Current-limiting Performance Research Articles

Study on Initial Current-Limiting Performance of the Resistive-Type SFCL Element According to the Electrical Coupling Condition With Cores and Coils

This paper was conducted to widen the use of the YBCO-coated conductor's superconducting current-limiting element under the electrical coupling condition with cores and coils. Using cores and coils, diverse winding directions and turn ratios were available, and the initial operating performance of the superconducting current-limiting element could be improved. In this paper, three kinds of YBCO-coated conductors with stabilization layers that had different specific resistivity values were used to fabricate superconducting current-limiting elements, and an electrical coupling condition, which did not produce resistance in the normal operating condition when it was combined with the superconducting current-limiting elements, was presented. After the superconducting current-limiting elements were combined with the electrical coupling condition, an overcurrent was applied, and the initial operation performance was examined. The initial operation performance indicators were the current-limiting rate, response time, and steep slope of the initial current-limiting curve. The current-limiting rate was excellent when the specific resistivity of the superconducting current-limiting element was high and when it was combined with the electrical coupling condition to increase the equivalent impedance. However, when the specific resistivity of the YBCO-coated conductors to the superconducting current-limiting elements was too low, the electrical coupling condition did not work properly. The response time and steep slope of the current-limiting curve characteristics showed that they did not depend on the specific resistivity of the superconducting current-limiting elements when the equivalent impedance of the electrical coupling condition was higher than the resistance of the superconducting current-limiting elements.

Study on Improvement of the Stability for the Superconducting Current-Limiting Element Using Cores and Coils

The stability test is one important test of the viability of using YBCO-coated conductors as superconducting current-limiting elements apart from the current-limiting capacity test. A decrease in stability will degrade the current-limiting performance of the current-limiting element and eventually damage the element. In this paper, a method of ensuring the stability of the superconducting current-limiting elements, which are made using YBCO-coated conductors, and the results of the method analysis are presented. The method of ensuring stability was applied to obtain the results using the relationship between the superconducting current-limiting element and the electrical coupling condition. The condition was a parallel connection of the superconducting current-limiting element to the secondary coil. With this method, superconducting current elements can be tested in a stable condition. In addition, the winding direction (the additive/subtractive polarity) can be changed, and diverse test conditions can be provided by adjusting the number of turns of the secondary coil. The additive and subtractive windings were used in the test with 3 : 1 and 3 : 2 primary-to-secondary turn ratios, and the test period was set at 5.5 cycles to correspond to the breaker operation time. The applied voltage and current were determined considering the minimum voltage level of the YBCO-coated conductor. The test results showed that with the additive polarity winding, the superconducting current-limiting element was thermally stable regardless of the turn ratio and the specific resistivity characteristic of the YBCO-coated conductor.

Design of Band Engineered HgCdTe nBn Detectors for MWIR and LWIR Applications

In this paper, we present a theoretical study of mercury cadmium telluride (HgCdTe)-based unipolar n-type/barrier/n-type (nBn) infrared (IR) detector structures for midwave IR and longwave IR spectral bands. To achieve the ultimate performance of nBn detectors, a bandgap engineering method is proposed to remove the undesirable valence band discontinuity that is currently limiting the performance of conventional HgCdTe nBn detectors. Our proposed band engineering method relies on simultaneous grading of the barrier composition and doping density profiles, leading to efficient elimination of the valence band discontinuity. This allows the detector to operate at |V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">bias</sub> | <;50 mV, rendering all tunneling-related dark current components insignificant and allowing the detector to achieve the maximum possible diffusion current limited performance.

Performance Modeling of Bandgap Engineered HgCdTe-Based nBn Infrared Detectors

In this paper, we present a theoretical study of a band engineered detector design, which significantly improves the performance of mercury cadmium telluride (HgCdTe)-based unipolar n-type/barrier/n-type (nBn) infrared (IR) detectors for the midwave IR and longwave IR spectral bands. This band engineered nBn detector is based on the assumption that the valence band offset, which is normally present between the barrier and n-type absorber layer, can be eliminated using a bandgap engineering approach. The valence offset is the key issue that currently limits the performance of HgCdTe-based nBn detectors. Eliminating the valence band offset allows the nBn detectors to operate at |V Bias | <; 50 mV, thus rendering insignificant all tunneling-related dark current components and allowing the detector to achieve the maximum possible diffusion current limited performance. The developed model allows the device performance to be optimized by an appropriate design of the conduction band barrier to block the flow of majority carrier electrons, while allowing minority carrier holes photogenerated in the absorber layer to reach the contact layer unimpeded. Furthermore, because of the absence of tunneling-related dark currents, it is shown that band engineered nBn detector architecture exhibits a better performance at maximum allowed absorber layer doping density compared with conventional nBn detector.

