A Superconducting Magnetic Energy Storage (SMES) is proposed to be used the stabilizing control of power systems. By simulations, we have been studying its control effect, the required energy for power system stabilization, and so on. We have also proposed the power system stabilizing control by SMES incorporated with the fuzzy logic switching control. Recently, a systematically designed 50kJ SMES system is installed at Kumamoto University. We have investigated the stabilizing effect of the proposed fuzzy logic switching control by means of experiments with the SMES system and a one-machine infinite-bus system. In the pervious paper, the experimental results about the SMES active power control is mentioned. In this paper, the experimental results of a simultaneous control of the SMES active and reactive power, which is incorporated with the fuzzy logic switching strategy, are shown and discussed. We make clear the effect of power system stabilizing control incorporated with the fuzzy logic switching control by SMES.

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Maximum short circuit current of modern power system is becoming so large that circuit breakers are not expected to be able to shut down the current in near future. Fault Current Limiter (FCL) is supposed to be an effective solution of this problem and recent progress of superconductivity technology and power electronics makes it possible to develop current limiting type FCL such as diode-bridge type FCL. Current limiting type FCL limits the current through the FCL and its equivalent impedance is not constant and depends on fault location, operating point of power system and the limit of the current through FCL. In this paper, a method to incorporate such FCL into short circuit current analysis is proposed. Also, an efficient method to find location of FCLs suitable to suppress short circuit currents of more than one fault locations is developed. The efficiency and effectiveness of these methods are shown by numerical examples.

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The purpose of this work is to study one dc reactor type three-phase current Iimiter(FCL) using high temperature superconducting(HTS) coil, connected with the secondary winding of a transformer through a diode bridge. HTS provides the advantages of a higher temperature operation, preferably applied to the dc reactor type FCL, where a superconducting coil can be operated at lower voltage and dc current. We propose one dc reactor type three-phase FCL incorporating only one HTS coil and present its test result. One reactor type three-phase FCL for 6.6 kV-2000 A is compared with the three reactors type from the point of view of a current limitation and the required HTS coil.

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A superconducting coil may be damaged by ohmic heating in itself when quench occurs. Therefore it is necessary to detect quench as fast as possible and to protect the superconducting coil from its overheating. However the conventional electric quench-detecting system is vulnerable to the electromagnetic noise, so it is required the high sensitive and reliable quench-detecting system.
In this paper, we propose a partial active power detecting method as a new type of the quench-detecting system. The active power consumed in the coil is used as the quench-detection. That is, when the active power gets to or is greater than the some threshold, it is recognized as quench in the coil. The active power has DC component in general. Therefore low pass filter (LPF) is available to eliminate the electomagnetic noise superposed on the detecting system. In order to deal with only the active power, reactive power is cancelled beforehand by the differential method. This detecting method is useful for the both cases of DC and AC power circuit. Experimental results show that this method is useful to detect the quench in the superconducting coil.

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We present experimental results for the magnetic filtration of magnetite fine particles using a high-gradient magnetic separation process as well as analysis based on a theoretical model. The experimental investigations were carried out using a superconducting magnet able to generate a magnetic field up to 6 T, to magnetize the magnetite particles and filter meshes. Comparing theoretical predictions by the particle trajectory analysis method against the experimental results, we concluded that the theoretical results are consistent with the experimental results up to a fluid velocity of 0.7m/s or a Reynolds number of 350 and that the magnetic separation process is effective for filteration of manetite fine particles.

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For the development of superconducting (SC) power apparatus, it is necessary to establish the high voltage technology with consideration of quench phenomena peculiar to SC environment. From the point of view, we have investigated so-called “dynamic” breakdown characteristics of liquid helium (LHe) under different quench conditions using ac SC wires and coils. As a result, electrical insulation performance of LHe was found to be drastically degraded in the thermal bubble disturbance by the quench of SC wires and coils.
In this paper, in order to systematize the insulation performance of LHe under non-uniform electric field, we obtained breakdown characteristics for various gap lengths, pressures of LHe and post-quench thermal energy injected into LHe. Experimental results revealed that the dynamic breakdown voltage increased and approached to the static breakdown voltage with increasing the gap length and pressure, because of the suppression of thermal bubble disturbance in LHe. All of the experimental data enabled us to establish the 3-D systematized diagram of the dynamic breakdown voltage of LHe as functions of post-quench thermal energy, gap length and pressure. This diagram is quite useful to determine which combination of gap length and pressure should be chosen under arbitrary post-quench thermal energy for the practical electrical insulation design of SC power apparatus.

