The application of superconducting fault current limiters (SCFCLs) in power systems is very attractive because SCFCLs offer superior technical performance in comparison to conventional devices to limit fault currents. Negligible impedance at normal conditions, fast and effective current limitation within the first current rise and repetitive operation with fast and automatic recovery are the main attributes for SCFCLs. In recent years there has been a significant progress in the research and development (R&D) of SCFCLs. This paper gives an extended review of different SCFCL concepts, SCFCL applications and the R&D status. Within the first part of this paper the most important SCFCLS and, to a limited extent, non-superconducting fault current limiter (FCL) concepts are explained and compared. The second part reviews interesting SCFCL applications at the distribution and transmission voltage level and the third part shows in detail the R&D status. It can be summarized that SCFCLs are, at present, not commercially available but several successful field tests demonstrated the technical feasibility of SCFCLs. First distribution level applications are expected soon. Considerable economical and technical benefits can be achieved by applying SCFCLs at the distribution and transmission voltage level.

https://iopscience.iop.org/article/10.1088/0953-2048/20/3/R01/pdf

High-temperature superconductor fault current limiters: concepts, applications, and development status

Development of high-temperature solders: Review

Recent progresses in the second generation REBa2Cu3O7 − x (RE123) coated conductor (CC) have paved a way for the development of superconducting solenoids capable of generating fields well above 23.5 T, i.e. the limit of NbTi−Nb3Sn-based magnets. However, the RE123 magnet still poses several fundamental and engineering challenges. In this work we review the state-of-the-art of conductor and magnet technologies. The goal is to illustrate a close synergetic relationship between evolution of high-field magnets and advancement in superconductor technology. The paper is organized in three parts: (1) the basics of RE123 CC fabrication technique, including latest developments to improve conductor performance and production throughput; (2) critical issues and innovative design concepts for the RE123-based magnet; and (3) an overview of noteworthy ongoing magnet projects.

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Progresses and challenges in the development of high-field solenoidal magnets based on RE123 coated conductors

Bulk high-temperature superconductors (HTSs) enable the opportunity to develop several unique applications in electrical power that are not feasible with superconducting or normal wires. The large current carrying capacity and low thermal conductivity of the HTSs allows relatively short lengths to carry large currents to low-temperature devices without introducing heat to the device. Such current leads can dramatically reduce the refrigeration requirements for devices such as SMES. The HTSs make a relatively sharp transition to a highly resistive state when the critical current density is exceeded, and this effect has suggested their use for resistive fault current limiters. The bulk HTSs may also take the form of large single-grained superconductors within which circulating currents may flow at large current density without loss. They are capable of developing magnetizations, similar to that of permanent magnets, but with much larger magnetic fields. In this case, they may be used as field-trapping components. Applications in this case include brushless synchronous motors, laboratory magnets, magnetic separation, and magnetron sputtering. The bulk HTSs may also be used as diamagnetic objects in magnetic circuits to provide new types of power devices. One application that uses this effect is an inductive fault current limiters, in which the HTS shields an iron core in an inductive circuit until some current level is exceeded. This transition increases the component from low impedance to high impedance. The diamagnetic property may also be used to create low-loss magnetic bearings for use in efficient energy-storage flywheel devices or sensitive instrumentation. The combination of diamagnetic shielding and field trapping has suggested their use in motor designs analogous to hysteresis motors. Laboratory prototypes for all of these devices have been constructed and tested, and in some cases the devices have been field tested in actual power systems. Improvements in HTS properties, such as flux pinning, mechanical strength, and the ability to grow large grains, have greatly improved the economics of applications that use bulk HTS.

