We have been developing a Superconducting Fault Current Limiting Transformer (SFCLT) with the functions of both superconducting transformer in normal operating condition and superconducting fault current limiter in fault condition. As the Step-5 of our SFCLT project, in this paper, we designed and fabricated a 2 MVA class HTS-SFCLT using YBCO coated conductors with the ratings of 3-phase and 22 kV/6.6 kV. The developed HTS-SFCLT is characterized by a hybrid structure of HTS coils using YBCO, YBCO/Cu and Bi2223 tapes for design flexibility as both the superconducting transformer and the superconducting fault current limiter. Fundamental tests of the HTS-SFCLT were carried out, and its design parameters as a superconducting transformer were verified.Eucas '09: The 9th European Conference on Applied Superconductivity (Dresden, Germany, 13–17 September 2009)journal articl

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Endo, F

Hayakawa, N

Kojima, H

Kotari, M

Okubo, H

Journal of Physics Conference Series

English

M Kotari

H Kojima

N Hayakawa

F Endo

H Okubo

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Development of 2 MVA Class Superconducting Fault Current Limiting Transformer (SFCLT) with YBCO Coated Conductors

Nagoya Repository

This content has been downloaded from IOPscience. Please scroll down to see the full text.Download details:IP Address: 133.6.32.9This content was downloaded on 07/11/2014 at 00:29Please note that terms and conditions apply.Development of 2 MVA Class Superconducting Fault Current Limiting Transformer (SFCLT)with YBCO Coated ConductorsView the table of contents for this issue, or go to the journal homepage for more2010 J. Phys.: Conf. Ser. 234 032070(http://iopscience.iop.org/1742-6596/234/3/032070)Home Search Collections Journals About Contact us My IOPscience      Development of 2 MVA Class Superconducting Fault Current Limiting Transformer (SFCLT) with YBCO Coated Conductors M Kotari1, H Kojima2, N Hayakawa2, F Endo2, H Okubo1 1 Department of Electrical Engineering and Computer Science, Nagoya University, Nagoya 464-8603, Japan 2 EcoTopia Science Institute, Nagoya University, Nagoya 464-8603, Japan  E-mail: koutari@okubo.nuee.nagoya-u.ac.jp Abstract. We have been developing a Superconducting Fault Current Limiting Transformer (SFCLT) with the functions of both superconducting transformer in normal operating condition and superconducting fault current limiter in fault condition. As the Step-5 of our SFCLT project, in this paper, we designed and fabricated a 2 MVA class HTS-SFCLT using YBCO coated conductors with the ratings of 3-phase and 22 kV/6.6 kV. The developed HTS-SFCLT is characterized by a hybrid structure of HTS coils using YBCO, YBCO/Cu and Bi2223 tapes for design flexibility as both the superconducting transformer and the superconducting fault current limiter. Fundamental tests of the HTS-SFCLT were carried out, and its design parameters as a superconducting transformer were verified. 1.  Introduction High temperature superconducting (HTS) power apparatus, e.g. transmission cables, fault current limiters, transformers, SMES, motors and generators, have been investigated and demonstrated [1]-[5]. The HTS power apparatus should be coordinated with a power system in order to improve the total efficiency and stability in a future power system. From the viewpoint of system coordination and functional diversification of superconducting power apparatus, we have proposed and have been developing a Superconducting Fault Current Limiting Transformer, abbreviated to “SFCLT”, with the functions of both superconducting transformer and superconducting fault current limiter from Step-1 to Step-4 [6]-[14]. As the Step-4 of our SFCLT project, we have designed, fabricated and tested HTS-SFCLT with the ratings of 3-phase, 100 kVA, 6600 V/210 V using YBCO coated conductors, and verified fundamental and excellent performance of both HTS transformer and fault current limiter. As the Step-5 of our SFCLT project, in this paper, we designed and fabricated a 2 MVA class HTS-SFCLT with YBCO coated conductors, with the ratings of 3-phase and 22 kV/6.6 kV. The HTS-SFCLT is characterized by the combination of different kinds of YBCO coated conductors in order to make the current limiting characteristics flexible and controllable. No-load, short-circuit and partial-load tests were carried out to confirm the design parameters and fundamental performance of the HTS-SFCLT as a superconducting transformer.  