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Ag HTS tape
Physica C 372–376 (2002) 939–941 www.elsevier.com/locate/physc
Location of normal zone generation point of Bi-2223/Ag HTS tape N. Nanato *, K. Nakamura Department of Systems Management and Engineering, Faculty of Engineering, Nagoya Institute of Technology, Gokiso, Showa, Nagoya 466-8555, Japan
Abstract In this paper, we present a method to locate a normal zone generation point of a short sample of a superconducting wire. In general, in order to locate the point, the voltages across many voltage taps soldered to the sample are measured. However, attaching many voltage taps makes the location system complicated and in a bad case the taps may be shortcircuited. In our proposed method, many taps are not needed and precise location can be realized. Ó 2002 Elsevier Science B.V. All rights reserved. Keywords: Normal zone generation point; Location; Short sample
1. Introduction Recently, low Tc superconducting (LTS) and high Tc superconducting (HTS) wires and equipments have been developed. It is one of the important subjects to analyze the transient behavior of the normal resistance generation in the superconducting wire during a quench process in order to design and protect the superconducting equipments. Therefore, the factors related to the normal resistance generation have been investigated [1,2]. One of the factors is the location of the normal zone generation point of the superconducting wire. In general, in order to locate the normal zone generation point, the voltages across many voltage taps soldered to the sample are measured. How-
ever, attaching many voltage taps makes the location system complicated and in a bad case the taps may be short-circuited. Therefore, a simple location system is needed. In this paper, we propose the simple and precise system/method to locate the normal zone generation point of the short superconducting wire (approximately several hundred millimeters long) using three voltage taps. In our proposed method, the normal zone generation point can be located by measuring the time variation of the resistance of the sample. Through the experimental result using the short sample (60 mm) of Bi-2223/Ag HTS tape cooled at 77 K, the feasibility of our proposed method is shown.
2. Principle of location method *
Corresponding author. Tel./fax: +81-52-735-5428. E-mail address: [email protected] (N. Nanato).
Fig. 1 shows the resistance during a quench process as a function of time. The left hand side
0921-4534/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 3 4 ( 0 2 ) 0 0 9 3 8 - 3
940
N. Nanato, K. Nakamura / Physica C 372–376 (2002) 939–941
of the wire (the distance between the two terminal taps) and x is the distance from the central tap to the normal zone generation point. Then, from the proportional distribution of the distance and time, the normal zone generation point x can be located/ calculated from x ¼ ðt2 t1 Þ=ðt3 t2 Þ l=2: Fig. 1. Resistance during a quench process as a function of time.
shows the superconducting wire with two terminal voltage taps and the right hand side shows the graph of the resistance vs. time. During the quench process, the normal zone grows in size and its temperature increases. Therefore, the resistance of the sample increases depending on two factors: the growth of the normal zone size and the temperature rise. When the normal zone has reached both ends of the sample, it does not grow in size anymore. Then the resistance of the sample increases depending on one factor: the temperature rise. In other words, when the whole sample becomes normally conducting, it is expected that a sharp slope change will appear in the resistance trace as shown in the graph of Fig. 1. By measuring the time of the sharp slope change, the normal zone generation point can be located. Fig. 2 shows the configuration of the location method. The left hand side shows the superconducting wire with three voltage taps (two terminal taps and a central one) and the right hand side shows the graph of the resistances (r1 ¼ m1 =i and r2 ¼ m2 =i) vs. time after a normal zone appeared between the left terminal tap and the central one. In the figure, t1 is the normal zone generation time, t2 is the r2 generation time, t3 is the time of the sharp slope change of the trace of r2 , l is the length
Fig. 2. Configuration of the location method.
ð1Þ
Eq. (1) is valid if the normal zone propagates with constant velocity.
3. Experimental result Fig. 3 shows the configuration of an experimental setup and Table 1 shows the specifications
Fig. 3. Configuration of an experimental setup.
