This paper reports a study of HTS pancake coils without turn-to-turn insulation. Three no-insulation (NI) pancake coils were wound: each single and double pancake coil of Bi2223 conductor and one single pancake of ReBCO conductor. An equivalent electrical circuit for modeling NI coils was verified by two sets of test: 1) charge-discharge; and 2) sudden discharge. Also, an overcurrent test in which a current exceeding a coil's critical current by 2.3 times was performed, and analysed, to demonstrate that in terms of stability NI HTS coils outperform their counterparts. The new NI winding offers HTS coils enhanced performance in three key parameters: overall current density; thermal stability; and mechanical integrity.

HTS Pancake Coils Without Turn-to-Turn Insulation

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

Strong magnetic fields are required in many fields, such as medicine (magnetic resonance imaging), pharmacy (nuclear magnetic resonance), particle accelerators (such as the Large Hadron Collider) and fusion devices (for example, the International Thermonuclear Experimental Reactor, ITER), as well as for other diverse scientific and industrial uses. For almost two decades, 45 tesla has been the highest achievable direct-current (d.c.) magnetic field; however, such a field requires the use of a 31-megawatt, 33.6-tesla resistive magnet inside 11.4-tesla low-temperature superconductor coils1, and such high-power resistive magnets are available in only a few facilities worldwide2. By contrast, superconducting magnets are widespread owing to their low power requirements. Here we report a high-temperature superconductor coil that generates a magnetic field of 14.4 tesla inside a 31.1-tesla resistive background magnet to obtain a d.c. magnetic field of 45.5 tesla—the highest field achieved so far, to our knowledge. The magnet uses a conductor tape coated with REBCO (REBa2Cu3Ox, where RE = Y, Gd) on a 30-micrometre-thick substrate3, making the coil highly compact and capable of operating at the very high winding current density of 1,260 amperes per square millimetre. Operation at such a current density is possible only because the magnet is wound without insulation4, which allows rapid and safe quenching from the superconducting to the normal state5–10. The 45.5-tesla test magnet validates predictions11 for high-field copper oxide superconductor magnets by achieving a field twice as high as those generated by low-temperature superconducting magnets. A copper oxide high-temperature superconductor magnet generates a direct-current magnetic field of 45.5 tesla—the highest value reported so far—using a design that enables operation at high current densities.

45.5-tesla direct-current magnetic field generated with a high-temperature superconducting magnet

https://cyberleninka.org/article/n/818074.pdf

Recent advances in iron-based superconductors toward applications

This paper presents experimental and analytical studies on the characteristic resistance of NI (no-insulation) ReBCO pancake coils, which are used in an equivalent circuit model to characterize 'radial as well as spiral' current paths within the NI coils. We identified turn-to-turn contact resistance as a major source of the characteristic resistance of an NI coil. In order to verify this, three single pancake NI HTS coils-60, 40, 20 turns-were fabricated with their winding tension carefully maintained constant. A sudden discharge test was performed on each coil to obtain its characteristic resistance, and the relation between the turn-to-turn contact and the characteristic resistance was investigated. Based on the characteristic resistance and the n-value model, an equivalent circuit model was proposed to characterize the time-varying response of the NI coils. Charging tests were performed on the three test coils and the experimental results were compared with the simulated ones to validate the proposed approach with the equivalent circuit model.

https://iopscience.iop.org/article/10.1088/0953-2048/26/3/035012/pdf

Turn-to-turn contact characteristics for an equivalent circuit model of no-insulation ReBCO pancake coil

This paper presents a study to determine the optimal resistive value of a superconducting fault-current limiter (SFCL) for enhancing the transient stability of a power system more effectively. A resistive type of SFCL, which provides quick system protection, is modeled. Then, the optimal resistive value of the SFCL connected in series with a transmission line during a short-circuit fault is systematically determined by applying the equal-area criterion based on the power-angle curves. To verify the effectiveness of the optimal value of the proposed SFCL for reducing the value of fault current, several case studies are carried out by both simulation and experimental tests, particularly including the 220-V/300-A-scale laboratory and 13.2-kV/630-A-scale distribution system hardware tests. The results show that the optimal resistive value of the SFCL determined by the proposed method improves effectively the transient stability and damping performances during a fault over the other values determined by an ad hoc approach.

Study on a Series Resistive SFCL to Improve Power System Transient Stability: Modeling, Simulation, and Experimental Verification

A no-insulation (NI) technique has been applied to wind and test a NI HTS (YBCO) double-pancake coil at 4.2 K. Having little detrimental effect on field-current relationship, the absence of turn-to-turn insulation enabled the test coil to survive a quench at a coil current density of 1.58 kA/mm2. The NI HTS coil is compact and self-protecting, two features suitable for large high-field magnets. To investigate beneficial impacts of the NI technique on >;1 GHz LTS/HTS NMR magnets, we have designed six new NI HTS inserts for our ongoing 1.3 GHz LTS/HTS NMR magnet, which require less costly LTS background magnets than the original insulated HTS insert. A net result will be a significant reduction in the overall cost of an LTS/HTS NMR magnet, at 1.3 GHz and above.

/pdf/no-insulation-ni-hts-inserts-for-1-ghz-lts-hts-nmr-magnets-4x8n1opg8j.pdf

No-Insulation (NI) HTS Inserts for $>$ 1 GHz LTS/HTS NMR Magnets

We present a No-Insulation (NI) Multi-Width (MW) winding technique for an HTS (high temperature superconductor) magnet consisting of double-pancake (DP) coils. The NI enables an HTS magnet self-protecting and the MW minimizes the detrimental anisotropy in current-carrying capacity of HTS tape by assigning tapes of multiple widths to DP coils within a stack, widest tape to the top and bottom sections and the narrowest in the midplane section. This paper presents fabrication and test results of an NI-MW HTS magnet and demonstrates the unique features of the NI-MW technique: self-protecting and enhanced field performance, unattainable with the conventional technique.

No-insulation multi-width winding technique for high temperature superconducting magnet.

This paper presents experimental and analytical studies on the time-varying behavior of an NI (no-insulation) high-temperature superconductor pancake coil, alone or magnetically coupled to an external coil. An NI coil and another insulated coil (as an external), both of identical winding i.d. and number of turns, were fabricated. Another external coil used in this study was a 300-mm/5-T low-temperature superconductor magnet. An equivalent circuit model is proposed to simulate the NI coil, and the external coil, under time-varying conditions. Good agreement between experiment and simulation shows that the proposed equivalent circuit model is valid to characterize the time-varying electromagnetic behavior of an NI coil, alone or magnetically coupled to an external coil.

Dong Keun Park

Papers

HTS Pancake Coils Without Turn-to-Turn Insulation

Study on a Series Resistive SFCL to Improve Power System Transient Stability: Modeling, Simulation, and Experimental Verification

No-Insulation (NI) HTS Inserts for $>$ 1 GHz LTS/HTS NMR Magnets

No-insulation multi-width winding technique for high temperature superconducting magnet.

No-Insulation Coil Under Time-Varying Condition: Magnetic Coupling With External Coil