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Applications of bulk high-temperature Superconductors

The paper contains a review of recent advancements in rotating machines with bulk high-temperature superconductors (HTS). The high critical current density of bulk HTS enables us to design rotating machines with a compact configuration in a practical scheme. The development of an axial-gap-type trapped flux synchronous rotating machine together with the systematic research works at the Tokyo University of Marine Science and Technology since 2001 are briefly introduced. Developments in bulk HTS rotating machines in other research groups are also summarized. The key issues of bulk HTS machines, including material progress of bulk HTS, in situ magnetization, and cooling together with AC loss at low-temperature operation are discussed.

http://iopscience.iop.org/article/10.1088/0953-2048/25/10/103001/pdf

An overview of rotating machine systems with high-temperature bulk superconductors

A new type of fault current limiter (FCL) utilizing series LC resonance circuit composed of a superconducting coil and a capacitor is proposed. The superconducting coil is wound by Bi-2223/Ag HTS tape conductor. The new FCL can suppress the rapid increase of a fault current by its energy storing capacity. Both theoretical analysis and experiments are carried out. The experimental result shows the current limiting ability of this FCL. The obtained experimental result agrees well with the theoretical one

Fundamental Characteristics of Superconducting Fault Current Limiter Using LC Resonance Circuit

The current limiting behavior of a 3-phase superconducting fault current limiting reactor (SCFCLR) in a model power system at a single-line-to-ground (SLTG) fault is experimentally confirmed. A small arc gap is attached on one phase of the model transmission line. A single-line-to-ground fault is activated. The behavior of the grounding current and the arc is observed. It is shown that: (1) the fault current is limited to a very small value by the large zero-phase-sequence reactance of the SCFCLR, and the self-extinction of the fault arc is observed; (2) the power flow is not disturbed by a SLTG fault at all, and no power system disturbances are observed; and (3) the windings do not quench for a SLTG fault. A supplementary experiment for a two-phase short circuit fault was also carried out. >

Single-line-to-ground fault test of a 3-phase superconducting fault current limiting reactor

The authors are investigating the possibility of using bulk magnets in the Maglev system. It is considered that bulk magnets for the Maglev system must be composed of numerous superconducting bulks arranged in rows and columns for each magnet pole because a bulk superconductor with a high critical current density doesn't have a sufficiently large size for Maglev magnet. Therefore, it is necessary to examine the flux-trapping characteristic of superconducting bulks arranged in array. Flux-trapping experiments are performed using the melt-processed YBaCuO superconducting bulks arranged in rows and columns, in which each bulk individually has a magnetizing coil, and the bulks are magnetized by field cooling. It is found that, when the superconducting bulks are arranged in rows and columns, the trapped flux density and the generated magnetic field are smaller than those when a superconducting bulk is used alone. The rate of decreases in the trapped flux density and the generated magnetic field becomes larger with increases in the number of superconducting bulks arranged in array. The trapped flux decreases conspicuously in particular at a superconducting bulk surrounded by other superconducting bulks.

Flux-trapping characteristics of oxide superconducting bulks in array

An ultrasonic quench-detection method for superconducting magnets is presented. This nondestructive method monitors the change of the acoustic transfer function of a superconducting magnet induced by a local temperature rise or an epoxy crack. Experiments were carried out on a small epoxy-impregnated magnet. The experimental results show that a local temperature rise of about 2-3 K can be detected by this method. It is concluded that the technique can provide early quench warning by monitoring continuously the change of the acoustic transfer function of the magnet. >

Quench detection of superconducting magnets using ultrasonic wave

A resonance-type superconducting fault current limiter (FCL) using Bi-2223 superconducting coils was developed and tested in order to demonstrate its actual operation. Over-current tests of the FCL were carried out for 50 Hz steady-state current of up to 120 A with relevant combinations of a superconducting reactor, an arrester, a capacitance and a copper reactor. The test results showed that the currents during faults were controlled within low levels. It was also demonstrated that the FCL could promptly recover to the steady state after the faults were cleared

Takeshi Ishigohka

Papers

Fundamental Characteristics of Superconducting Fault Current Limiter Using LC Resonance Circuit

Single-line-to-ground fault test of a 3-phase superconducting fault current limiting reactor

Flux-trapping characteristics of oxide superconducting bulks in array

Quench detection of superconducting magnets using ultrasonic wave

Test of Resonance-Type Superconducting Fault Current Limiter