Steffen Elschner

CURL 10: development and field-test of a 10 kV/10 MVA resistive current limiter based on bulk MCP-BSCCO 2212

Within the German project CURL 10 a full scale three-phase resistive current limiter was developed and successfully tested up to the nominal voltage and power (10 kV, 10 MVA). This is up today the largest HTS current limiter world wide. The device is based on bifilar coils of MCP-BSCCO 2212 bulk material and operates at T=66 K. Per phase 30 components are connected in series in order to obtain the required resistance. The electrical stabilization is based on a metallic shunt contacted continuously to the superconductor and allows electrical fields up to 0.6 V/cm. We report on the development of the superconducting components and their large-scale manufacturing processes including material, contacts, mechanical stabilization, high voltage insulation and quality control. In a series of preliminary small scale tests at different temperatures as well as in the final tests with the full scale prototype reliable current limitation could be demonstrated in the full range of prospective fault currents, also in the particular dangerous small load regime. Since April 2004 the demonstrator has been installed within a field test in the grid of RWE.

Investigation of high-Tc bulk material for its use in resistive superconducting fault current limiters

Superconducting fault current limiters (SCFCL) offer an attractive means to limit short-circuit currents in power systems. Comparisons of available HTS material led to the derision to investigate melt cast processed (MCP) BSCCO and melt textured polycrystalline YBCO for use in resistive SCFCLs. As a great length of a superconductor per unit element is preferred, the BSCCO samples are shaped as bifilar coils prepared from tubes and the YBCO samples are manufactured in a meander shaped geometry. Test results concerning contact resistances, E-J curves, AC losses as well as the quench behaviour of the samples are presented. The experiments reveal the requirement of a high material homogeneity as the main challenge.

Testing bulk HTS modules for resistive superconducting fault current limiters

Recent investigations show that high Tc bulk material is an attractive material option in resistive superconducting fault current limiters. Our investigation focuses on the short-circuit behavior of long samples of MCP-BSCCO2212 and polycrystalline melt-textured YBCO. The experiments have been performed for different operating temperatures, short-circuit duration and prospective short-circuit currents. The measurements demonstrate that a metallic bypass is needed to avoid destructive hot spots during quench. Quench and limitation tests of MCP-BSCCO2212 bifilar coils with integrated high resistive metallic shunt down to 65 K have successfully been performed. This type of module will be used for construction of a 10 MVA power system demonstrator.

Large shaped parts of melt cast BSCCO for applications in electrical engineering

A melt casting process (MCP) that is tailor made for BSCCO, especially for the 2212 phase, is described. It is reported that melt casting offers an easy access to a variety of different shapes and sizes. The properties of the material obtained by MCP have been significantly improved by admixing strontium sulphate. J/sub c/ values superior to those of sintered ceramics of YBCO or BSCCO have been obtained: J/sub c/ values at 55000 A/cm/sup 2/ (4 K) and 2200 A/cm/sup 2/ (77 K) were achieved without external fields; large bulk parts exhibited more than 2000 A (77 K) in their self-field. The peculiarities of MCP allow the integration of noble metal current contacts which exhibit total resistances <or=1 mu Omega (77 K), even under high currents. First tests of prototypes (rods and tubes for current leads, hollow cylinders for inductive current limiters) show promising results.<<ETX>>

Manufacturing and testing of MCP 2212 bifilar coils for a 10 MVA fault current limiter

A very promising option within the German 10 kV/10 MVA superconducting fault current limiter project CURL 10 is melt cast processed (MCP-) BSCCO 2212 bulk material. With tube shaped samples cut to bifilar coils and contacted in series, the required long lengths (160 m per phase) can easily be achieved. At the operating temperature of T=65 K the critical current density is near 4000 A/cm/sup 2/ and the voltage under limiting conditions reaches E/sub p/=0.5 V/cm. The contribution describes the design, manufacturing and testing of the superconducting components. In particular the development and characterization of a suitable electrical shunt is focused. Finally the finished components are characterized with respect to electrical homogeneity and under various limiting conditions. It could be confirmed that the single components each meet all the requirements defined within the project.

