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Development of 1 kA class HTS coil for superconducting power transformers
Physica C 469 (2009) 1733–1735
Contents lists available at ScienceDirect
Physica C journal homepage: www.elsevier.com/locate/physc
Development of 1 kA class HTS coil for superconducting power transformers H. Okamoto a,*, H. Hayashi a, M. Iwakuma b, Y. Iijima c, T. Saito c, T. Izumi d, Y. Yamada d, Y. Shiohara d a
Kyushu Electric Power Co., Inc., 2-1-43, Shiobaru, Minami-ku, Fukuoka 815-8520, Japan Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan Fujikura Ltd., 1440 Mutsuzaki, Sakura 285-8550, Japan d Superconductivity Research Laboratory, 1-1-13, Shinonome, Koto-ku, Tokyo 135-0062, Japan b c
a r t i c l e
i n f o
Article history: Available online 31 May 2009 PACS: 74.25.Fy 74.72.Bk 84.37.+q 84.70.+p 84.71.Mn
a b s t r a c t The winding technology with high current capacity is one of the important factors in power application of 20 MVA/66 kV-class superconducting power transformers. High-current power transformer is achieved by transposed conductors made of Rare Earth-based superconducting coated conductors. By transpositions, the improvement of uniformity of strand current distribution makes it possible to reduce the total number of strands and AC loss of coils. In this study, the high-Tc superconducting coil was made by transposed 24 strands of 5 mm-wide Rare Earth-based superconducting coated conductors and operated at a current of 1 kA. The test results of AC and DC current characteristics and AC loss are reported. Ó 2009 Elsevier B.V. All rights reserved.
Keywords: RE-based coated conductors HTS coil Transposition AC loss
1. Introduction Rare Earth (RE)-based superconducting wire, the second generation high-Tc superconducting (HTS) coated conductors, has been remarkably developed in superconducting characteristic and wire production technology for power applications. We have implemented the research and development (R&D) project aimed at the practical use of superconducting power transformers of 20 MVA (66/6.9 kV) class for the distribution substation. AC loss reduction with high current capacity is an important subject in R&D of HTS power transformers [1]. On this point, RE-based wire has merits on superconducting characteristic and thinning process in wire production compared with Bismuthbased superconducting wire. Therefore, RE-based wire has a capability to satisfy AC loss reduction as well as high current capacity. The rated current on the secondary winding of 20 MVA (66/ 6.9 kV) power transformers is 1674 A (rms value). On this account, the high current coil is necessary for the wire (strands) to be wound in paralleled. However, the current does not equally apply in the paralleled strands because of the difference in the magnitude of the leakage flux, etc. The strands are transposed
* Corresponding author. Tel.: +81 92 541 3035; fax: +81 92 551 1583. E-mail address: [email protected] (H. Okamoto). 0921-4534/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2009.05.036
for uniform current distribution among strands. In other words, the inductance of coil strands must be uniformed. The transposition is similarly adopted in a conventional oil-filled power transformer. The operating temperature of HTS power transformers was set at sub-cooled liquid nitrogen temperature (66 K) because an electric insulation characteristic and critical current characteristic were improved. The HTS coil was made by transposition of RE-based strands and operated at a current of 1 kA (rms value) at 66 K.
2. Model coil The specifications and a photograph of the high current model coil (model coil) are indicated in Table 1 and in Fig. 1, respectively. The strands have a multilayered structure consisting of a GdBCO superconducting layer by pulsed lazer deposition (PLD), a buffer layer by ion-beam-assisted deposition (IBAD) and a substrate of Hastelloy. The copper tape was soldered to the RE-based strands as a stabilizing layer for over-current operation. The model coil had a cylindrical structure on a GFRP bobbin. The conductor was made of RE-based strand width 5 mm. Twenty four strands were arranged in 12 stacks and 2 parallels, and transposed 11 times. The total length of the strands was about 960 m.
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H. Okamoto et al. / Physica C 469 (2009) 1733–1735
140
Table 1 Specifications of the model coil. 5.0 0.22 12 stack and 2 parallel £350 563 36 11
The Rogowski coils were located in each strand at the current lead position for measuring strand current. The model coil was installed in a GFRP cryostat. 3. Experimental
T=66K 120
Shunt current rate (%)
Cross-section of strand (mm) Structure of conductor Inner diameter (mm) Height of coil (mm) Number of turns Number of transpositions
100 80 60 40 20
The model coil was measured on DC voltage–current (V–I) characteristics, AC current property and AC loss at 77 K (in liquid nitrogen) and 66 K (in sub-cooled liquid nitrogen).
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Strand number
3.1. DC V–I characteristics The DC current measurement was carried out up to 1400 A at 77 K and 2000 A at 66 K for restriction of power supply. Fig. 2 shows an electric field–current (E–I) characteristic. The contact
Fig. 3. Shunt current rate in among strands at 1 kA and 66 K.
resistance voltage in the end terminal of the coil was removed. It indicates that operating current was less than a critical current defined by 1 lV/cm criterion. 3.2. AC current property The AC current (rms value) measurement was carried out up to 750 A at 77 K and 1000 A at 66 K for a similar reason. Fig. 3 shows shunt current rates among the strands at 1000 A and 66 K. It indicates that the range of distribution of strand current is among 20% to +30%. For the uniform current distribution among strands, the optimization of transposition number, etc. must be performed. It contributes to the reduction of paralleled strands number and AC loss. 3.3. AC loss property
Fig. 1. A photograph of the high current model coil.
