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Transient characteristic analysis of an HTS DC power cable using a multi-terminal based test-bed
Physica C 494 (2013) 302–306
Contents lists available at SciVerse ScienceDirect
Physica C journal homepage: www.elsevier.com/locate/physc
Transient characteristic analysis of an HTS DC power cable using a multi-terminal based test-bed q Jin-Geun Kim, Minh-Chau Dinh, Sung-Kyu Kim, Minwon Park ⇑, In-Keun Yu, Byeongmo Yang Changwon National University, 9 Sarim-Dong, Changwon 641-773, Republic of Korea KEPRI, 105 Munji-Ro, Daejeon 305-760, Republic of Korea
a r t i c l e
i n f o
Article history: Accepted 19 April 2013 Available online 11 May 2013 Keywords: AC loss High temperature superconductor HTS power cable YBCO
a b s t r a c t The current capacity of a power supply limits the experimental environment of higher capacity HTS power cable. Consequently, the transient characteristic analysis of an HTS DC power cable is difficult to assess. In this paper, a multi-terminal based test-bed is used to overcome those power supply capacity limitations. A 1 kA class HTS DC power cable was designed and the transient characteristics of the HTS DC power cable were analyzed using the multi-terminal based test-bed. Transient characteristics, such as resistance variation and critical current of the 1 kA class HTS DC power cable were successfully measured using small power sources in the multi-terminal based test-bed. Definitely, the suggested test system overcomes the assessment limits of the HTS power cable’s current capacity. Ó 2013 The Authors. Published by Elsevier B.V. All rights reserved.
1. Introduction A superconducting power cable uses superconducting materials instead of the copper or aluminum conventionally used to carry electricity in overhead power lines and underground cables. Superconducting materials can carry electrical current over 100 times more than current density of copper or aluminum, which in turn drives system economical, and that is fundamental reason why superconducting DC power cables compare favorably with conventional alternatives for long-distance power transmission. Secondly, when transmitting DC power, superconductors have no electrical resistance and introduce no electrical losses of their own [1–4]. There are several HTS power cable projects in the world. The critical current values of the Phase II of the Albany HTS cable project were 2.23 kA at 73 K and 2.8 kA at 69 K, respectively [1–3]. Since a 275 kV, 3 kA HTS power cable, which is the target of the Japanese power network project, has a power transmission capacity of 1.5 GVA, the HTS power cable has the potential for practical use as the backbone power line of the future [4]. The target of the NEDO project is to operate at 66 kV, 200 MVA HTS cable in the real grid in order to demonstrate its reliability and stable operation [5–7]. Before applying an HTS cable to a real power system, a characteristic analysis by simulation or experimentation is necessary. The q This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-No Derivative Works License, which permits non-commercial use, distribution, and reproduction in any medium, provided the original author and source are credited. ⇑ Corresponding author. Address: 55315, Changwon National University, Changwon 641-773, Republic of Korea. Tel.: +82 55 281 3150; fax: +82 55 281 3170. E-mail address: [email protected] (M. Park).
