Mathias Noe

High-temperature superconductor fault current limiters: concepts, applications, and development status

The application of superconducting fault current limiters (SCFCLs) in power systems is very attractive because SCFCLs offer superior technical performance in comparison to conventional devices to limit fault currents. Negligible impedance at normal conditions, fast and effective current limitation within the first current rise and repetitive operation with fast and automatic recovery are the main attributes for SCFCLs. In recent years there has been a significant progress in the research and development (R&D) of SCFCLs. This paper gives an extended review of different SCFCL concepts, SCFCL applications and the R&D status. Within the first part of this paper the most important SCFCLS and, to a limited extent, non-superconducting fault current limiter (FCL) concepts are explained and compared. The second part reviews interesting SCFCL applications at the distribution and transmission voltage level and the third part shows in detail the R&D status. It can be summarized that SCFCLs are, at present, not commercially available but several successful field tests demonstrated the technical feasibility of SCFCLs. First distribution level applications are expected soon. Considerable economical and technical benefits can be achieved by applying SCFCLs at the distribution and transmission voltage level.

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.

System technology and test of CURL 10, a 10 kV, 10 MVA resistive high-Tc superconducting fault current limiter

A full scale three-phase resistive high-Tc superconducting fault current limiter (SCFCL) designed for 10 kV, 10 MVA, has been developed, manufactured, and tested within a publicly funded German project called CURL 10. The device is based on 90 bifilar coils of MCP BSCCO-2212 bulk material. The operating temperature of 66 K is achieved by cooling of liquid nitrogen using two Stirling cryocoolers. Until today, this is the largest HTS fault current limiter world wide. We report on the design features, the composition, and the operation parameters of the SCFCL system. From April 2004 on CURL 10 is installed and tested within the network of the utility RWE at Netphen near the city of Siegen, Germany. The results of the laboratory test and the field test of CURL 10 are given.

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.

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.

ENSYSTROB—Resistive Fault Current Limiter Based on Coated Conductors for Medium Voltage Application

A new German government funded project for a resistive fault current limiter has started in September 2009 (ENSYSTROB) and is presented. The consortium includes partners from industry, research centers and utilities. It aims the construction of a 3-phase medium voltage current limiter (12 kV, 800 A) for the protection of the domestic supply in a power plant. A special feature of this application is the presence of large in-rush currents (4100 Ap for 50 ms, 1800 A for 15 s). The superconducting components are bifilar pancake coils consisting of pairs of YBCO-tapes in face to back configuration. Successful limitation experiments on prototype components with prospective currents in the whole range are shown. Also the stability with respect to high voltage could be demonstrated. The AC-losses under normal operation are shown, by simulation and experiment, to be smaller than the heat input of the current leads. The current limiting components are compared with similar elements based on BSCCO 2212 bulk material (Nexans SuperConductors).

Progress on the R&D of fault current limiters for utility applications

Mechanical and thermal stresses caused by short-circuits are a major design criterion of electric power systems. Conditional impedance increase during a fault from new fault current limiter (FCL) devices can reduce short-circuit current levels significantly without adding additional impedance during normal operation. This paper updates on the present R&D status of new FCL technologies. At present, superconducting FCLs (SCFCLs) are being introduced commercially after first field tests of medium voltage demonstrators showed the technical feasibility. Different types of SCFCLs and non-superconducting FCLs have been developed in order to best fit the specific application requirements. Several FCL projects are investigated in order to illustrate and discuss the progress on the way to meet the two major R&D objectives: developing high voltage SCFCLs (Gt100 kV) and producing simple and low cost SCFCLs for medium voltage levels (6-36 kV).

Conceptual Design of a 24 kV, 1 kA Resistive Superconducting Fault Current Limiter

In recent years many large scale demonstrators and prototypes of superconducting fault current limiters have been successfully developed and tested. Within the European Project ECCOFLOW (www.eccoflow.org), it is the first time that a resistive-type superconducting fault current limiter is developed for two different locations and that a permanent installation is foreseen. The limiter has a rating of 20 kV and 1 kA and will be tested in a busbar and transformer feeder application. The paper summarizes the conceptual design of this innovative limiter and reports in detail about the development of the super- conducting limiting elements, their integration into a cryostat and the design of the whole limiter including cooling and grid integration. As a main result it can be summarized that the ECCOFLOW limiter fulfills all requirements according to the two different specifications. Approximately 3 km of 12 mm wide YBCO tape will be used to realize a three phase system.

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.