- Email: [email protected]
Current limitation capability of bulk Bi2223 material
Physica C 372–376 (2002) 1598–1601 www.elsevier.com/locate/physc
Current limitation capability of bulk Bi2223 material D. Bourgault a
a,*
, S. Pavard a, R. Tournier a, L. Porcar b, N. Caillault c, L. Carbone c
CNRS/CRETA––Laboratoire de Cristallographie, BP 166, 38042 Grenoble Cedex 09, France b CNRS/CRTBT, BP 166, 38042 Grenoble Cedex 09, France c Schneider Electric Industries S.A. A3, rue Volta, 38042 Grenoble Cedex 09, France
Abstract Bulk sintered and textured Bi2223 materials have been prepared in view of current limiting applications. Pellets of large diameter (100 mm) have been compacted at 1 GPa before sintering and cutting in meander shape. The total length of the sintered conductor is 70 cm with a section of 0.25 cm2 . A homogeneous transport critical current (Ic ¼ 160 A) has been obtained for such a length. Pulsed measurements above the critical current have shown that the total (70 cm) length of the conductor goes to the normal state. A total voltage of 370 V has been obtained for a pulsed current of 3.3 kA in one sintered element of 100 mm of diameter. The parameters governing the transition to the normal state have been studied on sintered and textured 20 mm long samples with different Jc values. In Bi2223 material, the transition in the normal state is governed by the qflux flow Jc2 value. A textured sample with a Jc of 4500 A/cm2 has shown a transition in the normal state for a current lower than five times the critical current. This last result is very encouraging for the use of textured Bi2223 material as current limiting element operating at 77 K. Ó 2002 Elsevier Science B.V. All rights reserved. Keywords: Current limitation; Critical current density; Texturing; Bi2223
1. Introduction For bulk materials, bismuth compounds show critical current densities at 77 K lower than YBCO single crystal, but their current limitation potentiality is very important [1,2], because of a high capacity to support the energy dissipated during the superconducting–normal transition. In this paper, we present Jc performances and current limitation capability of Bi2223 sintered and textured materials. Long Bi2223 sintered
*
Corresponding author. Fax: +33-476-88-12-80. E-mail address: [email protected] (D. Bourgault).
conductors of 70 cm in length and 0.25 cm2 in section were obtained from £100 mm large pellets. Small textured bars with different Jc values were also studied for currents higher than their critical current. Silver junctions along the c-axis and along the ab planes were tested at high current with textured elements.
2. Experimental Pellets of 100 mm in diameter and 5 mm in height were pressed at 1 GPa. 800 tons were applied on the pellet surface using a mould specially
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 1 0 8 1 - X
D. Bourgault et al. / Physica C 372–376 (2002) 1598–1601
1599
3. Results 3.1. Sintered Bi2223
Fig. 1. Meander of 70 cm in length (without the turns) with the different potential taps.
designed to support such pressure. After sintering, such large pellets were cut into meander shape. Fig. 1 shows the meander prepared for transport critical current and current limitation measurements. The 10 different regions (strip 1 to 10) of the conductor were tested using the different potential taps. The total voltage with and without the current leads contacts was also recorded. Textured bars have been cut from £20 mm pellets pressed at high temperature [3]. With this technique, high Jc can be obtained in self-field [4]. Bars with different Jc values have been tested with currents higher than the critical current. Such bars allow to test low resistive junctions along the ab planes and the c-axis. Transport critical current measurements have been obtained using a 1 lV/cm electrical field criterion in dc current. The 10 strips of the 70 cm long sintered sample were measured with an electrical field criterion of 0.2 lV/cm. Pulsed measurements were obtained with a capacitor discharge system with a period time of 20 ms. The time was limited to 10 ms using a diode in serial.
The sintered 70 cm long conductor (without the turns) has been measured in dc and pulsed currents. A transport critical current of 160 A was obtained for the 0.25 cm2 cross-section. A pulsed current of 3300 A was injected through the meander during 10 ms (20 times Ic ). Fig. 2 shows the voltage obtained for the total length. A voltage of 370 V, corresponding to an electrical field of 530 V/m, has been obtained without material degradation. However, the meander was not pushed to its limit, in order to make other measurements. Therefore the maximum value could be higher. It is important to notice that no transition in the normal state occurred for the current leads. This is due to the low contact resistance (50 nX for the two current leads) but also to the geometry and to the position of the silver wire on the contacts. This last point is very important in particular for the connection of several conductors in serial. 3.2. Textured Bi2223 In the network, the limiter has to act as fast as possible. Electrotechnical functions require a transition in the normal state for a fault current of about four to five times the nominal current. The
Fig. 2. Voltage of the total length of the meander for a pulsed current of 3300 A during 10 ms. Dashed line corresponds to the current (4000 A) if no transition in the normal state occurred.
