Kurzschlussstrom-Begrenzung mittels Bi2212-Hochtemperatur-Supraleitern — Stand der Forschung

Limiting fault currents by means of superconducting current limiters has been topic of intensive international research for many years. Superconducting current limiters make use of the super-conducter’s transition from superconducting to normal conducting state, and therefore it works like a nonlinear resistance. Due to its intrinsic physical proterties the superconducting current limiter comes close to an ideal limiter.     

Operation of hybrid current limiter based on high-Tcsuperconducting thin film

A high-Tc superconducting (HTSC) thin film with an inductive shunt was investigated as the model of a hybrid current limiter based on the superconducting-normal state transition. In addition to features previously observed in operation of other current limiters, sharp peaks of rather high frequency were found to appear on the background of a basic low-frequency voltage signal. This is attributed to self-oscillations of temperature and current in the superconductor. The influence of the frequency and magnitude of the circuit current on the character of self-oscillations was experimentally investigated. Qualitative analysis of the conditions for appearance of the self-oscillations under dc and ac conditions was carried out     

Switching properties of a hybrid type superconducting fault currentlimiter using YBCO stripes

Presents investigations of a hybrid type superconducting fault current limiter (SFCL), which consists of transformers and resistive superconducting switches. The secondary windings of the transformer were separated into several electrically isolated circuits and linked inductively with each other by mutual flux, each of which has a superconducting current limiting unit of YBa₂Cu₃O ₇ (YBCO) stripes as a switch. Simple connection in series of the SFCL switches tends to produce ill-timed switching because of power dissipation imbalance between SFCL units. Both electrical isolation and mutual flux linkage of the switches provides a solution to power dissipation imbalance, inducing simultaneous switching by independent quenches and current redistribution of the YBCO films. This design enables increase of voltage ratings of SFCL with given YBCO stripes     

Superconducting control for surge currents

Systems designed to use superconductors to limit fault currents in power grids are undergoing testing. The authors describe superconducting fault current limiters (SCFCL) which may be categorised into resistive or shielded core types. The features and operation of each type of device are outlined. Both the shielded-core and resistive types of SCFCL use the same amount of superconductor material to achieve a given limitation behavior. This is because the rated power per volume of conductor is determined by the product of fault-induced field and critical current, which is the same for both devices, assuming the same type of superconducting material is employed. The shielded-core limiter works only with AC currents and is much larger and heavier than the resistive SCFCL. While there is only one large program left in the low-temperature type of SCFCL, more than 10 major projects are under way worldwide on the high-temperature type of device. The main reason is the lower HTS cooling cost     

Testing of an inductive current-limiting device based on high-Tc superconductors

An inductive current-limiting device (CLD) based on transition of a superconductor to the normal state is investigated. The device has low impedance under normal conditions of the circuit to be protected, and a high impedance developed rapidly in a self-switching mode under fault conditions. A model of the device consisting of a copper coil and a high-temperature superconducting ring, coupled magnetically, was tested. It is shown that the transition of the ring to the normal state and its return to the superconducting state take place in a relatively smooth manner, and do not lead to overvoltages across circuit elements. On the other hand, the rate of impedance rise is sufficient to limit both the steady-state and transient components of fault current. The influence of thermal processes in the ring on transient responses in the circuit with the CLD is discussed. Some considerations for a full a size design are also presented     

超欧姆型热库环境下互感效应对磁通量子比特退相干的影响

在二能级近似下运用Bloch-Redfield方程,研究了超导量子电路中的磁通量子比特退相干在超欧姆热库环境下受互感效应的影响。研究结果表明：（1）在超欧姆热库环境下,提高环境指标系数有利于延长超导磁通量子比特的退相干时间;（2）构建超欧姆型热库环境可以改进固态量子比特的退相干;（3）电感元件间的互感耦合对量子电路系统退相干的影响是比较复杂的,调控好电感元件间的互感耦合有利于提高退相干时间。     

Superconducting FCL: design and application

Design, parameters, and application areas of a superconducting fault current limiter (FCL) are analyzed on the basis of the requirements of power systems. The comparison of resistive and inductive designs is carried out. An example of the effective application of FCLs in distribution substations is considered and the gain from the FCL installation is discussed. It is shown that an FCL not only limits a fault current but also increases the dynamic stability of the synchronous operation of electric machines. The calculation procedure of the parameters of an inductive FCL for a specific application case is described.     