most important advantage of a superconducting cable is its high current density; however, difficulties arise when researchers experiment on HTS cables. An over current test under fault condition is particularly difficult because it needs large current source [5–12]. Furthermore, most HTS power cables whether AC or DC have not been tested for fault conditions in the laboratory scale. Previously, a field test was the only possible method to study HTS cables under fault conditions [13,10]. Another problem is the current distribution in the HTS power cable. Joint resistances between HTS wires and copper terminals are different. The transport currents of each HTS wire depend on their inductance, capacitance, and joint resistance. The inductance and capacitance of each HTS wire are the same because of the same cable structures. However, the connecting resistances of each HTS wire are different depending on the joint conditions. More precisely, the current distribution of the short length HTS DC cable in the laboratory setting depends on its joint resistance. In this paper, the authors analyzed the transient characteristic of a 1 kA class HTS DC power cables using a 200 A class power source. Multi-terminal based test-bed makes it possible to experiment an high capacity of HTS DC power cable by using a small power source. The structure of copper terminal in the multiterminal based test-bed is different than a general copper terminal of HTS power cables. The number of copper terminals is the same as the number of HTS wires in the tested HTS DC power cable. Each HTS wire was connected in series through a return path and separate copper terminals. This system can solve both current distribution and power source limitation problems. A 1 kA class HTS DC power cable was designed and fabricated (using eight HTS wires) for transient characteristic analysis in the multi-terminal
0921-4534/$ - see front matter Ó 2013 The Authors. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.physc.2013.04.069
J.-G. Kim et al. / Physica C 494 (2013) 302–306
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based test-bed. The critical current and transient characteristics of the HTS DC power cable were successfully measured in this test system, using just 1/8 of the current source of the HTS DC power cable. Under this system, the current of each HTS wire has the same value because of its multi-terminal structure. 2. Design of a multi-terminal based test-bed 2.1. Configuration of a multi-terminal based test-bed The multi-terminal based test-bed system includes an HTS DC power cable, a power source, and control and monitoring system. Power source and monitoring devices are the same as a general experiment system which uses a current amplifier, LabVIEW and SCXI data acquisition system. However, the structure of the HTS DC power cable differed from the general HTS power cable layout. In a general HTS cable, whether AC or DC, all HTS wires were connected in parallel to a single copper terminal. Fig. 1 shows the experimental system configuration of a multi-terminal based test-bed for an HTS power cable experiment. Front and back side cross sectional area of the HTS power cable of this system were shown in Fig. 2. This experiment system for experimentation requires separate copper terminals and a return current path. Thus, each HTS wire of the HTS DC power cable had its own copper terminals as shown in Fig. 2, and copper cables were used for the return current path in this system. Most large capacity current sources has limitation of output terminal voltage level, however, copper terminal may cause the voltage drop between terminals of power sources. Total resistance of series connected copper return cables, terminals, and joint area was 7.34 mX in this system.
Fig. 2. Cross sectional area of the HTS DC power cable.
2.2. Design of the 1 kA class HTS DC power cable Fig. 3. Fabrication of a multi-terminal HTS DC power cable.
A 1 kA class HTS DC cable was designed to verify the assessment of the cable’s transient characteristics in the multi-terminal based test-bed. The fabricated HTS DC power cable is depicted in Fig. 3, being attached to separate copper terminals. In this case, eight HTS wires and copper terminals were used and their specifications are summarized in Table 1. A SuNAM second-generation HTS wire was used in this experiment, and its critical current was more than 110 A at 77 K. The cable length was 1 m, and the critical current of
the tested short-length HTS wires was 140 A in liquid nitrogen (LN2). The rated current of the designed HTS DC power cable was 1000 A using eight HTS wires. The former diameter was 20 mm, and the former was made from Fiberglass Reinforced Plastics (FRPs). HTS wires, 8 m long, were used for a 1 m HTS DC power cable. The pitch length of this cable was 2 m. Insulation of the HTS DC power cable was not considered in this system, thus the
Fig. 1. Configuration of the multi-terminal based test-bed.
