Superconducting Fault Current Limiter Device Research Articles

Enhancing the DC Voltage Quality in EV Charging Station Employing SMES and SFCL Devices

The fast-response energy compensating feature from a superconducting magnetic energy storage (SMES) device is favored for suppressing instantaneous voltage fluctuations, while the self-triggering current limiting feature from a superconducting fault current limiter (SFCL) suits to suits to achieve automatic load protections in the electric vehicle (EV) charging stations. This paper investigates a new DC voltage quality enhancing scheme by using a combined superconducting power technology employing SMES and SFCL devices. Preliminary simulations demonstrate the feasibility of this SMES-SFCL-based voltage quality improver to avoid the voltage fluctuations during the EV load transients and suppress the fault current effectively during the short circuits simultaneously.

Fast Hotspot Detection in SFCLs by Exploiting Strain Response in Optical Fiber Sensing

Superconducting fault current limiters (SFCLs) can be used to limit fault currents in both meshed DC and AC grids by transitioning from superconducting to resistive state, in the presence of high currents. While the device is theoretically a great way to protect grids, the inherent inhomogeneity of critical current along the superconductor length can lead to localized heating, called hotspots, and ultimately destruction of the SFCL device. At EPFL under the European Union project Fastgrid, an extremely efficient Mach-Zehnder interferometer (MZI) based optical fiber sensing technique has been developed and patented that can detect even singular hotspots within 15 ms to protect SFCLs. The MZI response is characterized by a strain sensitive as well as a temperature sensitive contribution. This paper outlines an investigation by means of FEM modeling into the response sensitivity. A 2-D thermal model of the superconducting tape and optical fiber was made to study thermal transfer to the optical fiber from the REBCO tape. The simulation results showed that temperature rise observed in the optical fiber is slower than the MZI response time, proving a strain sensitive response in the experiment measurements. Sound mechanical coupling between the optical fiber and the superconductor tape can enhance strain transfer to the optical fiber and hence reduce hotspot detection time. With this improved performance, the health monitoring for SFCLs can be much more efficient and reliable.

Optical fibre sensing for fast hotspot detection in SFCLs

The health monitoring of superconducting fault current limiters (SFCL) is important for their large-scale exploitation in HVDC grids protection. The intrinsic non-homogeneity of critical current along the superconductor length can cause localized points of heating, called hotspots, in the SFCL device which can lead to device damage. In this paper we propose to use an extremely simple and cost-effective technique based on all-fibre Mach-Zehnder interferometers for hotspot detection in SFCLs, where the measurement arm of the interferometer is integrated with the SFCL and the reference arm remains in ambient. The system only consists of a laser, two optical fibre couplers and a photo detector. By studying the acquired interference patterns, even singular hotspots within the entire conductor length, can be informed in few milli-seconds, which is the fastest and most sensitive demonstration to the best of our knowledge that meets the SFCL requirement for fast hotspot detection.

Development of Superconducting Devices for Power Grids in Italy: Update About the SFCL Project and Launching of the Research Activity on HTS Cables

In the framework of the development of High Temperature Superconducting (HTS)-based solutions for modern power grids, Ricerca sul Sistema Energetico - RSE S.p.A. has gained a significant experience in design, testing, and installation of superconducting fault current limiters (SFCLs). After having successfully demonstrated the techno-economic feasibility of the first Italian three-phase BSCCO-based SFCL (9 kV/3.4 MVA) inside the distribution grid of A2A Reti Elettriche S.p.A. in the Milano area, RSE has initiated the development of a new upgraded three-phase SFCL, whose rated power has been enhanced in order to meet the utility's needs. Unlike the first prototype, the new SFCL device (9 kV/15.6 MVA) is YBCO-based: this choice allows reducing the needed tape length and cooling power, saving at the same time a significant amount of operational costs. The first phase was already assembled and tested in 2015, whereas the second phase was tested in February 2016. This paper will show the last outcomes from characterizations and short-circuit tests. Along with the SFCL project, RSE has also been focusing on superconducting cables and, in the framework of the European Project Best Paths, it has been involved in DEMO5, that is dedicated to the development of a HTS DC cable in MgB2 (10 kA/3.2GW). Taking the cue from the DEMO5 requirements, RSE has initiated a parallel research activity that is focused on studying the thermo-fluid dynamic behavior of cryogenic coolants flowing in forced convection regime inside the flexible cryostat. This paper will present the first simulation results and will give some anticipation on next steps.

