- Email: [email protected]
Observation of Transient Behavior of Magnetic Flux in Inductive-type Fault Current Limiter with YBCO Thin Film Disc
Available online at www.sciencedirect.com
Physics Procedia 36 (2012) 1254 – 1257
Superconductivity Centennial Conference
Observation of Transient Behavior of Magnetic Flux in Inductive-type Fault Current Limiter with YBCO Thin Film Disc Kosuke Higuchia*, Yin Guana, Yasunobu Yokomizua and Toshiro Matsumuraa a
Department of Electrical Engineering and Computer Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
Abstract Recently, the installation of fault current limiters (FCLs) in power systems is expected for controlling large shortcircuit currents. In this study, we focus on inductive-type FCLs having a YBCO superconducting thin film disc that is fabricated by metal-organic deposition. AC currents were injected into the FCL so that the periodic transient behavior of the apparent magnetic flux density around the FCL could be measured by using a pick-up coil. The magnetic flux density exhibited hysteresis when AC current was injected into the FCL. The transition between the conducting states in the YBCO layer was explained by the hysteresis relationship between the magnetic flux density and current.
© 2012 2011 Published Publishedby byElsevier ElsevierB.V. Ltd.Selection Selectionand/or and/orpeer-review peer-review under responsibility of Horst © under responsibility of the GuestRogalla Editors. and Peter Kes. Keywords: fault current limiter; YBCO; superconductivity; magnetic flux; power system stability; impedance; pick-up coil
1. Introduction Fault current limiters (FCLs) are essential for controlling the increase in fault currents in large power systems, which have dispersed generators. The FCL will help reduce the fault current and may also provide other benefits to the power system [1][2]. We have proposed an inductive-type FCL consisting of a pancake coil as the primary winding and a superconducting disc as the secondary winding [3]. This type of FCL modules can be easily scaled up to make large scale FCLs for use in practical applications. In this study, we used a YBCO thin film disc fabricated by metal-organic deposition (MOD) [4]. When the current flowing in the primary winding is at the load current level, the magnetic flux generated by the
* Corresponding author. E-mail address: [email protected]
1875-3892 © 2012 Published by Elsevier B.V. Selection and/or peer-review under responsibility of the Guest Editors. doi:10.1016/j.phpro.2012.06.285
1255
Kosuke Higuchi et al. / Physics Procedia 36 (2012) 1254 – 1257
primary current is canceled out by the magnetic flux generated by the current induced in the YBCO layer. When the fault current flows in the primary winding, a resistance is produced in the YBCO layer, and subsequently, an impedance is generated in the FCL. As a result, the fault current is limited. Thus, an understanding of the transient behavior of the magnetic flux is important for designing an inductive-type FCL. In this study, AC currents were injected into the FCL so that the periodic transient behavior of the apparent magnetic flux density around the FCL could be measured by a pick-up coil. The magnetic flux density exhibited hysteresis when AC current was injected into the FCL. The transition between the conducting states in the YBCO layer of the FCL was explained by the hysteresis relationship between the magnetic flux density and current. 2. FCL model and measurement method of magnetic flux density Fig. 1 shows the schematic arrangement of the FCL model and the pick-up coil. A 38-turn pancake coil, made of a 1-mm-diameter copper wire, was used as the primary winding of the FCL. For the secondary winding, we used a YBCO disc having outer and inner diameter of 100 and 12 mm, respectively. The YBCO disc was constructed of a sapphire substrate of 2 mm in thickness, cerium oxide interlayer of 40 nm in thickness and YBCO thin film layer of 165 nm in thickness. A 7200-turn, 60-layer pick-up coil having a 3.7-mm radius and 5.3-mm height was manufactured by winding a 22-μm-diameter copper wire around a 1-mm-diameter FRP rod; this coil was mounted 10 mm above the primary coil along the central vertical axis (z-axis). Fig. 2 shows the experimental circuit. The peak value of the output voltage vS of the autotransformer was varied from 6 to 40 V so that the AC current i flowing through the FCL was in the range of 3 to 20 Apeak. The electromotive force e was induced in the pick-up coil by the AC magnetic flux generated in the FCL. The magnetic flux density B [T] at the center of the FCL (r = 0, z = 0) can be estimated from e [V] as follows: B = - 9.78
³ edt
(1)
The coefficient -9.78 was derived by considering of the coil specifications and arrangements. 3. Measurement result of magnetic flux density at the FCL center Fig. 3 (a), (b), and (c) illustrates the waveforms of the injected current i, induced electromotive force e, and the estimated magnetic flux density B, respectively. When the peak value of vS was 6 V, there was hardly any magnetic flux generated at the center of the FCL; hence, it may be deduced that the YBCO layer remained in the superconducting state so that the magnetic flux generated by the injected current through the primary coil was canceled out by the magnetic flux generated by the current induced in the YBCO layer.
