Superconducting Fault Research Articles

Analysis of Transient Overvoltage in 220 kV Saturated Core HTS FCL

Saturated Core High Temperature Superconducting (HTS) Fault Current Limiter (FCL) is one kind of limiters that can work effectively on short-circuit current limitation. In this paper, an equivalent circuit model depending on ac coil of HTS FCL is built for voltage distribution analysis under transient overvoltage. The equivalent circuit components, such as the capacitances and inductances, are calculated by using finite element method. The voltage distribution and oscillation analysis of ac coil may benefit to the insulation design of HTS FCL.

Impact of Conductor Inhomogeneity on FCL Transient Performance

The superconducting (SC) fault current limiter (FCL) is a very effective tool to enhance the security and the power quality of electrical grids, two real demands today. This explains the great interest in it throughout the world. Only ReBaCuO coated conductor will be considered. The study of the constraints on the SC element is very important. The three phase clear short-circuit is a rather rare event and does not represent the most severe requirement for the SC element. Impedance faults or single-phase faults are more stringent. We have developed a model to represent the SC element in Matlab/Simulink through a resistance, which depends on the current and the conductor temperature. The temperature is the same across and along the conductor (isothermal block). The conductor is represented by two elements in parallel: the non-SC layers (substrate, shunt, ... ) and the ReBaCuO layer. This model has been validated on small FCL. Impedance short circuits have been investigated. Depending on the conductor, impedance faults may lead to a large temperature excursion for non-homogeneous I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> .

HTS-FCL EMTDC model considering nonlinear characteristics on fault current and temperature

One of the most serious problems of the KEPCO system is a higher fault current than the CB(Circuit breaker's SCC (Short Circuit Capacity). There are so many alternatives to reduce the higher fault current, such as the isolation of bus ties, enhancement of the CB's SCC, and the application of HVDC-BTB (Back to Back) or FCL (fault current limiter). However, these alternatives have drawbacks from the viewpoint of system stability and cost. As superconductivity technology has been developed, the resistive type (R-type) HTS-FCL (High Temperature Superconductor Fault Current Limiter) offers one of the important alternatives in terms of power loss and cost reduction in solving the fault current problem. To evaluate the accurate transient performance of R-type HTS-FCL, it is necessary for the dynamic simulation model to consider transient characteristics during the quenching and the recovery state. Against this background, this paper presents the new HTS-FCL EMTDC (Electro-Magnetic Transients including Direct Current) model considering the nonlinear characteristics on fault current and temperature.

Thermal behaviour of high-temperature superconducting fault current limiters: Application to microlimiters

Fault current limiters are one of the most promising applications of high-temperature superconductors. Two important and interrelated aspects of these devices are their thermal behaviour and their refrigeration. Here we will present some results of our recent researches about this topic concerning the possibility of using superconducting thin-film microbridges as very efficient microlimiters intended to operate at very low powers as could be superconducting microelectronics applications (SQUID based electronics, infrared detectors, etc.).

Discussion of Practical Applications of DC Breakers and 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 CO2 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, there is a possibility that this current cannot be interrupted by a circuit breaker alone. We propose that the fault current is 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.

션트리액터의 자기결합을 이용한 초전도전류제한기를 구성하는 초전도소자들의 전력부담 분석

The power burden of high-<TEX>$T_c$</TEX> superconducting (HTSC) elements comprising superconducting fault current limiter (SFCL) using magnetic coupling of shunt reactors was analyzed. The magnetically coupled shunt reactors play a role in distributing the even power burden between HTSC elements comprising the SFCL, which contributes to the effective current limiting and recovery characteristics of the SFCL. It was confirmed through the comparative analysis on the SFCLs with both the magnetically coupled and the magnetically uncoupled shunt reactors that the magnetically coupled shunt reactors could improve the SFCL's performance by equalizing the power burden of HTSC elements.