Limitation of DC currents by YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//-Au superconducting films

The limitation of dc fault currents is one of the issues for the development of dc networks or links. This paper shows for the first time the high potential of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//-Au bilayers for the design of dc current limiters. Such devices are based on the transition into the normal state of the superconducting YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// films above a current I/sup */>I/sub c/, where I/sub c/ is the critical current at the onset of dissipation. The study of the transition under current pulses shows that a thermally driven transition into the normal state can occur after a delay t/sub trans/. This duration is defined by the amplitude of the current pulse. For I/sup *//spl ap/3I/sub c/, this delay is less than 10 /spl mu/s. The abrupt transition into the normal state allows an efficient current limitation. A recovery of the superconducting state can also occur under current. This property can be extremely interesting for autonomous operation of a current limiter in an electrical network in case of transient over-currents coming from the starting of high-power devices.     

Surge protection for power grids

The new high temperature superconductors are well-suited for fault-current limiters, thanks to stable thermal properties and high operating temperatures. This article surveys efforts worldwide to develop a commercially viable superconducting fault-current limiter, but particularly focuses on one project, with which the author is associated, which developed a 2.4 kW, 3 kA prototype     

A novel energy efficient SFCL with a silver-free contact switchgear for application in electricity and transportation

A novel concept of a switchgear based on the combination of an AC superconducting fault current limiter (SFCL) and silver-free electrical contacts is proposed. In the combined system SFCL+switchgear, it is possible to employ cheaper materials for electrical contacts. The SFCL device includes inductive coupling of high-T/sub c/ superconducting active elements, in the form of layered flat rings of a Bi/sub 1.8/Pb/sub 0.3/Sr/sub 1.9/Ca/sub 2/Cu/sub 3/O/sub x/ compound, prepared by a solid-state reaction technique. Experimental results obtained by testing a prototype SFCL in short circuit regime at AC 50 Hz under quasistationary conditions are presented. The use of the superconducting rings enables a wide range variation of the dissipated power. Copper/diamond composites, prepared by explosive synthesis, are employed as contact materials for the switchgear. The addition of particles (<1 /spl mu/m) leads to improved mechanical characteristics and increased stability of the composite materials. The combination of switchgear with silver-free electrical contacts and SFCL allows a short circuit regime to withstand the switchgear and provides increased system reliability.     

Inductive Superconducting Fault Current Limiters With Y123 Thin-Film Washers Versus Bi2223 Bulk Rings as Secondaries

We present the comparison between the performance of an inductive superconducting fault current limiter operating with bulk$hboxBi_1.8hboxPb_0.26hboxSr_2hboxCa_2hboxCu_3hboxO_10+x$rings or$hboxY_1hboxBa_2hboxCu_3hboxO_7-delta$thin-film washers as secondaries. We have measured the impedance offered by the limiter under current faults and the recovery time once the faults are cleared. Our results show that the use of thin films can improve the impedance response of these devices and especially their recovery time, which can be about two orders of magnitude shorter than that of bulk samples.     

Fabrication of HTS dc Bias Coil for 35kV/90MVA SFCL

For a saturated iron core fault current limiter, superconductor is the only suitable material to make the dc bias coil, especially when the device is used in a high voltage power grid. Commonly, superconducting wires are used to wind the dc bias coil. Since the performance of the wires changes greatly under magnetic fields, the calculation of the field spatial distraction is essential to the optimization of the superconducting magnet. A superconducting coil with 141000 ampere-turns magnetizing capacity made of 17600 meters of BSCCO 2223 HTS tapes was fabricated. This coil was built for a 35kV/90MVA saturated iron-core fault current limiter. Computer simulations on magnetic field distribution were carried out to optimize the structural design, and experiments were done to verify the performance of the coil. The configuration and the key parameters of the coil will be reported in this paper.     

Cap that current [superconducting fault current limiters]

Superconducting fault-current limiters could transform the architecture and operation of electrical power networks. The authors outline the design principles and performance of a prototype device developed under the UK's LINK programme. The programme was organised in two stages, with stage one represented by a 400 V, 180 A 'bench top' demonstrator and stage two a 'full scale' prototype capable of operating at 11 kV carrying 400 A normal current and, most importantly of limiting a prospective 13.1 kA (250 MVA) fault to around 4.5 kA. Stage one was completed and tested successfully in August 1998, and stage two subjected to short-circuit tests in November 1999. Development work is now underway at the Reyrolle site of VA TECH T&D, with the object of delivering a full-scale three-phase high-temperature superconducting FCL for field trials in partnership with a major UK utility     

Improvement on current limiting performance of current limitingdevices with damping coils

