No-insulation Winding Technique Research Articles

A novel no-insulation winding technique of high temperature-superconducting racetrack coil for rotating applications: A progress report in Korea university.

This paper presents our recent progress on core technology development for a megawatt-class superconducting wind turbine generator supported by the international collaborative R&D program of the Korea Institute of Energy Technology Evaluation and Planning. To outperform the current high-temperature-superconducting (HTS) magnet technology in the wind turbine industry, a novel no-insulation winding technique was first proposed to develop the second-generation HTS racetrack coil for rotating applications. Here, we briefly report our recent studies on no-insulation (NI) winding technique for GdBCO coated conductor racetrack coils in the following areas: (1) Charging-discharging characteristics of no-insulation GdBCO racetrack coils with respect to external pressures applied to straight sections; (2) thermal and electrical stabilities of no-insulation GdBCO racetrack coils encapsulated with various impregnating materials; (3) quench behaviors of no-insulation racetrack coils wound with GdBCO conductor possessing various lamination layers; (4) electromagnetic characteristics of no-insulation GdBCO racetrack coils under time-varying field conditions. Test results confirmed that this novel NI winding technique was highly promising. It could provide development of a compact, mechanically dense, and self-protecting GdBCO magnet for use in real-world superconducting wind turbine generators.

Over-current quench test and self-protecting behavior of a 7 T/78 mm multi-width no-insulation REBCO magnet at 4.2 K

This paper presents the over-current quench test and post-quench operation results of a 7 T 78 mm winding diameter multi-width (MW), no-insulation (NI) magnet in a bath of liquid helium at 4.2 K. The MW-NI magnet consists of 13 double-pancake (DP) coils wound with GdBCO tapes having five different widths ranging from 4.1–8.1 mm. After the magnet reached 7.3 T at 253 A, the magnet current was further increased purposely until the magnet quenched at 312 A, corresponding to a current density of 895 A mm−2 for the central DP coils of the narrowest 4.1 mm tape. The NI DP coils showed a fast magnetically coupled quench propagation from the quenched DP to the rest of the ‘healthy’ DP coils. The stored magnetic energy of 25.4 kJ was completely dissipated in 0.3 s with an average dissipation power rate of 85 kW. The post-quench magnet, operated sequentially in baths of liquid nitrogen at 77 K and in liquid helium at 4.2 K, showed no discernable changes from the pre-quench magnet in their key parameters, except the magnet characteristic resistance, pre-1.4 mΩ versus post-3.6 mΩ. Thus, a forced quench of the magnet, thanks to the NI winding technique, kept the integrity—mechanical, electrical, and magnetic—of this NI magnet intact.

A High-Resolution 1.3-GHz/54-mm LTS/HTS NMR Magnet.

A high-resolution 1.3-GHz/54-mm low-temperature superconducting/high-temperature superconducting (HTS) nuclear magnetic resonance magnet (1.3 G) is currently in the final stage at the Massachusetts Institute of Technology Francis Bitter Magnet Laboratory. Its key component is a three-coil (Coils 1-3) 800-MHz HTS insert comprising 96 no-insulation (NI) double-pancake coils, each wound with a 6-mm-wide GdBCO tape. In this paper, after describing the overall 1.3-G system, we present innovative design features incorporated in 1.3 G: 1) an NI winding technique applied to Coils 1-3 and its adverse effect in the form of charging time delay; 2) persistent-mode HTS shims; 3) a "shaking" magnet; and 4) preliminary results of Coil 1 operated at 4.2 K.

Numerical Electromagnetic Simulation of Effective Partial-insulation NbTi Superconducting Coil

The no-insulation winding technique is a promising way of enhancing the thermal stability of NbTi superconducting coils. However, it takes a long time to charge a no-insulation superconducting coil, because the time constant is relatively large. Hence, a partial-insulation winding technique was also proposed to reduce the time constant with a high thermal stability. However, the time constant of the previously proposed partial-insulation NbTi superconducting coil could not drastically be improved, and the cause was investigated using a partial-element equivalent circuit model. Therefore, in this paper, we propose a new partial-insulation structure, and the effectiveness is verified using a partial element equivalent circuit model. The results show that a relatively small time constant is achieved when charging and discharging the proposed partial-insulation NbTi superconducting coil.