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Table 1 Specifications of the HTS DC power cable. Parameters
Value
Length of the HTS DC power cable Manufacture of HTS wire Width and thickness of HTS wires Critical current of a single HTS wire Number of HTS wires for the cable Critical current of the HTS DC power cable Former diameter Length of total HTS wires
1m SuNAM 4.2 mm/0.2 mm 148 A @ 77 K 8 1120 A @ 77 K 20 mm 8.17 m
cable has no insulation layers. The current direction of all HTS wires was the same as shown in Fig. 1. The separated HTS wire tested at the same time under the same amount of current and direction just like the single terminal test system. Hence, the field effect of the cable in the multi-terminal based test-bed is the same as the general single terminal cable configuration. 2.3. Testing system configuration Fig. 4 shows the configurations of the experiment’s system. A fabricated HTS DC power cable was installed in the LN2 and connected to return copper cables. One of the copper terminals was connected to the power supply. In the multi-terminal based testbed, the HTS DC power cable and copper return path cables were connected as shown in Fig. 4. The input currents and voltages of the HTS wires were measured using LabVIEW and the SCXI measurement system. The voltages of all HTS wires were measured to detect the quench and resistance of HTS wires. The power sources of this system can put out 200 A of current; however, if we had used the general experiment method, it is not enough to measure the transient characteristic of the HTS DC power cable because the cable’s critical current was 1.2 kA. The multi-terminal based test-bed has no limitation of current capacity for testing the HTS power cable. Hence, it is possible to increase the capacity of HTS power cable through the increment of copper terminals quantity. 3. Experiment results 3.1. Critical and fault current characteristics The critical current of the HTS DC power cable and each HTS wire were measured in LN2 at 77 K. The results are shown in Fig. 5 and the cable’s critical current was 1.2 kA. Thus, the critical
current of a 1 kA class HTS DC power cable was successfully measured using the developed multi-terminal based test-bed which has 200 A class power sources. The resistance variations of the HTS DC cable were also measured and the results are depicted in Fig. 6. The operating DC current is 80% of critical current and the fault current were 1.44 kA and 1.6 kA. The output current of the power source was 180 A and 200 A when the fault currents were 1.44 kA and 1.6 kA, respectively, because of the multi-terminal structure. The resistance of this cable increased to 27 mX when fault current was 1.6 kA and one of the HTS wires was damaged after 0.34 s. 3.2. Joint resistance of each terminal We measured the joint resistance of each terminal and the total resistance of the multi-terminal based test-bed. The results were shown in Fig. 7 and summarized in Table 2. Indium (In) was used for the soldering of HTS wires and copper terminals. The total resistance of the copper return cable and joint resistance was 7.34 mX and each joint resistance was 12 lX, 30 lX, 36 lX, 37 lX, 38 lX, 43 lX, 56 lX and 70 lX respectively. However, the current of each HTS wire was the same even as the joint resistances were different in this system. Because HTS wires in the HTS DC power cable were connected in series.
4. Conclusion The authors have developed the multi-terminal based test-bed to overcome limitations in power source capacity. The 1 kA class HTS DC power cable was fabricated from second-generation SuNAM HTS wires for the test system. The critical current and transient characteristics of the HTS DC power cable were successfully measured using a small power source; only 200 A of current were needed to measure the transient characteristics of the HTS DC cable. If we had used a general method of critical current measuring, we would have needed a current source exceeding 3 kA. Furthermore, even though each joint resistance was different, the current of each HTS wire was the same during experiment because of the series connected structure. The experiment results obtained by using the multi-terminal based test-bed were the same as the results obtained by a single terminal test system with a large power sources. The cable structure and current direction of all wires were identical for both multi-terminal based test-bed and the single terminal method as shown in Fig. 1.
Fig. 4. Experimental setup of the HTS DC power cable and current return path.
J.-G. Kim et al. / Physica C 494 (2013) 302–306
Fig. 5. V–I characteristic of the HTS DC power cable.
Fig. 6. Transient resistance variation of the HTS DC power cable.
Fig. 7. Measurement results of copper terminal joint resistance.
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J.-G. Kim et al. / Physica C 494 (2013) 302–306 Table 2 Resistance of terminal joint area.
References
Parameters
Value
HTS joint 1 HTS joint 2 HTS joint 3 HTS joint 4 HTS joint 5 HTS joint 6 HTS joint 7 HTS joint 8 Sum of resistance (joint + copper cable)
12 lX 30 lX 36 lX 37 lX 38 lX 43 lX 56 lX 70 lX 7.34 mX
Using the developed multi-terminal based test-bed, the testing of HTS power cables is much easier. Consequently, there is no limitation on the current capacity for testing HTS power cables. It merely depends on the design and the number of copper terminals used for the HTS power cable. It is possible to increase both the number of terminals and HTS power cable capacity as much as needed by using the proposed experimental concept. Acknowledgments This work was supported by the Power Generation & Electricity Delivery of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) Grant funded by the Korea government Ministry of Knowledge Economy (No. 2011101050002A).