1600
D. Bourgault et al. / Physica C 372–376 (2002) 1598–1601
Fig. 3. Jtrans =Jc for Bi2223 textured material with different Jc values.
Jc influence on the superconducting–normal transition has been studied using textured Bi2223 bars. Fig. 3 shows the ratio Jtrans =Jc obtained for different Jc values after a pulse of 10 ms. Jtrans corresponds to the current for which the transition in the normal state occurs. The larger Jc , the closer the magnetothermal transition to Jc . For Jc close to 4500 A/cm2 , transition occurs for a current lower than five times the critical current. For a pulse lower than 10 ms, the ratio increases because the temperature reached by the material is a function of qflux flow J 2 but also of Dt. For a pulse duration of 2.5 ms, the ratio reaches a value of 10. The transition in the normal state has to be homogeneous, firstly to avoid a material degradation due to a local heating excess and secondly to obtain the resistance corresponding to the whole conductor length. Several tests have been realized on textured 20 mm bars. Homogeneous electrical fields of at least 1 kV/m have been obtained on such textured bars, without degradation.
and lead to large progresses for applications like levitation and current leads. However, Jc differences between the ‘‘bulk’’ and the joint are nefast for current limitation application, because only the region near the joint goes in the normal state. Up to now, we focused on low resistive junctions (with silver). Different configurations have been tested using Bi2223 textured bars. The current is injected along the ab planes. The current passes from one Bi2223 conductor to another along the ab planes or along the c-axis. An ‘‘ab planes’’ junction can be seen in inset of Fig. 4. Junctions have been realized by silver coating between the two Bi2223 conductors and by annealing at high temperature in air. The different potential taps allow to measure the voltage of the ‘‘bulk’’ and the junction. The surface of the silver coating has been determined according to the critical current density anisotropy of bulk Bi2223 material. We observed (Fig. 4) that the transition in the normal state occurred firstly in the ‘‘bulk’’ when the assembling (along the ab planes on the figure) is submitted to a pulsed current higher than its critical current. The ‘‘bulk’’ goes in the normal state before the junction showing that the local heating near the junction is lower than the dissipation due to vortex motions. This result is very
3.3. Bi2223 junctions Although it is possible to obtain very long conductor from large pellet using cutting techniques, studies on assembling processes is a necessity. Critical current densities of about 104 A/cm2 in a magnetic field of 5 T have been obtained in YBCO bulk material [5]. These results are very interesting
Fig. 4. Response of the junction along the ab planes: the ‘‘bulk’’ shows a transition before the junction. In inset: silver junctions along the ab planes.
D. Bourgault et al. / Physica C 372–376 (2002) 1598–1601
important for the assembling of conductors in serials. Indeed, transition in the normal state has not to be initiated at the junction and the contact resistance must be as low as possible to minimize the losses in permanent regime (for current lower than the critical current). In our case, the absence of wire connections between conductors highly reduces losses. The behaviour for c-axis connection configuration is similar. The ‘‘bulk’’ transits before junction whatever the connection configuration.
1601
fields higher than 1 kV/m using textured Bi2223 material without degradation. A study of the assembling bars configurations proved that low resistive junctions having a similar transition behaviour than the ‘‘bulk’’ can be realized. All these points confirmed that textured Bi2223 material is a promising candidate for current limitation application.
Acknowledgements 4. Conclusion A total voltage of 370 V has been obtained on a 70 cm long conductor (Ic ¼ 160 A) cut from a sintered Bi2223 £ 10 cm pellet. The test of this conductor, which presents no resistive connection, shows that bulk Bi2223 material can support a high pulsed current (3300 A) during 10 ms and large electromechanical stresses without degradation. The demonstration of the efficiency of textured material has also been confirmed with small samples. A transition in the normal state occurred for a current near five times the critical current using a bar of 20 mm in length having a critical current density of 4500 A/cm2 . Homogeneous transitions are currently obtained with electrical
The authors are grateful to A. Clo^ıtre, J. Turc and J. Didier from Schneider-Electric for their help during pulsed measurements.
References [1] J.G. Noudem, L. Porcar, J. Sanchez, D. Bourgault, X. Chaud, J.M. Barbut, R. Tournier, Supercond. Sci. Technol. 10 (1997) 978. [2] S. Elschner, F. Breuer, A. Wolf, M. Noe, L. Cowey, J. Bock, IEEE Trans. Appl. Supercond. 11 (1) (2001) 2507. [3] J.G. Noudem, J. Beille, D. Bourgault, A. Sulpice, R. Tournier, Physica C 230 (1994) 42. [4] V. Rouessac, G. Poullain, G. Desgardin, B. Raveau, Supercond. Sci. Technol. 11 (1998) 1160. [5] C. Harnois, G. Desgardin, I. Laffez, X. Chaud, D. Bourgault, Physica C, accepted.
