• Progress in Superconductivity and Cryogenics
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• v.13 no.3
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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.

• Proceedings of the KIEE Conference
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• 2006.07b
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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.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.1
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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.

• Nuclear Engineering and Technology
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• v.30 no.4
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• pp.377-385
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• 1998

Many nuclear power plants have experienced unscheduled shutdown due to the leakage of steam generator tubes. The leakages are normally due to the crack, possibly stress corrosion cracking (SCC) near the tube expansion at the top of tubesheet or at the tangential point of the row-1 U-bend region. The conventional eddy current technique, which makes use of a differential bobbin coil, has been found to be inadequate for the early detection of SCC. During the in-service inspection, therefore, it is a general practice that the rotating pancake coil (RPC) is used for detecting the cracks. Even in using RPC, however, it is difficult to determine the depth of the cracks quantitatively. This paper attempts to determine the detectability and sizing ability of RPC technique for axial or circumferential cracks at the tube expansion region. The simulated cracks with various dimensions were fabricated by electro-discharge machining (EDM) method. Experimental results are discussed with theoretical calculations.

• Progress in Superconductivity and Cryogenics
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• v.15 no.1
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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.

• Proceedings of the KIEE Conference
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• 2001.04a
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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.

• Journal of Electrical Engineering and Technology
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• v.13 no.3
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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.

• 한국정보통신설비학회:학술대회논문집
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• 2006.08a
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• pp.241-245
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• 2006

In the examination of Steam Generator (SG) tube in Nuclear Power Plant (NPP) Eddy Current Testing (ECT) probes play an Important role in detecting the defects. Bobbin probe and Rotating Pancake Coil (RPC) probe is usually used for the inspection of SG tube. Bobbin probe is good at high speed inspection, but ability of detection of circumferential defect is very weak. On the contrary RPC probe, which moves for inspection in the direction of axial and circumferential simultaneously, has very slow inspection speed, but it was excellent detection capability fur small cracks, which is hardly detected by bobbin probe. Many examinations of SG tube examination of NPP are achieved during short period. Therefore, solution about this must develop probe of new form for examination performance and examination time shortening of other probe. In this paper, analyzed technological present condition of Bob-bin probe and RPC probe been using in Nondestructive Testing (NDT) for SG tube defect detection and Appeared about background theory and view of developed probe newly.

• Progress in Superconductivity and Cryogenics
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• v.4 no.2
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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.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.8 no.3
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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.