[1] T. Ishigohka, IEEE Trans. Appl. Supercond. 5 (2) (1995) 949–952. [2] Nomura, S. Tanaka, N. Tsuboi, K. Tsutsui, H. Tsuji-Iio, S. Tsuji-Iio, R. Shimada, in: 13th European Conference on Power Electronics and Applications EPE ’09, 2009, September 2009, pp. 1–10. [3] L. LUO, Y. LI, K. Nakamura, G. Krost, J. Li, J. Xu, F. Liu, Electr. Utility Deregul. Restruct Power Technol. (2008) 1868–1872. [4] G. Venkataramanan, B.K. Johnson, IEEE Trans. Appl. Supercond. 13 (2) (2003). [5] H. Yumura, Y. Ashibe, H. Itoh, M. Ohya, M. Watanabe, T. Masuda, C.S. Weber, IEEE Trans. Appl. Supercond. 19 (3) (2009) 1698–1701. [6] T. Masuda, H. Yumura, M. Watanabe, H. Takigawa, Y. Ashibe, C. Suzawa, T. Kato, Y. Yamada, K. Sato, S. Isojima, C. Weber, A. Dada, J.R. Spadafore, IEEE Trans. Appl. Supercond. 15 (2) (2005) 1806–1809. [7] T. Masuda, H. Yumura, M. Watanabe, H. Takigawa, Y. Ashibe, C. Suzawa, H. Ito, M. Hirose, K. Sato, S. Isojima, C. Weber, R. Lee, J. Moscovic, IEEE Trans. Appl. Supercond. 17 (2) (2007) 1648–1651. [8] C.S. Weber, R. Lee, S. Ringo, T. Masuda, H. Yumura, J. Moscovic, IEEE Trans. Appl. Supercond. 17 (2) (2007) 2038–2042. [9] S. Mukoyama, M. Yagi, T. Yonemura, T. Nomura, N. Fujiwara, Y. Ichikawa, Y. Aoki, T. Saitoh, N. Amemiya, A. Ishiyama, N. Hayakawa, IEEE Trans. Appl. Supercond. 21 (3) (2011) 976–979. [10] T. Masuda, H. Yumura, M. Ohya, Y. Ashibe, M. Watanabe, T. Minamino, H. Ito, S. Honjo, T. Mimura, Y. Kitoh, Y. Noguchi, IEEE Trans. Appl. Supercond. 21 (3) (2011) 1030–1033. [11] T. Masuda, H. Yumura, M. Ohya, T. Kikuta, M. Hirose, S. Honjo, T. Mimura, Y. Kito, K. Yamamoto, M. Ikeuchi, R. Ohno, IEEE Trans. Appl. Supercond. 19 (3) (2009) 1735–1739. [12] S. Honjo, T. Mimura, Y. Kitoh, Y. Noguchi, T. Masuda, H. Yumura, M. Watanabe, M. Ikeuchi, H. Yaguchi, T. Hara, IEEE Trans. Appl. Supercond. 21 (3) (2011) 967–971. [13] S. Mukoyama, M. Yagi, T. Yonemura, T. Nomura, N. Fujiwara, Y. Ichikawa, Yuji Aoki, Takashi Saitoh, Naoyuki Amemiya, Atsushi Ishiyama, Naoki Hayakawa, IEEE Trans. Appl. Supercond. 21 (3) (2011) 976–979.