Evaluation of the Current-Limiting Properties for a Superconducting Current-Limiting Element With the Winding Direction of the Reactor of the Second Coil

The 2Generation (2G) high-temperature superconductivity (HTS) coated conductor has such advantages in the manufacture of current-limiting devices as fast phase transition, high critical current density, small degradation of critical characteristics under mechanical deformation, and lower cost of the manufacture of the superconducting current-limiting element due to its lower material cost compared to that of the Y-Ba-Cu-O (YBCO) thin film and the Bi-Sr-Ca-Cu-O (BSCCO) wire and bulk. However, in a resistive-type superconducting fault current limiter that was manufactured with a current-limiting device produced with a 2G HTS coated conductor, the dimensions of the current-limiting device will be larger than those of other devices (e.g., a YBCO thin film and a BSCCO bulk) due to the physical characteristics of the 2G HTS coated conductor. Moreover, application of such resistive-type superconducting fault current limiter to an actual power system will produce high cooling expenses. Therefore, in this study, the electric-coupling condition for the reduction of the size of the superconducting current-limiting element was presented, a superconducting current-limiting element was manufactured using a 2G HTS coated conductor with a stainless-steel stabilization layer, and the manufactured superconducting current-limiting element was applied to the electric-coupling condition to evaluate its stability and current-limiting performance under such condition. The electric-coupling condition that was presented in this paper is the series connection of the primary coil (N1) and the secondary coil (N2), and the parallel connection of the secondary coil and the superconductive element.

Effect on Current-Limiting Performance of Combining Condition YBCO Thin-Film Wire Having Different Stabilization Layer With Superconducting Fault Current Limiter Using Iron Core and Coils

This study examined the effects of the turn ratio and direction of two serially connected coils on the current-limiting performance of YBCO thin-film wires with different stabilization layers. Three YBCO thin-film wires with different stabilization layers were used to manufacture current-limiting elements, and their current-limiting performance was evaluated. The test equipment that consisted of two serially connected coils was connected to the current-limiting superconducting elements that were manufactured with YBCO thin-film wires. Finally, the current-limiting characteristic of each current-limiting element and its operation as a superconducting fault current limiter (SFCL) were examined after the turn ratio and direction of the two coils were varied. The current-limiting characteristic of the current-limiting element and its operation as a SFCL were verified the resistance generation tendency, current-limiting ratio, and response time as indicator.

Experimental Research and Analysis of a Novel Liquid Metal Fault Current Limiter

This paper deals with the experimental research on a novel current limiter, which mainly takes advantage of the gas pressure in the liquid metal when arcing. A novel current-limiting principle is put forward on account of the pressure measurement results within an experimental device. According to this principle, a U-shape sliding part is designed and pushed upward under the gas pressure, which subsequently squeezes the arc into a narrow slot. Furthermore, a specially designed setup is employed to observe the moving process of the sliding part along with the arc behavior. It can be classified into three dynamic stages according to the frames obtained by a high-speed camera. The average velocity of the sliding part can reach about 11 m/s. Finally the influences on the current-limiting performance with the novel improved setup are explored and determined. It demonstrates that this novel method can enhance the current-limiting efficiency to some extent.

Evaluation on Current-Limiting Performance With the Fault Type of the 3-Phase Resistive Type SFCLs

Ground fault accounts for 70 to 80% of accidents in power systems. Failure to prevent ground fault at an early stage could lead to damage on other power equipment through the generation of abnormal voltages in the nominal lines. Therefore, it is very important to prevent ground fault at an early stage. This study performed the application tests of the fault currents for ground faults caused by the single-line-to-ground, double-line-to-ground, or triple-line-to-ground according to the fault types to develop the superconducting current-limiting elements and to evaluate the current-limiting capabilities. From the results, the current-limiting characteristics by the ground fault types were determined by the difference between the level of the fault current, which was applied at the fault point of R-phase 0° defined as the fault standard in the test, and the time of the quenching initiation of each phase.