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Normal transition behaviors such as minimum quench energy and normal-zone propagation velocity along longitudinal direction for two types of copper-stabilized Nb₃Sn conductors have been investigated at temperatures over 4.2K in He gas atmosphere compared with NbTi/CuNi composite conductor. Both of bronze-processed and powder-processed Nb₃Sn conductors show minimum quench energy several times as large as that of the NbTi conductor. Quench current for AC operation of the NbTi conductor is crucially degraded from critical current for DC operation. On the other hand, quench currents for the two types of Nb₃Sn conductors reach their respective critical currents. Normal-zone propagation velocities for both Nb₃Sn conductors are one order of magnitude lower than that of the NbTi conductor at the same temperature load factor. The experimental propagation velocity is well estimated by taking account of heat transfer from the conductor to its surroundings.

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The superconducting fault current limiter (SQFCL) is expected to be the first application of high-T_c superconductors (HTSs) in power systems. To develop a magnetic shielding type superconducting fault current limiter, we have carried out some fundamental experiments concerning the magnetic shielding characteristics of an HTS bulk cylinder. In this paper, the experimental results of magnetic flux penetration into Bi(2223) cylinder are shown. AC magnetic field is applied to the sample by a primary winding (copper coil) excited by AC triangular-and sinusoidal-waveform currents in the frequency range of 0.1 Hz to 100 Hz. We also developed a Finite Element Method (FEM) computer program for evaluation of the dynamic electromagnetic behavior of the HTS cylinder in a time-varying external magnetic field. The results of computer simulations considering the voltage-current (E-J) characteristic are compared with experiments. Then we carried out a current-limiting test with a small limiter model, and the developed FEM computer program successfully simulated the electromagnetic behavior in the current-limiting operation.

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Super-GM (Engineering Research Association for Superconductive Generation Equipment and Materials, Japan) has been conducting R&D on 70MW class superconductive generatorequipment and superconductors since FY 1988. We have been a part of Super GM and developed the Nb₃Sn superconductor by tube method for AC application since FY 1989. In this paper, we report the results of R & D which are the measurement results of the hysteresis losses of the Nb₃Sn superconducting wires from 4.2K to 10K, the properties of the AC Nb₃Sn superconducting cables with high current capacity and the AC elemental coil manufactured by R&W method.

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The AC quench current and AC losses of multi-strand Nb-Ti superconducting cables for S/N type fault current limiter are described. The Cu ratio for S/N type fault current limiter should be zero or less than 0.2, in order to increase normal state resistivity. The resistances of Nb-Ti/Cu-Ni strands with zero Cu content shall be 3.9_??_13.2Ω/m at 10K. A 72-strand 3kA-class cable showed higher AC (50Hz) quench currents with suppression of wire movements. The AC quench currents I_q's of multi-strand cables change with the phase angle difference (θ) between the magnet current and the sample current. A 7.6mm-dia cable from 360 pieces of Nb-Ti/Cu-Ni strands with zero Cu content and resistance of 6.7Ω/m at 10K each, showed I_q's of 4_??_4.5kA_rms at θ of 0° and 180° and 5.5_??_6.6kA_rms at θ of 90° and 270° at a bias field of 0.5T_peak, and showed those over 8kA_rms at θ of 0° 90°, 180° and 270° at a bias field of 0.2T_perk or under, both at a frequency of 51.41Hz. On the other hand, A 7.6mm-dia cable from 360 pieces of Nb-Ti/Cu-Ni/Cu strands with Cu ratio of 0.17 and resistance of 0.91Ω/m at 10K each, showed I_q's of 7_??_7.8kA_rms at θ of 0° and 180° and 8.5_??_9.3kA_rms at θ of 90° and 270° at a bias field of 0.5T_peak, and showed those over lOkA_rms at θ of 0° 90°, 180° and 270° at a bias field of 0.2T_peak or under, both at a frequency of 51.41Hz. Though the former cable from NbTi/Cu-Ni type strands shows lower stability due to the absence of Cu, it satisfies I_q, requirement for S/N type fault current limiter of 8kA_rms or over at its level fields of 0.2T_peak or less. Cables from 360 and 432 pieces of strands showed AC loses of 8_??_10kW/m³ at 0.5T_peak, and those less than 1.8kW/m³ at 0.2T_peak, both at 51.41Hz.
A non-inductive coil built from a 34m long 72-strand cable was operated in a 210V class experimental circuit assembled for generating short circuit current. The non-inductive coil has successfully limited 4kA_peak short circuit current (or, fault current interruted) to about lOOA_rms within about 10ms. Thus, the availability of the cables from NbTi/Cu-Ni base strands for fault current limiter has been assured.