An improved model of the current limiting devices such as the high-Tc superconducting fault current limiter (SFCL) and the reactor have been developed. The high-Tc SFCL mainly consists of the primary copper coil, the secondary high-Tc superconducting rings, and the damping coils, which are magnetically coupled through a three-legged magnetic core. Because a portion of the magnetic flux above the saturation point generated by the fault current is cancelled by the damping coil, thereby the magnetic core is prevented from getting into the saturated state. The limiting current level and the saturation of the core could be controlled by the air-gap length of the central leg with the damping coil. A new design of the SFCL is found to increase the effective impedance by about 60 to 70%, compared to the SFCL design without the damping coils     

Frequency-Selective Limiters and Their Application

The frequency-selective limiter is presented as an adaptive filter system element. The operating mechanisms of various types of frequency-selective limiters are described and classified. The transient response, small-signal suppression, and intermodulation characteristics are presented for comparison. The application of frequency-selective limiters in particular EMI situations is discussed, and required device parameters are shown to depend on the application.     

Applications of DC Breakers and Concepts for Superconducting Fault-Current Limiter for a DC Distribution Network

Many alternative energy power generation systems create dc electricity. Also, many devices consume dc converted from ac. Therefore, it may be possible to reduce conversion losses and $hbox{CO}_{2}$ emissions by adopting dc distribution. We assume that superconducting cables will be used for dc distribution because their electrical resistance is almost zero. However, if a superconducting cable is adopted, it is of great concern that if an excessive current flows because of, for instance, a short circuit, then there is a possibility that this current cannot be interrupted by a circuit breaker alone. We propose that the fault current be limited by a superconducting fault-current limiter (SFCL) and that this limited current is then interrupted by a dc circuit breaker. In this paper, we have separately investigated the SFCL and dc breaker and their use in combination.      

The analysis of the fault currents according to core saturation andfault angles in an inductive high-Tc superconducting fault currentlimiter

In this paper, we investigate the fault currents in an inductive high-Tc superconducting fault current limiter (SFCL). The currents can cause serious damage to the reliability and stability of the power system. To analyze the transient fault characteristics of the SFCL, we fabricated an inductive high-Tc SFCL and tested it under different fault conditions. To simulate a fault condition, a fault angle controller was connected to a load. As the firing angle of the triac in the fault angle controller was controlled, various angles of the fault instant can be selected. An important parameter for the design and the fabrication of the SFCL is the reduction of the fault currents. If abnormally high currents due to low impedance of SFCL do not occur in the network with SFCL, the currents flowing under fault conditions can be limited to a desired value within one cycle. The fault current reduction depends on saturation, normal zone propagation velocity, turns ratio, and the fault angle (the instant of the fault occurrence within a cycle)     

Fabrication of HTS dc Bias Coil for 35 kV/90 MVA SFCL

Abstract---For a saturated iron core fault current limiter, superconductor is the only suitable material to make the dc bias coil, especially when the device is used in a high voltage power grid. Commonly, superconducting wires are used to wind the dc bias coil Since the performance of the wires changes greatly under magnetic fields, the calculation of the field spatial distraction is essential to the optimization of the superconducting magnet. A superconducting coil with 141000 ampere-turns magnetizing capacity made of 17600 meters of BSCCO 2223 HTS tapes was fabricated. This coil was built for a 35 kV/90 MVA saturated iron-core fault current limiter. Computer simulations on magnetic field distribution were carried out to optimize the structural design, and experiments were done to verify the performance of the coil The configuration and the key parameters of the coil will be reported in this paper.     

Operational characteristics of a flux-lock-type high-T/sub c/ superconducting fault current limiter with a tap changer

The authors investigate the operational characteristics of a flux-lock-type high-T/sub c/ superconducting (HTSC) fault current limiter (SFCL) with a tap changer which could adjust the number of turns of the third winding. In the case of conventional flux-lock-type SFCL, the phase adjusting capacitor is connected in series with magnetic field coil to adjust the magnetic field applied to the HTSC element in phase with the current flowing through the HTSC element during a fault time. However, the current flowing at the third winding, which is connected with magnetic field coil, affects the fault current limiting characteristics. To analyze the influence of current flowing at the third winding on the fault current limiting characteristics, the fault current limiting characteristics of the flux-lock type SFCL, whose inductance of coil 3 could be adjustable through a tap changer, are investigated through the experiments and the computer-aided simulations. The relation of line currents flowing into the flux-lock-type SFCL during a fault time and numbers of turns of a tap changer is drawn.