• 한국전기전자재료학회논문지
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• 제16권5호
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• pp.418-423
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• 2003

AC loss is an important issue in the design of high-T$\sub$c/ superconducting power cables which consist of a number of Bi-2223 tapes wound on a former. In the cables, the tapes have different critical currents intrinsically. And they are electrically connected to each other and current leads. These make loss measurements considerably complex, especially for short samples of laboratory size. So special cautions are required in the positioning of voltage leads for measuring the true loss voltage. In this work we have prepared a conductor composed of three Bi-2223 tapes with different critical currents. The critical current and AC loss characteristics in the conductor have experimentally investigated. The results show that for uniform current distributions the conductor's critical current is proportional to the critical current of the Bi-2223 tape to which a voltage lead is attached. However it depends on the current non-uniformity parameter in the conductor rather than the tape's critical currents for nonuniform current distributions. The loss tests indicate that the AC loss is dependent on arrangements of voltage leads but not on their contact positions. The measured losses in the conductor also agree well with the sum of the transport losses measured in each Bi-2223 tape.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 하계학술대회 논문집 B
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• pp.792-794
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• 2003

AC loss is an important issue in the design of high-$T_c$ superconducting power cables which consist of a number of Bi-2223 tapes wound on a former. In the cables, the tapes have different critical currents intrinsically. And they are electrically connected to each other and current leads. In this work we have prepared a conductor composed of three Bi-2223 tapes with different critical currents. The critical current characteristics in the conductor have experimentally investigated. The results show that for uniform current distributions the conductor's critical current is proportional to the critical current of the Bi-2223 tape to which a voltage lead is attached. However it depends on the current non-uniformity parameter in the conductor rather than the tape's critical currents for nonuniform current distributions.

• Progress in Superconductivity
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• 제4권2호
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• pp.184-188
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• 2003

Voltage-current characteristics of High Temperature Superconductor(HTS) tapes after applying the current beyond their critical current was investigated. When over-current is applied, the current begins to flow through the metal sheath instead of superconductor. The HTS tapes quenched were analyzed using V-I curve with various magnitudes of current. Two kinds of tapes were compared with each other to examine the influence of critical current on quench development. As a result, it was found that the resistance of superconductors and joule heat due to the over-current affect current distribution in HTS tapes. Critical current of HTS tapes was considered as a main factor deciding over-current characteristics.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 B
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• pp.903-905
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• 2002

According to the improvement of the HTS wires performance, several types of HTS superconducting machines, such as, transformer, motors, current limiters, and transmission cables are being developed. Degradation of the critical current in HTS tape owing to external field is very important subject in developing the HTS machines. Considering that stacked HTS tapes are widely used to develop the large HTS machines, the critical current characteristics of stacked HTS tapes in external field need to be examined. In this paper, we present critical current characteristics of 4-stacked HTS tapes which are exposed to the external field. HTS tape with critical current of 4-stacked HTS tape. Test results prove that four times critical current of single HTS tape is smaller than critical current of stacked HTS tape in high external field.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 B
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• pp.961-963
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• 2002

When high temperature superconducting(HTS) tapes are wound on former for HTS cable application, their critical characteristics are likely to be degraded seriously because of mechanical stress. In this study, prior to fabricate prototype HTS cables, we investigated the variation of critical characteristics of HTS tapes according to their pitch angles. For this work, we prepared the samples of HTS tapes on the former of which diameter is 3cm. Pitch angles of HTS tapes are $0^{\circ}$, $00^{\circ}$, $20^{\circ}$, $30^{\circ}$, $40^{\circ}$, respectively. We applied current up to 160 $A_{rms}$ to HTS tapes and investigated E-I characteristics. The critical current of HTS tapes was decreased as pitch angle increased. In addition, when the applied current was beyond their critical current, the rate of resistance increase of HTS tapes was in proportion to their critical current. Finally, We concluded that the pitch angles affected resistance increase of HTS tapes as well as critical current.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제52권6호
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• pp.271-277
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• 2003