A YBCO-coated conductor for a fault current limiter: architecture influences and opticalstudy

YBaCuO-coated conductors (CC) are particularly interesting for the electric grid, especiallyfor superconducting (SC) fault current limiters (FCL). This innovative device should play animportant part in the future electric energy landscape. New network diagrams are indeedimagined with DC buses. The SC FCL would solve the delicate problem of DC faultcurrents. We have studied several YBaCuO-coated conductors with different architectures.A test bench for optical measurements has been developed to study the bubbledevelopment during limitation or over-current operation. The observations give usefulinformation about the quench initiation and its propagation. The images were recordedevery 0.2 ms (or less). Preliminary experiments have been carried out using a copper strip.Several operating temperatures have been investigated and important differences have beenobserved in some cases. The different YBaCuO CC studied show very differentbehaviours. Bubbles appear under the shape of strips across the tape or show ahomogeneous behaviour. These behaviours are correlated by electrical measurements.

Electrothermal Phenomena About Current Limitation With Coated Conductors

The superconducting (SC) fault current limiter (FCL) is very attractive to enhance the security and the power quality of the electricity grid, so its great interest throughout the world. Most of SC FCL uses the quench of a SC element and the thermal phenomena are fundamental. We study them with two approaches: experiments and calculations. For the experiments, we have developed temperature sensors deposited directly on coated conductors to achieve the best thermal coupling and a very short time response. The sensors are micron size copper meanders. A very thin polymer layer provides the electrical isolation. The sensor performances are very satisfying both in terms of time response and accuracy. The measurements are in good agreement with temperature calculations, performed using the current data during limiting experiments. The recovery phase is very important and has been studied using the temperature measurements. The cooling conditions such as bath temperature play an important part for the recovery. Several tests carried out on different samples are presented and analysed. These works are important for a better understanding of the complex phenomena occurring during a limitation and for the design of a conductor suitable for FCL.

Methods to Increase Current Capacity of Superconducting Thin-Film Fault Current Limiter Using Au-Ag Alloy Shunt Layers

We have proposed a superconducting thin-film fault current limiter (FCL) that uses high-resistivity Au-Ag alloy shunt layers for the protection against ldquohot spotsrdquo. Its design enables reduction of the total length of FCL elements that can withstand high electric fields E > 40 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">peak</sub> /cm, thus greatly reducing the cost of FCLs. In this paper, two methods to increase current capacity of the FCLs were demonstrated. The first method protects the films from hot spots by using capacitors in addition to external resistors. The capacitors decrease rapid voltage rise in the films at the moment of quenching. The second method maximizes the rated current of two parallel-connected thin films by using parallel connections via superconducting tapes, even if the critical currents of these films are largely different. We then successfully tested two parallel-connected YBCO films prepared by a low-cost, metal organic deposition (MOD) method. Over-current tests showed that (a) superconducting transport currents up to 380 A <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">peak</sub> flowed 5 cycles without quenching, which is more than 1.3 times larger than the peak value of the 200 A <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub> rated current and (b) after switching, E = 45.7 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">peak</sub> /cm was achieved without film degradation.

Manufacturing and Test of a 35 kV/90 MVA Saturated Iron-Core Type Superconductive Fault Current Limiter for Live-Grid Operation

We developed a saturated iron-core type 35 kV/90 MVA superconductive fault current limiter and installed the device in a transmission network at Puji substation of China Southern Power Grid for live-grid operation. Innovative design in the iron-core configuration ensures that the device has low impedance in normal power transmission and sufficiently high impedance for a fault current limiting action. A magnetization control circuit allows the iron-core to be saturated or de-saturated depending upon the functional requirements. An energy release and voltage-surge protection unit can promptly discharge the magnetic energy accumulated in the iron-core and suppress the induced and surge voltages of the dc circuit in a current limiting event. This device has been designed to reduce the magnitude of a fault current by about 50%, which will prevent the breaking capacity of the existing circuit breakers in the transmission network from being exceeded in the predictable future. This article presents structural and functional specifications and reports up-to-date live-grid operation data of the device.