9th European Conference on Applied Superconductivity (EUCAS 09) IOP PublishingJournal of Physics: Conference Series 234 (2010) 032070 doi:10.1088/1742-6596/234/3/032070c© 2010 IOP Publishing Ltd 1      2.  Concept of SFCLT The SFCLT proposed is characterized by the following concepts: (1) SFCLT works as a HTS transformer in the normal condition, and also as a HTS fault current limiter in the fault condition. (2) Quench-induced impedance of SFCLT is positively utilized as a fault current limiter in the fault condition. (3) Fault current limiting function of SFCLT improves the transient stability of power system in the fault condition. (4) Limiting impedance of SFCLT is activated in the fault condition, and leakage impedance of a transformer can be reduced, compared with that of conventional transformers. (5) Reduced leakage impedance of SFCLT enhances the transmission capacity and static stability of the power system in the normal condition. (6) After fault current limitation, SFCLT recovers into superconducting state after fault clearance. The concepts (1)~(3) are fundamental functions of SFCLT, and (4)~(6) can be regarded as novel functions to be expected for SFCLT in a power system. Especially, as for the recovery characteristics in (6), we have verified that SFCLT could recover into superconducting state by itself immediately after the fault clearance, i.e. self-recovery performance [9]-[11], [13]. Figure 1 shows an example of the current limitation and recovery characteristics in Step-4 using 2G materials [13]. Against the prospective current Ipro=980Apeak, the fault current was limited to 516 Apeak (52.6% of Ipro) at first peak and 330 Apeak (33.7% of Ipro) at the 5th cycle, respectively, after the fault. In this case, the load current ILV2 after the fault clearance was equal to ILV1 before the fault, which means that SFCLT exhibited self-recovery performance. Figure 2 shows the self-recovery characteristics of SFCLT in Step-4 as parameters of ILV1 and Ipro normalized by the critical current IC of HTS tapes. A criterion of the self-recovery was quantified by a dotted curve for different load and fault conditions, which can be reflected to appear in the design and operation of SFCLT.                          Figure 1. Current waveform of recovery test of HTS-SFCLT (Step-4)  6543210I PRO / IC  0.60.50.40.30.20.10.0ILV1 / ICFigure 2. Recovery characteristics of HTS-SFCLT (Step-4)  -1000-50005001000Low-voltage side current: ILV [A]0.200.150.100.050.00-0.05Time [s]ILV2ILV1IproFault clearanceFaultrecovery case non-recovery case 9th European Conference on Applied Superconductivity (EUCAS 09) IOP PublishingJournal of Physics: Conference Series 234 (2010) 032070 doi:10.1088/1742-6596/234/3/0320702      3.  Design and fabrication of HTS-SFCLT (Step-5) 3.1.  Transformer design The specifications and construction of HTS-SFCLT in the Step-5 are shown in Table 1 and Figure 3. We designed 3-phase HTS-SFCLT with the rating of 2 MVA, 22 kV/6.6 kV. As a single phase of the HTS-SFCLT, we fabricated 0.67 MVA, 12.7 kV/3.81 kV (Y-Y). HTS coils were arranged in both core legs (A-leg, B-leg) and immersed in liquid nitrogen at 77 K together with the iron core. Low-voltage coils (A1~A6, B1~B6; total 12 coils connected in series) were composed of two types of YBCO tapes, and high-voltage coils (A7~A10, B7~B10; total 8 coils connected in series) were composed of Bi2223 tapes. The specifications of each HTS tape are summarized in Table 2.                                  3.2.  Fault current limiter design Low-voltage coils of the HTS-SFCLT (Step-5) were divided into limiting coil (Tr/FCL coil) and non-limiting coil (Tr coil), as was the case with the Step-4 [12], [13]. In the Step-5, A1~A3 and B1~B3 are Tr/FCL coils using LV(I) YBCO tape in Table 2, and A4~A6 and B4~B6 are Tr coils using LV(II) YBCO/Cu tape in Table 2. Such a hybrid structure of HTS coils brings about the higher flexibility for both transformer and current limiter design by the variation of the ratio between Tr/FCL coil and Tr coil. Table 1. Specifications of  HTS-SFCLT (Step-5) Table 2. Specifications of 2G HTS tape (Step-5) 1)0.3V/cm  2)1.0V/cm  LV(I) LV(II) HV HTS layer YBCO YBCO Bi2223 Substrate Hastelloy Hastelloy － Buffer layer IBAD MgO IBAD MgO － Stabilizer Ag Cu Ag Width [mm] 12 12 2.6 Thickness [mm] 0.105 0.095 0.230 IC [A] @77K 2151) 2402) 732) Length [m] 124 147 1154  Phase 3 Frequency 60Hz Capacity 2MVA Rated voltage 22kV/6.6kV Rated current 