Hagyeong Lee

This paper presents the effects of the Lorentz force on the electrical behaviors of the no-insulation (NI) GdBCO racetrack pancake (RP) coil without turn-to-turn insulation by performing charging/discharging and sudden-discharging tests. The simulation results of the 2-dimensional finite element method showed that the Lorentz forces were generated towards the center of the winding pack consisting of 60- turn GdBCO CCs, which could enhanced the turn-to-turn contact within the RP coil. The chargin

A novel 2D process simulator has been developed which can handle local oxidation, implantation through arbitrary mask edges, non-planar surfaces, and high concentration diffusion. Through coupling of 2D process and device simulators, simple power law dependencies relating breakdown voltage and perimeter junction capacitance to field implantation dose and local oxidation time have been obtained.

This paper reports the optimization procedure for a no-insulation (NI) multi-width (MW) REBCO magnet, which enables the fabrication of a highly compact and competitively priced superconducting magnet. In order to identify the design considerations for the NI-MW magnet, the electromagnetic performances of 3 different magnets were investigated using the finite element method (FEM). Based on the comparison results, it was verified that the critical current distribution-factor (CCD-factor), which is

In this study, sudden discharge tests were performed on partially-insulated (PI) GdBCO coated conductor single-pancake coils to investigate the effects of a PI winding scheme on the discharge characteristics. Three sets of PI coils were constructed with insulation at 3 different intervals: every 2nd, 4th, and 8th turn. Each set included coils with 4 different insulation-angles: 90˚, 180˚, 270˚, and 360˚. Discharge delay of the PI coils was alleviated by increasing the insulation-interval or insu

An acoustic emission (AE) technique was introduced as a non-destructive method to monitor sudden deformation caused by local heat concentrations and micro-cracks within superconductors and superconducting magnets. However, the detection of AE signals in a high temperature superconductor (HTS) tape is not easy because of its low signal to noise ratio caused by the noise from boiling liquid cryogen or mechanical vibration from the cryo-cooler. Therefore, high performance piezoelectric ceramics are

To minimize most heat loss of current lead for high-temperature superconducting (HTS) rotating machine, the choice of conductor properties and lead geometry - such as length, cross section, and cooling surface area - are one of the various significant factors must be selected. Therefore, an optimal lead for large scale of HTS rotating machine has presented before. Not let up with these trends, this paper continues to improve of diminishing heat loss for HTS part according to different model. It

Recently, for improvement of the magnetic field of high temperature superconductor (HTS) apparatus, many studies investigating on operating in the range of 20 ~ 65 K with liquid helium or the conducting method using cryocooler are actively reviewed. Also, the cooling method using solid nitrogen as cryogen is being suggested. Since the nitrogen has very large specific heat in solid state, it is expected that it can be operated for a long time without a continuous supply of cooling energy. However

Abstract -- The properties of the conductor—mechanical, thermal, and electrical—are the key information in the design and optimization of superconducting coils. Particularly, in devices using second generation (2G) high temperature superconductors (HTS), whose base materials (for example, the substrate or stabilizer) and dimensionare s adjustable, a design process for conductor optimization is one of the most important factors to enhance electrical and the thermal performance of superconducting

In this study, we examined the chemical diffusion coefficient of oxygen out-diffusion (D out) in partially melted YBa₂Cu₃Oy (Y123)-Ag superconducting tape produced by the thermomechanical processing of the silverclad precursor (doped with 5 wt.% Ag) containing BaCuO2.5 at reduced oxygen partial pressure (PO2). The out value of Y123-Ag (O7.0 to O6.2), obtained by using the thermogravimetric relaxation technique at 950℃ and a PO2 of 0.28 kPa, was 1.0476 × 10-7 cm²/s.

The 22.9kV/630A superconducting fault current limiter (SFCL) is developed by the KEPRI-LSIS collaboration group. This resistive SFCL uses three pairs of conduction-cooled current leads. When the SFCL system is in the fault mode, the current flows 20 times more than the steady state. Therefore, it is important that the current lead is designed to have the thermal stability in order to minimize the heat input of the cold-end. This paper presents the design and performance results of a pair of cond

- We investigated fault current limitation characteristics of the resistive superconducting fault current limiter (SFCL) which consisted of a Bi-2212 bulk coil and a shunt coil. The Bi-2212 bulk coil and the shunt coil were connected in parallel. The Bi-2212 bulk coil was placed inside the shunt coil to induce field-assisted quench. The fault test was conducted at an input voltage of 200 Vrms and fault current of 12 kArms and 25 kArms. The fault conditions were asymmetric and symmetric, and the

For use in ultrasonic actuators, we investigated the structural and piezoelectric properties of (1-x)Pb(Zr0.515 Ti0.485)O3-xPb(Sb1/2Nb1/2)O3+0.5 wt% MnO2 [(1-x)PZT-xPSN+MnO2] ceramics with a variation of x (x=0.02, 0.04, 0.06, 0.08). All the ceramics, which were sintered at 1250℃ for 2h, showed a typical perovskite structure, implying that they were well synthesized. A homogeneous micro structure was also developed for the specimens, and their average grain size was slightly decreased to 1.3㎛ by

This study investigates the thermal and electrical characteristics of a silicon-based grease insulation (GI) GdBCOcoil with respect to the winding tension through charge, sudden discharge, and over-current tests. Charge and suddendischarge test results demonstrate that the charging/discharging delay time increases as the winding tensionincreases; this is because the characteristic resistance of the coil decreases due to the reduced contact resistance. The over-current test results confirm that t

Since a stabilizer of YBCO coated conductor (CC) plays a very important role of bypassing over-current and transferring heat generated in the moment of fault, it is one of big issues to determine the material of the stabilizer and its dimension for the high performance of the HTS power application system. Especially, in the case of a superconducting fault current limiter (SFCL), which requires it to react immediately to the occurrence of fault, characteristics of stabilizer are decisive in limit

This paper aims to evaluate the feasibility of using no-insulation High Temperature Superconducting (HTS) coil in persistent current mode system. A HTS coil in persistent current mode system usually includes one or more non-superconducting joints in its circuit. And the current decaying rate of the coil is affected by the resistance of joint in persistent current circuit. If the resistance of joint is large, decaying rate of the current drastically increases. Therefore, reducing the joint resist