Application of resistive superconducting fault current limiters in offshore oil production platforms

This manuscript presents an analysis of the integration of superconducting fault current limiters (SFCL) in floating, production, storage, and offloading (FPSO) platforms. Short-circuit studies based on dynamic simulations of an FPSO power system with an integrated SFCL were carried out. The simulation model used to reproduce the transient behavior of the SFCL device is based on the so-called thermal-electrical analogy. The results show that SFCLs are reliable devices for maintaining fault current levels within typical equipment ratings of the FPSO power system.

Application of a Resistive Superconducting Fault Current Limiter in a Distribution Grid

This article presents a study on short-circuit current limiting using resistive superconducting fault current limiters, based on a melt cast processed BSCCO-2212. The application of the resistive superconducting fault current limiter was analyzed when installed downstream of a substation, protecting a distribution feeder. The studied power system is based on a dynamic model of the IEEE 13-node test feeder considering a power system expansion scenario, including renewable power generation. As a result of the power system expansion, fault current levels tend to increase, and the resistive superconducting fault current limiter device is used for fault current mitigation. The main contribution of this article is the performance assessment of superconducting fault current limiters and its effects on power quality due to different fault locations in the system and by accounting the complexity of the power system topology. Results obtained demonstrate that the system expansion does not significantly raise fault current levels. It also demonstrated that the resistive superconducting fault current limiter has a desirable operation zone, and unwanted power interruption may occur due to its operation outside this zone.

Status of Superconducting Fault Current Limiter in Italy: Final Results From the In-Field Testing Activity and Design of the 9 kV/15.6 MVA Device

Ricerca sul Sistema Energetico—RSE S.p.A. has recently accomplished a more than two-year-long in-field activity on the first Italian superconducting fault current limiter (SFCL). In order to carry out the in-field activity, a 9-kV/3.4-MVA SFCL device was installed as single feeder protection inside the Milan MV distribution grid; further to this first success, the development of a new device to be installed in the same substation, but as a transformer protection, has been already initiated. After having briefly summarized the final result of the in-field activity on the 9-kV/3.4-MVA device, this paper is mainly focused on the new 9-kV/15.6-MVA upgraded device: in particular, the first small-scale HTS winding prototypes will be described and the power tests implemented to validate their performances will be discussed. The test results allowed to identify the best layout, consisting in two parallel-connected coaxially arranged 2G windings, each made of two layers anti-inductively wound on a fiberglass cylinder, and each featuring a total 2G tape amount of 96 m. The actual research plan foresees to install the upgraded device in the live grid in 2016.

Current limiting impedance comparison between different designs of iron cores of the flux‐lock‐type superconducting fault current limiter

Fault current limiters are playing an ever more important role in today's power systems and many of their different types have now reached maturity. Owing to the progress in superconducting technology, the superconducting fault current limiter (SFCL) has attracted increasing attentions. To investigate the efficacy of SFCL devices from a system point of view, the fault current limiting impedance is of great importance. This study proposed an improved structure of flux-lock type of SFCL and compares the current limiting impedance of different layouts. It focuses on the impacts of iron core shape on primary winding inductance. The analyses include simulations based on finite element method carried out in the simulation software ANAlysis SYStem (ANSYS). This study shows that an E-E-shaped core with an air gap is better than a closed core when being used for an SFCL. It is also found that for an iron core SFCL with fixed size, its rated fault current limiting impedance can be adjusted by changing the cross-sectional area of the iron core centre leg and the length of the air gap.

