A new type cable-in-conduit conductor composed of HTS tapes was proposed as a winding for high performance HTS coils with high current capacities and low ac losses. In the fabrication of the conductor, the twist of stacked tapes around their axes was made before inserting them inside conduits. The twist angle should be changed continuously along the axis to reduce face-on orientated magnetic fields applied to the tape in the winding conductor during coil operation. In order to confirm the high current capacity of this type conductor, two single-layered solenoidal coils wound with sample conductors composed of 5 stacked Bi-2223 tapes with bias angles of 20 and 0 degrees were fabricated and tested in liquid nitrogen. A copper magnet system was used in this experiment to generate the spread magnetic field with a spread angle of 20 degrees from the coil axis to the radial direction, which simulates the profile of magnetic fields near the edge windings of practical coils. A large improvement on critical-currents degradation affected by spread magnetic fields was successfully observed for the test coil wound with the 20-degree bias conductor.

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Superconducting Fault Current Limiting Transformer (SFCLT) is one of the promising superconducting power apparatus, since it has both functions of superconducting transformer in normal condition and superconducting fault current limiter in fault condition. In this paper, we have designed, fabricated and tested a high temperature SFCLT (HTc-SFCLT) with MCP-Bi2212 bulk coils at liquid nitrogen temperature. The rating of the designed HTc-SFCLT is 3-phase, 6.25 kVA, 275/105V. No-load test and short-circuit test were successfully carried out to verify the fundamental characteristics of HTc-SFCLT as a superconducting transformer. In addition, HTc-SFCLT also exhibited an excellent performance in current limiting test and recovery test at the prospective current of 800 A as a superconducting fault current limiter.

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We have been developing a magnetic levitating device with two-dimensional movement, namely a ’levitating X-Y transporter’. For a real design of the levitating X-Y transporter, it is necessary to clarify the levitation characteristics, such as lift, levitation height and stability against mechanical disturbances. In this paper, we examine the lift and the restoring force experimentally and newly developed a simulation code based on the three-dimensional hybrid finite and boundary element method to analyze the dynamic electromagnetic behaviors of YBCO bulk. We investigated the suitable permanent-magnet arrangement to enhance the levitation characteristics through experiments and numerical simulation. And we also performed the design of a levitating transporter which can levitate a load of 200kg with a gap of 16mm.

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Lack of data is an obstacle to realize accurate assessment of reliability. Dimensional reduction method was successfully used for reliability assessment with few data by means of multiple factors. In order to generalize the dimensional reduction method for reliability assessment and expand its application area widely, this paper presents a general definition of the concept, algorithm and application area of dimensional reduction method for reliability assessment and analyzes the properties of this method, such as selection of factors, uniqueness of dimensional reduction results, determination of dimensional reduction sequence, etc. Some simulations have been made based on the actual data to verify the effectiveness of dimensional reduction method for reliability assessment.

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This paper presents the investigation of the arc extinction capability of air load break switches (AS) used in overhead power distribution systems. The interrupting capability of the load break switches (LBS) is generally determined by mutual effects between the arc behaviors of LBS and the corresponding circuit conditions. In this paper, the interaction between the arc and the corresponding circuit was described by a black box arc model based on modified Mayr arc equation. The limit values of the arc time constant, which represents the lowest limits of the arc extinction capability was obtained by repetition calculation to the measured results. The results not only showed the limit values of the arc time constant which needed for AS to interrupt the load currents, but also confirmed that AS possesses sufficient arc extinction capability to interrupt the load currents.

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This paper describes the merit for power consumers brought by the combination use of photovoltaic generation and nighttime power storage using the storage battery. The merit of the combination system is calculated based on the insolation and consumers load pattern. The merit using insolation at the specific region and general load pattern has been already reported. This paper examines the influence due to regional and load pattern differences, and studies the changes of the merit and the optimal storage battery capacity. The other hand, it is difficult to measure the actual load pattern of the ordinary residence, so this paper uses the generalized load pattern to comparatively examine the difference in merit and optimal storage battery capacity from those for the actual load pattern.

