission system is capable of stabilizing the power swing as effectively as the SMES located at a generator terminal. In addition, the effectiveness of both load change compensation and power system stabilization is confirmed numerically. [ABSTRACT FROM AUTHOR]

With the progress in factory automation in industry has come the demand for higher speed drive and performance for an AGV (automated guided vehicle). A new steering control of the AGV by fuzzy control has been proposed to replace the PI control. However. much time is required to investigate the regulations and to adjust the scaling factors for excellent performance in the fuzzy control, In this paper, a new steering control for an AGV based on the neural network using the backpropagation method is proposed. The good steering control results by the fuzzy control are adopted for the teaching signal of the neural network. First, the effect of the number of learning and the learning errors on the steering control results are discussed by computer simulation using the AGV model. Further. the ability of generalization in the turning radius and the traveling speed also are investigated. It becomes clear that the AGV can travel along a designated route provided the neural network learns both the right and left turning at the maximum traveling speed and the minimum turning radius. Then it is proved by an experiment using the AGV constructed for the test that the proposed steering control method is very affective. [ABSTRACT FROM AUTHOR]

The matrix converter proposed by Venturini is very simple in structure and has powerful controllability. However, there are few applications especially in power electronics fields. This seems to be caused mainly by the fact that such power devices that were fast enough to suppress ringing oscillations in the supply lines and large enough to pay for more devices and more complicated control circuits than in conventional dc-link converter-inverter systems were not available. At present, static induction thyristors (SIThs) have been introduced and a new possibility for the matrix converter has been raised. This paper describes a new control strategy which is simple and practical and allows the output voltage of 0.866 times the supply voltage to be generated. Also, the new firing sequences which eliminate voltage and current spikes are proposed. Steady-state and distortion characteristics of the prototype PWM matrix converter with SITh are shown. [ABSTRACT FROM AUTHOR]

A new type of magnetic suspension system is proposed which uses a permanent magnet. In this system. the attractive force is adjusted by controlling the reluctance of the magnetic circuit. Since no electromagnet is necessary, this system is effective for saving energy and avoiding heat generation. The composition of this paper is as follows. First, the principle of this suspension system is explained and various types of magnetic circuits are introduced for reluctance control. Second, the possibility of one of them is examined from the viewpoint of linear control theory. Third, an experimental device is developed based on the proposed suspension method. The reluctance of this device is controlled by the air gap which is between the magnet and the suspended object, and which is adjusted by driving a permanent magnet by piezoelectric actuator. Experimental results support the theoretical predictions well. [ABSTRACT FROM AUTHOR]

When magnetic fields in electrical machines with moving conductors such as linear induction motors arc analyzed, eddy currents due to the movement of conductors should be taken into account. Although two kinds of coordinate systems (moving and fixed coordinate systems) can b¢ applicable to the analysis of eddy currents in moving conductors, the advantages and disadvantages of both coordinate systems are obscure. In this paper, methods for analyzing magnetic circuits with moving conductors arc classified systematically, and the moving and fixed coordinate systems are compared with each other from the standpoints of accuracy, memory requirement, and CPU time. It is shown that the moving coordinate system is superior to the fixed coordinate system for transient analysis. [ABSTRACT FROM AUTHOR]

When combined with a magnet having a magnetic field gradient (for example, a permanent magnet), a Y-based oxide superconductor is capable of forming a noncontact bearing with a strong levitational force. Since this bearing exhibits low rotational loss, it is very likely to form a highly efficient power storage system in combination with a flywheel. In this paper, an 8-MWh power storage system utilizing a flywheel was designed conceptually to examine its applicability and the possible effects of its introduction. It was found that this system was an effective power storage. [ABSTRACT FROM AUTHOR]

Optimal switching pattern planning is the main subject of distribution network reconfiguration to recover from a blackout or to avoid a blackout due to maintenance and construction. This is a combinatorial optimization problem, and an enumerative check of every pattern is necessary to obtain the optimal solution. In practice, successive heuristic search methods are adopted to obtain the quasi-optimal solution within a limited computation time. However, a very long computing time is still required when the problem size becomes slightly larger. The step-by-step nature of the methods results in many iterations, although it ensures satisfaction of the constraints. Reduction of the iterations is considered to be necessary to enhance processing speed. In this paper, ‘supply adequacy’ is introduced as a new criteria index to guess the solution, which is obtained by fuzzy inference for each possible pair of source and load zone. The reconfiguration pattern is obtained at once or in a few processing steps by assigning to each zone the source with the highest adequacy. Numerical examples show that the proposed method can obtain the solution faster than the ordinary method, more remarkably with the increase of problem size. [ABSTRACT FROM AUTHOR]

An experimental line of a magnetically levitated train (MAGLEV) using supeconducting 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 [ABSTRACT FROM AUTHOR]

From the viewpoint of maintenances and constructions, it is desirable that brushless and exciterless type three-phase synchronous generation 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 exciterles 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

To explain contact failure phenomena and their development in the gas-insulated switchgear (GIS), tests wee conducted by stimulating abnormal current-carrying conditions using an actual 300-kV, 2000-A GIS. This paper describes the process observed, ranging from contact failures to ground faults, deteriorative phenomena and some detection methods for initial contact failure conditions. A summary of this study is as follows: (1) The contact resistances are greatly dependent on the materials and construction of contacts. (2) The relation between the initial contact resistance and the carried current resulting in arching is derived with approximately constant Joule-heat generation. (3) Ground faults result from sagging of a shield melted by arching or a combination of two causes: (i) scattering of molten metal caused by arcing; and (ii) sagging of conductor caused by bolt melt down. (4) To detect initial contact failures, it is recommended to observe the contact resistance, the temperature rise on the tank surface, or the electrical partial discharges. [ABSTRACT FROM AUTHOR]