Andrade Jr., R. de

Dias, R.

Filho, O.

Lopes, F. C.

Polasek, A.

Silva, F. A. da

Sousa, W. T. B. de

English

KITopen

 Physics Procedia  36 ( 2012 )  1242 – 1247 1875-3892  © 2012 Published by Elsevier B.V. Selection and/or peer-review under responsibility of the Guest Editors. doi: 10.1016/j.phpro.2012.06.283 Superconductivity Centennial ConferenceShort-Circuit Tests and Simulations With a SCFCL ModularAssemblyW.T.B. de Sousaa,b, A. Polasekb, R. Diasb, F.A. Silvab, F.C. Lopesb, O. OrsinoFilhob, R. de Andrade Jr.aaCOPPE/UFRJ - Federal University of Rio de Janeiro, Av. Athos S. Ramos, 149, CT/UFRJ, I-148, Rio de Janeiro, 21941-209, BrazilbCEPEL - Electric Power Research Center, Av. Horacio Macedo,354, Rio de Janeiro, 21941-911, BrazilAbstractShort-circuit tests and simulations carried out with a resistive SCFCL modular assembly are presented. Each SCFCLmodule consists of a BSCCO 2212 bulk coil with a critical current of about 520 A at 77 K. Series and parallel connectionwere tested. In series connection, prospective current as high as 67 kArms was limited to about 11 kApeak in the first peak.In parallel connection, prospective current as high as 65 kArms was limited to about 20 kApeak in the first peak. Lowfault current tests were also carried out (current peaks of about 3Ic) and in this case the SCFCL module takes more timeto actuate, being considered satisfactory for ”inrush” currents. Computational simulations were done considering thebulk coil E-J curve and heat transfers between SCFCL components and the LN2 bath. The simulations can reasonablypredict the performance of the SCFCL assembly and provide additional information such as the temperature rise ofsuperconductor and shunt.c© 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Horst Rogalla and Peter Kes.Keywords: Superconducting Fault Current Limiter \ Short-Circuit Tests \ BSCCO-22121. IntroductionDue to increase of levels of fault currents around the world because of growing consumption of electric-ity, interconnection of generation and transmission systems and insertion of power plants unforeseen underthe original plan, the use of fault current limiters in electrical systems has become more frequent in recentyears.Among the fault current devices in study, superconducting fault current limiters (SCFCL) are one of themost promising due to their characteristics: does not need to be replaced after a short-circuit, presents lowimpedance under normal conditions and does not require any sensor or actuation system (self triggering).There are several types of SCFCLs. The resistive type is the most studied nowadays, due to its relativesimplicity, low inductance and size.In this paper we investigate the behavior of these devices when subjected to high and low fault currents.The term low faults describes peaks of fault currents that are only about three times the value Ic of thecomponents used. How we will see, the time of transition from superconducting state to normal state ofsuch devices depends on the level of the fault current. The low fault current test aimed to show how theSCFCL would react in the presence of an insrush current.Available online at www.sciencedirect.com 2 lished by Elsevier B.V. Selection and/o  p er-review under responsibility of the Guest Editors.Open access under CC BY-NC-ND license.Open access under CC BY-NC-ND license. W.T.B. de Sousa et al. /  Physics Procedia  36 ( 2012 )  1242 – 1247 1243The tests were performed with 12 modules manufactured by Nexans Superconductors GmbH (MCP-BSCCO-2212). These modules have a CuNi alloy soldered throughout their whole length, which acts as ashunt resistor, to avoid hot spots during the transition from superconducting to normal state (quenching) [1].The total length of a single component is 270 cm and the transversal section area of the superconductingmaterial is 0.534 cm2. The components were tested in series and parallel connection.A simple computational method was developed to simulate the behavior of these devices allowing theassessment of the temperature rise during a short-circuit. The temperature rise is a hard parameter to measureand the simulation of this parameter helps us to predict the final temperature of the components.2. Procedures2.1. TestsThe twelve SCFCL components were cooled in a liquid nitrogen bath (77 K) in the High Current Lab-oratory of ELETROBRAS CEPEL (Electric Power Research Center) and subjected to short-circuits tests.The test circuit is composed of impedances that controls the value of the prospective fault current (withoutthe SCFCL) and transformers that controls the voltage of circuit. A better description of test circuit can befound in [2]. In table 1, we summarize the main characteristics of three tests performed (T1, T2 and T3).Table 1. Short-Circuit Test ParametersTest Fault Current (kArms) Voltage (kVrms) Connection Branches Fault Duration (s)T1 67 1.0 Series 1 × 12 0.08T2 65 0.5 Parallel 2 × 6 0.08T3 1.2 0.135 Single Component 1 × 1 2.0The peak values of fault current does not correspond to rms value ×√2, since the prospective currentsare not symmetric. T3 corresponds to the low fault test, carried out to study the slow transition from super-conducting to normal state of these devices when subjected to currents in order of 3Ic (Ic = 526 A).2.2. Computational SimulationsThe computational simulations were made considering the heat exchange of SCFCL with N2 bath inorder to approximate our simulations to a more realistic condition. We consider a uniformly heating ofsuperconducting material and shunt resistance along their lenght [3]. The following equations (1, 2 and 3)describes the termal behavior of model.