10
AC loss was measured by electrical measurement shown in Fig. 4. An inductance component voltage in the coil was detected by the cancel coil. A resistance component voltage was obtained by subtracting the inductance component voltage from the coil terminal voltage. AC loss was obtained by the product of the transport current and the resistance component voltage.
-6
Resistance voltage divider 10
-7
Power supply
Electrical field E (V/cm)
77K 66K
Model coil
Digital osilloscope Cancel coil 10
-8
200
400
600 8001000
Current I (A) Fig. 2. E–I characteristics at 77 K and 66 K.
3000
5000
Noninductive shunt Fig. 4. Experimental set-up for measuring AC loss.
H. Okamoto et al. / Physica C 469 (2009) 1733–1735
loss characteristic of the RE-based strand. Both results agreed with except a low current region. The nonuniformity of the strand currents had a little influence on AC loss. The cause is seemed that the transport current was less than the critical current of the model coil.
Tranport current loss Q (W)
1000 Measurement at 77K Measurement at 66K Calculation at 77K Calculation at 66K
100
1735
4. Conclusions The model coil by the transposed RE-based strands was operated at a current of 1000 A at 66 K. In the future, the increase of transport current and the reduction of AC loss should be performed by the optimization of transposition in the coil. We will establish the coil winding technique with higher current capacity.
10
1
Acknowledgments
0.1
10
100
1000
Transport Curent Irms(A) Fig. 5. Comparison between measurement and calculation of AC loss at 77 K and 66 K. Solid line and broken one are calculation.
This study regarding the project of the Development of Fundamental Technologies for Superconductivity Applications was supported by the New Energy and Industrial Technology Development Organization (NEDO), Japan. The authors also show appreciation for the support of Fuji Electric systems. References
Fig. 5 shows AC loss between the measurement and the calculation at 77 K and 66 K. The calculation value was estimated by the magnetic field distribution of the coil and the magnetization
[1] H. Okamoto, H. Hayashi, A. Tomioka, M. Konno, M. Owa, A. Kawagoe, F. Sumiyoshi, M. Iwakuma, K. Suzuki, T. Izumi, Y. Yamada, Y. Shiohara, Physica C 468 (2008) 1731.
Contents lists available at ScienceDirect
Physica C journal homepage: www.elsevier.com/locate/physc
Development of 1 kA class HTS coil for superconducting power transformers H. Okamoto a,*, H. Hayashi a, M. Iwakuma b, Y. Iijima c, T. Saito c, T. Izumi d, Y. Yamada d, Y. Shiohara d a
Kyushu Electric Power Co., Inc., 2-1-43, Shiobaru, Minami-ku, Fukuoka 815-8520, Japan Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan Fujikura Ltd., 1440 Mutsuzaki, Sakura 285-8550, Japan d Superconductivity Research Laboratory, 1-1-13, Shinonome, Koto-ku, Tokyo 135-0062, Japan b c
a r t i c l e
i n f o
Article history: Available online 31 May 2009 PACS: 74.25.Fy 74.72.Bk 84.37.+q 84.70.+p 84.71.Mn
a b s t r a c t The winding technology with high current capacity is one of the important factors in power application of 20 MVA/66 kV-class superconducting power transformers. High-current power transformer is achieved by transposed conductors made of Rare Earth-based superconducting coated conductors. By transpositions, the improvement of uniformity of strand current distribution makes it possible to reduce the total number of strands and AC loss of coils. In this study, the high-Tc superconducting coil was made by transposed 24 strands of 5 mm-wide Rare Earth-based superconducting coated conductors and operated at a current of 1 kA. The test results of AC and DC current characteristics and AC loss are reported. Ó 2009 Elsevier B.V. All rights reserved.
Keywords: RE-based coated conductors HTS coil Transposition AC loss
1. Introduction Rare Earth (RE)-based superconducting wire, the second generation high-Tc superconducting (HTS) coated conductors, has been remarkably developed in superconducting characteristic and wire production technology for power applications. We have implemented the research and development (R&D) project aimed at the practical use of superconducting power transformers of 20 MVA (66/6.9 kV) class for the distribution substation. AC loss reduction with high current capacity is an important subject in R&D of HTS power transformers [1]. On this point, RE-based wire has merits on superconducting characteristic and thinning process in wire production compared with Bismuthbased superconducting wire. Therefore, RE-based wire has a capability to satisfy AC loss reduction as well as high current capacity. The rated current on the secondary winding of 20 MVA (66/ 6.9 kV) power transformers is 1674 A (rms value). On this account, the high current coil is necessary for the wire (strands) to be wound in paralleled. However, the current does not equally apply in the paralleled strands because of the difference in the magnitude of the leakage flux, etc. The strands are transposed
* Corresponding author. Tel.: +81 92 541 3035; fax: +81 92 551 1583. E-mail address: [email protected] (H. Okamoto). 0921-4534/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.physc.2009.05.036
for uniform current distribution among strands. In other words, the inductance of coil strands must be uniformed. The transposition is similarly adopted in a conventional oil-filled power transformer. The operating temperature of HTS power transformers was set at sub-cooled liquid nitrogen temperature (66 K) because an electric insulation characteristic and critical current characteristic were improved. The HTS coil was made by transposition of RE-based strands and operated at a current of 1 kA (rms value) at 66 K.