It is important to control layer current distributions of coaxial multi-layer HTS cables, because a homogeneous layer current distribution decreases AC loss and can supply the largest operational current. We have extended the theory that treat the operational current more than the critical current by considering V-I nonlinear characteristics of HTS tapes including flux flow resistance and contacting resistance between the cable and terminals. It is important to investigate the current distribution under the condition of operational current more than the critical current of cable, because the cable has experiences of fault current. In order to verify the extended theory, we have fabricated a two layers cable with the same twisting layer pitch. It was observed that almost all the operational current less than the critical current flowed on the outer layer because of its lower inductance. In case of operational current more than critical currents of layers, the flux flow resistances affect strongly current waveform and thereby the currents of layers were determined by the flux flow resistances. And we investigated breakdown characteristics in $LN_{2}$/paper composite insulation system for the application to a HTS cable. In this experiment, we got some information out of that the electrical characteristics of the insulation materials depends on the condition of butt gap.

• 한국초전도ㆍ저온공학회논문지
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• 제17권3호
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• pp.47-50
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• 2015

The high temperature superconducting (HTS) magnet has been developed for the high magnetic field applications such as NMR, MRI and other industrial machinery. In designing process of these HTS magnets, the accurate estimation on the critical current (Ic) is essential to predict and secure the electromagnetic performance. The critical current of 2G HTS tape has anisotropic Ic degradation characteristics with the application of magnetic field - angular dependency of critical current. It is known that the perpendicular magnetic field to the face of HTS tape makes dominant degradation on the critical current for conventional 2G HTS tape. However, recently developed 2G HTS tape has more complex characteristics due to the artificial pinning center. Therefore, the method for Ic estimation reflecting such characteristics of 2G HTS tape needs to be devised. The method considering the angular dependency is introduced in this paper. And the result of newly devised method is compared with that of previous method.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제53권7호
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• pp.424-429
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• 2004

The 4-probe method with a voltage tap on terminals has been used for the measurement of the critical current of multi-strand high-T$_{c}$ superconducting(HTS) cables. And the critical current of cables is obtained as the measured total current divided by the number of conductor when the terminal voltage exceeds the predetermined criterion of critical current. However, because of the non-uniform current distribution due to the different critical current, shapes, and other characteristics of each conductor, this is not applicable method to the multi-strand HTS cable. To determine the critical current of multi-strand HTS cable, the critical current of each conductor must be measured with different method. h this paper, the current distribution and the critical current of each conductors in multi-strand cable were measured with specially made Pick-up coils and voltage taps. It is presented that the real critical current of multi-strand is smaller than sum of each conductors. The main cause of non-uniform current distribution is the difference between the resistances appeared in each HTS wires.s.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2003년도 추계학술대회 논문집
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• pp.254-259
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• 2003

The 4-probe method with a voltage tap on terminals has been used for the measurement of the critical current of multi-strand high-Tc superconducting (HTS) cables. And the critical current of cables is obtained as the measured total current divided by the number of conductor when the terminal voltage exceeds the predetermined criterion of critical current. However, because of the non-uniform current distribution due to the different critical current, shapes, and other characteristics of each conductor this is not applicable method to the multi-strand HTS cable. To determine the critical current of multi-strand HTS cable the critical current of each conductor must be measured with different method. In this paper, the current distribution and the critical current of each conductor in multi-strand cable were measured with specially made pick-up coils and voltage taps. It is presented that the real critical current of multi-strand is smaller than sum of each conductors. The main cause of non-uniform current distribution is the different resistances appeared in each HTS wires.

• 한국초전도ㆍ저온공학회논문지
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• 제14권2호
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• pp.1-7
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• 2012

In this review paper, we report the characteristics of the critical current density in FeAs based superconductors which is newly discovered by Hosono group of Tokyo Institute of Technology on 2008. Since the many specimens in present stage are not single crystals, there are two kinds of critical current density observed in the specimens which are so-called local and global critical current densities. Therefore, it is necessary to evaluate both kinds of critical current densities. The history effect in which the global critical current density shows different values in increasing and decreasing magnetic field is also observed when the specimens have the local and the global critical current densities. The wire which critical current is 180 A is successfully developed with using the knowledge of abovementioned characteristics of two kinds of critical current densities and the history effect.