ρc(Tsp) dTspdt= EJ − Q2 − Q1 (1)Q1 = h1A1 (Tsh − 77) (2)Q2 =h2A2C2(Tsp − Tsh)(3)In 1 - 3, Tsp is the temperature of superconducting material (K), Tsh is the temperature of shunt resistance(K), Q1 is the rate of convective heat transfer between the shunt resistance and liquid nitrogen, Q1 is the rateof conduction heat transfer between the superconducting material and the shunt resistance, A1 is the surfacearea of shunt for convective heat transfer, h1 is convective heat transfer coefficient (0.02 W/cm2K), h2 is theconduction heat transfer coefficient (5.0×10−4 W/cmK), A2 is the surface area of solder between BSCCO2212 and shunt, C2 is the solder thickness between BSCCO 2212 and shunt (0.2 mm), ρ is the volumetricdensity (6.0 g/cm3) and c(Tsp) is the specific heat (J/kgK) of the superconducting material.The simulations are done considering the superconducting material as a variable resistor, according withE-J curve described in [4], connected in parallel with the shunt resistance. A linear dependence of critical1244   W.T.B. de Sousa et al. /  Physics Procedia  36 ( 2012 )  1242 – 1247 current Jc density on temperature Tsp of BSCCO 2212 was also taken in account [5]. In normal state, theresistance of a single limiter module was modeled according with the linear behavior of BSCCO 2212 aboveits onset critical temperature Tc (104 K) [6] obtained from a experimental resistance × temperature curve. Ahomogeneous Tc distribution is assumed in our simulation model. All simulations were developed using theAlternative Transient Program (ATP) version of EMTP and ATPDraw for Windows via MODELS language.3. Results and DiscussionIn Fig. 1 we observe the results of short circuit tests performed in CEPEL’s High Current Lab. For thetest T1 the first current peak without SCFCL of 98.8 kApeak was limited to 11.0 kApeak with the SCFCLassembly in series connection. The subsequent current peaks are about 3.15 kApeak. In the test T2 thefirst current peak without SCFCL of 109.9peak kA was limited to 20.6peak kA with the SCFCL assembly inparallel connection. The subsequent current peaks are about 6.6 kApeak.(a) (b)Figure 1. Tests results; comparison between prospective current and limited current for a) Series connection (T1) with prospectivecurrent = 67.0 kArms subjected to 1.0 kVrms and b) Paralell connection (T2) with prospective current = 65.0 kArms subjected to 0.5kVrms.These behaviors suggests that the transition from superconducting to normal state occurs in the first cy-cle of current once after that, the current remains in a quasi ”steady-state” regime. This can be explained offollowing way: after transition of superconductor material, its resistance becomes much higher than resis-tance of CuNi metal (shunt). Because they are soldered one in another, the current flows almost completelyin the shunt.Figures 2 and 3 show experimental results of limited current and voltage compared with the respec-tive simulated results for T1 and T2 respectively. In both simulations (T1 and T2) we observe a suddenchange in the second peak of simulated limited currents with a correspondent voltage spike occurring atthe same instant. These differences between calculated and measured data probably came from the sharpsuperconducting-normal transition in the simulation which did not happen in the measurement, since mag-netic fields were not taken into account in our model and the superconducting material was approximatedto a single homogeneous material. In fact there are intrinsic heterogeneities that lead to changes in thevalue of Tc along the superconductor material. In addition, a homogeneous distribution of temperature uponquenching was also assumed, but the temperature may vary in function of the position in the bulk.From these simulations we can also estimate the temperature rise of the BSCCO 2212 and CuNi shuntduring the tests, as shown in figure 4. We note, a fast heating of BSCCO 2212 during the transition fromsuperconducting to normal state in both curves. After the transition of BSCCO material, the temperaturerises smoothly because the current flows almost entirely through the shunt. For this reason, the temperatureof shunt is higher than temperature of superconductor material at the end of tests. W.T.B. de Sousa et al. /  Physics Procedia  36 ( 2012 )  1242 – 1247 1245(a) (b)Figure 2. Comparison between