• 한국초전도ㆍ저온공학회논문지
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• 제20권4호
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• pp.65-69
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• 2018

Due to large in-field current carrying capacity and strong mechanical strength, a REBCO wire has been regarded as a viable high temperature superconductor (HTS) option for high field MRI and > 1 GHz (>23.5 T) NMR magnets. However, a REBCO magnet is well known to have an inherent problem of field inhomogeneity, so-called 'Screening Current induced magnetic Field (SCF)'. Recently, 'field shaking' and 'current overshoot operation' techniques have been successfully demonstrated to mitigate the SCF and enhance the field homogeneity by experiments. To investigate the effectiveness of current overshooting operation technique, a numerical simulation is conducted for a test REBCO magnet composed of a stack of double pancake coils using '2D edge-element magnetic field formulation' combined with 'domain homogenization' scheme. The simulation result demonstrates that an appropriate amount of current overshoot can negate the SCF. To verify the simulation results, current overshoot experiments are conducted for the REBCO magnet in liquid nitrogen. Experimental results also demonstrate the possible application of current overshoot technique to mitigate the SCF and enhance the field homogeneity.

• 한국초전도ㆍ저온공학회논문지
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• 제9권3호
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• pp.32-36
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• 2007

On the contrary of a conventional motor with very narrow air-gap. it is difficult to calculate the accurate magnetic field distribution and the performance of an air-cored superconducting motor by 2 dimensional analysis. which does not use high permeability material except outer machine shield. This paper aims to do analysis of magnetic field and force distribution from the 3 dimensional modelling of a 1MW class superconducting synchronous motor. Especially. the field coil composed of Bi-2223 high-temperature superconductor and the outer machine shield are modelled by finite element analysis software according to their structures and the self-inductance and Lorentz force are calculated based on the 3 dimensional magnetic field calculation. Moreover. the influence of an important parameter, synchronous reactance, has been analyzed on the machine performances such as voltage variation and output power.

• 대한기계학회논문집B
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• 제35권1호
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• pp.93-100
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• 2011

액체질소 온도부근에서 작동하는 고온초전도 케이블 시스템을 개발하기 위해서는 고온초전도 케이블 시스템에 사용되는 극저온 절연재료의 정확한 열물성 자료가 필요하다. 금속재료와 달리, 비금속 계열의 재료는 열저항이 크기 때문에 정확한 열 유입량을 측정하기 위해서는 특별한 주의가 요구된다. 본 연구에서는 극저온 냉동기를 이용하여 30K 부터 상온 사이에서 절연재료의 열전도도를 정확하게 측정할 수 있는 시스템을 개발하였다. 설계와 제작과정을 포함한 열전도도 측정 시스템을 자세하게 기술하였다. 또한 상온으로부터 침입하는 불가피한 열유입량을 최소화하기 위한 열전도도 측정 시스템의 최적화 과정을 소개한다.

• KEPCO Journal on Electric Power and Energy
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• 제6권4호
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• pp.467-472
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• 2020

The superconducting synchronous generator is one of the breakthrough elements for direct-drive wind turbines because it is light and small. Normally the superconducting one has copper armature windings in the stator and superconducting field windings on the rotor. The high resistance of the armature can make large copper losses, comparing with the conventional generators with a gear box. One of the solutions for the large copper losses could be a fully superconducting generator. But the high magnetic fields from the superconducting field windings on the rotor also make high perpendicular magnetic fields on the superconducting tapes in the armature windings. We have proposed a fully superconducting synchronous generator with dual field windings. It could immensely decrease the circumferential component of the magnetic field from the field windings at the armature windings. In this paper, we conceptually designed 3 types of superconducting synchronous generators. The first one is the fully superconducting one with conventional structure, which has superconducting armature windings in the stator and superconducting field windings on the rotor. The second one is the one with dual superconducting field windings and superconducting armature windings between them. The last one is the same as the third one except the structure of the armature. If the concentrated armature windings are superconducting ones with cryostats, then they cannot be installed within the span of 2 poles. So, we adopted 3 phases windings within 4 poles system. It makes more AC losses but can be manufactured really.

