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A non-inductive coil is an essential element of a resistive superconducting fault current limiter (FCL). A bifilar pancake type non-inductive coil, which is most common type, has two drawbacks; difficulty of paralleling tapes and a high risk of electrical breakdown at the terminal part. Although the bifilar type is simple as an element, large-scale FCL needs quite a number of series and parallel connections between elements. To make a non-inductive coil using conventional inductive elementary coils, we propose a novel structure of the coil. It looks like a toroid but entire inductance is near zero. This coil can overcome the drawbacks of conventional bifilar coil. In this paper, we confirm the new concept by numerical analyses. A few kinds of new models are compared, and then we concluded the proposed toroidal shape one is most suitable. This new structure coil can help implement of a hybrid FCL which is to generate the magnetic field at only fault. [ABSTRACT FROM AUTHOR]

The power grid, especially distribution grid, has been more complicated due to distributed generations (DGs) with renewable energy sources and the smart grid. The complexity changes two things in terms of a fault; higher prospective fault current and the temporal variation of sources and loads. To correspond to those remarkable changes, we propose a fault current controller (FCC) named “smart FCC.” The smart FCC consists of a superconducting coil with a freewheeling diode if necessary, four thyristors, and a control unit. Smart FCC can not only limit but also control the current when a fault occurs. The smart grid technology can provide so enough information that it is possible to estimate which level of limited current should be the best in the real-time situation of the grid. Based on a real-time calculation of optimal fault current using the smart grid monitoring technologies, this new device is always ready to adjust the fault current. In this paper, we introduce a concept of the smart FCC and prove the concept. Various topologies have been proposed and simulated. Finally, a case study on a distribution class of 22.9 kV smart FCC has been conducted based on a conceptional system design. [ABSTRACT FROM AUTHOR]

This paper reports results, experimental and analytical, of the nonlinear behavior of a shim coil in the presence of an HTS coil assembled with double-pancake (DP) HTS-tape coils. The experimental results are from: 1) operation of a 700 MHz LTSIHTS NMR magnet (LH700) consisting of a 600 MHz LTS NMR magnet (L600) equipped with superconducting shim coils and a 100 MHz DP-assembled HTS insert (H100) and; 2) an experiment with a room-temperature (RT) Z1 shim coil coupled to a 50 MHz DP-assembled HTS insert (H50). A field mapping theory with a harmonic analysis is applied to interpret both results. Based on experimental results and analyses, we conclude that the screening-current-induced field (SCF) generated by a DP-assembled HTS insert is primarily responsible for the nonlinear behavior, including strength degradation, of a shim coil. [ABSTRACT FROM AUTHOR]

This paper addresses adverse effects of dimensional uncertainties of an HTS insert assembled with double-pancake coils on spatial field homogeneity. Each DP coil was wound with Bi2223 tapes having dimensional tolerances larger than one order of magnitude of those accepted for LTS wires used in conventional NMR magnets. The paper presents: 1) dimensional variations measured in two LTS/HTS NMR magnets, 350 MHz (LH3SO) and 700 MHz (LH700), both built and operated at the Francis Bitter Magnet Laboratory; and 2) an analytical technique and its application to elucidate the field impurities measured with the two LTSIHTS magnets. Field impurities computed with the analytical model and those measured with the two LTSIHTS magnets agree quite well, demonstrating that this analytical technique is applicable to design a DP-assembled HTS insert with an improved field homogeneity for a high-field LTSIHTS NMR magnet. [ABSTRACT FROM AUTHOR]

This paper presents the results of work, experimental and simulation, performed on an YBCO pancake coil to develop a detect-and-activate-the-heater (DAH) protection technique. In this DAH protection technique a "protection heater" (PH) is activated, upon the detection of a quench zone in a coil, to create an additional normal zone to absorb the stored magnetic energy sufficient to keep the initially quenched zone (hot spot) from overheating. It is computed that a protection heater for most coils needs to cover only a fraction of the winding to keep the quenched zone from overheating. The pancake coil used in the experiment, 100-mm i.d., 190-mm 04., and 4.3-mm height, is dry-wound with copper plated YBCO tape, 4.3-mm wide, 96.3-μm thick, 100-m long, and is turn-to-turn insulated with 38-μm thick Nomex spacer. The pancake stores a magnetic energy of 30 J at an operating current of 80 A at 65 K. Because the smaller the magnet size, the less applicable the assumption of adiabatic conditions is and also the more beneficial NZP becomes that would otherwise be negligible in "large" magnets, the hot spot temperature observed in the experiment with this "small" test coil was much less than that computed based on the assumptions of adiabatic conditions and no NZP. To validate the basic concept and consequences of DAH protection technique either a test coil has to be large or if the same coil is to be used, it should be tested at the temperature range close to 20-30 K so that the coil can carry a large current and thus store a large magnetic energy. [ABSTRACT FROM AUTHOR]