O
0.165 μm
10 mm
i
YBCO Sapphire Coil
i
Resistance 2.1 Ω
Pick-up coil 2 mm 1 mm 1 mm 1 mm
z
Lead line
Bobbin (FRP)
Fig. 1. Schematic arrangement of FCL and pick-up coil
r
100 V ᳸ 60 Hz
vs
Autotransformer 0~130 V
FCL
i
Fig. 2. Experimental circuit
Kosuke Higuchi et al. / Physics Procedia 36 (2012) 1254 – 1257
Magnetic flux density B [mT]
0.4 0.2 0 -0.2 -0.4 0
(vS)peak = 40 V 30 V 20 V 10 V 6V
(vS)peak = 40 V
10 0.01
0.02
0.03
0.04
Time t [s] (a) Current i (vS)peak = 40 V
0.05
30 V 20 V 10 V 6V
0.01
0.02
0.03
0.04
0.05
Time t [s] (b) Induced electromotive force e
No YBCO thin film
Magnetic flux density B [mT]
20 10 0 -10 -20 0
Induced electromotive force e [V]
Current i [A]
1256
30 V 20 V 10 V 6V
0
(vS)peak = 40 V
30 V 20 V 10 V 6V
10 0
-10
-10 0
0.01
0.02
0.03
Time t [s] (c) Magnetic flux density B
0.04
Fig. 3. Measured waveforms in overcurrent carrying examinations
0.05
-20
-10
0
Current i [A]
10
20
Fig. 4. Hysteresis relationship between magnetic flux density and current
On the other hand, for peak values greater than 10 V, the changes observed in the magnetic flux density are significant and depend on the injected current. This implies that a resistance has to be produced in the YBCO layer so that the shielding current in the YBCO layer does not always cancel the magnetic flux generated by the primary coil. 4. Discussion on periodic behavior of magnetic flux density in FCL In order to discuss the instantaneous behavior of the magnetic flux produced in the FCL, the instantaneous magnitudes of the magnetic flux density B are plotted against those of the injected current i (Fig. 4); the B-i curve for a stand-alone primary coil without the YBCO disc is also plotted. When the peak value of vS is 6 V, the YBCO layer is considered to be in the superconducting state, as mentioned above. Thus, in this state, the B-i characteristic is expressed as a linear line with a very small gradient. When the peak value of vS is 10 V or higher, each B-i characteristic exhibits hysteresis, as shown in Fig. 4. As an example, let us discuss the case when the peak value of vS is 30 V. The B-i characteristic has a high gradient in the period where the current i increases from approximately -7 A to the peak of 15 A. This gradient is similar to that of the stand-alone coil. Therefore, the YBCO layer is considered to transit from the superconducting state to resistance-generation state. Therefore, the shielding current induced in the YBCO layer is restricted to a certain magnitude (possibly to the critical current) by the generation of resistance; hence, the shielding current can no longer cancel out the increase in the magnetic flux in the primary winding. Thus, the FCL generates an inductance. In contrast, the B-i characteristic has a low gradient in the period where the current i reduces from the peak of 15 A to approximately 7 A. This gradient is the same as that of the 6 V peak. The YBCO layer is therefore considered to be in the superconducting state. When the instantaneous value of the primary current begins to decrease after attaining the peak value the magnetic flux induced by the primary current also begins to decrease, and then, the current must begin to flow in the opposite direction to cancel out the
Kosuke Higuchi et al. / Physics Procedia 36 (2012) 1254 – 1257
1257