Development and Test of a Small Resistive Fault Current Limiting Device Based on a SmBaCuO Ceramic

Since the development of Low Critical Temperature Superconducting (low-Tc) materials, various studies have been published regarding this experimental concept. Recently, researchers have focused on the design and application of high-Tc superconductor (high-Tc) materials to develop fault current limiting circuit breakers. The operation of this circuit requires large prospective/limited current ratios, especially in hazardous areas. In spite of this, several studies describing the Superconducting Fault Current Limiter (SFCL) containing members of the bismuth, mercury or yttrium family cuprate have already been described. However, none of these studies included samarium cuprates. Consequently, we have conducted a study of a small superconducting current limiter device based on SmBa2Cu3O7-d samples. The preliminary results indicated that samarium cuprates could be applied to build superconducting fault current limiter devices. In tests using a polycrystalline sample, the superconducting properties were retained without modifications to its stoichiometry. These results suggest the possibility of future investigations into SFCL devices based on these superconducting ceramics. Keywords: High-Tc, Sm-123, Device, Fault current limiter.

Development and test of a small resistive fault current limiting device based on Hg, Re-1223 and Sm-123 ceramics

Several reports describing Superconducting Fault Current Limiter (SFCL) containing members of the bismuth or yttrium ceramics were already described. However, none of these included the mercury and samarium cuprates. Consequently, we have conducted a study of a resistive-type superconductor fault current limiter based on Hg0.82Re0.18Ba2Ca2Cu3O8+d samples and SmBa2Cu3O7-d ceramics. All polycrystalline samples were prepared by solid-state reaction method using commercial oxide and carbonate powders. The superconducting ceramic with 2.4 × 2.6 × 6.0 mm³ dimensions was set up such that the electrical current flew through the area of 2.6 × 6.0 mm². All measurements were done at 77K and without applied magnetic field (Happ = 0). In the case mercury sample, the fault current of 16.1 Apeak was reduced to 8.1 Apeak by the superconducting element and sustained for 100 ms. The prospective/limited of current ratio observed in this experiment was ~ 2.0, as considered a 2.4 mm pellet thickness. When the test was realized with the samarium sample, the prospective/limited current ratio observed was approximately 1.2, for same ceramic thickness. The tests confirmed the capability of the resistive type SFCL to limit the fault current. These results open the possibility of future investigations into SFCL devices based on those superconducting ceramics in low power electronics and electrical motor.

The first Italian Superconducting Fault Current Limiter: Results of the field testing experience after one year operation

Ricerca sul Sistema Energetico S.p.A. (RSE) has been gaining a relevant experience in the simulation, design and installation of resistive-type Superconducting Fault Current Limiter (SFCL) devices for more than five years in the framework of a R&D national project funded by the Ricerca di Sistema (RdS). The most recent outcome of this research activity is the installation of a resistive-type BSCCO-based 9 kV / 3.4 MVA SFCL device in a single feeder branch of the Medium Voltage (MV) distribution network managed by A2A Reti Elettriche S.p.A (A2A) in the Milano area. This installation represents the first SFCL successfully installed in Italy. In this paper, we report on the main outcomes after a more than 1-year long steady-state field testing activity. The design of an upgraded device to be installed in the same substation has already been initiated: the new SFCL will allow to protect four different feeders, therefore implying a device upgrade up to 15.6 MVA.

Live-Grid Installation and Field Testing of the First Italian Superconducting Fault Current Limiter

Since 2009, Ricerca sul Sistema Energetico S.p.A. has been involved in the development of a resistive-type superconducting fault current limiter (SFCL) for MV applications to be installed in the A2A Reti Elettriche S.p.A. distribution grid in the Milan area. The project started with simulations, design, and testing activities for a single-phase device; this first step paved the way for developing, testing, and live-grid installation at the hosting utility site of the final three-phase SFCL prototype. The result of this research activity is a resistive-type 9 kV/3.4 MVA SFCL device, based on first-generation (1G) BSCCO tapes, nowadays permanently installed as a single-feeder fault protection. This device is the first SFCL successfully installed in Italy. In this paper, we report on installation of the three-phase device and field-testing activity. The next step of the R&D activity will consist in the design of a three-phase SFCL demonstrator 9 kV/15.6 MVA to be installed at the same substation in an incoming feeder to limit the contribution of this feeder to the total short-circuit current of the network. This application is very demanding in terms of SFCL reliability and availability, but also the most interesting one for the A2A hosting utility needs.

