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

This paper presents a new numerical model for computing the current density, field distributions and AC losses in superconductors. The model, based on the direct magnetic field H formulation without the use of vector and scalar potentials (which are used in conventional formulations), relies on first-order edge finite elements. These elements are by construction curl conforming and therefore suitable to satisfy the continuity of the tangential component of magnetic field across adjacent elements, with no need for explicitly imposing the condition . This allows the overcoming of one of the major problems of standard nodal elements with potential formulation: in the case of strong discontinuities or nonlinearities of the physical properties of the materials and/or in presence of sharp corners in the conductors' geometry, the discontinuities of the potentials' derivatives are unnatural and without smoothing artifices the convergence of the algorithm is put at risk. In this work we present in detail the model for two-dimensional geometries and we test it by comparing the numerical results with the predictions of analytical solutions for simple geometries. We use it successively for investigating cases of practical interest involving more complex configurations, where the interaction between adjacent tapes is important. In particular we discuss the results of AC losses in superconducting windings.

https://iopscience.iop.org/article/10.1088/0953-2048/20/1/004/pdf

Development of an edge-element model for AC loss computation of high-temperature superconductors

Increased renewable energy integration and international power trades have led to the construction and development of new HVDC transmission systems. HVDC cables, in particular, play an important role in undersea power transmission and offshore renewable energy integration having lower losses and higher reliability. In this paper, the current commercial feasibility of HVDC cables and the development of different types of HVDC cables and accessories are reviewed. The non-uniform electric field distribution caused by the applied voltage, temperature dependent conductivity, and space charge accumulation is briefly discussed. Current research in HVDC cable for higher operation voltage level and larger power capacity is also reviewed with specific focus on the methodologies of space charge suppression for XLPE extruded cables.

Review of high voltage direct current cables

Two major problems that are faced by doubly fed induction generators are: weak low-voltage ride-through capability and fluctuating output power. To solve these problems, a superconducting fault-current limiter-magnetic energy storage system is presented. The superconducting coil (SC) is utilized as the energy storage device for output power smoothing control during normal operation and as a fault-current limiting inductor to limit the surge current in the stator or rotor during the grid fault. The SC can also weaken the rotor back electromotive force voltage, and thus enhance the controllability of the rotor-side converter (RSC), which helps to protect both the RSC and the gearbox. Simulation results verify the efficacy of the proposed approaches.

Enhancing Low-Voltage Ride-Through Capability and Smoothing Output Power of DFIG With a Superconducting Fault-Current Limiter–Magnetic Energy Storage System

A reliable, modular, production quality narrow-band KrF excimer laser capable of producing 10 mJ laser pulses at 1000 Hz with a bandwith of about 0.6 pm or less. The present invention is especially suited to long-term round-the-clock operation in the lithographic production of integrated circuits. Improvements over prior art lasers include a single upstream preionizer tube (56) and acoustic baffles. A preferred embodiment includes reduced fluorine concentration, an anode support bar shaped to reduce aerodynamic reaction forces on blower bearings, a modified pulse power system providing faster pulse rise time, an output coupler (65) with substantially increased reflectivity, a line narrowing module with CaF prism beam expanders, a more accurate wavemeter, a laser computer controller programmed with new and improved pulse energy control algorithm.

RELIABLE, MODULAR, PRODUCTION QUALITY NARROW-BAND KrF EXCIMER LASER

A 6.6 kV single-phase fault current limiter (FCL) using a high-Tc superconducting coil as a limiting coil was developed. The development is a preliminary step to investigate the feasibility of the FCL application for high-voltage transmission lines. The FCL is of the rectifier type and is mainly comprised of a limiting coil, a sub-cooled nitrogen cryostat with a cryocooler, and a rectifier bridge. The limiting coil, wound as a solenoid by Ag/Mn sheathed Bi-2223 tapes, has an inductance of 30 mH. It is immersed in a liquid nitrogen bath in the cryostat. A Gifford-McMahon cryocooler cools the cryogen below 77.3 K. A pressure regulator keeps the cryogen at an atmospheric pressure. The coil has a critical current of 70 A at 64 K and endures a 50 Hz overvoltage of 22 kV against the ground. In a fault current limiting test with a short-circuit generator, a short-circuit current of 12.5 kA was limited to 1.2 kA.