N. Nanato, K. Nakamura / Physica C 372–376 (2002) 939–941
941
Table 1 Specifications of a short sample of Bi-2223/Ag HTS tape Width Thickness Length (distance between the taps A and B) Ratio of silver Filament number Critical temperature Tc Critical current Ic (at 77 K, Ec ¼ 1 lV=cm)
1.5 mm 0.2 mm 60 mm 3.5 37 109.2 K 5.9 A
of a short sample of Bi-2223/Ag HTS tape. The short sample with three voltage taps (A, B, and C) and a heater is covered with a styrene foam and cooled by liquid nitrogen (LN2 ). A heater was used to create a normal zone. It was fixed at 15–18 mm from the central tap B (the heater length was 3 mm) between the taps A and B. The styrene foam makes the sample to be in adiabatic condition so that the normal zone can be created with a small injection of energy from the heater. In the normal zone generation, the current with amplitude 5.9 Apeak and frequency 60 Hz flowed through the sample. Fig. 4 shows experimental results of the resistances r1 and r2 as a function of time. In the figure, t1 , t2 , and t3 are 2.45, 6.96, and 15.0 s, respectively. From Eq. (1), the normal zone generation point x is calculated as follows: x ¼ ð6:96 2:45Þ=ð15:0 6:96Þ 60=2 ¼ 16:8 mm: ð2Þ
The result, 16.8 mm, is in good agreement with the heater position 15–18 mm. Through the experimental result, the feasibility of our proposed method is approved. In this experiment, we used a Bi-2223/Ag HTS tape as a sample, however it is expected that our proposed method will be able to locate the normal zone generation point of any short sample (e.g. LTS wires, HTS bulk, and so on) because Eq. (1) has no term related to the materials of the superconductor.
Fig. 4. Resistances (r1 and r2 ) vs. time.
4. Conclusions The location of the normal zone generation point is one of the important factors related to the transient behavior of the normal resistance generation during a quench process. In this paper, we proposed a method to locate the normal zone generation point of the short sample and its feasibility was shown from experimental results. In the future work, we will investigate a more precise and simpler method to locate the normal zone generation point of a superconducting wire and coil.
Acknowledgements We would like to gratefully express our special thanks to Mr. N. Otani of Showa Electric Wire & Cable Co., Ltd., for his support of our work. This work was partially supported by a research grant of the Ministry of Education, Science, Sports and Culture for Research Fellow of the Japan Society for the Promotion of Science, 2053.
References [1] R.H. Bellis, Y. Iwasa, Cryogenics 34 (2) (1994) 129–144. [2] H. Shimizu, K. Taketa, Y. Yokomizu, T. Matsumura, Cryogenics 38 (10) (1998) 977–982.
Location of normal zone generation point of Bi-2223/Ag HTS tape N. Nanato *, K. Nakamura Department of Systems Management and Engineering, Faculty of Engineering, Nagoya Institute of Technology, Gokiso, Showa, Nagoya 466-8555, Japan
Abstract In this paper, we present a method to locate a normal zone generation point of a short sample of a superconducting wire. In general, in order to locate the point, the voltages across many voltage taps soldered to the sample are measured. However, attaching many voltage taps makes the location system complicated and in a bad case the taps may be shortcircuited. In our proposed method, many taps are not needed and precise location can be realized. Ó 2002 Elsevier Science B.V. All rights reserved. Keywords: Normal zone generation point; Location; Short sample
1. Introduction Recently, low Tc superconducting (LTS) and high Tc superconducting (HTS) wires and equipments have been developed. It is one of the important subjects to analyze the transient behavior of the normal resistance generation in the superconducting wire during a quench process in order to design and protect the superconducting equipments. Therefore, the factors related to the normal resistance generation have been investigated [1,2]. One of the factors is the location of the normal zone generation point of the superconducting wire. In general, in order to locate the normal zone generation point, the voltages across many voltage taps soldered to the sample are measured. How-
ever, attaching many voltage taps makes the location system complicated and in a bad case the taps may be short-circuited. Therefore, a simple location system is needed. In this paper, we propose the simple and precise system/method to locate the normal zone generation point of the short superconducting wire (approximately several hundred millimeters long) using three voltage taps. In our proposed method, the normal zone generation point can be located by measuring the time variation of the resistance of the sample. Through the experimental result using the short sample (60 mm) of Bi-2223/Ag HTS tape cooled at 77 K, the feasibility of our proposed method is shown.
2. Principle of location method *
Corresponding author. Tel./fax: +81-52-735-5428. E-mail address: [email protected] (N. Nanato).