Development, Testing and Installation of a Superconducting Fault Current Limiter for Medium Voltage Distribution Networks

Since 2009 Ricerca sul Sistema Energetico (RSE S.p.A.) has been involved in the design of resistive-type Superconducting Fault Current Limiter (SFCL) for MV applications to be installed in the A2A Reti Elettriche S.p.A distribution grid in the Milano area. The project started with simulations, design and testing activities for a singlephase device; in this paper we report on the successive step, which is concerned with developing, testing and installation at the hosting utility of the final three-phase SFCL prototype. The result of this research activity is a resistive-type 9 kV/3.4 MVA SFCL device, based on first generation (1G) BSCCO tapes, developed by RSE in the framework of a R&D national project. Owing to the positive test results of partial discharge, dielectric and shortcircuit results the three-phase SFCL device is being to be installed in the A2A distribution grid in the Milano area and it is going to be soon energized starting a one-year long field-testing activity.

Fast insertion impedance of 2G HTS superconductors for megawatt AC and repetitive pulsed power operation

Within the past few years a newer, more robust type of superconductor known as 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> Generation (2G) High Temperature Superconductors (HTS) wire capable to operate in LN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> has become available in sufficient quantity and lengths for developers to build prototype devices and test their capabilities. 2G HTS made possible to reduce size, weight and volume of electrical apparatus in few orders of magnitude and provide a fast switching power and energy transitions with negligible impedance in superconducting stage and fast transitions impedances in resistive stage. This transition is typically called quenching and is useful for driving high impedance loads, limiting fault currents and developing large steep insertion impedances useful in many pulsed power applications. Electrical equipments made out of copper or aluminum typically shows high current transitions, inrush and short circuiting faults currents that can reach 100's of kA. There is a need for having repeatable fast insertion impedance to transform high current transitions, useful for impedance matching, stabilization, robustness of large current transients and proper dielectric operation in Megawatt installations. Development of Superconducting Fault Current Limiters (SFCLs) has been pursued for decades and has been limited thermally and/or mechanically by the available superconducting materials performance characteristics. However, this new 2G material has re-invigorated the worldwide race to develop a successful SFCL device that meets the stringent demands of Megawatt power equipment. SuperPower is pursuing the development of modular SFCL based on its proprietary 2G HTS wire and SFCL technologies. We will discuss testing and improvements made to optimize Recovery Under Load (RUL) performance. We also discuss high power tests and the influence of the different variables that have an important impact in RUL. A wide operating RUL window has been tested in order to define where RUL is feasible. We will show the manufacturing and latest tests and capabilities of sub-cooled of the SFCL device and modules designed for distribution and transmission lines. We show the advantages and superior performance of the new 2 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">nd</sup> Generation HTS superconductors under sub-cooled liquid nitrogen operation when used in SFCL.

Performance of 2G HTS Tapes in Sub-Cooled LN2 for Superconducting Fault Current Limiting Applications

Within the past few years a newer, more robust type of superconductor known as 2nd Generation High Temperature Superconductor (HTS) wire, has become available in sufficient quantity and lengths for developers to build prototype devices and test their capabilities. This new material offers the potential for revolutionary changes in superconducting transformers and Super conducting Fault Current Limiters to enable better thermal stability and fast quenching capabilities that can meet the stringent demands of large transient faults for distribution and transmission power lines. This manuscript discusses the manufacturing and latest tests and capabilities of sub-cooled superconducting fault current limiter device and modules designed for distribution and trans mission lines. We will also discuss the advantages and superior performance of the new 2nd Generation HTS superconductors under sub-cooled liquid nitrogen operation when used in super conducting fault current limiters. The feasibility demonstration and performance of sub-cooled SFCL superconducting modules for distribution and transmission SFCL devices will be discussed.

