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.

https://iopscience.iop.org/article/10.1088/0953-2048/20/3/R01/pdf

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

Bulk high-temperature superconductors (HTSs) enable the opportunity to develop several unique applications in electrical power that are not feasible with superconducting or normal wires. The large current carrying capacity and low thermal conductivity of the HTSs allows relatively short lengths to carry large currents to low-temperature devices without introducing heat to the device. Such current leads can dramatically reduce the refrigeration requirements for devices such as SMES. The HTSs make a relatively sharp transition to a highly resistive state when the critical current density is exceeded, and this effect has suggested their use for resistive fault current limiters. The bulk HTSs may also take the form of large single-grained superconductors within which circulating currents may flow at large current density without loss. They are capable of developing magnetizations, similar to that of permanent magnets, but with much larger magnetic fields. In this case, they may be used as field-trapping components. Applications in this case include brushless synchronous motors, laboratory magnets, magnetic separation, and magnetron sputtering. The bulk HTSs may also be used as diamagnetic objects in magnetic circuits to provide new types of power devices. One application that uses this effect is an inductive fault current limiters, in which the HTS shields an iron core in an inductive circuit until some current level is exceeded. This transition increases the component from low impedance to high impedance. The diamagnetic property may also be used to create low-loss magnetic bearings for use in efficient energy-storage flywheel devices or sensitive instrumentation. The combination of diamagnetic shielding and field trapping has suggested their use in motor designs analogous to hysteresis motors. Laboratory prototypes for all of these devices have been constructed and tested, and in some cases the devices have been field tested in actual power systems. Improvements in HTS properties, such as flux pinning, mechanical strength, and the ability to grow large grains, have greatly improved the economics of applications that use bulk HTS.

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Applications of bulk high-temperature Superconductors

The introduction of new generating facilities by independent power producers and increasing load demand can result in fault-current over-duty on existing transmission system protective equipment. Conventional solutions to fault current over-duty such as major substation upgrades, splitting existing substation busses or multiple circuit breaker upgrades could be very expensive and require undesirable extended outages and result in lower power system reliability. Less expensive solutions such as current limiting reactors may have unwanted side effects, such as increase in system losses, voltage regulation problems or possibly could compromise system stability. This paper discusses the benefits of superconducting Fault Current Limiters (FCLs) which can be economically competitive with expensive conventional solutions. Superconducting FCLs are invisible in normal operation and do not introduce unwanted side effects. The performance of a particular type of limiter, the Matrix Fault Current Limiter (MFCL) is presented and examples are provided on how it could relieve fault current over-duty problems. The use of this device in a particular application in the American Electric Power (AEP) 138 kV transmission grid is also discussed.

Applications of superconducting fault current limiters in electric power transmission systems

The development of superconducting systems for electric power is driven by the promise of improved efficiency, smaller size, and reduced weight as compared to existing technologies and by the possibility of new applications. Superconducting power components can also contribute to improved power quality and increased system reliability. This paper addresses historical developments and technology status of four superconducting power applications: cables, superconducting magnetic energy storage (SMES), fault-current limiters, and transformers. Today, SMES is the only fully functional superconducting system and it has seen only limited use at grid power levels. A few model or demonstration units exist for each of the other three applications. Superconductivity faces several hurdles on the path to widespread use. Perhaps the most important is the need for operating voltages of 100 kV or more. Though progress in this and other areas has been rapid, considerable development is needed before superconducting devices perform reliably in the utility environment. As a result, today, most initial installations are aimed at niche applications and will be installed where space is limited, where power demands are increasing over existing corridors, and/or where initial development costs can be offset by enhanced power grid performance.

Electric power applications of superconductivity

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.

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

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.

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

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.

Testing bulk HTS modules for resistive superconducting fault current limiters

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.

F. Breuer

Papers

Applications of superconducting fault current limiters in electric power transmission systems

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

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

Testing bulk HTS modules for resistive superconducting fault current limiters

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