Fig. 1 shows the resistance during a quench process as a function of time. The left hand side
0921-4534/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 3 4 ( 0 2 ) 0 0 9 3 8 - 3
940
N. Nanato, K. Nakamura / Physica C 372–376 (2002) 939–941
of the wire (the distance between the two terminal taps) and x is the distance from the central tap to the normal zone generation point. Then, from the proportional distribution of the distance and time, the normal zone generation point x can be located/ calculated from x ¼ ðt2 t1 Þ=ðt3 t2 Þ l=2: Fig. 1. Resistance during a quench process as a function of time.
shows the superconducting wire with two terminal voltage taps and the right hand side shows the graph of the resistance vs. time. During the quench process, the normal zone grows in size and its temperature increases. Therefore, the resistance of the sample increases depending on two factors: the growth of the normal zone size and the temperature rise. When the normal zone has reached both ends of the sample, it does not grow in size anymore. Then the resistance of the sample increases depending on one factor: the temperature rise. In other words, when the whole sample becomes normally conducting, it is expected that a sharp slope change will appear in the resistance trace as shown in the graph of Fig. 1. By measuring the time of the sharp slope change, the normal zone generation point can be located. Fig. 2 shows the configuration of the location method. The left hand side shows the superconducting wire with three voltage taps (two terminal taps and a central one) and the right hand side shows the graph of the resistances (r1 ¼ m1 =i and r2 ¼ m2 =i) vs. time after a normal zone appeared between the left terminal tap and the central one. In the figure, t1 is the normal zone generation time, t2 is the r2 generation time, t3 is the time of the sharp slope change of the trace of r2 , l is the length
Fig. 2. Configuration of the location method.
ð1Þ
Eq. (1) is valid if the normal zone propagates with constant velocity.
3. Experimental result Fig. 3 shows the configuration of an experimental setup and Table 1 shows the specifications
Fig. 3. Configuration of an experimental setup.
N. Nanato, K. Nakamura / Physica C 372–376 (2002) 939–941
941
Table 1 Specifications of a short sample of Bi-2223/Ag HTS tape Width Thickness Length (distance between the taps A and B) Ratio of silver Filament number Critical temperature Tc Critical current Ic (at 77 K, Ec ¼ 1 lV=cm)
1.5 mm 0.2 mm 60 mm 3.5 37 109.2 K 5.9 A
of a short sample of Bi-2223/Ag HTS tape. The short sample with three voltage taps (A, B, and C) and a heater is covered with a styrene foam and cooled by liquid nitrogen (LN2 ). A heater was used to create a normal zone. It was fixed at 15–18 mm from the central tap B (the heater length was 3 mm) between the taps A and B. The styrene foam makes the sample to be in adiabatic condition so that the normal zone can be created with a small injection of energy from the heater. In the normal zone generation, the current with amplitude 5.9 Apeak and frequency 60 Hz flowed through the sample. Fig. 4 shows experimental results of the resistances r1 and r2 as a function of time. In the figure, t1 , t2 , and t3 are 2.45, 6.96, and 15.0 s, respectively. From Eq. (1), the normal zone generation point x is calculated as follows: x ¼ ð6:96 2:45Þ=ð15:0 6:96Þ 60=2 ¼ 16:8 mm: ð2Þ
The result, 16.8 mm, is in good agreement with the heater position 15–18 mm. Through the experimental result, the feasibility of our proposed method is approved. In this experiment, we used a Bi-2223/Ag HTS tape as a sample, however it is expected that our proposed method will be able to locate the normal zone generation point of any short sample (e.g. LTS wires, HTS bulk, and so on) because Eq. (1) has no term related to the materials of the superconductor.
Fig. 4. Resistances (r1 and r2 ) vs. time.
4. Conclusions The location of the normal zone generation point is one of the important factors related to the transient behavior of the normal resistance generation during a quench process. In this paper, we proposed a method to locate the normal zone generation point of the short sample and its feasibility was shown from experimental results. In the future work, we will investigate a more precise and simpler method to locate the normal zone generation point of a superconducting wire and coil.
Acknowledgements We would like to gratefully express our special thanks to Mr. N. Otani of Showa Electric Wire & Cable Co., Ltd., for his support of our work. This work was partially supported by a research grant of the Ministry of Education, Science, Sports and Culture for Research Fellow of the Japan Society for the Promotion of Science, 2053.
References [1] R.H. Bellis, Y. Iwasa, Cryogenics 34 (2) (1994) 129–144. [2] H. Shimizu, K. Taketa, Y. Yokomizu, T. Matsumura, Cryogenics 38 (10) (1998) 977–982.