Experimental Study on Low-Pass Filtering Characteristic of Axial Magnetic Field of No-Insulation and Partial-Insulation HTS Coils Carrying a DC-Biased AC Current

This paper deals with the low-pass filtering characteristic of the axial magnetic field of no-insulation and partial-insulation high temperature superconducting (HTS) coils carrying a dc-biased ac current. Recently, the no-insulation winding technique has been issued as a key technique to enhance the performance of HTS coils in terms of the overall current density, thermal stability, and mechanical integrity. In this paper, to verify the effect of time-varying external distortion on no-insulation HTS coils, an experimental analysis is carried on three HTS coils-insulation, no-insulation, and partial-insulation coils. To simulate the environment in which time-varying external distortion influences the HTS coils, a dc-biased ac current is carried by the HTS coils. The axial magnetic fields of no-insulation, partial insulation, and insulation HTS coils are experimentally tested and analyzed. When the coils carry a dc-biased ac current, the no-insulation and partial-insulation coils have a tendency to attenuate the high-frequency components and to act as a low-pass filter on the axial magnetic field; however, the insulation coil does not attenuate the high-frequency components of the axial magnetic field. The analysis of the experimental results can be useful data for the adoption of no-insulation and partial-insulation windings in superconducting applications.

Partial-Insulation Winding Technique for NbTi Coils

In 2010, we reported, for the first time, the no-insulation (NI) winding technique for high-temperature superconducting (HTS) pancake coils. Based on our test results of small NbTi NI coils, reported in 2011, the key benefits, i.e., enhanced mechanical integrity, compactness, and thermal stability, of the NI winding technique, appear intact for low-temperature superconducting (LTS) windings. However, the intrinsic charging delay observed in NI coils, caused by the lack of insulation, is more pronounced in LTS coils of a bare round wire than in HTS pancakes of thin, wide tape. Thus, to significantly reduce the charging delay in LTS coils of a bare round wire, we proposed a partial-insulation (PI) winding technique, a variation of the NI technique. In the PI winding of a bare round wire, a thin insulation sheet is introduced every few layers-note that in the PI winding, there are no turn-to-turn insulations. This paper reports results, experimental and analytical, of the PI winding technique in which bare-round-wire NI and PI coils were prepared to quantify the effects of PI winding technique. Three LTS coils of the identical dimension and magnet constant were wound with 0.4 mm diameter NbTi mono-filament wire and tested in a bath of liquid helium at 4.2 K, respectively, with three winding techniques: insulated (INS); NI; and PI. We analyzed the experimental results by applying an equivalent circuit model that had earlier been successfully applied to another set of experimental results. A graph model of resistance matrix was applied to estimate characteristic resistance of both NI and PI coils.

Numerical Simulation of Superconducting Coil Wound With No-Insulation NbTi Wire

A no-insulation winding technique for an NbTi superconducting coil is expected to improve its dynamic stability during charging or discharging. Experimental results, recently reported, demonstrated the charging stability enhancement of an NI coil. In an NI winding, an amount of current can bypass to adjacent wires to avoid the generation of a local hot spot and, as a result, the dynamic stability is improved. In spite of the potential technical merits of the NI technique, the charging responses of an NI coil, including the non-uniform current distribution under a time-varying condition, have not been investigated analytically yet. In this paper, we propose a simulation method using an equivalent circuit equation for an NI coil with its inductance and the contact turn-to-turn resistances taken into consideration. The simulation results were analyzed in three aspects: terminal voltage, loss energy, and stored magnetic energy.

Investigation of HTS Racetrack Coil Without Turn-to-Turn Insulation for Superconducting Rotating Machines

This paper reports a study of two HTS racetrack coils wound with GdBCO coated conductors, one without turn-to-turn insulation and the other with Nomex insulation. The coils were characterized by charge-discharge, over-current, and sudden discharge tests. Thermal and electrical characteristics of the GdBCO racetrack coil without insulation outperformed the insulated one. The test results confirmed that although the coil without insulation has a slow charging/discharging time constant, the no-insulation winding technique may enable a compact and protection-free racetrack-typed coil with enhanced mechanical integrity as well as better thermal and electrical stabilities.