• 한국초전도ㆍ저온공학회논문지
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• 제24권3호
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• pp.24-29
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• 2022

One of the recent proposals with nuclear magnetic resonance (NMR) is a multi-bore NMR which consists of array of magnets which could present possibilities to quickly cope with pandemic virus by multiple inspection of virus samples. Low temperature superconductor (LTS) can be a candidate for mass production of the magnet due to its low price in fabrication as well as operation by applying the helium zero boil-off technology. However, training feature of LTS magnet still hinders the low cost operation due to multiple boil-offs during premature quenches. Thus in this paper, LTS magnet with low mechanical stress is designed targeting the "training-free" LTS magnet for mass production of magnet array for multi-bore NMR. A thorough process of an LTS magnet design is conducted, including the analyses as the followings: electromagnetics, mechanical stress, cryogenics, stability, and protection. The magnet specification was set to 4.7 T in a winding bore of 85 mm, corresponding to the MR frequency of 200 MHz. The stress level is tolerable with respect to the wire yield strength and epoxy crack where mechanical disturbance is less than the minimum quench energy.

• Composites Research
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• 제12권6호
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• pp.22-30
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• 1999

$Nb_3Sn$ 복합초전도 테이프는 금속간 화합물로서 다른 초전도 재료에 비하여 임계밀도가 높아 MRI등에 널리 이용되고 있다. 한편 $Nb_3Sn$층은 화합물이므로 bending이나 winding등의 코아 제작시 테이프 도체에 응력이 작용하면 화합물층에 취성으로 인한 크랙이 발생하여 부분적으로 파단이 일어나 임계전류 특성이 열화하며 무응력 상태에 비하여 크게 저하된다. 따라서 이와 같은 $Nb_3Sn$복합초전도 테이프의 실질적인 적용을 위해서는 선재의 제조과정 뿐만 아니라 가동 중에 기계적 응력에 대한$Nb_3Sn$복합 초전도 테이프의 미시적 거동 특성을 필히 이해하여야 할 필요가 있다. 본 연구에서는 음향방출기법(Acoustic Emission)을 이용하여 $Nb_3Sn$ 복합초전도 테이프에 대해서 일정변형속도(constant extension rate)제어로 인장하중이 작용할 경우 발생하는 AE 신호특성과 이에 대응하는 각 화합물층의 미시적 변형거동 특성과의 상관관계를 분석하였다.

• 조명전기설비학회논문지
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• 제22권2호
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• pp.80-84
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• 2008

본 논문은 다중권선의 비접촉 변압기를 이용한 비접촉 전력공급 방식을 제안한 논문이다. 논문에서 제안한 전력공급 방식은 엘리베이터 카에 신뢰성 높은 전력을 전송하기 위하여 공진주파수 추적 기법을 사용하였다. 제안된 시스템을 검증하기 위하여 ICAP4와 Maxwell을 사용하여 시뮬레이션을 수행하였으며, 5[kW]급 비접촉 전력전송시스템을 제작하여 실험을 수행하였다.

• 한국초전도ㆍ저온공학회논문지
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• 제25권4호
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• pp.40-44
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• 2023

For high-temperature superconducting power applications that need large current capacity, a large current conductor manufactured using multiple superconducting tape is required. Conductors being studied for large currents capacity such as CORC, TSTC, and RACC have advantages and disadvantages, and in order to use these conductors in coil form and apply them to AC power devices, research on magnetization loss occurring in superconductors due to external magnetic fields is essential. To accurately measure magnetization loss in a conductor that is twisted by stacking straight conductors like TSTC, the correlation between the measuring system and the shape of the sample must be clearly known to accurately measure the loss. In this paper, we will confirm the difference in magnetization loss measurement values according to the correlation between the length of the pickup coil and the twist pitch of the sample in CORC and TSTC shapes, and review considerations for accurate magnetization loss measurement from the results.

• 로봇학회논문지
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• 제8권3호
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• pp.186-196
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• 2013

Since its introduction (e.g., [4, 6]), virtual coupling technique has been de facto way to connect a haptic device with a virtual proxy for haptic rendering and control. However, because of the single dependence on spring-damper feedback action, this virtual coupling suffers from the degraded transparency particularly during contact tasks when large device/proxy-forces are involved. In this paper, we propose a novel virtual coupling technique, which, by utilizing passive decomposition, reduces device-proxy position deviation even during the contact tasks while also scaling down (or up) the apparent inertia of the coordinated device-proxy. By doing so, we can significantly improve transparency between multiple degree of freedom (possibly nonlinear) haptic device and virtual proxy. In other to use passive decomposition, disturbance observer of [3] is adopted to estimate human force with some dead-zone modification to avoid "winding-up" force estimation in the presence of device torque saturation. Some preliminary experimental results are also given to illustrate efficacy of the proposed technique.

