Current-limiting Element Research Articles

Voltage Sag Mitigation Effect Considering Failure Probability According to the Types of SFCL

The development of industrial technology is based on electronic devices that are sensitive to power quality. Thus, the demand for high-quality and reliable power supplies is increasing. Voltage sag results in severe problems in the manufacturing process of power quality-sensitive industrial loads. When a fault occurs in a multi-ground power distribution system, the magnitudes of the fault current and voltage sag in the faulted and nonfaulted feeders become high. Hence, installing a superconducting fault current limiter (SFCL) is an effective method of compensating for fault current limitation and voltage sag. This study evaluates the effects of improving the magnitude, duration, and frequency of the voltage sag according to the type of SFCL used. First, a fault in the power distribution system is analyzed using PSCAD/EMTDC, a power system simulation software, according to the fault current-limiting element (CLE) and the type of SFCL. Second, the expected voltage sag frequency caused by a feeder fault in the power distribution system is assessed. Finally, the voltage sag improvement effect according to the CLE and the type of SFCL are compared. The trigger-type SFCL with a resistor as a CLE has been evaluated and found to be effective in improving voltage sag.

Recovery performance of partially-joined porous-stabilized REBCO tape for resistive type superconducting fault current limiters

In the case of using rare-earth barium copper oxide (REBCO) tape as a current-limiting element, there are three requirements: high normal state resistance, high thermal stability, and quick recovery to the superconducting state. In this study, a new type of REBCO tape with a metal porous medium as a stabilizer (a porous-stabilized REBCO tape) was proposed, which has high resistance compared to bulk material and prevents film boiling due to its strong capillary force. First, a numerical simulation was performed to evaluate the current-limiting performance of the porous-stabilized REBCO tape with a Ni–Cr porous medium. The results showed that the current-limiting performance was dramatically improved by placing indium partially on the REBCO tape to join the porous medium compared to placing indium wholly. Then, the porous-stabilized REBCO tapes with various arrays of indium were manufactured, and tested to confirm its recovery characteristics. The experimental results indicated that the partially-joined Ni–Cr porous-stabilized REBCO tape reduced the recovery time by 69% compared to that of the stabilizer-free REBCO tape.

Heating by Electrical Current of Stainless Steel-Stabilized Current Limiting Elements Made from 2G HTSC Tapes and Its Dependence on Heat Transfer Parameters to Liquid Nitrogen

The heating of current-limiting elements made of second-generation HTSC tapes stabilized with a stainless steel tape is studied experimentally. It is shown that the heating rate depends little on the degree of stabilization with stainless steel. Using a mathematical model that takes into account the heat sink parameters (the medium is liquid nitrogen), the capabilities and limitations of increasing the area of the current-limiting element for reducing its temperature in the current limiting mode are demonstrated.

A Novel Topology of a Liquid Metal Current Limiter for MVDC Network Applications

A liquid metal current limiter (LMCL) utilizing a fast switch and a parallel connecting path and consisting of several serial current limiting elements (CLEs) has the potential for use in a dc system. The current commutation ability is vital to the reaction time and the current limiting efficiency of this LMCL. In this paper, the characteristics of a natural current commutation driven by the arc voltage between contacts are first revealed; this method can only be applied in a low-voltage system. To fulfill the demands of a medium-voltage direct current system, an innovative LMCL topology is recommended due to the forced current commutation driven by an auxiliary magnetic induction module. A specially designed structure of magnetic coupling coils with a high coupling coefficient is proposed to improve the current commutation ability. The forced current commutation characteristic is analyzed via simulation and verified experimentally. Furthermore, the arc V–I characteristics of CLEs are deeply discussed to guide the selection of serial quantity of the CLE. Finally, a prototype for the complete LMCL is designed, assembled, and tested in the laboratory. The current limiting coefficient of the LMCL is less than 0.464, the peak value of arc voltage is approximately 6.3 kV, and the current limiting reaction time is 1.53 ms.

Study on Voltage Rating Improvement of the YBCO Thin-Film Superconducting Wire its Application for the Power Apparatus

A superconducting fault current limiter plays the role of quickly limiting the fault current when a failure occurs in an electric power system. The SF12050 YBCO thin-film superconducting wire is used as the current-limiting element of superconducting current limiters due to its high voltage rate and fast superconducting to normal conduction phase transition speed. However, SF12050 has a thin (2000-nm-thick) stabilizing layer. Therefore, it may be damaged by thermal quenches while carrying a fault current. The stabilizing layer is the part that is responsible for the thermal burdens on YBCO thin-film wires. If such thermal burdens could be reduced by improving the structure of the stabilizing layer, superconducting current limiting elements with enhanced performance could be manufactured. Thus, in this study, the thickness of the stabilizing layer of SF12050, an Ag layer, was increased to 500 nm to improve its structure using the thermal deposition method, and to verify the increases in the thermal stability and voltage rate (increased electric capacity).