Current limitation capability of bulk Bi2223 material D. Bourgault a
a,*
, S. Pavard a, R. Tournier a, L. Porcar b, N. Caillault c, L. Carbone c
CNRS/CRETA––Laboratoire de Cristallographie, BP 166, 38042 Grenoble Cedex 09, France b CNRS/CRTBT, BP 166, 38042 Grenoble Cedex 09, France c Schneider Electric Industries S.A. A3, rue Volta, 38042 Grenoble Cedex 09, France
Abstract Bulk sintered and textured Bi2223 materials have been prepared in view of current limiting applications. Pellets of large diameter (100 mm) have been compacted at 1 GPa before sintering and cutting in meander shape. The total length of the sintered conductor is 70 cm with a section of 0.25 cm2 . A homogeneous transport critical current (Ic ¼ 160 A) has been obtained for such a length. Pulsed measurements above the critical current have shown that the total (70 cm) length of the conductor goes to the normal state. A total voltage of 370 V has been obtained for a pulsed current of 3.3 kA in one sintered element of 100 mm of diameter. The parameters governing the transition to the normal state have been studied on sintered and textured 20 mm long samples with different Jc values. In Bi2223 material, the transition in the normal state is governed by the qflux flow Jc2 value. A textured sample with a Jc of 4500 A/cm2 has shown a transition in the normal state for a current lower than five times the critical current. This last result is very encouraging for the use of textured Bi2223 material as current limiting element operating at 77 K. Ó 2002 Elsevier Science B.V. All rights reserved. Keywords: Current limitation; Critical current density; Texturing; Bi2223
1. Introduction For bulk materials, bismuth compounds show critical current densities at 77 K lower than YBCO single crystal, but their current limitation potentiality is very important [1,2], because of a high capacity to support the energy dissipated during the superconducting–normal transition. In this paper, we present Jc performances and current limitation capability of Bi2223 sintered and textured materials. Long Bi2223 sintered
*
Corresponding author. Fax: +33-476-88-12-80. E-mail address: [email protected] (D. Bourgault).
conductors of 70 cm in length and 0.25 cm2 in section were obtained from £100 mm large pellets. Small textured bars with different Jc values were also studied for currents higher than their critical current. Silver junctions along the c-axis and along the ab planes were tested at high current with textured elements.
2. Experimental Pellets of 100 mm in diameter and 5 mm in height were pressed at 1 GPa. 800 tons were applied on the pellet surface using a mould specially
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 1 0 8 1 - X
D. Bourgault et al. / Physica C 372–376 (2002) 1598–1601
1599
3. Results 3.1. Sintered Bi2223
Fig. 1. Meander of 70 cm in length (without the turns) with the different potential taps.
designed to support such pressure. After sintering, such large pellets were cut into meander shape. Fig. 1 shows the meander prepared for transport critical current and current limitation measurements. The 10 different regions (strip 1 to 10) of the conductor were tested using the different potential taps. The total voltage with and without the current leads contacts was also recorded. Textured bars have been cut from £20 mm pellets pressed at high temperature [3]. With this technique, high Jc can be obtained in self-field [4]. Bars with different Jc values have been tested with currents higher than the critical current. Such bars allow to test low resistive junctions along the ab planes and the c-axis. Transport critical current measurements have been obtained using a 1 lV/cm electrical field criterion in dc current. The 10 strips of the 70 cm long sintered sample were measured with an electrical field criterion of 0.2 lV/cm. Pulsed measurements were obtained with a capacitor discharge system with a period time of 20 ms. The time was limited to 10 ms using a diode in serial.
The sintered 70 cm long conductor (without the turns) has been measured in dc and pulsed currents. A transport critical current of 160 A was obtained for the 0.25 cm2 cross-section. A pulsed current of 3300 A was injected through the meander during 10 ms (20 times Ic ). Fig. 2 shows the voltage obtained for the total length. A voltage of 370 V, corresponding to an electrical field of 530 V/m, has been obtained without material degradation. However, the meander was not pushed to its limit, in order to make other measurements. Therefore the maximum value could be higher. It is important to notice that no transition in the normal state occurred for the current leads. This is due to the low contact resistance (50 nX for the two current leads) but also to the geometry and to the position of the silver wire on the contacts. This last point is very important in particular for the connection of several conductors in serial. 3.2. Textured Bi2223 In the network, the limiter has to act as fast as possible. Electrotechnical functions require a transition in the normal state for a fault current of about four to five times the nominal current. The
Fig. 2. Voltage of the total length of the meander for a pulsed current of 3300 A during 10 ms. Dashed line corresponds to the current (4000 A) if no transition in the normal state occurred.
