• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 춘계학술대회 논문집
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• pp.7-8
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• 2009

Non-contact critical current measurement apparatus was developed using hall probe which measures the magnetic field distribution across the width of superconducting tape. The hall probe consists of 7 independent hall sensors which lie in a line 600 ${\mu}m$. The difference between maximum and minimum magnetic field in the magnetic filed distribution is a main parameter to determine the critical current. As preliminary research, we calculated the magnetic field intensity at the middle sensor, which is a minimum magnetic field and generated by the circular shielding current modeled by Bean model. We confirmed that there are some parameters that affect on the minimum magnetic field; the distance between superconducting layer and hall sensor, the width of superconducting tape, and the critical current distribution across the width of superconducting tape. Among these parameters, the distance between superconducting layer and hall sensor highly influences on the minimum magnetic field.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2010년도 춘계학술대회 논문집
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• pp.12-12
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• 2010

The hall probe measurement system was used to measure the critical current distribution of superconducting coated conductor. The system consists of reel to reel moving apparatus, 7 array hall probe, a rotary encoder and permanent magnet. The magnetic field profile across the width of superconducting coated conductor using Bean's critical state model was calculated. The effect of various parameters of the formulas on the magnetic field distribution and the effect of shape and size of artificial defects, which were formed on the surface of SmBa2Cu3O7-d(SmBCO) coated conductor using laser marking system, on the hall probe magnetic field signal of the hall probe measurement system was investigated.

• 한국초전도ㆍ저온공학회논문지
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• 제10권1호
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• pp.32-36
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• 2008

An HTS conductor with parallel HTS tapes is essential for a large power HTS device to flow a large current. One of the most important factor for this conductor is a current distribution. Non-uniform current distribution in parallel tapes makes the critical current of the conductor low and the AC losses high. In this paper we proposed a non-contact method which measured each current in parallel tapes by using an array of Hall sensors. A matrix can be derived from this array for calibration. The current distributions of 4 and 6 parallel tapes were measured.

• 한국초전도ㆍ저온공학회논문지
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• 제14권2호
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• pp.20-23
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• 2012

With continuous development of the 2nd generation HTS conductor, the critical current of the conductor is also increasing. However, many applications require more than 2 conductors in parallel to transport large current. Applications such as HTS power cables and some HTS current leads usually need much larger transport current than that provided by a single conductor and they require more than several tens of HTS conductors. In the case of parallel connection of multiple HTS conductors, the current distribution depends on the contact resistance of each conductor at the terminals for DC operation. The non-uniform distribution of the terminal resistances results in a non-uniform distribution of the current. The resultant current non-uniformity affects on the measurement of the I-V curve and the thermal performance of the multiple conductors. This paper describes the I-V curves obtained from multiply connected HTS conductors with different terminal contact resistances to investigate the relationship between the distorted I-V curve and heat generation.

• 한국전기전자재료학회논문지
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• 제20권7호
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• pp.626-630
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• 2007

The AC loss is an important issue in the design of the high temperature superconductor (HTS) power cables and fault current limiters. In these applications, a cylindrical HTS conductor is often used. In commercialization of these apparatuses, AC loss is a critical factor but not elucidated completely because of complexities in its measurement, e.g. non-uniform current distribution and phase difference between currents flowing in an individual HTS tape. We have prepared two cylindrical conductors composed of a Bi-2223 tape with different critical current density. In this paper, the AC loss characteristics of the conductors have been experimentally investigated and numerically analyzed. The result show that the measured losses for two conductors are not dependent on both arrangements and contact positions of a voltage lead. This implies that most of loss flux is only in the conductors. The loss for the Bi-2223 conductor with low critical current density is in good agreement with the calculated loss from Monoblock model, whereas the loss measured for the Bi-2223 conductor with high critical current density doesn't coincide with the loss calculated from the Monoblock model. The measured loss is also different from numerically calculated one based on the polygon model especially in low transport current.

• 한국초전도ㆍ저온공학회논문지
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• 제10권3호
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• pp.1-4
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• 2008

For the effective evaluation of superconducting properties of a coated conductor, with a long length, a non destructive characterization technique including a reel-to-reel (R2R) Hall measuring system have been developed. A non-contact R2R Hall sensor array system was particularly designed to measure the superconducting property of coated conductors. The superconducting properties of long length coated conductors were measured by using this device. It was demonstrated that this system was convenient to measure the intensity and distribution of the magnet field applied perpendicular to the surfaces of the coated conductors. Using this device, the defect and low critical current density(Jc) area of coated conductors could be detected in real-time measurement.