• 전력전자학회논문지
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• 제13권3호
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• pp.229-236
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• 2008

최근 중대용량의 교류전동기 구동에 다단 H-브릿지 인버터의 적용이 늘어나고 있다. 이 인버터의 주된 장점 중의 하나는 입력전류에 고조파성분이 적다는 것으로 이는 2차측이 다중의 위상이동 권선으로 이루어진 변압기를 사용함으로써 이루어진다. 본 논문은 다단 H-브릿지 인버터에 적용되는 위상이동 변압기의 권선 설계의 기본 방안과 입력전류 고조파의 이론적인 해석을 제시하고 있다. I부에서는 먼저 위상이동변압기의 입출력 전압관계식을 유도하고 위상이동과 변압기 설계와의 관련성에 대하여 서술하고 있다.

• 한국초전도ㆍ저온공학회논문지
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• 제9권2호
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• pp.7-10
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• 2007

Persistent mode HTS pancake coil has been fabricated using a coated conductor by a "wind-and-flip" method. A coated conductor with the length of 1.2 meters was divided at the center along the length. The sliced coated conductor was wound on a pair of bobbins with a diameter of around 4 cm and two pancake coils connected superconductively without a resistive joint were prepared. By flipping one of the pancake coils, the magnetic field generated by each coil is to be aligned to the same direction and generate meaningful magnetic field while the magnetic fields of two spit coils are canceled without flipping. Permanent current was induced by flowing current to the coil immersed in liquid nitrogen pool using a power supply. A magnetic field of 48.8 Gauss was generated when 20 A of current was flowing in the pancake coils. The "Wind and flip" method can be applied for the fabrication of a long solenoid magnet by winding a sliced coated conductor on a cylindrical bobbin. It is also introduced that the construction of multiple sets of pancake (or solenoid) coils is possible by a "wind-and-flip" method using a wide coated conductor.

• 한국초전도ㆍ저온공학회논문지
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• 제10권3호
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• pp.23-26
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• 2008

Constructions of coated conductor which is differently from Bi-2223 is comprised multiple coatings on a base material or substrate and designed to achieve the highest degree of alignment possibility of the atoms in the superconductor material. In this study, we are measured and analyzed degradations of critical current according to diameter. In addition to study the effects of bending strain, we observed the AC loss of coated conductor and carried out analytical study for relation between Ic degradation and AC loss as well. The measurement of AC loss and numerical calculation was carried out based on Norris theory to compare with experimental results. The relationship between critical current and AC loss of HTS tapes with partial deformation by mechanical stress was studied. These results will amount the most important basis data in the of HTS cable, magnet, etc that winding work is required.

• 대한기계학회논문집B
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• 제40권8호
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• pp.543-556
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• 2016

본 연구에서는 5 MW 급 대형 풍력터빈 절연커플링의 시험평가 장치를 자체설계 개발하였다. 3 MW 급 대형 풍력터빈용 절연커플링에 대한 공인성능시험평가를 수행하고 시험장치에 대해서는 개발요구도, 장치설계, 기능적 고려사항, 구조진동해석 및 검토 결과를 제시하였다. 본 연구에서 고려한 대형 풍력용 절연커플링 모델과 같이 필라멘트와인딩 공법으로 제작된 두꺼운 유리섬유 복합재 파이프의 경우 shell 요소 기반의 유한요소 해석기법과 두께 효과를 정확하게 모델링 할 수 있는 복합재 적층형 3D solid 모델링 기법의 비교결과를 제시하였다. 또한 다수의 판스프링이 적층된 형태로 제작된 디스크팩 구조에 대한 효과적인 비선형 유한요소 해석기법을 제시하고 시험평가 결과와 비교 검증을 수행하였다.

• 한국안전학회지
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• 제33권3호
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• pp.15-20
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• 2018

There have been a number of major fatal fire accidents in Korea recently. The number of fires in 2017 were 44,178, which is not only increasing number of fires but also increasing in casualties. Particularly, the fire at Jecheon Sports Center, which suffered many casualties, is expected to have a huge impact. The cause of the fire has not been determined yet, but heat waves on the ceiling have also been pointed out. As such, the copper heating waves, which are used as a preventive measure against damage of pipes due to freezing of pipes, etc., always have a fire hazard. To determine the possibility of a flame-resistant heated fire, a positive electric cable product was used to artificially ignite and analyze the results. In case of a short circuit, the external covering of the positive electric cable is damaged, but not short circuit unless the heating material surrounding the wire is damaged. Due to the characteristics of heating cable for preventing copper waves, the chances of insulation becoming more severe due to moisture and temperature changes are higher than normal wires. If the internal heating system is carbonized by insulating deterioration without damage to the outer coating, it is likely to cause trekking, to form a winding loop in the heating materials, and to cause short circuit in the heated materials. For the positive temperature line, if the middle is shorted, the current continues to flow to the short circuit unless the breaker disconnects. Consequently, a heated fire that does not cut off the power immediately may leave multiple marks or cuts.