Contents lists available at SciVerse ScienceDirect
Physica C journal homepage: www.elsevier.com/locate/physc
Transient characteristic analysis of an HTS DC power cable using a multi-terminal based test-bed q Jin-Geun Kim, Minh-Chau Dinh, Sung-Kyu Kim, Minwon Park ⇑, In-Keun Yu, Byeongmo Yang Changwon National University, 9 Sarim-Dong, Changwon 641-773, Republic of Korea KEPRI, 105 Munji-Ro, Daejeon 305-760, Republic of Korea
a r t i c l e
i n f o
Article history: Accepted 19 April 2013 Available online 11 May 2013 Keywords: AC loss High temperature superconductor HTS power cable YBCO
a b s t r a c t The current capacity of a power supply limits the experimental environment of higher capacity HTS power cable. Consequently, the transient characteristic analysis of an HTS DC power cable is difficult to assess. In this paper, a multi-terminal based test-bed is used to overcome those power supply capacity limitations. A 1 kA class HTS DC power cable was designed and the transient characteristics of the HTS DC power cable were analyzed using the multi-terminal based test-bed. Transient characteristics, such as resistance variation and critical current of the 1 kA class HTS DC power cable were successfully measured using small power sources in the multi-terminal based test-bed. Definitely, the suggested test system overcomes the assessment limits of the HTS power cable’s current capacity. Ó 2013 The Authors. Published by Elsevier B.V. All rights reserved.
1. Introduction A superconducting power cable uses superconducting materials instead of the copper or aluminum conventionally used to carry electricity in overhead power lines and underground cables. Superconducting materials can carry electrical current over 100 times more than current density of copper or aluminum, which in turn drives system economical, and that is fundamental reason why superconducting DC power cables compare favorably with conventional alternatives for long-distance power transmission. Secondly, when transmitting DC power, superconductors have no electrical resistance and introduce no electrical losses of their own [1–4]. There are several HTS power cable projects in the world. The critical current values of the Phase II of the Albany HTS cable project were 2.23 kA at 73 K and 2.8 kA at 69 K, respectively [1–3]. Since a 275 kV, 3 kA HTS power cable, which is the target of the Japanese power network project, has a power transmission capacity of 1.5 GVA, the HTS power cable has the potential for practical use as the backbone power line of the future [4]. The target of the NEDO project is to operate at 66 kV, 200 MVA HTS cable in the real grid in order to demonstrate its reliability and stable operation [5–7]. Before applying an HTS cable to a real power system, a characteristic analysis by simulation or experimentation is necessary. The q This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-No Derivative Works License, which permits non-commercial use, distribution, and reproduction in any medium, provided the original author and source are credited. ⇑ Corresponding author. Address: 55315, Changwon National University, Changwon 641-773, Republic of Korea. Tel.: +82 55 281 3150; fax: +82 55 281 3170. E-mail address: [email protected] (M. Park).
most important advantage of a superconducting cable is its high current density; however, difficulties arise when researchers experiment on HTS cables. An over current test under fault condition is particularly difficult because it needs large current source [5–12]. Furthermore, most HTS power cables whether AC or DC have not been tested for fault conditions in the laboratory scale. Previously, a field test was the only possible method to study HTS cables under fault conditions [13,10]. Another problem is the current distribution in the HTS power cable. Joint resistances between HTS wires and copper terminals are different. The transport currents of each HTS wire depend on their inductance, capacitance, and joint resistance. The inductance and capacitance of each HTS wire are the same because of the same cable structures. However, the connecting resistances of each HTS wire are different depending on the joint conditions. More precisely, the current distribution of the short length HTS DC cable in the laboratory setting depends on its joint resistance. In this paper, the authors analyzed the transient characteristic of a 1 kA class HTS DC power cables using a 200 A class power source. Multi-terminal based test-bed makes it possible to experiment an high capacity of HTS DC power cable by using a small power source. The structure of copper terminal in the multiterminal based test-bed is different than a general copper terminal of HTS power cables. The number of copper terminals is the same as the number of HTS wires in the tested HTS DC power cable. Each HTS wire was connected in series through a return path and separate copper terminals. This system can solve both current distribution and power source limitation problems. A 1 kA class HTS DC power cable was designed and fabricated (using eight HTS wires) for transient characteristic analysis in the multi-terminal