Effect of the Resistance of Two Different Coated Conductor on the Current-Limiting Performance of Flux-Lock Type Superconducting Fault Current Limiters

The recent increase in power demand has been pressuring industries to continuously extend or expand power sources and transmission and transformer systems. On the other hand, the equivalent impedance of power systems is decreasing. Accordingly, the fault current magnitude in power systems is increasing. Because of such developments, and the rising need to counter this trend, current-limiting technology has been getting much attention as it can efficiently limit the short-circuit faults and improve power system reliability. For this purpose, studies are being carried out on the superconducting fault current limiter (SFCL). In particular, studies on SFCL where normal-conducting devices are combined, instead of the resistor-type SFCL that depends only on the superconductor, are being continued. The development of the element that is suitable for the superconducting fault current limiter combined with the normal-conducting device is also underway. In this study, YBCO thin-film wires that have and do not have a stainless steel stabilizer layer, which is recently studied as the superconducting current-limiting element, were used as superconducting elements of the flux-lock and transformer-shape SFCL consisting of normal-conducting core and coil. The effect of the difference between the resistance values of the two elements on the current-limiting performance of the flux-lock and trans former-shape current limiter was evaluated. For this purpose, the resistance values trend of the two superconducting elements was examined. The initial operational characteristics were compared in terms of quenching time (I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ini</sub> , I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Imi</sub> , and T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> ) and stability (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> ).

Evaluation on current-limiting performance of the YBCO thin-film wire considering electric coupling condition

The basic way to improve the performance of a superconducting current limiter is to apply and evaluate a superconducting device that is appropriate to the superconducting current limiter. Among the many types of superconducting devices, the YBCO thin film wire has excellent current-limiting performance that is appropriate for actual system application. For the application of the YBCO thin film wire to superconducting current limiters, its current-limiting performance as a unit device must be accurately evaluated, and measures to improve its current-limiting performance must be sought. Accordingly, to evaluate the current-limiting performance of the YBCO thin film wire, this study was conducted to evaluate its resistance-increasing trend, Vmax, Tr, Imax, Iqt, and current-limiting rate as a unit device, after which the electric coupling condition that consists of a core and windings was used to evaluate the current-limiting performance of the YBCO thin film wire.

Experiment and Simulation Research on the Influence of Different Main Contact System on the Interruption Performance of Control and Protective Switch

Research on the interruption process of control and protective switch devices (CPS) is helpful for improving its current-limiting performance. Three different structures of the main contact system are proposed and experimentally investigated on their influence on CPS's interruption performance first. Then, a calculation model that enables us to simulate the interruption process of a low-voltage apparatus with a complex mechanical structure is realized by carrying out the second development of ADAMS, in which a set of differential equations describing the coupling of complex mechanical movements, electric circuits, magnetic fields, and dynamic mathematic arc models is constructed. With this model, further investigations on the interruption process, arc movement, and arc characteristic variation of CPS with the three main contact systems are carried out. The improvement mechanism of the current-limiting performance of CPS using an arc run-on plate is especially analyzed with the calculation model.

Current Limiting Characteristics of a Novel Flux-Coupling Type Superconducting Fault Current Limiter

A novel flux-coupling type superconducting fault current limiter (SFCL) is proposed in this paper. This type SFCL is composed of two superconducting coupling coils, a controlled switch and two metal oxide arresters (MOAs). The primary coil and the secondary coil, which are wound in the reverse direction and are respectively in parallel with the two MOAs, are connected in parallel through the controlled switch and a main circuit breaker. Under normal condition, due to the non-inductive coupling characteristics between the two superconducting coils, the impedance of the proposed SFCL will be too small to affect the main circuit. After the fault happens, the controlled switch will be opened from its initial closed state, and meanwhile the MOAs will prevent the two coils from being damaged by the overvoltage caused by the switching operation. Since the flux between the coils cannot cancel out each other, the non-inductive coupling will disappear, and then the limiting impedance will be triggered for current-limitation. In order to evaluate the current-limiting performance of the novel flux-coupling type SFCL, a laboratory scale prototype was made. The two superconducting coils were fabricated with Bi2223/Ag, and an anti-parallel IGBT pair was chosen as the controlled switch. According to the test results, it was found that, the fault current could be limited quickly and effectively, and there was no overvoltage during the operation process of the controlled switch.