Superconducting fault current limiter application in a power-dense marine electrical system

Power-dense, low-voltage marine electrical systems have the potential for extremely high fault currents. Superconducting fault current limiters (SFCLs) have been of interest for many years and offer an effective method for reducing fault currents. This is very attractive in a marine vessel in terms of the benefits arising from reductions in switchgear rating (and consequently size, weight and cost) and damage at the point of fault. However, there are a number of issues that must be considered prior to installation of any SFCL device(s), particularly in the context of marine applications. Accordingly, this study analyses several such issues, including: location and resistance sizing of SFCLs; the potential effects of an SFCL on system voltage, power and frequency; and practical application issues such as the potential impact of transients such as transformer inrush. Simulations based upon an actual vessel are used to illustrate discussions and support assertions. It is shown that SFCLs, even with relatively small impedances, are highly effective at reducing prospective fault currents; the impact that higher resistance values has on fault current reduction and maintaining the system voltage for other non-faulted elements of the system is also presented and it is shown that higher resistance values are desirable in many cases. It is demonstrated that the exact nature of the SFCL application will depend significantly on the vessel&apos;s electrical topology, the fault current contribution of each of the generators, and the properties of the SFCL device, such as size, weight, critical current value and recovery time.

A superconducting fault current limiter integrated in the cold heat exchanger of athermoacoustic refrigerator

In this work we probe a compact superconducting fault current limiter (SFCL) integrated in the coldheat exchanger of a thermoacoustic refrigerator. A design for an SFCL device with a power of about2.2 kW is presented and described in detail. A thermoacoustic refrigerator isalso proposed which, under fault conditions, must be able to remove around50 Wat 80 K. A simulation routine is run to test the performance of the SFCL, based on YBCO films,in terms of both the limiting capacity and the energy to be dissipated and removed insidethe heat exchanger.

Superconducting fault current limiter device based on (Hg,Re)-1223 superconductor

A preliminary study of a small superconducting current limiter device based on Hg0.8Re0.2Ba2Ca2Cu3O8+δ, (Hg,Re)-1223 ceramic is described. A fault current test at 60Hz confirmed a reduction in the density of current value, from 1.55×102to0.82×102Apeak∕cm2. The prospective/limited density of current ratio observed was ∼1.9 for a 0.24cm thick sample, without any damage to the (Hg,Re)-1223 superconductor. A recovery test indicated that the polycrystalline sample kept its superconducting properties and had not shown modifications in its stoichiometry. In conclusion, (Hg,Re)-1223 can be used to build superconducting fault current limiter devices.

Resistive Fault Current Limiter Prototypes: Mechanical and Electrical Analyses

The problem of excessive short-circuit currents has become an important issue for power systems operators and there are clear indications for a growing interest in superconducting fault current limiter devices for MV and HV grids. In this work, we report on both simulation and electrical testing on single-phase SFCL prototypes developed in the framework of an Italian RTD project to be completed with a 3-phase SFCL unit by the end of 2005.

Simulations and Electrical Testing of Superconducting Fault Current Limiter Prototypes

The Superconducting Fault Current Limiter (SFCL) is a device of particular interest to electricity companies since it is aimed to maintain fault current levels on electricity networks to acceptable values, i.e. within electrical component design limits. The use of high temperature superconductors (HTS) allows the fabrication of effective SFCL devices with different configurations. In this work, we report on simulations and electrical testing of resistive-type SFCL prototypes. Short-circuit testing of several HTS windings has been carried out at CESI facility. Prospective symmetrical and asymmetrical fault currents 40 times larger than the nominal current value have been applied for 40-160 ms on single-phase devices. As a result, the prospective peak short-circuit current of 4,5 kA has been effectively reduced to 300 A-800 A depending of applied voltage. Time evolution of limited current, voltage across SFCL prototypes, dissipated energy and heating phenomena are reported and discussed.