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.

The Application of Active Superconducting DC Fault Current Limiter in Hybrid AC/DC Power Supply Systems

This paper presents a new topology of the active superconducting DC fault current limiter (DC-SFCL) applied in the hybrid AC/DC power supply systems. The proposed DC-SFCL is composed of superconducting transformer, DC chopper and voltage source converter (VSC). The primary winding of the transformer is connected in series with DC transmission line, and the second winding is connected with AC power system through the VSC and the DC chopper. The active DC-SFCL can suppress the fault current of DC system through power exchange between the DC and the AC system. Moreover, the DC-SFCL can act as an active power filter for both the DC system and the AC system to solve the problem of power quality. Using MATLAB SIMULINK, the simulation model of the hybrid AC/DC power supply systems with the proposed DC-SFCL is created. Simulation results validate the dynamics of system, and the performance of the active DC-SFCL is confirmed.

Development of a 13.2 kV/630 A (8.3 MVA) High Temperature Superconducting Fault Current Limiter

This paper deals with fabrication and development of a high temperature superconducting (HTS) fault current limiter (FCL) based on YBCO coated conductor (CC) wire for distribution systems. The capacity of the developed HTS FCL is 8.3 MVA and its rated voltage is 13.2 kV which corresponds to a three-phase power equipment voltage class of 22.9 kV. Tests of the developed prototype HTS FCL were conducted at Korea Electrotechnology Research Institute (KERI) accredited as a testing laboratory by the Korea Laboratory Accreditation Scheme (KOLAS). A short-circuit test and an AC dielectric withstand voltage test for the HTS FCL were conducted under sub-cooled liquid nitrogen (LN2 ) conditions of 3 bar and 65 K. The magnitude of an asymmetric short- circuit current without FCL reached 30 kApeak in a short-circuit test. The superconducting coil quenched instantaneously after the fault, and the magnitude of the fault current was limited to 3.6 kApeak within quarter cycle by the developed resistance of the superconducting coil. An AC dielectric withstand voltage test was performed, and the HTS FCL successfully withstood 143 kV for 1 minute. Also, it was found that there was no electrical or mechanical damage on the superconducting coil after the tests.

Quench Characteristics of High Temperature Superconducting Coil for Fault Current Limiting Application

Hyundai Heavy Industries Co., Ltd. (HHI) has developed a prototype of high temperature superconducting (HTS) fault current limiter (FCL) in Dec. 2006. The ratings of the HTS FCL were 13.2 kV in voltage and 630 A in current at normal condition. This HTS FCL had a HTS coil composed of 7 concentric HTS windings for current limiting element which are wound by using unique bifilar method with YBCO coated conductor (CC). The CC wound on the bobbin was insulated with Kapton tape and the HTS coil was completed assembling the windings using copper connection parts. The HTS coil was cooled down to 65 K for the enhancement of cryo-dielectric performance and critical current capacity. The short-circuit test was performed with the asymmetrical prospective fault current of 10 kA. The resistance of HTS coil began to rise up from 0.624 ms after the fault. At about 1/4 cycle after the fault, the temperature of HTS coil exceeded its critical temperature. The resistance and temperature of HTS coil after 0.1 s from the fault was calculated to be about 11.8 Omega and 250 K respectively which was designed to be about 13 Omega and 300 K.

Optimal design of superconducting fault detector for superconductor triggered fault current limiters

We have designed and tested a superconducting fault detector (SFD) for a 22.9 kV superconductor triggered fault current limiters (STFCLs) using Au/YBCO thin films. The SFD is to detect a fault and commutate the current from the primary path to the secondary path of the STFCL. First, quench characteristics of the Au/YBCO thin films were investigated for various faults having different fault duration. The rated voltage of the Au/YBCO thin films was determined from the results, considering the stability of the Au/YBCO elements. Second, the recovery time to superconductivity after quench was measured in each fault case. In addition, the dependence of the recovery characteristics on numbers and dimension of Au/YBCO elements were investigated. Based on the results, a SFD was designed, fabricated and tested. The SFD successfully detected a fault current and carried out the line commutation. Its recovery time was confirmed to be less than 0.5 s, satisfying the reclosing scheme in the Korea Electric Power Corporation (KEPCO)’s power grid.