Design and test results of 6.6 kV high-Tc superconducting fault current limiter

The authors have developed and tested a 6.6-kV/1.5-kA-class fault current limiter wound with a 42-strand AC superconducting wire having ultrafine NbTi filaments in a high-resistivity matrix. In experiments, voltages up to 7.2 kV were applied to the limiter with phase angles of 0, 45, and 90 degrees . The limiter was able to limit the fault current to 1.8 kA from the 55-kA short-circuit current that would flow in a circuit without a limiter. >

6.6 kV/1.5 kA-class superconducting fault current limiter development

A Japanese national project called “Materials & Power Applications of Coated Conductors (M-PACC)” started in FY2008. In this project, we are developing a 66 kV/5 kA large-current high-temperature superconducting (HTS) cable and 275 kV/3 kA high-voltage HTS cable, using rare-earth barium copper oxide (REBCO) tapes. These HTS cables are expected to offer a compact cable with a large capacity and low power transmission loss. After the cable design has been studied and elemental technologies for each component of the cable system, such as ac loss reduction, protection against over-current, and high-voltage electrical insulation have been developed, two cable systems will be constructed and verified to meet the required specifications in FY2012. This paper describes the progress and status of these HTS cable developments in the M-PACC project.

Development of 66 kV and 275 kV Class REBCO HTS Power Cables

One of the items included in the Super-conductive AC Equipment (Super-ACE) project, being performed from 2000 to 2004, is a development of a 66 kV/750 A high-T/sub c/superconducting (HTS) fault current limiter (FCL) magnet. This research focuses on fundamental technical items essential for a 66 kV class fault current limiter, that is, high current capacity, high voltage insulation and sub-cooled nitrogen cooling. This paper describes the design of the magnet and the test results obtained so far. The magnet mainly consists of a vacuum vessel, a nitrogen bath, a pair of current leads, cryocoolers, and six sets of unit-coils wound with Bi2223 tapes. The rated current of each coil is about 125 A at 70 K, and so the total current capacity of the magnet is 750 A. The insulation voltage of the magnet is of the 66 kV class. By the end of FY2002, three sets of the unit coils were set connected in the cryostat and some evaluation tests were implemented as a milestone of the program. In the cooling down test, sub-cooled nitrogen of 65 K was obtained with homogenous temperature distribution in the cryogen. In the overvoltage test, no breakdowns were observed in the case of applying both ac voltage of 140 kV for one minute and lightning impulse voltage of 350 kV. Voltage-current characteristics of the coils were measured in sub-cooled nitrogen. The rated current of 375 A was successfully obtained for both direct and alternate current tests. All the targets constituting the milestone of the 66 kV/750 A magnet development were achieved.

Development of 66 kV/750 A High-T/sub c/ superconducting fault current limiter magnet

There is disclosed a current limiter having a plurality of current limiting units provided for electric paths constituting a plurality of phases, Each current limiting unit is constituted by a superconducting coil functioning as a first current limiting element formed in a non-inductive winding manner by connecting two superconducting coils in series, which superconducting coils are wound in opposite directions and equal in size and number of turns, and a superconducting coil functioning as a second current limiting element connected in parallel to the first current limiting element and having a predetermined impedance value. These current limiting units are contained within a cryostat and separated by a magnetic shield member for electromagnetically isolating the respective phases.

T. Ohkuma

Papers

Design and test results of 6.6 kV high-Tc superconducting fault current limiter

6.6 kV/1.5 kA-class superconducting fault current limiter development

Development of 66 kV and 275 kV Class REBCO HTS Power Cables

Development of 66 kV/750 A High-T/sub c/ superconducting fault current limiter magnet

Superconducting fault current limiter