decrease in the primary magnetic flux. This implies that the current induced in the YBCO layer decreases, and consequently, the YBCO layer recovers to the superconducting state. In conclusion, the YBCO layer transits repeatedly between the superconducting state and a resistancegeneration one (possibly a flux-flow state) during each cycle of the AC current. Thus, the FCL repeats the generation and extinction of the inductance depending on the magnitude of the instantaneous current i. Similar B-i curves were observed for vS = 10, 20, and 40 V. The primary-current ranges shift according to vS when the YBCO layer is considered to be in the superconducting state. However, these widths, approximately 8 A, are always independent of vS. From these facts, it might be estimated that the constant current of the critical current IC flowed in the YBCO layer when it was in the non-superconducting state, whereas the shielding current consisting of DC and AC components flowed in the YBCO layer when the layer was in the superconducting state. 5. Conclusion AC overcurrent injection experiments were performed for an inductive-type superconducting FCL with a pancake coil and a YBCO thin film disc as the primary and secondary windings, respectively. An FCL model was constructed with a YBCO layer of 0.165-μm thickness. Magnetic flux densities at the center of the FCL were measured using a pick-up coil. The results are summarized as follows: (1) When a small AC current was injected into the primary coil, (a) the YBCO layer was always in the superconducting state. (b) instantaneous magnitudes of the magnetic flux density B hardly varied with those of the injected current i. (2) When a large AC current was injected into the primary coil, (a) the YBCO layer transited repeatedly between the superconducting state and resistancegeneration state (possibly a flux-flow state) during each cycle of the AC current. (b) a hysteresis relationship was observed between the instantaneous magnitudes of the magnetic flux density B and the injected current i. (c) the B-i curves showed hysteresis, which was considered to be brought about by the transitions in the YBCO-layer state. Acknowledgements This study was supported in part by a Grant-in-Aid for Scientific Research (C) (20560265) from the Japan Society for the Promotion of Science. The YBCO thin film discs were fabricated by the National Institute of Advanced Industrial Science and Technology. References [1] T. Ise, N. H. Nguyen and S. Kumagai. IEEE Trans Appl Supercond 2001; Vol. 11, No. 1, pp. 1932-1935 [2] M. C. Ahn, H. Kang, D. K. Bae, D. K. Park, Y. S. Yoon, S. J. Lee and T. K. Ko. IEEE Trans Appl Supercond 2005; Vol. 15, No. 2, pp. 2102-2105 [3] T. Matsumura, K. Mutsuura, Y. Yokomizu, H. Shimizu, M. Shibuya, T. Nitta, H. Kado and M. Ichikawa. IEEJ Trans 2006; Vol. 1, No. 3, pp. 276-284 [4] T. Manabe, J. H. Ahn, I. Yamaguchi, M. Sohma, W. Kondo, K. Tsukada, K. Kamiya, S. Mizuta and T. Kumagai. IEICE Trans Electron 2006; Vol. E89-C, No. 2, pp. 186-190
Physics Procedia 36 (2012) 1254 – 1257
Superconductivity Centennial Conference
Observation of Transient Behavior of Magnetic Flux in Inductive-type Fault Current Limiter with YBCO Thin Film Disc Kosuke Higuchia*, Yin Guana, Yasunobu Yokomizua and Toshiro Matsumuraa a
Department of Electrical Engineering and Computer Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
Abstract Recently, the installation of fault current limiters (FCLs) in power systems is expected for controlling large shortcircuit currents. In this study, we focus on inductive-type FCLs having a YBCO superconducting thin film disc that is fabricated by metal-organic deposition. AC currents were injected into the FCL so that the periodic transient behavior of the apparent magnetic flux density around the FCL could be measured by using a pick-up coil. The magnetic flux density exhibited hysteresis when AC current was injected into the FCL. The transition between the conducting states in the YBCO layer was explained by the hysteresis relationship between the magnetic flux density and current.
