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Superconductivity Centennial Conference 2011- EUCAS–ISEC–ICMC (18-23 Sep 2011, The Hague, The Netherlands)

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Limitadores de corrente supercondutores resistivos (LCSR) são dispositivos com características elétricas próximas ao ideal quando ocorre a transição do estado supercondutor para o estado normal, limitando a corrente de falta através da inserção rápida de uma resistência na rede. A viabilidade técnica e econômica destes limitadores aumentou após o desenvolvimento dos supercondutores de alta temperatura crítica HTS. A primeira geração de fitas HTS (BSCCO) consiste em multifilamentos de material supercondutor embutidos em uma matriz de prata. A densidade de corrente crítica típica é de aproximadamente 140 A/mm2. Contudo, a resistência alcançada pelo LCSR quando atinge o estado normal não é suficiente para limitar a corrente de falta, sendo necessários longos comprimentos de fitas (~5 km) para que a corrente seja limitada. O recente desenvolvimento de fitas supercondutoras de YBCO com filmes finos texturizados e com substrato de alta resistividade superou o desempenho das fitas de BSCCO para esta aplicação. Com uma densidade de corrente crítica de 136 A/mm2, as fitas de YBCO são bem conhecidas pelo seu alto valor de índice n (aproximadamente 30), rápida resposta de transição após falta e alta resistência elétrica no estado normal. Neste trabalho foram analisados o comportamento elétrico e magnético das fitas de BSCCO e YBCO (em amostras curtas de 0,2 m) utilizando diferentes técnicas de caracterização das propriedades das fitas HTS. A partir destes resultados, medidas com pulsos de corrente DC e AC com intensidades de 3 a 7 vezes a corrente crítica do sistema (I=720 A a 1700 A) com duração de 1 a 5 ciclos da rede em 60 Hz (16 a 80 ms) foram realizados de forma a obter as características do tempo de recuperação em um elemento contendo 4 fitas em paralelo (0,4 m). Os resultados permitiram o projeto, construção e medidas em corrente AC de um protótipo LCSR (Ipico = 2 kA) contendo 16 elementos sob condições normais de operação da rede (220 V - 60 Hz). / Resistive Superconducting fault current limiter (SFCL) are devices with electrical behavior near the ideal when it changes its state from the superconducting to the normal state, limiting the fault current by the insertion of a fast transition resistance in the grid. The technical and economical feasibility of these limiters arose after the development of the high critical temperature superconductors HTS. First generation HTS tapes (BSCCO) consist of multifilamentary composite tapes embedded in a silver matrix. The typical critical current density is approximately 14 kA/cm2. However, the resistance reached by the SFCL when normal state occurs is not high enough to limit the fault current, making necessary long lengths of tapes (~5 km) for limiting purposes. The recently development of coated conductors composites with high resistivity metal substrate have succeeded the BSCCO tapes which are based on YBCO textured film. Upon carrying a critical current density of 13.6 kA/cm2, YBCO tapes are well known for their high n-index value (approximately 30), fast transition response after fault, and high electrical resistance in the normal state. In this work, we will present the electrical and magnetic performance of BSCCO and YBCO tapes (short samples of 0.2 m) using several techniques to characterize the properties of the HTS tapes. It was also performed analysis with DC and AC currents peaks with strength of 3 to 7 times the critical current (I=720 A to 1700 A) lasting 1 to 5 cycles (16 to 80 ms) in order to verify the recovery characteristics in an element with 4 tapes in a parallel connection. And with those characteristics we designed and constructed and measured in AC current a SFCL prototype (Ipeak = 2 kA) consisting in 16 elements to use in the grid (220 V - 60 Hz) under operational conditions.