0921-4534/$ - see front matter Ó 2013 The Authors. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.physc.2013.04.069
J.-G. Kim et al. / Physica C 494 (2013) 302–306
303
based test-bed. The critical current and transient characteristics of the HTS DC power cable were successfully measured in this test system, using just 1/8 of the current source of the HTS DC power cable. Under this system, the current of each HTS wire has the same value because of its multi-terminal structure. 2. Design of a multi-terminal based test-bed 2.1. Configuration of a multi-terminal based test-bed The multi-terminal based test-bed system includes an HTS DC power cable, a power source, and control and monitoring system. Power source and monitoring devices are the same as a general experiment system which uses a current amplifier, LabVIEW and SCXI data acquisition system. However, the structure of the HTS DC power cable differed from the general HTS power cable layout. In a general HTS cable, whether AC or DC, all HTS wires were connected in parallel to a single copper terminal. Fig. 1 shows the experimental system configuration of a multi-terminal based test-bed for an HTS power cable experiment. Front and back side cross sectional area of the HTS power cable of this system were shown in Fig. 2. This experiment system for experimentation requires separate copper terminals and a return current path. Thus, each HTS wire of the HTS DC power cable had its own copper terminals as shown in Fig. 2, and copper cables were used for the return current path in this system. Most large capacity current sources has limitation of output terminal voltage level, however, copper terminal may cause the voltage drop between terminals of power sources. Total resistance of series connected copper return cables, terminals, and joint area was 7.34 mX in this system.
Fig. 2. Cross sectional area of the HTS DC power cable.
2.2. Design of the 1 kA class HTS DC power cable Fig. 3. Fabrication of a multi-terminal HTS DC power cable.
A 1 kA class HTS DC cable was designed to verify the assessment of the cable’s transient characteristics in the multi-terminal based test-bed. The fabricated HTS DC power cable is depicted in Fig. 3, being attached to separate copper terminals. In this case, eight HTS wires and copper terminals were used and their specifications are summarized in Table 1. A SuNAM second-generation HTS wire was used in this experiment, and its critical current was more than 110 A at 77 K. The cable length was 1 m, and the critical current of
the tested short-length HTS wires was 140 A in liquid nitrogen (LN2). The rated current of the designed HTS DC power cable was 1000 A using eight HTS wires. The former diameter was 20 mm, and the former was made from Fiberglass Reinforced Plastics (FRPs). HTS wires, 8 m long, were used for a 1 m HTS DC power cable. The pitch length of this cable was 2 m. Insulation of the HTS DC power cable was not considered in this system, thus the
Fig. 1. Configuration of the multi-terminal based test-bed.
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J.-G. Kim et al. / Physica C 494 (2013) 302–306
Table 1 Specifications of the HTS DC power cable. Parameters
Value
Length of the HTS DC power cable Manufacture of HTS wire Width and thickness of HTS wires Critical current of a single HTS wire Number of HTS wires for the cable Critical current of the HTS DC power cable Former diameter Length of total HTS wires
1m SuNAM 4.2 mm/0.2 mm 148 A @ 77 K 8 1120 A @ 77 K 20 mm 8.17 m
cable has no insulation layers. The current direction of all HTS wires was the same as shown in Fig. 1. The separated HTS wire tested at the same time under the same amount of current and direction just like the single terminal test system. Hence, the field effect of the cable in the multi-terminal based test-bed is the same as the general single terminal cable configuration. 