© 2012 2011 Published Publishedby byElsevier ElsevierB.V. Ltd.Selection Selectionand/or and/orpeer-review peer-review under responsibility of Horst © under responsibility of the GuestRogalla Editors. and Peter Kes. Keywords: fault current limiter; YBCO; superconductivity; magnetic flux; power system stability; impedance; pick-up coil
1. Introduction Fault current limiters (FCLs) are essential for controlling the increase in fault currents in large power systems, which have dispersed generators. The FCL will help reduce the fault current and may also provide other benefits to the power system [1][2]. We have proposed an inductive-type FCL consisting of a pancake coil as the primary winding and a superconducting disc as the secondary winding [3]. This type of FCL modules can be easily scaled up to make large scale FCLs for use in practical applications. In this study, we used a YBCO thin film disc fabricated by metal-organic deposition (MOD) [4]. When the current flowing in the primary winding is at the load current level, the magnetic flux generated by the
* Corresponding author. E-mail address: [email protected]
1875-3892 © 2012 Published by Elsevier B.V. Selection and/or peer-review under responsibility of the Guest Editors. doi:10.1016/j.phpro.2012.06.285
1255
Kosuke Higuchi et al. / Physics Procedia 36 (2012) 1254 – 1257
primary current is canceled out by the magnetic flux generated by the current induced in the YBCO layer. When the fault current flows in the primary winding, a resistance is produced in the YBCO layer, and subsequently, an impedance is generated in the FCL. As a result, the fault current is limited. Thus, an understanding of the transient behavior of the magnetic flux is important for designing an inductive-type FCL. In this study, AC currents were injected into the FCL so that the periodic transient behavior of the apparent magnetic flux density around the FCL could be measured by a pick-up coil. The magnetic flux density exhibited hysteresis when AC current was injected into the FCL. The transition between the conducting states in the YBCO layer of the FCL was explained by the hysteresis relationship between the magnetic flux density and current. 2. FCL model and measurement method of magnetic flux density Fig. 1 shows the schematic arrangement of the FCL model and the pick-up coil. A 38-turn pancake coil, made of a 1-mm-diameter copper wire, was used as the primary winding of the FCL. For the secondary winding, we used a YBCO disc having outer and inner diameter of 100 and 12 mm, respectively. The YBCO disc was constructed of a sapphire substrate of 2 mm in thickness, cerium oxide interlayer of 40 nm in thickness and YBCO thin film layer of 165 nm in thickness. A 7200-turn, 60-layer pick-up coil having a 3.7-mm radius and 5.3-mm height was manufactured by winding a 22-μm-diameter copper wire around a 1-mm-diameter FRP rod; this coil was mounted 10 mm above the primary coil along the central vertical axis (z-axis). Fig. 2 shows the experimental circuit. The peak value of the output voltage vS of the autotransformer was varied from 6 to 40 V so that the AC current i flowing through the FCL was in the range of 3 to 20 Apeak. The electromotive force e was induced in the pick-up coil by the AC magnetic flux generated in the FCL. The magnetic flux density B [T] at the center of the FCL (r = 0, z = 0) can be estimated from e [V] as follows: B = - 9.78
³ edt
(1)
The coefficient -9.78 was derived by considering of the coil specifications and arrangements. 3. Measurement result of magnetic flux density at the FCL center Fig. 3 (a), (b), and (c) illustrates the waveforms of the injected current i, induced electromotive force e, and the estimated magnetic flux density B, respectively. When the peak value of vS was 6 V, there was hardly any magnetic flux generated at the center of the FCL; hence, it may be deduced that the YBCO layer remained in the superconducting state so that the magnetic flux generated by the injected current through the primary coil was canceled out by the magnetic flux generated by the current induced in the YBCO layer.
O
0.165 μm
10 mm
i
YBCO Sapphire Coil
i
Resistance 2.1 Ω
Pick-up coil 2 mm 1 mm 1 mm 1 mm
z
Lead line
Bobbin (FRP)
Fig. 1. Schematic arrangement of FCL and pick-up coil
r
100 V ᳸ 60 Hz
vs
Autotransformer 0~130 V
FCL
i
Fig. 2. Experimental circuit
Kosuke Higuchi et al. / Physics Procedia 36 (2012) 1254 – 1257
Magnetic flux density B [mT]
0.4 0.2 0 -0.2 -0.4 0
(vS)peak = 40 V 30 V 20 V 10 V 6V
(vS)peak = 40 V
10 0.01
0.02
0.03
0.04
Time t [s] (a) Current i (vS)peak = 40 V
0.05
30 V 20 V 10 V 6V
0.01
0.02
0.03
0.04
0.05
Time t [s] (b) Induced electromotive force e
No YBCO thin film
Magnetic flux density B [mT]
20 10 0 -10 -20 0
Induced electromotive force e [V]
Current i [A]
1256
30 V 20 V 10 V 6V
0
(vS)peak = 40 V
30 V 20 V 10 V 6V
10 0
-10
-10 0
0.01
0.02
0.03
Time t [s] (c) Magnetic flux density B
0.04
Fig. 3. Measured waveforms in overcurrent carrying examinations
0.05
-20
-10
0
Current i [A]
10
20
Fig. 4. Hysteresis relationship between magnetic flux density and current