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We have designed and manufactured a large capacity of Superconducting Nb-Ti conductors for AC (50Hz) use. The conductor is a triply-stacked multi-strand (6×6×12) type. The elementary strand has Nb-Ti filaments of 0.15μm diameter in Cu-Ni matrix, and Cu stabilizer divided into 19 parts, surrounded by Cu-Ni barrier, located in the center of a strand and Cu filaments in the peripheral of filamentary region. The twist pitch and direction of a strand and conductor is designed to minimize a magnetic instability due to a longitudinal field along the strand. The performances of the conductor in 0.5T_peak, 50Hz field were as below. The maximum current and current density was 10.6kA_rms and 167A_rms/mm². The attained level of the current is nearly 100% of the critical one on the load line.

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Muntilayered wires, consisting of Bi-superconducting layers and silver layers, have been developed in order to realize high critical current density (J_c), subject optional wire forms. For instance, a Bi-2212 round wire having J_c=37.4 kA/cm² at 4.2K and 10T; a Bi-2223 tape wire, with a silver ratio of 1.3, measured J_c=21.3 kA/cm² at 77K, OT. Several multilayered wires underwent test of J_c-B characteristic, mechanical property and AC losses, in search for their adaptability to electric power equipment. Moreover, assembling multilayered wires was studied in light of AC and DC characteristics, using conductors, each of which was comprised of tape or round wires. In the last place, two solenoid coils of Bi-2212 round wires and a double-pancake coil of Bi-2223 tape wires were fabricated and found to generate magnetic fields of 1.1T at 4.2K, 0.44T at 18K and 42mT at 77K, respectively; their electromagnetic and thermal behaviors were tested as DC operated.

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With an increasing demand for electric power, the electric power system becomes more and more complicated. Therefore, the supply of electric power with stability and high reliability is required. However, we have two big problems, that are a large fault current and power system unstability. In particularly, fault currents occuring in power system tend to increase. To solve this problem, superconducting fault current limiters (SCFCLs) are developed. The SCFCL is not only the problems of fault currents but also the power system stability are expected to be solved.
This paper describes experimental results about SCFCL, on improvement of power system stability and supressing fault currents by using power transmission simulators. The experiment by using R-type SCFCL in power system have been done. The R-type SCFCL is simulated by using a resistor and an electromagnetic contactor with thyristors. It is found that the SCFCL in the electric power system gives the improvement of the supressing fault current and power system transient stabilities.

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The superconducting AC power applications have been actively investigated in these days. In order to develop AC superconducting power apparatus, it is necessary for developing 10kA-1T class AC superconducting magnet as a fundmental technology. From such a viewpoint, the authors have been investigating AC superconducting coils which have a large AC transport current capacity.
In this paper, the specification and experimental results of the experimental 1kA-1T class AC superconducting coil which has been fabricated as a first step for developing AC superconducting power apparatus are shown. Two experimental AC coils whose conductors are the sub-cable and single strand of the 1kA-1T class AC superconducting coil conductor are also fabricated and tested to investigate the stability of AC superconducting coils.
The quench current of these 3 AC coils are measured and are compared to the DC critical current characteristics of the strand. From the result of the comparison, it is confirmed that the AC quench current of each superconducting coil is close to the DC quench current, and is also close to the current which is determined by the critical current characteristics defined by 0.1μV/cm criterion. Furthermore, it is confirmed that the quench point of the developed AC coil reaches to 288A_(peak)-1.396T_(peak).

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The Nb₃Sn superconducting wire for a. c. use was developed by in-situ method. In order to decrease a. c. loss, the diameter of the in-situ composite cores were very fine by increasing the core number. The conductor was made of this wire by cabling. Characteristics of the 2nd cabling conductors and the 3rd cabling conductors with a. c. current were tested by the short sample. The a. c. quench current value of the 3rd cabling conductor was 5.8kArms at 0.5T.

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Nb₃Sn strands of high current density and low hysteresis loss have been developed using bronze process and internal tin diffusion process for fusion superconducting pulse magnets. 13.6 tons of strands have been manufactured in total. Critical current has been improved up to 125-150% and hysteresis losses have been reduced to 1/3-1/4 compared with strands developed in the past in JAERI. Using strands, large scale conductors for ITER demonstration have been manufactured, which are designed to carry an operating current of 46kA under a field of 13 T.