2.3. Testing system configuration Fig. 4 shows the configurations of the experiment’s system. A fabricated HTS DC power cable was installed in the LN2 and connected to return copper cables. One of the copper terminals was connected to the power supply. In the multi-terminal based testbed, the HTS DC power cable and copper return path cables were connected as shown in Fig. 4. The input currents and voltages of the HTS wires were measured using LabVIEW and the SCXI measurement system. The voltages of all HTS wires were measured to detect the quench and resistance of HTS wires. The power sources of this system can put out 200 A of current; however, if we had used the general experiment method, it is not enough to measure the transient characteristic of the HTS DC power cable because the cable’s critical current was 1.2 kA. The multi-terminal based test-bed has no limitation of current capacity for testing the HTS power cable. Hence, it is possible to increase the capacity of HTS power cable through the increment of copper terminals quantity. 3. Experiment results 3.1. Critical and fault current characteristics The critical current of the HTS DC power cable and each HTS wire were measured in LN2 at 77 K. The results are shown in Fig. 5 and the cable’s critical current was 1.2 kA. Thus, the critical
current of a 1 kA class HTS DC power cable was successfully measured using the developed multi-terminal based test-bed which has 200 A class power sources. The resistance variations of the HTS DC cable were also measured and the results are depicted in Fig. 6. The operating DC current is 80% of critical current and the fault current were 1.44 kA and 1.6 kA. The output current of the power source was 180 A and 200 A when the fault currents were 1.44 kA and 1.6 kA, respectively, because of the multi-terminal structure. The resistance of this cable increased to 27 mX when fault current was 1.6 kA and one of the HTS wires was damaged after 0.34 s. 3.2. Joint resistance of each terminal We measured the joint resistance of each terminal and the total resistance of the multi-terminal based test-bed. The results were shown in Fig. 7 and summarized in Table 2. Indium (In) was used for the soldering of HTS wires and copper terminals. The total resistance of the copper return cable and joint resistance was 7.34 mX and each joint resistance was 12 lX, 30 lX, 36 lX, 37 lX, 38 lX, 43 lX, 56 lX and 70 lX respectively. However, the current of each HTS wire was the same even as the joint resistances were different in this system. Because HTS wires in the HTS DC power cable were connected in series.
4. Conclusion The authors have developed the multi-terminal based test-bed to overcome limitations in power source capacity. The 1 kA class HTS DC power cable was fabricated from second-generation SuNAM HTS wires for the test system. The critical current and transient characteristics of the HTS DC power cable were successfully measured using a small power source; only 200 A of current were needed to measure the transient characteristics of the HTS DC cable. If we had used a general method of critical current measuring, we would have needed a current source exceeding 3 kA. Furthermore, even though each joint resistance was different, the current of each HTS wire was the same during experiment because of the series connected structure. The experiment results obtained by using the multi-terminal based test-bed were the same as the results obtained by a single terminal test system with a large power sources. The cable structure and current direction of all wires were identical for both multi-terminal based test-bed and the single terminal method as shown in Fig. 1.
Fig. 4. Experimental setup of the HTS DC power cable and current return path.
J.-G. Kim et al. / Physica C 494 (2013) 302–306
Fig. 5. V–I characteristic of the HTS DC power cable.
Fig. 6. Transient resistance variation of the HTS DC power cable.
Fig. 7. Measurement results of copper terminal joint resistance.
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J.-G. Kim et al. / Physica C 494 (2013) 302–306 Table 2 Resistance of terminal joint area.
References
Parameters
Value
HTS joint 1 HTS joint 2 HTS joint 3 HTS joint 4 HTS joint 5 HTS joint 6 HTS joint 7 HTS joint 8 Sum of resistance (joint + copper cable)
12 lX 30 lX 36 lX 37 lX 38 lX 43 lX 56 lX 70 lX 7.34 mX
Using the developed multi-terminal based test-bed, the testing of HTS power cables is much easier. Consequently, there is no limitation on the current capacity for testing HTS power cables. It merely depends on the design and the number of copper terminals used for the HTS power cable. It is possible to increase both the number of terminals and HTS power cable capacity as much as needed by using the proposed experimental concept. Acknowledgments This work was supported by the Power Generation & Electricity Delivery of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) Grant funded by the Korea government Ministry of Knowledge Economy (No. 2011101050002A).
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