• 한국초전도ㆍ저온공학회논문지
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• 제5권3호
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• pp.34-37
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• 2003

A 1 MVA single-phase high temperature superconducting (HTS) transformer with BSCCO-2223 wire was designed in this paper. The rated voltages of each sides of the transformer are 22.9 kV and 6.6 kV respectively. Double pancake HTS windings arranged reciprocally will be used for the transformer windings, because of the advantages of insulation and distribution of surge voltage in case of a large power and high voltage transformer. Single HTS wire was used for the primary windings and four parallel wires were used for the secondary windings of the transformer with transposition. A core of the transformer was designed as a shell type core separated with the windings by a cryostat made of GFRP with a room temperature bore. The operating temperature of the HTS windings will be about 65K with sub-cooled liquid nitrogen. A cryogenic cooling system using a GM-cryocooler for this HTS transformer by natural convection of liquid nitrogen was designed. This type of cooling system can be a good option for compactness, efficiency, and reliability of the HTS transformer.

• 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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• 제21권5호
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• pp.501-509
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• 2001

증기발생기 전열관에서 1차측 응력부식균열의 발생빈도가 증가하고 있으므로 이의 정확한 탐지와 평가를 위해서는 균열 형상에 따른 와전류 신호특성을 규명하고 적합한 탐촉자를 선정하는 것이 매우 중요하다. 본 연구에서는 증기발생기 전열관의 내면 축방향 균열에 대한 와전류 검사의 검출능과 크기예측에 대한 신뢰도를 정량적으로 평가하고 pancake coil과 plus coil과의 신호특성 차이를 비교하였다. 이를 위하여 전열관 내면에 EDM으로 노치를 가공한 시편과 실제 증기발생기에서 1차측 응력부식균열이 발생하여 인출한 전열관을 시험편으로 사용하였다. 본 연구에서 얻어진 결과를 토대로 내면 축방향 균열에 대한 와전류 검사 신뢰도 향상을 위한 방안을 제시하였다.

• Progress in Superconductivity
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• 제4권1호
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• pp.86-89
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• 2002

In this paper, the design of a IMVA single-phase high temperature superconducting(HTS) power transformer with BSCCO-2223 HTS tapes is presented. The rated voltages of each sides of the transformer are 22.9 ㎸ and 6.6 ㎸, respectively The winding of 1MVA HTS transformer is consisted of double pancake type HTS windings, which have advantages of insulation and distribution of high voltage, and are cooled by subcooled liquid nitrogen of 65K. Four HTS tapes were wound in parallel for the windings of low voltage side and the four parallel conductors are transposed. The design of 1MVA HTS transformer, a shell type core made of laminated silicon steel plate is chosen, and the core is separated with the windings by a cryostat with a room temperature bore. The cryostat made of non-magnetic and non-conducting material and a liquid nitrogen sub-cooling system is designed in order to maintain the coolant's temperature of 65K. For electromagnetic analysis of 1MVA HTS transformer, a finite element method of an axis of symmetry is used. The maximum perpendicular component of magnetic flux density of pancake windings is about 0.15T. And through analyzing the magnetic field distribution, an optimal winding arrangement of 1MVA HTS transformer is obtained.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2003년도 하계종합학술대회 논문집 Ⅲ
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• pp.1573-1576
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• 2003

스타 그래프와 팬케익 그래프는 하이퍼큐브가 갖는 좋은 성질을 가지면서 하이퍼큐브보다 망 비용이 적은 값을 갖는 상호연결망이다. 본 논문에서는 그래프의 에지 정의를 이용하여 스타 그래프 S/sub n/은 팬케익 그래프 P/sub n/에 연장율 4, 확장율 1에 임베딩 가능함을 보인다.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2005년도 High Temperature Superconductivity Vol.XV
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• pp.66-66
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• 2005

• 한국초전도ㆍ저온공학회논문지
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• 제5권1호
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• pp.52-55
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• 2003

For the dielectric insulation design of any high temperature superconducting (HTS) apparatus in the electrical power systems, the breakdown properties of cryogenic coolants such as $LN_2$ are an important factor of the insulating engineering. Therefore, this paper presented an experimental investigation of breakdown phenomena in $LN_2$ under AC voltage. And we studied the breakdown properties of LN2 with decreasing temperature. Also, the Weibull plots of the breakdown voltage of subcooled $LN_2$ at 65 K for the needle-plane electrode with electrode distance d= 10 mm are studied. The dependence of breakdown voltage for needle-plane and pancake coil-pancake coil electrode on temperature is illustrated. The experimental data suggested that the breakdown voltage of L$N_2$ depend strongly on the temperature of $LN_2$. The breakdown characteristics of $LN_2$ under quasi-uniform and non-uniform electrical field for temperature ranging from 77 K to 65 K were clarified.

• 한국초전도ㆍ저온공학회논문지
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• 제5권2호
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• pp.46-50
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• 2003

In the dielectric insulation design of any high temperature superconducting (HTS) apparatus as well as HTS fault current limiter in the electrical power systems, the breakdown characteristics of cryogenic coolants such as liquid nitrogen ($LN_2$) are an important factor of the insulating engineering. Previous reports concerned with the breakdown characteristics of liquid nitrogen have pointed out that bubbles and gaseous nitrogen have a treat influence on their breakdown phenomena, However, useful data for practical insulation design of HTS fault CUITent limiter operating at subcooled L$N_2$ have not been obtained enough. Therefore, this paper presents an experimental investigate of breakdown phenomena in liquid nitrogen under AC voltage, And, we observed the breakdown voltage (BDV) of liquid nitrogen with lowering temperature. The Weibull plots of the breakdown voltage of subcooled $LN_2$ for the needle-plane electrode with d= 10 mm are studied, The dependence of breakdown voltage for needle-plane and pancake coil-pancake coil electrode on temperature is illustrated, The relationship between the AC breakdown characteristics and the temperature were clarified.

• Progress in Superconductivity
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• 제5권2호
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• pp.149-152
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• 2004

The design and the fabrication of a 1 MVA single-phase HTS transformer are presented in this paper, The rated voltages are 22.9 ㎸ for primary and 6.6 ㎸ for secondary, and the rated currents are 44 A and 152 A respectively. The transformer has HTS double pancake type windings. This type of winding has many advantages such as ease of fabrication and maintenance, good distribution of surge voltage and insulation of windings. Single HTS wire was used for primary winding and four HTS parallel wires were used for secondary winding. These windings are arranged reciprocally with the shell type iron core. An FRP cryostat with room temperature bore was fabricated to isolate the iron core from the coolant. The winding will be cooled down to 65 K with sub-cooled liquid nitrogen using a GM-cryocooler. The sub-cooled liquid nitrogen has advantages of good insulation because of no bubbles as well as increased current capacity of HTS wire.

• 한국초전도ㆍ저온공학회논문지
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• 제6권4호
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• pp.32-36
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• 2004

AC loss is one of the important parameters in HTS (High Temperature Superconducting) AC devices. Among the HTS AC power devices, the transformer is an essential part in electrical power system. But, AC loss is one of the most serious problems of the HTS transformer, especially with pancake windings, because high alternating magnetic field is applied perpendicularly to the surface of BSCCO wire in HTS windings of that, comparing with the other HTS AC power devices. For the reason above the calculation of AC loss generated in the HTS windings should be carried out in advance when designing the HTS transformer. In the paper we performed study for optimization of winding design to minimize the magnetization loss of HTS winding such as the spaces between pancake windings and operating temperature of HTS wire. The calculation of the AC loss was accomplished by 2-demensional Finite Element Method.