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Superconducting generators have many advantages such as increasing generation efficiency, improving power system stability and reducing size and weight in comparison with conventional generators. In Japan, 70MW class superconducting generators (model machine) are being developed. Manufacture of “70MW class slow response excitation type rotor” started in 1992 and factory tests were conducted in 1996. Succeeding to the factory tests, the rotor was combined to the stator with air gap windings in the verification test facility (in Osaka power station) and verification tests were conducted in 1998. Satisfactory results which represent the advantages and the reliability of superconducting generators were obtained.
In this paper, test results of electrical characteristics of 70MW model generator such as “electrical constants” and “No load open/short circuit characteristics” are discussed. Evaluation by 3D magnetic analysis are also described. The main results are summarized below.
•The synchronouce reactance (X_d) was 0.42 p. u. which is 1/4_??_1/5 of conventional generators. X_d can be analyzed precisely by 3D magnetic field analysis which is now taken into account for the effect of the armature end windings on electrical characteristics.
•X_d''' which is originated in “double layer damper system” was separated clearly from 3-phase sudden short circuit test.
These reactances can be analyzed by quasi-3D analysis considering the boundary condition of rotor surface.
•By means of these magnetic analyses, fundamental design methods considering the end windings were established. These are applicable to the design of “200MW class pilot superconducting generator”.

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We have been developing 70MW class superconducting generators (called model machines) till now. The model machines are composed of two slow response excitation type rotors (called A and B type) and one quick response type rotor, and a commonly used stator for three rotors. A and B type machines were already installed in the verification test facility and were completed investigation by September 1998. Recently, quick response type machine has been tested. Superconducting generators have different characteristic and structure from conventional generator. For example, electric resistance of field winding for superconducting generators is nearly zero, and damper components in rotor are multiple. So, it is difficult to define some constants of superconducting generators by conventional methods. Therefore, according to the test results of these superconducting generators, we will propose and describe a practical investigation into some constants of the superconducting generators as below.

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R & D on Nb-Ti and Nb₃Sn superconducting cables for AC use has been carried out toward power applications. As for Nb-Ti conductors, three types of stranded cables were developed aiming at armature winding of generators, shunt reactors/transformers and fault current limiters. Structures of stranded cables were optimized based on the AC losses and the AC quench current (Iq) degradation in the applied magnetic field ranges of each apparatus. As a result, 10kA_rms in Iq and 10kW/m³ in AC losses (0.5T, 51Hz) were achieved. As for Nb₃Sn cables, effective improvement of both AC losses and Iq were made by addition of magnetic elements in the matrix and filaments and by optimizing the filament diameter and spacing. Moreover, we utilized the knowledge of Nb-Ti stranded cables in establishment of Nb₃Sn cable structures. As a result, 5kA_rms in Iq and 10kW/m³ in AC losses (0.5T, 51Hz) were achieved.

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A national project of development of a superconducting generator (SCG) has been carried out since 1988 in Japan under the New sunshine Project of AIST, MITI. A superconducting generator is supposed to have merits of stability improvement on transmission line, higher efficiency and compactness. A 70MW-class superconducting generator is the goal of the project.
Hitachi Ltd has been developing a rotor having superconducting field winding and a stator having air-gap armature winding.
The superconducting generator was tested in the Hitachi works, and a full-scale demonstration test was finished on December in 1997 in the Super-GM test site. The machine showed excellent performances, which are enough for a 70MW-class generator.

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This paper describes an application of the Lightning Location and Protection (LLP) system to lightning protection design for transmission lines through the observation of lightning characteristics. At first, we investigate relationships between lightning characteristics obtained from LLP system and actual lightning outage data on transmission lines, and examine the validity of lightning protection designs for 187kV transmission lines with a single ground wire. These results clearly show the possibilities to predict lightning striking conditions to transmission lines and lightning performances of transmission lines combining the lightning stroke current values measured by the LLP system with the Electro Geometric Model (EGM) method. A prediction method of lightning performance of transmission lines based on the results is proposed. The proposed method consists of the observation of lightning characteristics by the LLP system, the lightning shielding model based on the EGM method and the calculation model for lightning surge analysis based on the EMTP. Estimated results, that are the relationship between lightning current values and shielding characteristics, lightning outage rates on transmission lines, show good agreement with the observations.

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An analytical formula of a transient recovery voltage and its dv/dt across a circuit breaker has been derived for the case of a transformer secondary fault. A comparison of the calculated results with field test and EMTP simulation results has proved its satisfactory accuracy. Applying the formula, the effect of various circuit parameters on the transient recovery voltage and its dv/dt have been made clear. The dv/dt, defined conventionally as the ratio of the crest value and the time to the crest, is found to be about 2/3 of the maximum value of the dv/dt given as a function of the time. Also, a formula has been developed to give critical circuit parameters by which the dv/dt across a vacumn circuit breaker reaches the critical condition i.e. the circuit breaker fails to interrupt a fault current.

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This paper proposes a new measuring method of electric resistivity of outer-semiconductive layer of XLPE cable, which may substitute the conventional method. The resistivity can be obtained easily by measuring resistance between two electrodes which are attached to a circumferential edge on one side of the outer-semiconductive layer of a cable core sample.

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