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In recent years, installed capacity of wind power generation has significantly increased in the countries including Japan. This increase gives rise to growing concerns on power quality of a power system with large penetration of wind power because fluctuation of its output power is significantly larger than that of conventional power sources. Tower shadow effects, the fluctuation frequency of which is determined by rotating speed of a wind turbine, considerably contribute to the fluctuation. While the power fluctuation due to tower shadow effects can cause flicker and thereby deteriorate power quality, its amplitude varies with constants of induction generators and impedance of the distribution/transmission system connected to the generators.
This paper examines the relationship between the amplitude of the power fluctuation and input torque of an induction generator while making machine constants or back impedance at the connection point parameters. The study derives a transfer function describing the relationship by linearizing related differential equations and verifies its validity through a simulation study with MATLAB/Simulink. Implication of the results on amplitude of 3N components of wind power output is discussed.

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The allowable current of an underground power cable system is evaluated on the basis of the temperature rise of a conductor. Generally, the steady allowable current is evaluated on the basis of saturated temperature rise. Because there is a large difference between the time constant of heat conduction in a cable and that in soil, loss factor (L_f) is generally used. However, when an allowable current is calculated using L_f, there is a possibility of overestimation, such as in a shallow laying case. We previously developed programs for evaluating the transient temperature rise of power cables in a protection pipe with actual transient load change. Using these programs, we can evaluate the overestimation due to L_f in this study. Among the cases we assumed to be normal, there occurred 5°C of overheating of a protection pipe and 3°C of overheating of a conductor.

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There has been a lot of productive research done in the field of photovoltaic (PV) power generation, but there are still some problems including the energy generated by PV systems is fairly small in comparison to the expected energy, and the output dispersion of individual systems is also large. In order to evaluate whether the expected energy can be obtained, the evaluation of generated energy has been carried out using coefficients such as “the performance ratio" which divides the actual generated energy produced for one year by the calculated output energy of the PV array for an equal period. However, there are some limitations, such as that long-term continued measurement of data is necessary, it is hard to investigate factors which lower the generated energy and improve the system efficiency, etc. The authors have carried out research in accurately evaluating generated energy. A method for classifying loss due to solar temperature rise has also been researched and clarified by the measurement of data over a short time period. Further, the loss on the MPPT operation (P_max operation) could similarly be classified and analyzed.

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Cloud-to-ground lightning frequency is one of the most important factors to establish the rational insulation design of power transmission systems. Ten-year lightning occurrence data 1992 through 2001 with lightning location systems of electric utilities in Japan have been collected and analyzed. As a result, it is found that the annual number of the lightning strokes varies at the level of about 0.6 million on an average, but it is small in 1993 and extremely large in 2000 and 2001. This is considered due to the abnormal meteorological conditions in summer. Seasonal variations and annual variations of lightning occurrence have been clarified from the seasonal and annual lightning stroke frequency maps made by the above data. It is shown that the variations are different from those of thunderstorm days. Furthermore, comparison between the thunderstorm days observed by the lightning location systems and thunderstorm day data collected by the Japan Meteorological Agency is made.

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Dynamic load models for power system stability analysis are discussed. It is concluded that two-input model is preferable to single-input model for the purpose of properly modeling the load dynamics. Node frequency is inappropriate as an input to dynamic load model. A dynamic load model employing voltage phasor as input is proposed. Note that, in proposed model, “absolute" phasor angle is used as input quantity instead of small change in phasor angle since phasor angle may increase monotonically even in a steady-state.

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Since excessive magnetizing currents may lead to the occurrence of the accident which reaches the whole circuit, theoretical and experimental research in such systems are assumed to be special importance. This paper describes the return map of the transformer magnetizing current caused by DC interrupted excitations. he results of the numerical simulation show the effectiveness of the return map.

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