Proof-of-concept prototype test results of a superconducting fault current limiter for transmission-level applications

SuperPower, Inc. and Nexans SuperConductors GmbH have partnered to develop a superconducting fault current limiter for transmission level applications. The device employs SuperPowers Matrix Fault Current Limiter (MFCL) technology and BSCCO-2212 bulk material manufactured by Nexans melt cast processing technique. The development program has been underway since June 2002 and is divided into a series of prototype demonstrations of progressive capability, culminating in a Beta prototype that will be installed at a host utility on a 138 kV line. This paper describes the test results of the first major program milestone, a proof-of-concept prototype at distribution level voltage. The test results show the expected current limiting performance of the MFCL technology to provide fast current limiting and dynamic resistance development before the first peak of the fault. The fault current evenly distributes among the elements of the MFCL array, which employs a resistive-inductive approach for limiting the current. The results also show the excellent electric field performance of the BSCCO-2212 material.

Development and successful testing of MCP BSCCO-2212 components for a 10 MVA resistive superconducting fault current limiter

The German government funded resistive superconducting fault current limiter project CURL 10 is based on bulk material and aims at the development of a three-phase prototype for the medium voltage level (10xa0kV, 10xa0MVA). The key element of the project is the development of suitable robust superconducting components. On the basis of the well known melt cast process (MCP) for BSCCO-2212, these are manufactured by cutting superconducting tubes to bifilar coils. At the operation temperature of 65xa0K a current density of 4000xa0Axa0cm−2 was achieved. In order to protect the superconductor during limitation the component was equipped with an electrical shunt contacted on its entire length. Single-phase tests with nine of these components in series, corresponding to a protected load of 1.2xa0MVA, have been successfully accomplished and are described in detail. These tests include different types of short circuits as specified by the utilities within the project and included lightning surge loads up to 75xa0kV.

Influence of granularity on the critical current density in melt-cast processed Bi2Sr2CaCu2Ox

The microstructural analysis of melt-cast processed Bi2Sr2CaCu2Ox reveals the existence of grain boundaries on two different length scales. Plate-shaped crystal grains of approximately 10 mu m length are textured along the c direction on a scale of 200-300 mu m, forming bundles of arbitrary orientation. To investigate the impact of the grain boundaries within and between bundles on the critical current density the authors have analysed the variation of the magnetic hysteresis with the sample size using different powder fractions and bulk material. It could be shown that the boundaries between the platelets within a bundle limit the overall transport current density in bulk material, whereas the boundaries between bundles do not further reduce its value. The results are in agreement with a TEM analysis of the grain boundaries.

Characterization of BSCCO 2212 bulk material for resistive current limiters

It is demonstrated that melt cast processed (MCP) BSCCO 2212 bulk material is an excellent candidate for resistive superconducting current limiters. For rod shaped samples it could be shown that a homogeneous voltage of more than 1 V/cm can be established over the whole length of the sample leading to a substantial limiting of short circuit current. The require long lengths of superconducting material can be easily obtained by machining the MCP-tubes into (bifilar) coils. The measured critical current density and its homogeneity over these large lengths were determined and proven to be sufficient for the designated application.

High voltage design, requirements and tests of a 10 MVA superconducting fault current limiter

In recent years the development of superconducting fault current limiters (SCFCLs) has made significant progress. Within the frame of the German project CURL10 a 10 kV, 10 MVA demonstrator of a resistive SCFCL, using MCP-BSCCO 2212 bifilar coils, has been developed and successfully tested. A world-wide first field test of a resistive SCFCL started in 2004. This paper reports about the high voltage design aspects and summarizes the high voltage tests performed within this project. The different tests confirm that the design requirements of 28 kV AC voltage and 75 kV lightning voltage are fulfilled. Even at worst case conditions of a quench and a lightning pulse at the same time no breakdown was observed.