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The priority for determining the performance of the superconducting current limiter depends on the manufacture and adoption of the superconducting current limiting element with excellent features. The basic conditions for the superconducting current limiting element are a high critical current density and index value, and simultaneously the stable normal operation against the diverse accident conditions within the power system. Further, as the superconducting current limiting element is operated in an extreme low-temperature environment, it should be manufactured with a compact structure, which can reduce the coolant consumption. Such superconducting current limiting element is beneficial as it is applicable to diverse superconducting current limiters. Based on the above premise, this study manufactured the superconducting current limiting element using coated conductors without a laminate layer. Using the manufactured superconducting current limiting element, the current limiting performance test against the fault current was carried out, the superconductivity recovery test conducted by measuring the time required for the superconductivity recovery was also carried out, and the temperature distribution was analyzed. For the test of the performance of the superconducting current limiting element that limits the fault current, the results of testing the effective limiting of the applied fault current according to the established fault angles were presented. Further, the superconductivity recovery test derived the required time for the recovery of the superconductivity state by the superconducting current limiting element according to the applied voltage size and power application cycles. Lastly, the temperature distribution analysis according to the applied voltage size and current transport cycles offered the data for the applicable maximum voltage per unit length of the superconducting current limiting element, and this became the evaluation index for determining the voltage rating of such element.

This paper proposes the spray cooling method in conducting the extremely low temperature cooling of the superconducting wire, and presents the results of cooling performance tests and characteristics of the spray cooling method. To that end, extremely low-temperature containers were designed and manufactured to enable the testing of immersion, conduction, and spray cooling methods. Then, a cooling performance test and dc transport current test were carried out according to individual cooling methods. The test results are outlined below for each cooling method. Similar trends were shown in the initial cooling performance and cooling maintenance performance of the existing immersion cooling method and the spray cooling method. Similar trends were also shown in voltage-current characteristics according to dc transport current. Thus, in order to observe the cooling characteristics of the spray cooling method further, additional tests were carried out to define temperature characteristics according to spray pressure, and the voltage-current characteristics based on spray duration. The test results confirmed that higher spray pressure resulted in better cooling performance, and longer refrigerant time resulted in more stable conduction of dc. Accordingly, quench voltage was detected as low.

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.

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.

Windings are essential to the manufacture of a current limiting element using the YBCO thin film superconducting wire that has the form of a tape. Considering the results of the preceding study, the current limiting performance of the YBCO thin film superconducting wire seems to be influenced by the winding method and the radius of curvature of the wire. The radius of curvature of the YBCO thin film superconducting wire is an important factor of its current limiting performance and modularization. In this study, three YBCO thin film superconducting wires (two with copper and stainless steel stabilization layers, respectively, and one with no stabilization layer) with unique specific resistance characteristics were used to manufacture the current limiting element by winding them around spiral formers, which had a radius 25% greater than the minimum radius of curvature. The current limiting performances of such wires were examined according to the diameter of the spiral former at the 90, 180, and 250 K. To summarize the study results, the current limiting performance of the current limiting elements were influenced by the changes in the radius of curvature of the wires while fault currents were being applied.

In this study, we reduced the cable former (hereinafter, “copper wire”) diameter to verify the possibility of realizing the fault-current-limiting-type superconducting cable while maintaining the current-limiting ratio and the cable stability. Current application properties in the parallel connection of the copper stranded wire were analyzed with the superconducting wire with a different degree of non-resistance. Items that were verified included the change in the total current (the limited fault current), the voltage characteristics, and the results of the thermal stability evaluation through a resistance analysis. The verification targets included the combination of the superconducting wire without a stabilization layer and the copper wire (0.75 SQ and 1 SQ), the combination of the superconducting wire with a stainless stabilization layer and the copper wire (0.75 SQ and 1 SQ), and the combination of the superconducting wire with a copper stabilization layer and the copper wire (0.75 SQ and 1 SQ). Result showed that with the increasing degree of the superconducting wire non-resistance and the decreasing copper wire diameter, the limiting performance of the total current improved, but thermal stability was not stabilized. In addition, the superconducting wire volume was shown to have affected thermal stability.