Extraction of the characteristics of current-limiting elements from field emission measurement data

In this contribution, the authors will present an algorithm to extract the characteristics of nonideal field emission circuit elements from saturation-limited field emission measurement data. The method for calculating the voltage drop on current-limiting circuit elements is based on circuit theory as well as Newton's method. Since the only assumption the authors make on the current-limiting circuit is a connection in series, this method is applicable to most field emission data showing saturation. To be able to determine the significance of any parameter output, the uncertainties of data and extracted parameters as well as the parameter correlations are fully taken into account throughout the algorithm. N-type silicon samples with varying external serial resistors are analyzed. All results show a good agreement to the nominal resistor values. Additionally, several p-type samples are analyzed, showing a diodelike behavior. The extracted current-limiting characteristics of the p-type samples are in good agreement with a pn-junction model. The stability of the emission current of the p-type samples is measured by constant voltage measurements and compared to the extracted current-limiting characteristics. The application of the algorithm to measurement data shows that the given algorithm is a valuable tool to analyze field emission measurement data influenced by nonemissive processes.

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.

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.

Durability Test of Fault Current Limiter Made of 2G Wire Having Stainless Steel as a Stabilization Layer Taking Into Account Fault Angle

A superconducting current limiter should secure the stability of a power system by making it durable. That is, even if a fault current is applied repeatedly to a superconductor, its characteristics should remain unchanged. The fault angle at the fault time within a power system varies depending on the failure position, cause, and type. Therefore, to investigate the durability of a superconducting current-limiting element, it is necessary to examine the quenching characteristics based on the fault angles. In this paper, a YBCO-coated conductor, whose current-limiting ability and stability had been proven in previous studies, was used to manufacture superconducting current-limiting elements and conduct a durability test. The durability test measured the quenching characteristics while a fault current was applied repeatedly at certain intervals depending on the fault angles. The superconducting wire used in the durability test was a YBCO-coated conductor with a stainless stabilization layer, which showed the best mechanical characteristics among the various thin-film-type wires.

Effect of inductors to mitigate the hot-spot problem in parallel-connected superconducting thin-film fault current limiting elements

We have been developing superconducting thin-film fault current limiter (FCL) elements, in which high-resistivity Au–Ag alloy shunt layers are used to protect YBa2Cu3O7 (YBCO) thin films deposited on CeO2-buffered sapphire substrates. The high resistance of the thin films enables the element to withstand high electric fields of more than 40 Vpeak cm−1 during the current-limiting period after quenching, thus greatly reducing the amount of YBCO thin film needed and, consequently, the cost of an FCL. We have succeeded in fabricating and testing 500 V/200 A FCL modules using two 20 cm long YBCO films connected in parallel. In the present study, we performed extensive switching experiments on FCL elements, in which two YBCO films are connected in parallel to achieve higher rated currents, and confirmed the previously observed phenomenon that the hot-spot problem causing film damage just after quench initiation becomes more severe when the total critical current of the thin films is higher. We have investigated the origin of this phenomenon and found that a rapid current transfer from the first-quenched film with lower critical current to the other film causes higher current in the secondly-quenched film that sometimes leads to hot spots. It is demonstrated that the serious hot-spot problem can be mitigated by the use of inductors when the high-resistance FCL elements are connected in parallel. Based on these findings we propose an appropriate architecture of a high electric-field superconducting thin-film FCL that can be used in a real power grid.

Combined Effect of the SFCL and Solenoid Coils

As the capacity of power facilities increases with the power demand, the fault current also increases in the case of a power system fault. Many studies are underway to limit the increasing fault current. They especially include superconducting fault current limiters (SFCLs). The existing SFCLs operate almost without loss because of their zero resistance characteristic in the normal condition, but limit the fault current by generating impedance in the event of a fault. However, this mechanism gives a significant burden on the SFCL. In this study, a high-speed interrupter and a normal conduction current-limiting unit were applied to the SFCL. In this structure, the current flows through the b-switch of a high-speed interrupter and the current-limiting element in the normal condition, but in the event of a fault, the current was bypassed to the current-limiting unit by the quench of superconducting units and interrupter switching operations. In this case, the magnitude of the fault current was covered by the SFCL, and after the switching operation, the current was limited by the normal conduction current-limiting unit. The results of this study showed that this structure reduced the power burden on the expensive superconducting element, and limited a high fault current that was initially generated from the fault.

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.

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.

Evaluation on Resistance Tendency and Recovery Characteristics of 2G Wire With Insulation Layer

The application of the superconducting current limiter in a power system using a superconductor is not a subject for the future, but for the present. In line with the current change due to the superconducting current limiter, the study of its application in a power system, among many current studies on it, has become very important. The study on the application of the superconducting fault current limiter in a power system consists of the operation of the superconducting fault current limiter in a power system and the improvement and evaluation of the characteristics of the superconducting elements. Especially, the research on the role of insulation in the improvement and evaluation of the superconducting elements is so important that it can never be overlooked. Accordingly, in this study, the quenching characteristics and the recovery characteristics depending on the insulation layer were investigated by estimating the arising resistance and the temperature changes on YBCO-coated conductors (one with a stainless-steel stabilization layer and the other without), which are most frequently used when studying the superconducting current-limiting element. The experiment results showed that the resistance after the quenching did not significantly affect the recovery time, but that the increased cross-sectional areas of the superconducting elements due to the stabilization and insulation layers significantly affected the recovery time.