• 한국초전도ㆍ저온공학회논문지
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• 제21권1호
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• pp.31-35
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• 2019

The lumped-parameter circuit model for a no- insulation (NI) high temperature superconductor (HTS) magnet has been well understood after many experimental and analytic studies over a decade. It successfully explains the non-linear charging behaviors of NI magnets. Yet, recently, multiple groups reported that the post-quench electromechanical behaviors of an NI HTS magnet may not be well explained by the lumped circuit model. The characteristic resistance of an NI magnet is one of the key parameters to characterize the so-called "NI behaviors" of an NI magnet and recently a few groups reported a potential that the characteristic resistance of an NI magnet may substantially vary during a quench. This paper deals with this issue, the increment of contact resistance of the no-insulation (NI) REBCO magnet during a quench and its impact on the post-quench behaviors. A 7 T 78 mm NI REBCO magnet that was previously built by the MIT Francis Bitter Magnet Laboratory was chosen for our simulation to investigate the increment of contact resistance to better duplicate the post-quench coil voltages in the simulation. The simulation results showed that using the contact resistance value measured in the liquid nitrogen test, the magnitude of the current through the coil must be much greater than the critical current. This indicates that the value of the contact resistance should increase sharply after the quench occurs, depending on the lumped circuit model.

• 한국초전도ㆍ저온공학회논문지
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• 제7권1호
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• pp.47-50
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• 2005

The AC loss is an important issue in the design of the high temperature superconductor (HTS) power cables, which consist of a number of lli 2223 tapes wound on a former. In the cables, the tapes have different critical currents intrinsically. And they are electrically connected to each other and current leads. These make loss measurements considerably complex, especially for short samples of laboratory size. In this work we have prepared a multi-tape conductor composed of Bi-2223 tapes. The at losses of the conductor have experimentally investigated. The loss tests indicate that the effect of tapes critical currents on AC loss measurement in the multi tape conductor is negligible only if currents in the tapes flow uniformly Moreover, the measured tosses of the conductor are in good agreement with the sum of the transport losses in the tapes. However, in the case of non-uniform current distributions, the measured AC losses considerably depend on the current distribution parameter of the positioning of a voltage lead. Thus special cautions should be needed for the measurement of the true AC losses in the short power cable samples.

• 한국산업정보학회논문지
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• 제25권1호
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• pp.25-30
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• 2020

3상 다층 고온 초전도 동축 케이블은 초전도 선재 사용량의 감소 및 케이블의 소형화와 같은 이점 때문에 활발히 연구되고 있다. 3상 다층 고온 초전도 동축 케이블의 전기적 특성은 기존 초전도 케이블과 차이를 가지므로 실제 시스템에 적용하기 위해 충분한 분석이 필요하다. 본 논문에서는 PSCAD/EMTDC 기반 시뮬레이션을 통하여 22.9 kV, 60 MVA급 3상 다층 고온 초전도 동축 케이블을 모델링하고 과도 특성을 분석하였다. 결과적으로 3상 다층 고온 초전도 동축 케이블에서 고장전류가 발생하면 대부분의 고장전류가 구리 포머층을 통해 우회한다. 이때, 케이블 전체 온도는 약 5 K 증가하였다. 본 논문을 통해 3상 다층 고온 초전도 동축 케이블의 과도 상태에 대한 신뢰성을 확인할 수 있으며 향후 케이블의 실 계통 적용에 도움이 될 수 있다.

• 새물리
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• 제68권12호
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• pp.1293-1301
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• 2018

시판 중인 고온초전도 GdBCO 박막선재의 기본적인 자기적 특성들을 PPMS-VSM 장비를 이용하여 조사하였다. ZFC m(T) 곡선으로부터 $T_c$ 는 ~93 K였다. m(H) 배경데이터를 제거한 후, GdBCO 초전도층의 알짜 m(H) 데이터를 얻고, ${\Delta}m_{irr}$ 을 구하였다. $H_{irr}(T)$ 곡선은 $H_{irr}=H_{irr}(0)(1-T/T_c)^n$ 관계식과 잘 일치하고, n 값은 1.19이다. GdBCO 박막선재의 $J_c$ 와 H의 $J_c{\propto}{\Delta}M_{irr}{\propto}{\Delta}m_{irr}{\propto}H^{-{\delta}}$ 관계식의 ${\delta}$ 값으로부터 자속 특성을 조사하였다. 독립적인 자속고정효과를 나타내는 ${\delta}{\approx}0$ 인 영역, 상호작용의 집단적인 자속고정효과를 나타내는 ${\delta}{\approx}0.6{\sim}1.2$인 영역, 그리고 로렌츠 힘을 받아 자속들이 자유롭게 움직이는 ${\delta}{\gg}2$ 영역 등으로 구분할 수 있다. ${\delta}{\approx}0$ 특성에서 ${\delta}{\approx}0.6{\sim}1.2$ 특성으로 변화하는 자기장을 $H_1$ 으로, ${\delta}{\approx}0.6{\sim}1.2$ 특성에서 ${\delta}{\gg}2$ 특성으로 전이하는 자기장을 $H_2$ 라 하였다. $H_1$ < H < $H_2$ 영역에서 ${\delta}(T)$ 관계를 구하였고, 온도가 감소함에 따라 ${\delta}$ 값은 점차적으로 줄어들었다.