Study on resistance characteristics and operating conditions of YBCO thin-film wire for current limitation considering insulation layer

The YBCO thin-film wire has a high index value and a fast phase transition speed when a fault current is applied to it. Its critical properties are also superior to those of the existing Bi–Sr–Ca–O wire. Moreover, it can choose its stabilizing layers and control the magnitude of the resistance it generates in with the specific-resistance of the stabilizing layers. Thus, many researchers are studying the application of the Y–Ba–Cu–O(YBCO) thin-film wire to superconducting power machines. Being particularly studied are the properties of the YBCO thin-film wire as a current-limiting element material. In this study, to evaluate the basic properties of superconducting current-limiting elements that contain insulating layers, test samples were manufactured using the YBCO thin-film wire according to the absence and presence as well as the thickness of the insulating layers. Then a fault current was applied to the test samples to examine their quenching resistance trends and operational properties according to the fault angles. Towards those ends, a current was applied to various YBCO thin-film wires with different stabilizing layers to test their properties, and the YBCO thin-film wire that exhibited superior current-limiting performance was selected. Also, a fault current was applied to the selected YBCO thin-film wire with insulating layers to test their properties. Using the test results, the resistance occurrence trends were examined at the critical temperature of 90K, the perfect quenching temperature of 250K, and the middle temperature of 180K. Also, to increase the current limiters’ capacity, the element’s operational properties, such as its maximum voltage, maximum current, initial limited current, and response time were observed at 90K, 180K, and 250K according to the fault angles.

Inductance Ratio of Flat Type Fault Current Limiter With High Tc Superconducting Disks

We have proposed a flat type of the superconducting fault current limiter (FCL) which is a modified version of a magnetic shielding type of the fault current limiter. The flat type FCL basically consists of a pancake coil and doughnut-like form high T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> superconductor (HTS) disk, each of which works as a primary winding and a secondary one-turn winding, respectively. In order to clarify the static current-limiting performance of the flat type FCL, the magnetic field analyses were carried out for the small modules of the FCL. The inductance values of the FCL in the superconducting state and normal-conducting state of the HTS disk, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">limit</sub> , were calculated and their ratio <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">limit</sub> / <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> was estimated. The high performance of the FCL must be brought about by the large inductance ratio. It was confirmed that lower <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> was derived by sandwiching the pancake primary winding with two HTS disks and by using thin spacer between them, and larger <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">limit</sub> a is produced by connecting the built-up pancake primary windings in series. This suggests that a full-scale FCL may be designed and produced by building up many modules whose pancake winding is sandwiched with the HTS disks.

Theoretical Calculation of Inductance of Flat Type Fault Current Limiter with High Tc Superconducting Plate

A flat type fault current limiter (FCL) proposed by us consists of a spiral primary winding and high Tc superconducting (HTS) plate. In order to clarify the static current-limiting performance of the flat type FCL, the magnetic field analyses were carried out for small modules of the FCL. The inductance of the FCL was calculated by analyzing the magnetic field. The magnetic field analysis suggested that a high inductance ratio might be realized by radically enlarging both the primary winding and the HTS plate, installing the high permeability material such as an iron on the FCL and stacking the FCL modules vertically in layers. It is also pointed out that the volume of the flat type FCL is smaller than that of the cylinder type FCL with same magnitude of the limiting inductance.