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> ).

Study on the application filed of HTS power apparatus of YBCO thin film wire through analysis of current transport characteristics

The advantages of the YBCO thin film wire, which is creating expectations as a next-generation superconducting current-limiting element, are its high index value, current density, and convenience when its capacity is increased by increasing its length. In particular, the stabilization layer of the YBCO thin film wire, which determines its abnormal current protection and excitation characteristics, can diversify its applications to superconducting power devices, depending on the specific resistance of the material of its stabilization layer. Thus, an analysis of the excitation characteristics of the YBCO thin film wire according to the material of its stabilization layer and the existence of the stabilization layer is a very important study subject. Accordingly, this study was conducted to evaluate the capabilities of the YBCO thin film wire as a current-limiting element using a YBCO thin film wire with no stabilization layer. For this purpose, the voltage–current characteristics of the YBCO thin film wire immediately after the quenching, according to the size and time of the fault current applied from the voltage source, were analyzed. Additionally, the wire’s resistance-increasing tendency and its tendency to return to its superconducting state immediately after the quenching were examined. The results of this study present the evaluation data for the verification of the phase transition characteristics of the YBCO thin film wire with no stabilization layer and its potential as a superconducting element for the superconducting current limiter.

직렬 연결된 두 코일과 YBCO Coated Conductor로 구성된 초전도 전류제한기의 권선방향과 권선 비에 따른 전류제한 특성 분석

The ongoing Superconducting Fault Current Limiter(SFCL) development mainly has focused on the application of commercializaton and power system through combining with normal-conducting device, moving away from current-limiting method, which is solely dependant on the existing superconductor. Compared to the structural development above, on the other hand, the research on applying superconducting current-limiting element to SFCL, the heart of SFCL, still has a lot left to do, apart form traditional resistive type SFCL. In this study, we looked into the current limiting characteristic of SFCL using core and coil. YBCO coated conductor with stainless steel stabilizer layer was verified by the excellent of current-limiting element of the resistive type SFCL that has a high Jc and index as well as being superior in mechanical property. Also, we study temperature characteristics and resistance characteristics, max voltage, response time and current-limiting ability that can be an indicator as current-limiting element while applying to superconducting current-limiting element caused by variation of winding direction, winding ratio of SFCL using core and coil.

Study on Maximum Operating Condition of Resistive Type SFCL Using YBCO Coated Conductor

The most important thing in developing a superconducting fault current limiter (SFCL) is to find the maximum operating condition for each current-limiting element to increase its SFCL capacity. The maximum operating condition can be defined using Vmax, Tr, Imax and Iq, which are detected after the quenching of the SFCL. In this study, YBCO coated conductor whose characteristics were proved as the superconducting fault current limiting element was used to test the operating characteristics of the unit current limiting element and to find the maximum operating condition using Vmax, Tr, Imax and Iq, which are detected after the quenching against the fault current according to the fault angle. YBCO coated conductors used in the test are one wire with stainless-steel stabilizing layer and one wire with no stabilizing layer. Critical current value is 70 Arms and the critical temperature is 90 K. The YBCO coated conductor with non stabilizing layer had a critical current of 80 Arms and a critical temperature of 90 K. Therefore, the two YBCO coated conductors in this study had different critical currents and an identical critical current of 90 K.

Study on stability evaluation and quench characteristics of non-stabilizing layer YBCO thin-film wire wound with the radius of curvature for application of SFCLS

The YBCO thin-film wire for superconducting fault current limiters shows promise with the following characteristics. (1) It has a high index value that enables a quick phase transition. (2) It has a high current density. (3) It experiences little change in the critical current in high magnetic fields. (4) It has varying quenching phenomena according to its stabilizing layers. Thus, it is being actively studied in many countries for application to power transmission and distribution systems. Based on current research results, this study examined the quenching occurrence trends in the YBCO thin-film wire that has been verified as a superconducting fault current limiter element and that has no stabilizing layers. This was done according to the wire’s radii of curvature and in terms of the increase in its resistance, initial limited current, and quenching occurrence time. Five kinds of spiral-shaped formers were produced with the radii increasing from the minimum radius by 25%, taking into account their changing critical properties due to bending stress. The YBCO thin-film wire without stabilizing layers was wound around these formers. Then an alternating over-current was applied to the current limiting elements that were produced according to the radii of curvature. The resulting trends in resistance enhancement were examined to evaluate the stability of the produced current limiting elements. Finally, the produced current limiting elements’ initial limited current and quenching occurrence time were observed at 90K, 180K, and 250K to evaluate the performance of the current limiting elements.