1600
D. Bourgault et al. / Physica C 372–376 (2002) 1598–1601
Fig. 3. Jtrans =Jc for Bi2223 textured material with different Jc values.
Jc influence on the superconducting–normal transition has been studied using textured Bi2223 bars. Fig. 3 shows the ratio Jtrans =Jc obtained for different Jc values after a pulse of 10 ms. Jtrans corresponds to the current for which the transition in the normal state occurs. The larger Jc , the closer the magnetothermal transition to Jc . For Jc close to 4500 A/cm2 , transition occurs for a current lower than five times the critical current. For a pulse lower than 10 ms, the ratio increases because the temperature reached by the material is a function of qflux flow J 2 but also of Dt. For a pulse duration of 2.5 ms, the ratio reaches a value of 10. The transition in the normal state has to be homogeneous, firstly to avoid a material degradation due to a local heating excess and secondly to obtain the resistance corresponding to the whole conductor length. Several tests have been realized on textured 20 mm bars. Homogeneous electrical fields of at least 1 kV/m have been obtained on such textured bars, without degradation.
and lead to large progresses for applications like levitation and current leads. However, Jc differences between the ‘‘bulk’’ and the joint are nefast for current limitation application, because only the region near the joint goes in the normal state. Up to now, we focused on low resistive junctions (with silver). Different configurations have been tested using Bi2223 textured bars. The current is injected along the ab planes. The current passes from one Bi2223 conductor to another along the ab planes or along the c-axis. An ‘‘ab planes’’ junction can be seen in inset of Fig. 4. Junctions have been realized by silver coating between the two Bi2223 conductors and by annealing at high temperature in air. The different potential taps allow to measure the voltage of the ‘‘bulk’’ and the junction. The surface of the silver coating has been determined according to the critical current density anisotropy of bulk Bi2223 material. We observed (Fig. 4) that the transition in the normal state occurred firstly in the ‘‘bulk’’ when the assembling (along the ab planes on the figure) is submitted to a pulsed current higher than its critical current. The ‘‘bulk’’ goes in the normal state before the junction showing that the local heating near the junction is lower than the dissipation due to vortex motions. This result is very
3.3. Bi2223 junctions Although it is possible to obtain very long conductor from large pellet using cutting techniques, studies on assembling processes is a necessity. Critical current densities of about 104 A/cm2 in a magnetic field of 5 T have been obtained in YBCO bulk material [5]. These results are very interesting
Fig. 4. Response of the junction along the ab planes: the ‘‘bulk’’ shows a transition before the junction. In inset: silver junctions along the ab planes.
D. Bourgault et al. / Physica C 372–376 (2002) 1598–1601
important for the assembling of conductors in serials. Indeed, transition in the normal state has not to be initiated at the junction and the contact resistance must be as low as possible to minimize the losses in permanent regime (for current lower than the critical current). In our case, the absence of wire connections between conductors highly reduces losses. The behaviour for c-axis connection configuration is similar. The ‘‘bulk’’ transits before junction whatever the connection configuration.
1601
fields higher than 1 kV/m using textured Bi2223 material without degradation. A study of the assembling bars configurations proved that low resistive junctions having a similar transition behaviour than the ‘‘bulk’’ can be realized. All these points confirmed that textured Bi2223 material is a promising candidate for current limitation application.
Acknowledgements 4. Conclusion A total voltage of 370 V has been obtained on a 70 cm long conductor (Ic ¼ 160 A) cut from a sintered Bi2223 £ 10 cm pellet. The test of this conductor, which presents no resistive connection, shows that bulk Bi2223 material can support a high pulsed current (3300 A) during 10 ms and large electromechanical stresses without degradation. The demonstration of the efficiency of textured material has also been confirmed with small samples. A transition in the normal state occurred for a current near five times the critical current using a bar of 20 mm in length having a critical current density of 4500 A/cm2 . Homogeneous transitions are currently obtained with electrical
The authors are grateful to A. Clo^ıtre, J. Turc and J. Didier from Schneider-Electric for their help during pulsed measurements.
References [1] J.G. Noudem, L. Porcar, J. Sanchez, D. Bourgault, X. Chaud, J.M. Barbut, R. Tournier, Supercond. Sci. Technol. 10 (1997) 978. [2] S. Elschner, F. Breuer, A. Wolf, M. Noe, L. Cowey, J. Bock, IEEE Trans. Appl. Supercond. 11 (1) (2001) 2507. [3] J.G. Noudem, J. Beille, D. Bourgault, A. Sulpice, R. Tournier, Physica C 230 (1994) 42. [4] V. Rouessac, G. Poullain, G. Desgardin, B. Raveau, Supercond. Sci. Technol. 11 (1998) 1160. [5] C. Harnois, G. Desgardin, I. Laffez, X. Chaud, D. Bourgault, Physica C, accepted.