• 비파괴검사학회지
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• 제33권6호
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• pp.505-510
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• 2013

An encircling send-receive type pulsed eddy current (PEC) probe is designed for use in aluminum tube inspection. When bare receive coils located away from the exciter were used, the peak time of the signal did not change although the distance from the exciter increased. This is because the magnetic flux from the exciter coil directly affects the receive coil signal. Therefore, in this work, both the exciter and the sensor coils were shielded in order to reduce the influence of direct flux from the exciter coil. Numerical simulation with the designed shielded encircling PEC probe showed the corresponding increase of the peak time as the sensor distance increased. Ferrite and carbon steel shields were compared and results of the ferrite shielding showed a slightly stronger peak value and a quicker peak time than those of the carbon steel shielding. Simulation results showed that the peak value increased as the defect size (such as depth and length) increased regardless of the sensor location. To decide a proper sensor location, the sensitivity of the peak value to defect size variation was investigated and found that the normalized peak value was more sensitive to defect size variation when the sensor was located closer to the exciter.

• 대한기계학회논문집A
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• 제27권6호
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• pp.930-937
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• 2003

The extension of design life among power plants is increasingly becoming a world-wide trend. Kori #1 unit in Korea is operating two cycle. It has two man-ways for tube inspection in a steam generator which is one of the important components in a nuclear power plant. Especially, stud bolts fur man-way cover have damaged by disassembly and assembly several times and degradation for bolt materials for long term operation. It should be evaluated and compared by ASME Code criteria for integrity evaluation. Integrity evaluation criteria which has been made by the manufacturer is not applied on the stud bolts of nuclear pressure vessels directly because it is controlled by the yield stress of ASME Code. It can apply evaluation criteria through FEM analysis to damaged female threads and to evaluated safety fer helical-coil method which is used according to Code Case-N-496-1. From analysis results, we found .that it is the same results between stress intensity which got from FEM analysis on damaged female threads over 10％ by manufacture integrity criteria and 2／3 yield strength criteria on ASME Code. It was also confirmed that the helical-coil repair method would be safe.

• 비파괴검사학회지
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• 제6권2호
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• pp.7-16
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• 1987

Eddy Current Examination is expected as the effective technique for nondestructive inspection of steam generator and various kinds of heat exchanging tubes made of STS - 304. In Case of E. C. T, a study on the various factors which have an effect on coil impedance is very important to the sensitivity of defect detection and the ratio of signal to noise. Therefore, this study analyzed coil impedance by means of the variational principle, the minimized theory of energy functional and the application of Finite Element Method. Really by using E. C. T, the relationship between the size of defects and the intensity of Eddy Current Signals can be obtained. Signal intensity becomes maximum at certain frequency. This frequency is affected by the characteristics and the position of signal sources.

• 비파괴검사학회지
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• 제23권6호
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• pp.622-634
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• 2003

This paper is concerned with a computational method for recovering a crack shape of steam generator tubes of nuclear plants. Problems on the shape identification are discussed arising in the characterization of a structural defect in a conductor using data of eddy current inspection. A surface defect on the generator tube ran be detected as a probe impedance trajectory by scanning a pancake type coil. First, a mathematical model of the inspection process is derived from the Maxwell's equation. Second, the input and output relation is given by the approximate model by virtue of the hybrid use of the finite element and boundary element method. In that model, the crack shape is characterized by the unknown coefficients of the B-spline function which approximates the crack shape geometry. Finally, a parameter estimation technique is proposed for recovering the crack shape using data from the probe coil. The computational experiments were successfully tested with the laboratory data.

• 비파괴검사학회지
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• 제13권1호
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• pp.40-45
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• 1993

The steam generator tubes of the nuclear power plant should be inspected using eddy current techniques. Recently the crack-like defects become a major concern for the integrity of the steam generator tubes. These defects could be detected by the MRPC(Motorized Rotating Pancake Coil) method, not by the conventional bobbin coil method. In this paper it has been attempted to estimate the length of the cracks at the tube expansion region using of MRPC technique. The lengths of both axial and circumferential cracks show a tendency of overestimation compared to the real lengths. As the depths of the defects decrease from 100% through 50% of the wall thickness, the error of the length estimation is increased.