• 한국초전도ㆍ저온공학회논문지
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• 제25권3호
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• pp.38-42
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• 2023

The evaluation of no-insulation (NI) high-temperature superconducting (HTS) typically uses the lumped equivalent circuit (LEC) model. Constant parameters in the NI HTS LEC model accurately predict voltage and central magnetic field at currents below the critical current. However, it is difficult to find constant circuit parameters that simultaneously satisfy the measured voltage and magnetic field under overcurrent conditions. Recent research highlights changes in contact resistance during transient conditions, which may impact power loss estimation in NI HTS coils. Therefore, we confirm the influence of contact resistance changes on loss calculation in the transient state for NI HTS coil. To achieve this, we introduce a measurement data analysis method based on the LEC model and compare it with the LEC model using constant circuit parameters.

• 한국초전도ㆍ저온공학회논문지
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• 제16권4호
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• pp.21-25
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• 2014

In order to develop 2nd generation (2G) high-temperature superconducting (HTS) wires as commercial products, it is necessary to perform a high speed investigation of their superconducting performance. Room-temperature and non-contact optical scanning tools are necessary to verify the microstructure of the superconducting materials, the current flow below the critical temperature, and the critical current density. In this paper, we report our results of an inspection of the electrical transport properties of coated conductors. The samples that we used in our study were highly qualified rare-earth based coated conductors produced via co-evaporation, and $SmBa_2Cu_3O_{7-y}$ (SmBCO) was the superconducting materials used in our studies. A film grown on IBAD-MgO templates shows larger than 400 A/cm at 77 K and a self-field. The local transport properties of the films were investigated by room-temperature imaging by thermal heating. The room-temperature images show structural inhomogeneities on the surface of the films. Bolometric response imaging via low-temperature bolometric microscopy was used to construct the local current mapping at the surface. These results indicate that the non-uniform regions on the surface disturb the current flow, and laser scanning images at room-temperature and at a low-temperature suggest a correlation between the structural properties and transport properties. Thus this method can be effective to evaluate the quality of the coated conductors.

• Journal of Mechanical Science and Technology
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• 제15권3호
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• pp.291-299
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• 2001

Recently, severe wear on the shutdown rod cladding of Ulchin Nuclear Power Plant #1, #2 were observed by the Eddy Current Test(E.C.T.). In particular, the wear at the sixth card location was up to 75%. The test results indicated that the Flow Induced Vibration(F.I.V.) might be the cause of the fretting wear resulting from the contact between Rod Cluster Control Assemblies(RCCAs) and their spacing cards(guide plates) arranged in the guide tube. From reviewing RCCAs fretting wear repots and analyzing the general characteristics of F.I.V. mechanism in the reactor, geometric layout and flow conditions around the control rod, it is concluded that the turbulence excitation is the most probable vibration mechanism of RCCA. To identify the governing mechanism of RCCA vibration, an experiment was performed for a representative rod position in which the most serious fretting wear experienced among the six rod positions. The experimental rig was designed and set up to satisfy the governing nondimensional numbers which are Reynolds number and mass damping parameter. The vibration amplitude measurement by the non-contact laser displacement sensor showed good agreements in the frequency and the maximum wearing(vibration) location with Ulchin E.C.T. results and Framatome report, respectively. The sudden increase in the vibration amplitude was sensed around the 6th guide plate with mass flow rate variation. Comparing the similitude rod behaviour with the idealized response of a cylinder in flow induced vibration, it was found that he dominant mechanism of vibration was transferred from turbulence excitation to periodic shedding at the mass flow ate 90ι/min. Also the critical velocity of the vibration in RCCAs was determined and the vibration can be prevented by reducing the bypass flow rate below the critical velocity.

• Progress in Superconductivity
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• 제13권1호
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• pp.7-11
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• 2011

조성경사법을 이용하여 LMO/IBAD-MgO template 상에 EDDC 증착법을 이용하여 $Sm_{1+x}Ba_{2-x}Cu_{3+y}O_{7-d}$ 초전도 박막을 증착하였다. 테이프 형상의 기판상에 길이방향으로 $Sm_{1+x}Ba_{2-x}Cu_{3+y}O_{7-d}$ 박막의 조성비가 연속적으로 변하는 샘플을 얻을 수 있었고, 비접촉 Hallprobe를 이용하여 임계전류를 측정한 결과 조성비에 대응하는 연속적인 임계전류분포를 측정할 수 있었다. 본 조성비 영역 중 Sm:Ba:Cu = 1.01:1.99 :4.87의 조성비에서 최대의 임계전류를 보였다. 이 조성비에서 SmBCO 박막표면에 전체적으로 roof tile 형상의 결정립들이 관찰되었으며 국소적으로 2차상들이 관찰되었다. 조성 경사법을 이용하면 광범위한 조성비영역에서 신뢰도 높은 초전도특성, 결정배향성, 박막표면 형상 등을 조사할 수 있을 것으로 예상된다.