Limitadores de corrente supercondutores resistivos (LCSR) são dispositivos com características elétricas próximas ao ideal quando ocorre a transição do estado supercondutor para o estado normal, limitando a corrente de falta através da inserção rápida de uma resistência na rede. A viabilidade técnica e econômica destes limitadores aumentou após o desenvolvimento dos supercondutores de alta temperatura crítica HTS. A primeira geração de fitas HTS (BSCCO) consiste em multifilamentos de material supercondutor embutidos em uma matriz de prata. A densidade de corrente crítica típica é de aproximadamente 140 A/mm2. Contudo, a resistência alcançada pelo LCSR quando atinge o estado normal não é suficiente para limitar a corrente de falta, sendo necessários longos comprimentos de fitas (~5 km) para que a corrente seja limitada. O recente desenvolvimento de fitas supercondutoras de YBCO com filmes finos texturizados e com substrato de alta resistividade superou o desempenho das fitas de BSCCO para esta aplicação. Com uma densidade de corrente crítica de 136 A/mm2, as fitas de YBCO são bem conhecidas pelo seu alto valor de índice n (aproximadamente 30), rápida resposta de transição após falta e alta resistência elétrica no estado normal. Neste trabalho foram analisados o comportamento elétrico e magnético das fitas de BSCCO e YBCO (em amostras curtas de 0,2 m) utilizando diferentes técnicas de caracterização das propriedades das fitas HTS. A partir destes resultados, medidas com pulsos de corrente DC e AC com intensidades de 3 a 7 vezes a corrente crítica do sistema (I=720 A a 1700 A) com duração de 1 a 5 ciclos da rede em 60 Hz (16 a 80 ms) foram realizados de forma a obter as características do tempo de recuperação em um elemento contendo 4 fitas em paralelo (0,4 m). Os resultados permitiram o projeto, construção e medidas em corrente AC de um protótipo LCSR (Ipico = 2 kA) contendo 16 elementos sob condições normais de operação da rede (220 V - 60 Hz). / Resistive Superconducting fault current limiter (SFCL) are devices with electrical behavior near the ideal when it changes its state from the superconducting to the normal state, limiting the fault current by the insertion of a fast transition resistance in the grid. The technical and economical feasibility of these limiters arose after the development of the high critical temperature superconductors HTS. First generation HTS tapes (BSCCO) consist of multifilamentary composite tapes embedded in a silver matrix. The typical critical current density is approximately 14 kA/cm2. However, the resistance reached by the SFCL when normal state occurs is not high enough to limit the fault current, making necessary long lengths of tapes (~5 km) for limiting purposes. The recently development of coated conductors composites with high resistivity metal substrate have succeeded the BSCCO tapes which are based on YBCO textured film. Upon carrying a critical current density of 13.6 kA/cm2, YBCO tapes are well known for their high n-index value (approximately 30), fast transition response after fault, and high electrical resistance in the normal state. In this work, we will present the electrical and magnetic performance of BSCCO and YBCO tapes (short samples of 0.2 m) using several techniques to characterize the properties of the HTS tapes. It was also performed analysis with DC and AC currents peaks with strength of 3 to 7 times the critical current (I=720 A to 1700 A) lasting 1 to 5 cycles (16 to 80 ms) in order to verify the recovery characteristics in an element with 4 tapes in a parallel connection. And with those characteristics we designed and constructed and measured in AC current a SFCL prototype (Ipeak = 2 kA) consisting in 16 elements to use in the grid (220 V - 60 Hz) under operational conditions.

With the rapid increase in electrical loads, a considerable percentage of global power systems have been stretched to their designed capacity, leading to a sharp rise in the fault current. High fault current levels have severe impact on power systems. They can increase the likelihood of overcurrent damage, which may destroy electrical facilities or even cause system blackout. The resistive-type superconducting fault current limiter (RSFCL) is a device that can help to mitigate the increasing level of fault currents. It can also contribute to the performance, stability and efficiency of electricity grids. In order to promote the RSFCL more effectively, it is essential to study the device itself and conduct simulations regarding the performance and applicability from the system point of view. Chapter 1 and Chapter 2 of this thesis introduced fundamentals of superconductivity and RSFCLs, respectively. In Chapter 3, a power system model was built, and the transient analysis of short-circuit currents was given. Then, the operating principle of RSFCL was explained, and a step-resistance RSFCL model was introduced. To validate the current limiting performance of the SFCL module, wind farm protection schemes were studied under various fault scenarios. After thorough analysis it was concluded that the optimal allocating strategy of SFCLs was the installation of one SFCL at the integrating point of the system model. Chapter 4 presented a comprehensive study on the performance and optimal allocation strategy of RSFCLs. The two power system models used in this chapter were built based on the UK network standard. To assess the impact of incorporating SC material properties on the performance of SFCLs, three different models were compared throughout the study. Although computing time can be reduced when step-resistance and exponential equation models were used, such simplifications led to strong overestimations of the SFCL performance and resulted in wrong conclusion of optimal installing strategies. For both power system models, the simultaneous use of three SFCLs was the best protection strategy in terms of the performance, economic efficiency and reliability of the overall grids. To draw this conclusion, all the potential combinations of two, three, four, and five SFCLs were studied under a wide number of fault scenarios and measuring strategies. In Chapter 5, a series of experiments were performed to study the magnetic field-angular dependence of the critical current of different commercial YBCO samples. We selected ten 2G-HTS tapes with broad differences in width, fabrication process, and laminar structure. The obtained I_c (B,θ) characteristics of HTS samples were applied in the simulation of RSFCLs, showing unneglectable effect on the first peak limiting performance during faults. This study is helpful to the design and simulation of RSFCLs and other HTS applications which require superconducting wires operating inside magnetic fields. In Chapter 6, we presented a High Frequency (HF) AC-assisted quench study of the YBCO conductor. The differences in quench processes triggered by HF AC field were recorded and studied. We found that AC signals of 10 kHz can trigger quench of the HTS tape. Also, the device proved to be effective at guaranteeing uniform quench of the sample. After then, we placed the experimental device in a magnet, to study whether the quench process can be accelerated by external DC magnetic field. It was found that the DC field can reduce the quench time, but its performance was dependent on the amplitude of transport current and the characteristics of HF AC signals. In addition, the angle between the DC magnetic field and the tape surface showed a huge impact on the quench time. Finally, a comprehensive field-angular dependence study about the quench time of the YBCO sample was conducted, revealing the same pattern as J_c (θ,B) dependence of the tape, but with a greater anisotropy. To summarize, this technique showed outstanding performance regarding quench acceleration and tape protection, and therefore has huge potential to be applied in RSFCLs.