• 한국생산제조학회지
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• 제22권1호
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• pp.131-137
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• 2013

Gas springs have been widely used in motor vehicles as well as in most areas of industry. Instead of coil springs, these gas springs are easily operated to extrusion process or compression process the doors because $N_2$ gas with high pressure and oil are charged in tube. Gas spring sustain the constant elasticity change rate in the high reaction force and long stroke, and they have compact design, appearance and an excellent assembling ability to be mounted easily with any applicatory products. By means of these aspects, gas springs have been widely used in stead of coil springs in the over all industries. In this study, using acommonly used program, ANSYS, the basic research about the heat transfer and equivalent stress change of bimetal.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 1999년도 High Temperature Superconductivity Vol.IX
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• pp.291-291
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• 1999

Long 19-filamentary Bi-2223 tapes were prepared using the so called "powder-in-tube" method. In the preparation, two types of precursor powders and two different reduction rates during rolling were used. Also two rolling method, which resulted in different filament geometry, were used. The characteristics of the tapes will be presented. Also A coil was prepared using two 56 m-long 19-filament tape. It was consisted of two double pancake coils. Each pancake, which is separated by FRP spacer, was composed of 98 turns. The experimental results will be presented and compared to the simulation result.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제48권3호
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• pp.173-178
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• 1999

In this paper, the characteristics of the shielded inductive superconducting fault current limiter(FCL) were simulated and analyzed. After determining parameters fo design for superconducting tube, iron core and primary coil, simple power system composed of shielded inductive FCL was simulated by the numerical analysis. The currents flowing under the fault condition could be limited below 50 A successfully. It was suggested that as the important factors of operational characteristics, the turns of primary coil and size of iron core play a major role for whether the shielded inductive SCFCL operated as inductive type or resistive type FCL.

• 교육시설 논문지
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• 제18권3호
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• pp.35-41
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• 2011

Performance of a small-capacity solar absorption cooling system was investigated experimentally. Ten sets of evacuative-tube solar-heat collectors and a 5 kW single-stage absorption cooler were combined to produce a hybrid cooling system. The performance of the cooling system was measured using a tim-coil unit installed in a small plastic storage. It was found from the test on a sunny day of May that when the temperature of the hot water supplied from the solar collectors to the generator of the absorption cooler reached $60^{\circ}C$, the absorption cooler started cooling and the cold water temperature measured from the fan-coil unit reached $18^{\circ}C$. The COP, which is defined as the ratio of the cooling power to the total electrical power input was higher than 1.0.

• 비파괴검사학회지
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• 제21권6호
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• pp.650-657
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• 2001

본 논문에서는 핵연료 피복재 튜브를 검사하기 위한 차폐된 관통형 원격장와전류 탐촉자의 설계과정을 설명하고, 이 탐촉자에 의한 결함신호의 특성을 조사하였다. 먼저, 자기 에너지가 튜브 내부로 관통될 수 있도록 여자코일 외부를 전기적으로 절연된 얇은 철 박판을 적층시켜 차폐시켰다. 그리고 유한요소 해석을 통하여 차폐의 효과와 탐상 주파수를 연구하였으며, 센서코일의 위치를 결정하였다. 그러나 이렇게 설계된 탐촉자를 사용하여 예측된 결함신호는 센서코일이 결함을 지날 때의 결함지시가 명확하지 않았으며, 여자코일이 결함을 지날 때의 결함지시도 차폐체로부터의 영향이 나타나는 등 여자코일로부터 자속이 직접적으로 센서코일에 영향을 미친다는 사실을 알게 되었다. 따라서 센서코일도 여자코일과 같은 형태로 차폐시켰는데 이 차폐의 효과는 놀라울 정도로 결함신호의 특성을 향상시켰다. 최종적으로 설계된 탐촉자를 사용하여 수치 모델링을 수행한 결과는 관내삽입 원격장와전류 탐촉자를 사용하였을 때의 신호와 매우 흡사한 신호특성을 보였다. 즉, 위상신호는 내부결함과 외부결함에 대하여 거의 동일한 민감도를 보였으며, 위상신호의 세기와 결함의 깊이 사이에 선형적인 관계가 있음이 관찰되었다.