measured and simulated results of limited current and voltage across SCFCL assembly. Fault current:67.0 kArms, subjected to 1.0 kVrms (T1 - series connection)(a) (b)Figure 3. Comparison between measured and simulated results of limited current and voltage across SCFCL assembly. Fault current:65.0 kArms subjected to 0.5 kVrms (T2 - parallel connection).The temperatures of shunt and BSCCO reaches high values on test T2 because of parallel connection,once in this kind of connection, higher currents flows in each limiter module than in series connection (T1),as we can observe in figures 2 (a) and 3 (a).The results of low fault test T3 can be observed in figures 5 and 6. In the figure 5 (a) we show thefirst 0.3 second of test and observe that the SCFCL does not actuate, once there is no much differencebetween currents of circuit with and without the SCFCL module. Figure 5 (b) shows the voltage across theSCFCL terminals and confirms the idea that the superconductor material still does not develop a considerableresistance because the voltage is lower than 2.5 Vpeak. This voltage rises due the resistance contact of SCFCLmodule with the circuit.However, the resistance of superconductor material starts to develop on the time once the current peakof circuit is about 3Ic. In the figure 6 (a) we observe differences on current peaks of circuit with and withoutthe SCFCL module in last 0.3 second of test (between 1.7s and 2.0s). Due the development of resistanceof SCFCL module, the voltage across its terminals rise as showed in figure 6 (b). This voltage does notreach values higher than 20 V what indicates that BSCCO 2212 material is just initiating the transition tothe normal state.1246   W.T.B. de Sousa et al. /  Physics Procedia  36 ( 2012 )  1242 – 1247 (a) (b)Figure 4. Temperature rise during short-circuit for a) Test T1 - series connection and b) Test T2 - parallel connection.(a) (b)Figure 5. Result of T3 in the first 0.3 seconds: a) The current of circuit with and without the SCFCL and b) Voltage across the SCFCLmodule.(a) (b)Figure 6. Result of T3 in the last 0.3 seconds: a) Comparison current of circuit with and without the SCFCL and b) Voltage across theSCFCL module W.T.B. de Sousa et al. /  Physics Procedia  36 ( 2012 )  1242 – 1247 1247(a) (b)Figure 7. Results for Test T3, a)Temperature rise during low fault test and b) Comparison between measured and simulated currents.The simulation model was used to estimate the temperature rise during test T3, as we can observe infigure 7 (a). This simulation result show us that the BSCCO 2212 does not really transited to normal stateonce the final temperature 99.5 K was lower than its onset critical temperature Tc (104 K). Figure 7 (b) showus the comparison between measured current and simulated current for the time between 1.7 s and 2.0 s ontest T3. The simulation result agrees well with the measured current.4. ConclusionsThis work aimed to study the behavior of a resistive SCFCL, by simulating and testing SCFCL BSCCO2212 components when subjected to high and low fault current levels. According to test and simulationresults, we conclude that these devices can be considered effective for protecting circuits against problemscaused by raising short circuit current levels, since they limited fault currents of about 65 kArms and 67 kArmsto 11 kApeak and 20 kApeak at first peak. We also conclude from test T3 that at low faults the superconductormaterial of these components takes more time to develop a considerable resistance value and might not moveto normal state. This result can be considered satisfactory for ”inrush” currents, when the SCFCL shouldnot actuate.Although our simulations presented some differences in comparison to experimental results, we canconsider the algorithm satisfactory for practical purposes. The simulation method developed in the presentwork can be further improved, by considering heterogeneous temperature and Tc distributions, as well as byincluding the effect of the magnetic field.5. AcknowledgmentsThe authors are thankful to the Brazilian agencies CNPq and FAPERJ for part of the financial support.W.T.B. de Sousa would like to thanks the IEEE and EUCAS-ISEC-ICMC 2011 organizers for supportinghis participation in this conference.References[1] S. Elschner, et al., IEEE Trans. App. Superconductivity, vol. 18, No 2 (2003) 1980.[2] A Polasek, R Dias, E T Serra, O. Filho and D. Niedu, J. Phys.: Conf. Ser. No. 234 (2010) 32048.[3] C. Kurupakorn, et al., J. Phys.: Conf. Ser. No. 43 (2006) 950.[4] W.Paul, et al., Physica C, 354 (2001) 27.[5] J. Langston, M. Steureur, et al., IEEE Trans. App. Superconductivity, vol. 15, No. 2 (2005) 2090.[6] W.T.B. de Sousa, et al., IEEE Trans. App. Superconductivity, submitted for publication, 2011.

Short-Circuit Tests and Simulations with a SFCL Modular Assembly

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Short-Circuit Tests and Simulations with a SFCL Modular Assembly

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