The Effect of Sectioning on Superconducting Fault Current Limiter Operation

Various types of fault currents limiters have been proposed to reduce the fault currents in power transmission lines. The transformer type superconducting (SC) fault current limiter is one of them and has many advantages such as design flexibility. In normal operation mode the impedance is that of short-circuit transformer and has its minimum value. In the event of a load to fault an increase of the primary winding current causing a subsequent current increasing in the secondary SC winding (ring) and its quenching to the normal state. In this case the impedance turns to one in a no-load operation mode, i.e. is maximal performing the fault current limitation in the circuit to be protected. There has been investigated an effect of this sectioning of short-circuit SC windings or rings on the operation. A configuration of the transformer with symmetrical alternatively positioned disc windings is shown to be the optimal.

Electrical Insulation Design of 13.2 kV/630 A Bifilar Winding Type HTS Fault Current Limiter

In this study, electrical insulation design for the development of 13.2 kV/630 A bifilar winding type high temperature superconducting (HTS) fault current limiter (FCL) with YBCO coated conductor (CC) wire was conducted. At first, operating conditions of the temperature and the pressure were determined considering the effects of bubble suppression and breakdown withstand voltage in quench state. The electrical insulation design for HTS coil was performed based on electric field calculation under normal and quench states. Furthermore, new concept of cryostat which is beneficial to the sub-cooling and the electrical insulation was proposed. Finally, two high voltage lead designs were evaluated taking into account the insulation environment of the HTS FCL and the new cryostat design.

Analysis of Unsymmetrical Faults in High Voltage Power Systems With Superconducting Fault Current Limiters

An analysis of unsymmetrical faults for a 110 kV sub-grid coupling with a superconducting fault current limiter is conducted in this contribution. For the design of the super-conducting fault current limiters it is essential to identify the highest possible voltage during the limitation process. As reference the symmetric three phase fault which generally leads to the highest short-circuit currents is used. Unsymmetrical faults like single line-to-ground fault, line-to-line fault and double line-to-ground fault are investigated in dependence of the superconducting fault current limiter impedance. The analysis shows that the double line-to-ground fault leads to the highest voltage drop during the limitation in the relevant range of impedance. Consequently, this fault is a crucial factor for the design of the superconducting fault current limiter.

${\rm MgB}_{2}$ Sample Tests for Possible Applications of Superconducting Fault Current Limiters

Cheap to make and easy to shape, Magnesium Di-boride (MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) throws the field of applied superconductivity wide open. Great efforts have been made to develop a superconducting fault current limiter (SFCL) using MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . With a superconducting transition temperature of 39 K, MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> can be conveniently cooled with commercial cryocoolers. A cryogenic desktop test system, an ac pulse generation system and a real time data acquisition program in LabView/DAQmx were developed to investigate the quench behavior of MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> wires under pulse overcurrents at 25 K in self-field conditions. The experimental results on the current limitation behavior show the possibilities for using MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> for future SFCL applications.

Study on the Effect of Fault Current Limiter in Power System With Dispersed Generators

Dispersed generators are being introduced to power systems to secure the electric power supply. However, a short-circuit capacity of the power system increases with the introduction of dispersed generators. As a result, there is concern that a fault current will increase further, and instantaneous voltage sag might be caused. It is proposed to apply a superconducting fault current limiter in the distribution system with dispersed generators to solve these issues. In this paper, the effect of superconducting fault current limiter in this power system is studied by the analysis with EMTP and the confirmation test is conducted with a simulator.