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.

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.

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.

When an abnormal condition occurs due to a fault current at a consumer location where electricity is supplied through a high-capacity and high- superconducting(HTS) cable, the HTS cable would be damaged if there is no appropriate measure to protect it. Therefore, appropriate measures are needed to protect HTS cables. The fault-current-limiting HTS cable that was suggested in this study performs an ideal transport current function in normal operations and plays a role in limiting a fault current in abnormal operation (i.e., when a fault current is applied). It has a structure that facilitated its self-current-limiting ability through device change and reconfiguration in the existing HTS cable without extra switching equipment. To complete this structure, it is essential to investigate about the selection of the superconducting wire. Therefore, in this paper, HTS wire using two types of different stabilization layer is compared and examined the stability and current limiting properties under the existence of a fault current.

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 (Iini, IImi, and Tr) and stability (Vmax).

The analysis of the steady and transient states is very important for the application of the superconducting wire to electric devices. Through many studies, the detailed evaluation technology for BSCCO wire, referred to as “the first-generation superconducting wire,” has been established to some extent. Meanwhile, the detailed analysis of the steady and transient states of YBCO thin-film wire, the second-generation wire that is increasingly being applied to more electric devices, is insufficient. Accordingly, in this study, the quench behavior at a below-critical temperature was evaluated, especially in the flux flow state, using two types of commercial YBCO thin-film wires, to determine the electric devices to which the wire can be applied, and to define its operating conditions. For this, YBCO thin-film wires with copper and stainless-steel stabilizer layers, which were manufactured considering the specific resistance and conductivity of the stabilizer layer, were prepared. The critical currents of the two wires were 85 A and 70 A, respectively, but their critical temperatures were identical at 90 K. The resistance values of both wires increased over time, within the range above the critical temperature, but they were different within the range below the critical temperature, according to the stabilizer layer. This can be an index that clearly represents the conducting and current-limiting characteristics of YBCO thin-film wire. Therefore, in this study, the two wires' current division characteristics were examined within the temperature range of 77 K (at which the liquid nitrogen starts to boil) to 90 K (the critical temperature) to determine which of the two wires was the conduction wire and which was the current-limiting wire. In addition, the conduction region was defined based on the trend of increase resistance below and above the critical temperature.

The yttrium-barium-copper-oxide (YBCO) coated conductor, which supplement the fault of the existing superconducting current-limit materials YBCO thin film, bismuth-strontium-calcium-copper-oxide(BSCCO) wire and bulk, has been improved its mechanical weakness and has high index; hence, after quench YBCO coated conductor could limit the fault current effectively because of fast resistance occurrence speed. Furthermore, it has wide applicable area as an current limit material because it shows different resistance occurrence tendency by the thickness and kind of stabilization material sputtered on the superconducting layer. Therefore, many researchers are carrying out the study of application of YBCO coated conductor to superconducting fault current limiter (SFCL) for making high quality current limit element, based on resistance type. On the other hand, the study for other type except resistance type has been rarely conducted for the application of YBCO coated conductor to SFCL as an current limit element. Consequently, in this study, YBCO coated conductor with different stabilization layer Cu and Stainless steel, is applied to SFCL using iron core and coil, and examine the many index points as an current limit element, such as current limit characteristic, the tendency of resistance occurrence, response time, the temperature trend for stability.

The improved flux-lock type superconducting fault current limiter (SFCL) is composed of a series transformer and superconducting unit of the yttrium-barium-copper-oxide (YBCO) coated conductor. In this paper, we investigated current limiting characteristics through winding direction of coil 2 and variable number of coil 1 and coil 2 in improved flux-lock type SFCL. The better fault current characteristics and the burden of YBCO coated conductor can be confirmed from the experimental result in the higher turn ratio of coil 1 and coil 2 in the additive conditions. In case of subtractive condition, we can confirm a similar result in the same case of experimental conditions. but the burden of YBCO coated conductor has been increased from an increase in winding numbers of coil 2.

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.

