• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 B
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• pp.725-726
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• 2006

In large scale superconducting rotating machine, HTS field coils are constructed with many stacks of single or double pancake coils connected in series. In spite of its higher thermal stability, HTS field coil experiences some quench, which results in some part of burn-out in the field coils. Thus in the view point of the HTS rotating machine field coil design and testing, it was very important to predict the possibility of quench occurrence in the designed field coils. In this paper, a HTS racetrack coil constructed with two single pancake coils and one double pancake coil was tested in LN2 and cooling by GM refrigerator. It is wound using the Bi-2223 tape. The experimental details and results are presented in this paper.

• 한국초전도ㆍ저온공학회논문지
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• 제13권3호
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• pp.24-30
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• 2011

The stability issue of high temperature superconducting (HTS) racetrack coils is one of the most important factors for the development of large-scale rotating machines, such as ship propulsion motors and power generators. However, The stability and normal zone propagation characteristics of HTS racetrack pancake (RP) coils are not sufficient yet. In this study, quench tests for a GdBCO racetrack pancake coil were carried out under the condition of $LN_2$ at 77 K. Minimum quench energy and two-dimensional normal zone propagation velocities of the coil are also discussed. Normal zone propagation velocity in the coil's curved section is faster than in its straight section due to stress effects. The test results show that the protection of the straight section is of greater importance than that of the curved section when GdBCO racetrack pancake coils are applied to large-scale rotating machines.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 춘계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.3-5
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• 2001

Racetrack coils are used in many areas of superconductivity applications such as generators, motors, maglev, wiggler magnets and so on. The fabrication and characteristics of race-track type High Tc Superconducting (HTS) magnets were carried out. The Magnet is composed of 3 pancake coils wound by 37-filamental Bi-2223/ Ag-alloy tapes. Quench current ($I_q$) of both whole magnet and 3 pancake coils were measured. At 77K under the self-field, $I_q$ of magnet was 12A, while in the case of middle pancake coil, $I_q$ was 15A. The upper pancake coils of racetrack magnet with iron plates, magnet having optimized current distribution and initial magnet are compared with each other through 3D FEA, manufacturing and testing these magnets. The measured performance of the upper pancake coil #3 with iron plates improved by 50% on the basis of initial pancake coil #3. Quench current ($I_q$) of field winding was 12A. In addition, the fabrication processes and the characteristics of HTS magnet are described.

• 비파괴검사학회지
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• 제34권5호
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• pp.356-361
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• 2014

회전형 탐촉자(RPC)는 증기발생기 전열관의 결함 탐지 및 크기 측정 목적으로 널리 사용되고 있다. 손상이 탐지된 전열관에 대한 건전성 평가는 비파괴검사에서 얻어진 열화의 크기 정보를 바탕으로 수행되기 때문에 검사기술의 성능은 전열관의 건전성 평가에 직접적으로 영향을 미치게 된다. 동일 전열관의 인접한 거리에 다중균열이 존재할 경우 검사 기술의 결함 분해능에 제약이 따를 수 있으며 그 영향이 클 경우 근접한 다중균열이 상대적으로 큰 단일균열로 평가될 수 있으므로 전열관의 구조건전성 평가에 오류를 유발할 수 있게 된다. 따라서 본 연구에서는 방전가공으로 균열을 모사한 인공결함에 대한 RPC 탐촉자의 결함 분해능을 관찰하고 전열관의 구조건전성 평가에 미치는 영향을 살펴보았다. 동일 직선상에 놓인 다중균열은 매우 근접한 거리까지 개별균열 식별이 가능하여 건전성 평가에 미치는 영향이 없는 반면, 인접한 거리에 평행하게 놓인 균열의 경우는 RPC 탐촉자의 분해능이 낮아서 부정확한 결함 크기 정보가 얻어지므로 결함관의 파열압력 예측에 영향을 미칠 수 있다.

• 비파괴검사학회지
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• 제26권1호
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• pp.25-29
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• 2006

In this paper, the eddy current signals come from a pair oi transmit-receive (T/R) pancake coil on ECT array Probe are analyzed with the variations of the lift-of and of the distance between transmit and receive coils. To obtain the electromagnetic characteristics of the probes, the governing equation describing the eddy current problems is derived from Maxwell's equation and is solved using three-dimensional finite element method. Eddy current signals from T/R coils on ECT array probe have quite different characteristics compared with ones from impedance coil on rotating pancake coil probe. The results in this paper ran be helpful when the field eddy current signals from ECT array probe are evaluated.