On the other hand, for peak values greater than 10 V, the changes observed in the magnetic flux density are significant and depend on the injected current. This implies that a resistance has to be produced in the YBCO layer so that the shielding current in the YBCO layer does not always cancel the magnetic flux generated by the primary coil. 4. Discussion on periodic behavior of magnetic flux density in FCL In order to discuss the instantaneous behavior of the magnetic flux produced in the FCL, the instantaneous magnitudes of the magnetic flux density B are plotted against those of the injected current i (Fig. 4); the B-i curve for a stand-alone primary coil without the YBCO disc is also plotted. When the peak value of vS is 6 V, the YBCO layer is considered to be in the superconducting state, as mentioned above. Thus, in this state, the B-i characteristic is expressed as a linear line with a very small gradient. When the peak value of vS is 10 V or higher, each B-i characteristic exhibits hysteresis, as shown in Fig. 4. As an example, let us discuss the case when the peak value of vS is 30 V. The B-i characteristic has a high gradient in the period where the current i increases from approximately -7 A to the peak of 15 A. This gradient is similar to that of the stand-alone coil. Therefore, the YBCO layer is considered to transit from the superconducting state to resistance-generation state. Therefore, the shielding current induced in the YBCO layer is restricted to a certain magnitude (possibly to the critical current) by the generation of resistance; hence, the shielding current can no longer cancel out the increase in the magnetic flux in the primary winding. Thus, the FCL generates an inductance. In contrast, the B-i characteristic has a low gradient in the period where the current i reduces from the peak of 15 A to approximately 7 A. This gradient is the same as that of the 6 V peak. The YBCO layer is therefore considered to be in the superconducting state. When the instantaneous value of the primary current begins to decrease after attaining the peak value the magnetic flux induced by the primary current also begins to decrease, and then, the current must begin to flow in the opposite direction to cancel out the
Kosuke Higuchi et al. / Physics Procedia 36 (2012) 1254 – 1257
1257
decrease in the primary magnetic flux. This implies that the current induced in the YBCO layer decreases, and consequently, the YBCO layer recovers to the superconducting state. In conclusion, the YBCO layer transits repeatedly between the superconducting state and a resistancegeneration one (possibly a flux-flow state) during each cycle of the AC current. Thus, the FCL repeats the generation and extinction of the inductance depending on the magnitude of the instantaneous current i. Similar B-i curves were observed for vS = 10, 20, and 40 V. The primary-current ranges shift according to vS when the YBCO layer is considered to be in the superconducting state. However, these widths, approximately 8 A, are always independent of vS. From these facts, it might be estimated that the constant current of the critical current IC flowed in the YBCO layer when it was in the non-superconducting state, whereas the shielding current consisting of DC and AC components flowed in the YBCO layer when the layer was in the superconducting state. 5. Conclusion AC overcurrent injection experiments were performed for an inductive-type superconducting FCL with a pancake coil and a YBCO thin film disc as the primary and secondary windings, respectively. An FCL model was constructed with a YBCO layer of 0.165-μm thickness. Magnetic flux densities at the center of the FCL were measured using a pick-up coil. The results are summarized as follows: (1) When a small AC current was injected into the primary coil, (a) the YBCO layer was always in the superconducting state. (b) instantaneous magnitudes of the magnetic flux density B hardly varied with those of the injected current i. (2) When a large AC current was injected into the primary coil, (a) the YBCO layer transited repeatedly between the superconducting state and resistancegeneration state (possibly a flux-flow state) during each cycle of the AC current. (b) a hysteresis relationship was observed between the instantaneous magnitudes of the magnetic flux density B and the injected current i. (c) the B-i curves showed hysteresis, which was considered to be brought about by the transitions in the YBCO-layer state. Acknowledgements This study was supported in part by a Grant-in-Aid for Scientific Research (C) (20560265) from the Japan Society for the Promotion of Science. The YBCO thin film discs were fabricated by the National Institute of Advanced Industrial Science and Technology. References [1] T. Ise, N. H. Nguyen and S. Kumagai. IEEE Trans Appl Supercond 2001; Vol. 11, No. 1, pp. 1932-1935 [2] M. C. Ahn, H. Kang, D. K. Bae, D. K. Park, Y. S. Yoon, S. J. Lee and T. K. Ko. IEEE Trans Appl Supercond 2005; Vol. 15, No. 2, pp. 2102-2105 [3] T. Matsumura, K. Mutsuura, Y. Yokomizu, H. Shimizu, M. Shibuya, T. Nitta, H. Kado and M. Ichikawa. IEEJ Trans 2006; Vol. 1, No. 3, pp. 276-284 [4] T. Manabe, J. H. Ahn, I. Yamaguchi, M. Sohma, W. Kondo, K. Tsukada, K. Kamiya, S. Mizuta and T. Kumagai. IEICE Trans Electron 2006; Vol. E89-C, No. 2, pp. 186-190