YBCO coated conductor is named by second generation superconductor tapes. It is different with first generation superconductor tapes. YBCO coated conductor`s specific difference with Bi-2223/Ag tape is more strong mechanical durability. This is important role to apply to superconducting machines. For mechanical transforming of YBCO coated conductors, we are using the well designed former. The merit of transformation is several. First, we vary the superconducting characteristics according to mechanical stress. Second, we reduce the volume of superconductor, so we achieve reducing the volume of superconducting machines. On this study, we experiment the transporting current characteristics of one types YBCO coated conductor. YBCO coated conductor with Ie of 70 A and voltage grade of 0.6 V/cm were connected to spiral former to conduct current application test.

The YBCO coated conductor is an important element that forms the superconducting power equipment. The first advantage of applying YBCO coated conductor to superconducting power equipment is that it can effectively addresses the normal and fault currents using less quantity of wire than when using Bi tape due to its high critical current density. Second, it can limit the fault current fast because its index value is high. so that the resistance can be produced fast when it is applied to the superconducting current limiting element. Third, the type of stabilization layer that surrounds the YBCO superconductor is selectable and the magnitude of the resistance that is produced from quenching can be adjusted. This study researched into the manufacture of current-limiting element of using YBCO coated conductor, into the characteristics of current limiter that considered by combining the manufactured element with the resistive-type superconducting fault current limiter.

We investigate the comparison of fault current characteristics between the separates three-phase flux-lock type superconducting fault current limiter(SFCL) and integrated three-phase flux-lock type superconducting fault current limiter(SFCL). The single-phase flux-lock type SFCL consists of two coils. The primary coil is wound in parallel to the secondary coil on an iron core and superconducting elements are connected to secondary coil in series. Superconducting elements are used by the YBCO coated conductor. The separated three-phase flux-lock type SFCL consists of single-phase flux-phase type SFCL in each phase. But the integrated three-phase flux-lock type SFCL consists of three-phase flux-reactors wound on an iron core. Flux-reactor consists of the same turn`s ratio between coil 1 and coil 2 for each single phase. To compare the current limiting characteristics of the separated three-phase flux-lock type SFCL and integrated three-phase flux-lock type SFCL, the short circuit experiments are carried out fault condition such as the single line-to-ground fault. The experimental result shows that fault current limiting characteristic of the separated three-phase flux-lock type SFCL was better than integrated three-phase flux-lock type SFCL. And the integrated three-phase flux-lock type SFCL has an effect on sound phase.

The separated three-phase flux-coupling type superconducting fault current limiter(SFCL) is composed of a series transformer and superconducting unit of the YBCO coated conductor. The primary and secondary coils in the transformer were wound in series each other through an iron core and the YBCO coated conductor was connected with secondary coil in parallel. In this paper, we investigated the current limiting characteristics through winding number of coil 2 and winding direction in the flux-coupling type SFCL. Through the analysis, it was shown that additive polarity condition and lower winding number of coil 2 have advantaged from the point of view of fault current limiting and burned of YBCO coated conductor.

YBCO coated conductors (CC) with high critical current density and index values are expected to be applied to superconducting power device. In particular, it is characterized by possibilities of selecting a stabilizing material surrounding YBCO CCs so that they could be applied to superconducting fault current limiters (SFCLs) and superconducting cables according to their physical properties. In this study, we conducted experiments by selecting YBCO CCs having different stabilizers of copper and stainless steel. First, we investigated the voltage-current variations with applied over-current beyond their critical currents and temperature variation generated by Joule heating. From the results, YBCO CC with copper stabilizer was more suitable for the current carrying characteristics and the CC with stainless steel showed successful current limiting properties. Finally, The 2 YBCO CCs were connected in series and electrical properties were investigated. From the results, we confirmed that the safe current carrying operation with fault current limitation could be carried out successfully.