2. Model coil The specifications and a photograph of the high current model coil (model coil) are indicated in Table 1 and in Fig. 1, respectively. The strands have a multilayered structure consisting of a GdBCO superconducting layer by pulsed lazer deposition (PLD), a buffer layer by ion-beam-assisted deposition (IBAD) and a substrate of Hastelloy. The copper tape was soldered to the RE-based strands as a stabilizing layer for over-current operation. The model coil had a cylindrical structure on a GFRP bobbin. The conductor was made of RE-based strand width 5 mm. Twenty four strands were arranged in 12 stacks and 2 parallels, and transposed 11 times. The total length of the strands was about 960 m.
1734
H. Okamoto et al. / Physica C 469 (2009) 1733–1735
140
Table 1 Specifications of the model coil. 5.0 0.22 12 stack and 2 parallel £350 563 36 11
The Rogowski coils were located in each strand at the current lead position for measuring strand current. The model coil was installed in a GFRP cryostat. 3. Experimental
T=66K 120
Shunt current rate (%)
Cross-section of strand (mm) Structure of conductor Inner diameter (mm) Height of coil (mm) Number of turns Number of transpositions
100 80 60 40 20
The model coil was measured on DC voltage–current (V–I) characteristics, AC current property and AC loss at 77 K (in liquid nitrogen) and 66 K (in sub-cooled liquid nitrogen).
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Strand number
3.1. DC V–I characteristics The DC current measurement was carried out up to 1400 A at 77 K and 2000 A at 66 K for restriction of power supply. Fig. 2 shows an electric field–current (E–I) characteristic. The contact
Fig. 3. Shunt current rate in among strands at 1 kA and 66 K.
resistance voltage in the end terminal of the coil was removed. It indicates that operating current was less than a critical current defined by 1 lV/cm criterion. 3.2. AC current property The AC current (rms value) measurement was carried out up to 750 A at 77 K and 1000 A at 66 K for a similar reason. Fig. 3 shows shunt current rates among the strands at 1000 A and 66 K. It indicates that the range of distribution of strand current is among 20% to +30%. For the uniform current distribution among strands, the optimization of transposition number, etc. must be performed. It contributes to the reduction of paralleled strands number and AC loss. 3.3. AC loss property
Fig. 1. A photograph of the high current model coil.
10
AC loss was measured by electrical measurement shown in Fig. 4. An inductance component voltage in the coil was detected by the cancel coil. A resistance component voltage was obtained by subtracting the inductance component voltage from the coil terminal voltage. AC loss was obtained by the product of the transport current and the resistance component voltage.
-6
Resistance voltage divider 10
-7
Power supply
Electrical field E (V/cm)
77K 66K
Model coil
Digital osilloscope Cancel coil 10
-8
200
400
600 8001000
Current I (A) Fig. 2. E–I characteristics at 77 K and 66 K.
3000
5000
Noninductive shunt Fig. 4. Experimental set-up for measuring AC loss.
H. Okamoto et al. / Physica C 469 (2009) 1733–1735
loss characteristic of the RE-based strand. Both results agreed with except a low current region. The nonuniformity of the strand currents had a little influence on AC loss. The cause is seemed that the transport current was less than the critical current of the model coil.
Tranport current loss Q (W)
1000 Measurement at 77K Measurement at 66K Calculation at 77K Calculation at 66K
100
1735
4. Conclusions The model coil by the transposed RE-based strands was operated at a current of 1000 A at 66 K. In the future, the increase of transport current and the reduction of AC loss should be performed by the optimization of transposition in the coil. We will establish the coil winding technique with higher current capacity.
10
1
Acknowledgments
0.1
10
100
1000
Transport Curent Irms(A) Fig. 5. Comparison between measurement and calculation of AC loss at 77 K and 66 K. Solid line and broken one are calculation.
This study regarding the project of the Development of Fundamental Technologies for Superconductivity Applications was supported by the New Energy and Industrial Technology Development Organization (NEDO), Japan. The authors also show appreciation for the support of Fuji Electric systems. References
Fig. 5 shows AC loss between the measurement and the calculation at 77 K and 66 K. The calculation value was estimated by the magnetic field distribution of the coil and the magnetization
[1] H. Okamoto, H. Hayashi, A. Tomioka, M. Konno, M. Owa, A. Kawagoe, F. Sumiyoshi, M. Iwakuma, K. Suzuki, T. Izumi, Y. Yamada, Y. Shiohara, Physica C 468 (2008) 1731.