Abstract: Recently, YBCO coated conductor (CC) called as second generation (2G) wire has been developed rapidly. The CC has a stabilizer layer for protecting the wire during a quench of the wire. In resistive superconducting fault current limier (SFCL), the stabilizer makes the resistance and limits the fault current during the fault. Therefore, specification of the stabilizer is one of important design factors in SFCL. This paper describes the current limiting characteristics of three coated conductors with respect to the specifications of the stabilizer. Two samples made by American Superconductors® have copper stabilizers attached by soldering. However, the two samples have not same structures. One has one-sided stabilizer, the other has both-sided stabilizer. On the other hand, another sample made by IGC-SuperPower® has copper stabilizer attached by electroplating, and the stabilizer layer surrounds the whole cross-section of the wire. Over-current tests of the three samples with various stabilizers were performed. Each sample has 8cm in length. From the results, the SFCL using the CC wire could be designed. [Copyright &y& Elsevier]

The conduction-cooled cryogenic cooling system for 1.2 kV/80 A inductive Superconducting Fault Current Limiter (SFCL) was fabricated and tested for its cooling characteristics in 2002. The observed thermal stability of the conduction-cooled system was very unreliable and precarious for the applied superconducting equipment with very large variation of currents like SFCL. Therefore, we replaced the conduction-cooled system with the sub-cooled nitrogen system for the 6.6 kV/200 A SFCL. In this paper, the design techniques and test results of cooling characteristics were introduced. The conditions for achieving the sub-cooled nitrogen state were 1 atm and 64 K. First, the temperature of 64 K was achieved by using the rotary pump and then the pressure of 1 atm was achieved by GHe. The characteristics of liquid nitrogen were strongly enhanced in these conditions. This fabricated cryogenic system merely for the short run operation test SFCL. Finally, the cryogenic system for the long run operation test SFCL was introduced. [ABSTRACT FROM AUTHOR]

A high-Tc superconducting (HTS) DC reactor has been developed as a part of DC reactor type superconducting fault current limiter (SFCL) rated on 6.6 kV/200 A. The DC reactor was a solenoid coil and was wound with a 4-parallel stacked tape. This coil has 5 layers which are connected in series each other. The inductance of the coil is about 84 mH. This paper deals with the design, fabrication and testing of the DC reactor. For this design of the coil, a prototype solenoid coil had been used. Using the experimental result of a prototype solenoid, the number of stacks and the inductance were designed. The winding machine for the HTS solenoid was manufactured. Using this machine, the large-scale HTS solenoid using a Bi-2223 tape was fabricated successfully. Characteristics of the fabricated coil were observed through a measurement of voltage as current transportation. [ABSTRACT FROM AUTHOR]

As a part of the 21st Century Frontier R&D Program in Korea being performed from 2001, a DC Reactor type Superconducting Fault Current Limiter (SFCL) is being developed. The target of the first phase is to develop a 6.6 kV/200 A class 3-phase SFCL as a prototype for a 154 kV class. This prototype SFCL has a magnet wound with a high-Tc superconducting wire (Bi-2223) operating at 65 K. The magnet uses solenoid bobbins with grooves for the tape wire. Its inductance is about 84 mH. An AC-DC power converter was made with Light Trigger Thyristor (LTT) having a phase controller. The maximum voltage is 7 kV. The DC reactor, which is cooled by sub-cooled nitrogen, uses a three phase transformer with dual tap for series connection with a power line. Through several experiments this SFCL shows current limiting performance about 50% of short circuit current at short run tests. [ABSTRACT FROM AUTHOR]

The High Temperature Superconducting (HTS) electric equipment using Bi-2223 wire successfully commercialized 1st generation HTS wire, has been developing by many research groups. HTS coil is one of the most important parts in HTS electric equipment. To enlarge the critical current, the operating temperature of the equipment tends to go down and number of HTS wire tends to increase. Thus, it is very important to determine the whole critical current of HTS coil for the stable operation of HTS equipment. The whole critical current of multi-stacked wire of HTS solenoid coil is not equal to the sum of the critical current of each stacked wire because of nonuniform current sharing occurs in multi-stacked HTS wires and each HTS path does not has the same critical current. In this paper, current sharing in two types of 5-stacked HTS solenoid coils, made up of 1 copper layer which is a current buffer layer of HTS coil and 4 HTS wire layers, was analyzed. One was wound with Bi-2223 wire insulated with polyimide tape and the other was wound with noninsulated Bi-2223 wire. All of the Bi-2223 wires were reinforced with stainless steel. The simulation results of current sharing in multi-stacked HTS coils coincided well with the experimental results. Based on these results, the current sharing ratio of large scale HTS coil was also expected. The copper layer acted as a good current path when all the HTS wires were quenched. [ABSTRACT FROM AUTHOR]