We investigated the fault current characteristics of the separates three-phase flux-lock type superconducting fault current limiter(SFCL) according to the variation of inductances. The single-phase flux-lock type SFCL consists of two coils. The primary coil is wound in parallel to the secondary coil on an iron core. And superconductor is series connected on secondary coil. Superconductor is using the YBCO coated conductor. The separated three-phase flux-lock type SFCL consists of single-phase flux-phase type SFCL in each phase. To analyze the current limiting characteristics of a three-phase flux-lock type SFCL, the short circuit experiments were carried out fault such as the triple line-to-ground fault. The experimental result shows that fault current limiting characteristics of additive polarity winding was better than subtractive polarity winding and when the inductances of coil 2 was lower, resistances of YBCO CC was more generated.

YBCO coated conductor called the second-generation superconducting tapes have resistance increase significantly more than BSCCO tapes in terms of the speed or amount when quench occurs, they may have different ranges of application. Such characteristics are thought to get different properties by selection of stabilizing materials in manufacturing superconducting tapes. It is important in selecting superconducting tapes which will be applied to power devices in the future. In this study, one kind of BSCCO tapes and two kinds of YBCO CC with different stabilizing materials and one kind of YBCO CC with non stabilizing materials were used to compare and examine transport characteristics in flux-flow state and quench state with each tape joint of HTS tapes.

The integrated three-phase flux-lock type superconducting fault current limiter (SFCL) consists of three-phase flux- lock reactor wound on an iron core with the same turn's ratio between the primary coils and the secondary coils for each phase. When a SFCL is operating under normal condition, and assuming that the leakage flux is neglected, the magnetic flux generated between the primary and the secondary coils of each phase is canceled out perfectly. Therefore, the impedance of the SFCL is zero and the power system can operate normally without any loss. However, when a fault occurs, quench happens in high-TC superconducting (HTSC) elements and the magnetic flux generates in an iron core. Therefore, the impedance of the SFCL is large enough to limit fault currents. In this paper, we investigated the fault current limiting characteristics according to the fault angle in SFCL in fault types such as the single-line-to-ground fault, the double-line-to-ground fault and the triple-line-to-ground fault. Experiment results show that the fault current limiting characteristics of the SFCL are dependant on the quench characteristics of HTSC elements in each phase.

As a fundamental study for the safe operation of high temperature superconducting (HTS) machines, AC over-current characteristics of HTS tapes and the method for the protection using superconducting fault current limiters (SFCLs) were investigated. Firstly, the AC over-current characteristics of a Bi-2223/Ag tape were investigated. Various amounts of AC over-currents were applied and the quench behavior was analysed, measuring resistance increase with applying time. Secondly, based on the over-current characteristics of the HTS tapes, SFCLs made of YBCO thin films was applied to the protection of the HTS tapes for the safe operation. At this time, the quench characteristics of the HTS tape and the SFCL were considered simultaneously and each electrical operation was compared. At the transition range from super- to normal state in the HTS tape, quench behavior of both materials was investigated in detail. From the experiments, the safe operation state of HTS tapes was achieved and the optimal design factors for the SFCL applications were acquired.

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.

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.

Advantages of YBCO thin film type wires are as follows. First, their high critical current density allows effective handling of normal and fault currents. Second, high index values can lead to fast fault current limiting because of the rapid build-up of resistance. Third, a variety of stabilizing materials can be employed in YBCO thin film type wire, resulting in more flexible adjustment of limiting resistance after the quench. In this study, the wires for the current limiter and cable were selected through an over-current conducting (transport) test that took into account the characteristics of the YBCO thin film type wire. The current limiting characteristics of the wires for the current limiter and cable according to the fault type and fault angle were examined. The tests were conducted in three phases, and the fault type and fault angle were examined for single-line-to-ground fault, double-line-to-ground fault and triple-line-to-ground fault at the fault point of R-phase 0 that was defined as the fault standard in the test. The YBCO thin film type wire for the current limiter with a critical current of 80 Arms, critical temperature of 90 K and voltage rating of 0.6 Vrms/cm had stainless steel stabilization layer, while the Bi-2223Ag wire for HTS cable with a critical current of 110 Arms, critical temperature of 106 K and voltage rating of 2.5 Vrms/cm had silver stabilization layer. The required lengths were determined considering the voltage rating of wires, and the wires were respectively wound on a straight former and a spiral former.