Modulation-doping in 3–5 μm GaAs/AlAs/AlGaAs double barrier quantum well infrared photodetectors: an alternative to achieve high photovoltaic performance and high temperature detection

In this work we propose new detector designs, which allow achieving mid-infrared photovoltaic (PV) detection at temperatures as high as 180 K. The devices, which are grown by molecular beam epitaxy, are modulation-doped (MD) double barrier quantum well infrared photodetectors (QWIPs) based on AlGaAs/AlAs/GaAs. As the photocurrent spectra and I– V characteristics (in the dark and under infrared illumination) show that the dopant location is a relevant design parameter regarding the performance of PV QWIPs, we begin our work with a comparison of the performance of a set of MD samples (where we have varied the dopant location in the AlGaAs barriers) with respect to a well-doped sample of nominally the same structure. We find that the responsivity and detectivity of the MD devices seem to be higher than those of the well-doped detector, specially when the dopant is located in the substrate-sided barrier. Then, in order to improve the dark current-limited performance, we designed a new set of substrated-sided MD detectors that exhibit an extremely low dark current, even at high temperatures, otherwise no drop in the zero bias peak responsivity. Therefore, the association of the notable PV signal detection in the 3–5 μm range of these MD detectors together with the dark current reduction of the new structures has allowed us to achieve a 140 K zero bias peak responsivity of 0.015 A/W and a 180 K zero bias peak responsivity of 0.01 A/W at 4.4 μm.

Novel Application and Current-Limiting Performance of a Three-Phase, Solid-State, Fault Current Limiter

In this paper, the authors propose a novel application for a three-phase, solid-state, fault current limiter (FCL), consisting of a three-phase full-bridge rectifier and a DC reactor (DCR). Its configuration, operating principle, and a simple design method of the DCR, are presented. The proposed method is a combination of the FCL and a synchronous generator, and the FCL is connected to the neutral-point of the synchronous generator. As a result, an indispensable transformer in the conventional FCL can be removed, and a feature that maintains the current-limiting effect at a one-line ground fault is also obtained. To construct a guideline for creating the optimum DCR design, the current-limiting performance of the proposed method is theoretically analyzed, and the relationship between the fault current to be limited and the required DCR-inductance is derived. The experimental results obtained on a laboratory model demonstrate the effectiveness of the proposed method and validate the theoretical analysis.

Development of passive fault current limiter in parallel biasing mode

So far literature reports on the magnetic fault current limiter (FCL) are based on the series biasing mode in which the flux due to line current flows through the permanent magnet. As a result there is a high possibility of demagnetization of the permanent magnet. A passive fault current limiter is a combination of passive elements such as permanent magnet and saturable core. The permanent magnet is used to bias the core. In order to avoid severe demagnetization of the permanent magnet, we have investigated the performance of passive fault current limiters based on permanent magnet and saturable core in parallel biasing mode. The functional characteristics have been analyzed by Tableau approach and the simulation results are presented, The experimental results for a small scale prototype model are also presented for verification.

Detection of and protection for internal low-current winding faults in overhead distribution transformers

Changing protection practices for overhead power distribution transformers involves mounting the arrester on the transformer tank and using lightning-surge-tolerant fuses to provide protection. Concerns about protecting transformers against low-magnitude internal winding faults as a result of this practice are addressed in this paper. An analysis of a high-power test involving primary and secondary winding faults is presented. The magnitude, duration, and signature of the winding faults are determined and categorized. An analysis of the response of surge-tolerant fuses shows that they often will not detect low-current winding faults before they propagate to the available system fault current. Testing also demonstrated the performance of current-limiters to effectively reduce the available system fault current, thereby minimizing stress to the transformer. The use of current limiters is recommended with surge-tolerant fuses. The pressure rise in the tank for primary winding faults is mainly caused by low-fault current and, when protected with current limiters, the relief device easily vents the gases. The pressure rise for secondary winding faults is more rapid and can exceed the capability of the relief device to limit the overpressure.

Quenching of high-T/sub c/-superconductors and current limitation numerical simulations and experiments

Numerical simulations of the combined thermal and electrical behavior have been carried out to study the influence of inhomogeneities along the HTSC length on the quenching behavior. A two-dimensional finite difference method (FDM) has been used to investigate the current-limiting performance of YBCO film with a critical current density around 10/sup 6/ A/cm/sup 2/ on a ceramic substrate, 1% of the length was assumed to have reduced critical current and temperature. The equalization properties of an additional thin conducting layer on the quench process has been demonstrated for varying degrees of inhomogeneity. Furthermore a sample of YBCO film was investigated experimentally and compared to calculated data. The results of the experiments show good agreement with the numerical simulations.