• 한국초전도ㆍ저온공학회논문지
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• 제15권1호
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• pp.35-39
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• 2013

The superconducting Homopolar motor is manufactured and tested. Homopolar motor system is simple and solid as the field coil of the motor is fixed near the stator coil without rotating system. In this paper, a 5 kW fully superconducting homopolar motor which has high temperature superconducting armature and field coils is manufactured and tested in liquid nitrogen. The critical current test results of the used 2G superconducting wire, pancake coil for rotor winding and race-track coils for armature winding are reported. Also, the test result of rotating and operating performance is presented. The operating frequency is to be 5 Hz for low-speed rotating. The developed fully superconducting Homopolar motor is the world's first.

• 한국초전도ㆍ저온공학회논문지
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• 제4권2호
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• pp.31-37
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• 2002

A 100 〔HP〕 rated synchronous motor with superconducting rotating field winding has been designed based on the formulated equations established from 2 dimensional magnetic field distributions in a cylindrical coordinate The cross-section was drawn based on calculated design results via Fortran program and then modeled with FEM (Finite Element Method) to investigate the machine performances. First of all, the magnetic field distributions are analysed in many ways according to the field directions and the armature currents. Especially after the rotating Held winding is arranged with BSCCO-2223 high-temperature superconducting(HTS) pancake coils, the exerted magnetic field normally on the HTS tape is calculated through FEM. And the machine output power is calculated according to the torque ang1es which lie between the field and the armature main flux lines. Moreover, this Paper includes the eddy-current loss variations of a copper damper located between the field and the armature coils and design considerations of the 100 HP HTS motor utilizing ferro-magnetic material.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2001년도 학술대회 논문집
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• pp.104-107
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• 2001

Racetrack coils are used in many areas of superconductivity applications such as generators, motors, maglev, wiggler magnets and so on. Especially now a days a few advanced nations including U.S., Japan are developing high temperature superconducting(HTS) wire which has better performance than low temperature superconducting(LTS) wire. Most of HTS wires such as BSCCO-2223 are manufactured with PIT(Power In Tube) process, so the shape of the wire looks like tape different from LTS wire with round cross-sectional appearance like normal conductors. Generally HTS racetrack coils are composed of a few partial double-pancake colis and then the double-pancakes are jointed each other according to their applications.

• Journal of Electrical Engineering and Technology
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• 제13권3호
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• pp.1166-1172
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• 2018

Degradation due to delamination occurs frequently in the high temperature superconductors (HTS) coil of rotating machines made with 2nd generation (2G) HTS wire, and the authors have observed other similar cases. Since an HTS field coil for a rotating machine is required to have stable current control and maintain a steady state, co-winding techniques for insulation material and epoxy resin for shape retention and heat transfer improvement are applied during coil fabrication. However, the most important limiting factor of this technique is delamination, which is known to be caused by the difference in thermal expansion between the epoxy resin and 2G HTS wire. Therefore, in this study, the experimental results of mixing the ratio of epoxy resin and alumina ($Al_2O3$) filler were applied to the fabrication of small and large test coils to solve the problem of degradation. For the verification of this scheme, eight prototypes of single pancake coils with different shapes were fabricated. They showed good results. The energization and operation maintenance tests of the stacked coils were carried out under liquid neon conditions similar to the operation temperature of an MW-class rotating machine. In conclusion, it was confirmed that the alumina powder mixed with epoxy resin in an appropriate ratio is an effective solution of de-lamination problem of 2G HTS coil.

• 한국압력기기공학회 논문집
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• 제8권3호
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• pp.7-12
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• 2012

Steam generator tubes are critical boundary of the primary and secondary side in nuclear power plants. Eddy current testing is commonly used as the method of non-destructive testing for the safety and integrity of steam generator tubes in the nuclear power plants. Changes in the geometric shape act as a stress concentration factor likely to cause a defect during the steam generator operation. The mixed-signals with the geometric shape are distorted and attributes that are difficult to detect signals. An example is bending stress due to compression process at a U-bend occurring in the intrados region which has a small radius of curvature. The resulting change in the geometric shape may lead to a dent like occurrences. The dent can cause stress concentration and generates stress corrosion cracks. In this study, the steam generator tubes of nuclear power plant were selected to study for analysis of mixed-signal containing dent and stress corrosion cracks.