52.5A/175A Turn ratio 1334/396 Leakage impedance 6.1% Magnetic flux density 1.7T    HV (Tr coil) LV(Ⅰ) (Tr/FCL coil) LV(Ⅱ) (Tr coil)   Figure 3. Construction of HTS-SFCLT (Step-5) (a) Total structure (b) Cross-section and coil arrangement B-leg coils A-leg coils A1~A3 A4~A6 A7~A10 Iron core  FRP cylinder 9th European Conference on Applied Superconductivity (EUCAS 09) IOP PublishingJournal of Physics: Conference Series 234 (2010) 032070 doi:10.1088/1742-6596/234/3/0320703                                    (a) YBCO tape Figure 4 shows the current and voltage waveforms for YBCO and YBCO/Cu tapes with the effective length of 90 mm. In Figure 4 (a), against the prospective current Ipro=1164 Apeak (4.5×IC), the current was limited to 715 Apeak (61% of Ipro) at the first peak and 340 Apeak (29% of Ipro) at the 5th cycle. On the other hand, in Figure 4 (b), YBCO/Cu tape exhibited no current limiting characteristics against Ipro=920 Apeak (4.0×IC), because of the stabilizing copper. Figure 5 shows the electric field at the first peak as a function of current normalized by IC for each short sample of YBCO, YBCO/Cu and Bi2223 tapes. The YBCO tape has an electric field two orders higher than the YBCO/Cu tape, which is suitable to realize the flexible current limiting characteristics at low-voltage coil by controlling the length and its ratio between YBCO and YBCO/Cu tapes.  (b) Low-voltage coil Figure 6 shows the current and terminal voltage waveforms of YBCO coil A1 for Ipro=336 Apeak. In Figure 6, the current was limited to 309 Apeak (92% of Ipro) at the first peak and 241 Apeak (72% of Ipro) at the 5th cycle. Due to the reactance of the YBCO coil, the terminal voltage gradually increased while decreasing its phase difference against the current waveform during the current limitation. Figure 7 shows the current limiting characteristics at the 5th cycle as a function of Ipro for low-voltage coils (A1~A3, B1~B3) using YBCO tapes. The current limitation can be seen for the current level Ipro>250 Apeak, and is remarkable for Ipro>300 Apeak. The difference in the saturated levels of 250-300 Apeak for the limited current would be attributed to the difference in the generated resistance of each coil, which might be related to the length, coil diameter and inherent scatterings of YBCO coils.  10-224610-1246100246101Electric field [V/cm] 12 3 4 5 6 7 8 9102I1st / IcYBCO (LV(I)) YBCO/Cu (LV(II)) Bi2223Figure 5. Electric field at first peak for YBCO, YBCO/Cu and Bi2223 tapes (short sample tape: 90 mm) Figure 4. Current and voltage waveforms for different short tapes of YBCO for low-voltage coils  (a) YBCO, LV(I) (Ipro=1164Apeak) (b) YBCO/Cu, LV(II) (Ipro=920Apeak)  -1000-50005001000Current [A]100806040200 Time [ms]-10-50510Voltage [V]CurrentVoltage -1000-50005001000Current [A]100806040200 Time [ms]-10-50510Voltage [V]CurrentVoltage9th European Conference on Applied Superconductivity (EUCAS 09) IOP PublishingJournal of Physics: Conference Series 234 (2010) 032070 doi:10.1088/1742-6596/234/3/0320704                                        4.  No-load, short-circuit and partial-load tests of HTS-SFCLT (Step-5) The assembled HTS-SFCLT (Step-5) was immersed in liquid nitrogen at atmospheric pressure. No-load and short-circuit tests were carried out in order to confirm the design parameters of the HTS-SFCLT as a superconducting transformer. In both tests, the turn ratio between high-voltage and low –voltage coils was confirmed to agree well with the design value. The results of no-load test are shown in Figure 8; (a) exciting current and (b) no-load loss. At the rated voltage of 3.81 kVrms, the exciting current was 0.55 Apeak, whereas the no-load loss was 411 W. The leakage impedance obtained in the short-circuit test was 6.0%, which is also closely matches the design value of 6.1%. The partial-load test was carried out by connecting a resistive load of 1  between the low-voltage terminals. Figure 9 shows the current and voltage waveforms at the partial-load test, where the current in the low-voltage coil was 92 Apeak, i.e. 37% of the rated current. The relationship in current and voltage waveforms between high-voltage and low-voltage coils was verified to be appropriate to a superconducting transformer.      -400-2000200400Current [A]100806040200Time [ms]-80-4004080Terminal voltage [V]VoltageCurrentFigure 6. Current and terminal voltage waveforms at current limitation (Coil A1, Ipro=336Apeak) Figure 7. Current limiting characteristics at 5th cycle for low-voltage coils (A1~A3, B1~B3)  4003002001000Limited current [Apeak]4003002001000Prospective current : Ipro [Apeak] A1 B1 A2 B2 A3 B3 Ipro9th European Conference on Applied Superconductivity (EUCAS 09) IOP PublishingJournal of Physics: Conference Series 234 (2010) 032070 doi:10.1088/1742-6596/234/3/0320705                                      5.  Key technologies for SFCLT development From the viewpoints of transformer, fault current limiter, material and power system, key technologies for SFCLT development can be listed as follows: ・As for the transformer function, electrical insulation techniques and test procedure should be established. AC loss reduction of HTS tapes and the optimization of leakage impedance of SFCLT are expected. ・As for the fault current limiter function, electrical insulation techniques and test procedure are also inevitable, especially under quench-induced thermal/electrical combined stress. The flexibility and controllability of current limitation and self-recovery performance should be enhanced. ・From the material viewpoint, the performance of HTS tapes should be balanced in large current capacity, low ac loss, high electric field in overcurrent condition, etc, under the operating and cooling environment at the optimum temperature and pressure. ・From the power system viewpoint, the static and transient stability should be coordinated and optimized.     5004003002001000No-load loss [W]43210LV voltage : VLV [kVrms] 0.60.50.40.30.20.10.0Exciting current [Apeak]43210LV voltage : VLV [kVrms]Figure 8. No-load test results of HTS-SFCLT (Step-5) (a) Exciting current  (b) No-load loss  Figure 9. Current and voltage waveforms at partial-load test (ILV = 92 Apeak)  -100-50050100Current [A]100806040200Time [ms]-1000-50005001000Voltage [V]VLVVHVIHVILVRated  voltage Rated  voltage 9th European Conference on Applied Superconductivity (EUCAS 09) IOP PublishingJournal of Physics: Conference Series 234 (2010) 032070 doi:10.1088/1742-6596/234/3/0320706      6.  Conclusions As the Step-5 of the SFCLT project, we developed 2 MVA class HTS-SFCLT with YBCO coated conductors, and carried out the no-load test, short-circuit test and partial-load test as a superconducting transformer. The main results are summarized as follows: ・The design ratings of the HTS-SFCLT (Step-5) are 3-phase, 2 MVA, 22 kV/6.6 kV. A single phase of HTS-SFCLT was fabricated. ・Low-voltage coils were composed of YBCO tape for limiting coil (Tr/FCL coil) and YBCO/Cu tape for non-limiting coil (Tr coil). High-voltage coils were composed of Bi2223 tape. Electric field and current limiting characteristics of each tape and coil were verified. ・No-load, short-circuit and partial-load test results verified that the HTS-SFCLT would exhibit the fundamental performance with the design parameters as a superconducting transformer. The developed HTS-SFCLT (Step-5) will be tested by current limiting test and recovery test after the current limitation. Acknowledgement This work was supported by the Grant-in-Aid for Scientific Research (S) of the Ministry of Education, Culture, Sports, Science and Technology, Japan. References [1] M.J.Gouge et al., 2009 IEEE Trans. on Appl. Supercond. 19 1744-1747 [2] H.Yumura et al., 2009 IEEE Trans. on Appl. Supercond. 19 1698-1701 [3] M.Noe et al., 2007 Supercond. Sci. Technol. 20 R15 [4] H.-W.Neumueller et al., 2009 IEEE Trans. on Appl. Supercond. 19 1950-1955 [5] K.Shikimachi et al., 2009 IEEE Trans. on Appl. Supercond. 19 2012-2018 [6] N.Hayakawa et al., 2000 Cryogenics 40 325-331 [7] N.Hayakawa et al., 2001 IEEE Trans. on Appl. Supercond. 11 1936-1939 [8] H.Kagawa et al., 2002 Physica C 372-376 1706-1710 [9] C.Kurupakorn et al., 2004 IEEE Trans. on Appl. Supercond. 14 900-903 [10] C.Kurupakorn et al., 2005 IEEE Trans. on Appl. Supercond. 15 1859-1862 [11] C.Kurupakorn et al., 2006 J.Physics: Conference Series, 43 950-953 [12] H.Okubo et al., 2007 IEEE Trans. on Appl. Supercond. 17 1768-1771 [13] H.Kojima et al., 2008 J.Physics: Conference Series, 97 012154 [14] K.Omura et al., 2009 IEEE Trans. on Appl. Supercond. 19 1880-1883 9th European Conference on Applied Superconductivity (EUCAS 09) IOP PublishingJournal of Physics: Conference Series 234 (2010) 032070 doi:10.1088/1742-6596/234/3/0320707

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Development of 2 MVA Class Superconducting Fault Current Limiting Transformer (SFCLT) with YBCO Coated Conductors

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