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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.

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.

The distribution submarine cables are normally used for power supply at island, which are mostly installed in the southern coast of KOREA, and partially installed in the west coast and Jeju-Island. There are two way of submarine cable burying system, buried and unburied type. Since 2003, KEPCO is entirely being constructing the distribution submarine cable by buried type. In this case, `burial depth` is key index for evaluating the suitability of the buried situation. Therefore, the measurement accuracy of `burial depth` is a big issue for burying system in the distribution submarine cable. This paper demonstrates the measurement error of burial depth that is affected by electrical factor such as grounding type of submarine cable in case of magnetic field detection method, and indicates the method to reduce the measurement error in buried type of distribution submarine cable system.

Since transmission and distribution neutral wires are connected with a substation grounding grid, it is very difficult to measure grounding resistance of isolated substation grounding grid after the substation is energized. It is impractical to isolate the grounding grid from other parallel connections such as distribution line neutrals and overhead ground wires for grounding resistance measurement only. In this paper, we proposed and demonstrated a novel measurement method of grounding resistance of isolated substation grounding grid. For this method, grounding current division factor and conventional FOP(Fall-Of-Potential) profiles were measured at power supplying 154[kV] substation. The obtained FOP profile was processed with the measured grounding current division factor to produce the grounding resistance of isolated grounding grid. Simulated FOP profile agreed well with the measured one showing the validity of the proposed method.

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 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.

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.

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.

In this paper, we report the improved and integrated matrix-type superconducting fault current limiter (MFCL). The new MFCL proposed in this work has a structure that easily improves the quench characteristics of superconducting elements. This integrated MFCL is simply constructed by mounting a trigger element and superconducting elements in a single reactor, whereas older MFCL designs require several complex reactors for proper operation. Also this integrated type of structure provides a uniform and strong magnetic field with superconducting elements, compared with an old type MFCL. We designed and characterized the integrated MFCL with 1 times 3 superconducting modules and 2 times 3 superconducting modules. From experimental results, we confirmed that our integrated MFCL had advantages including a compact design, better quench characteristics and an easily adjustable increment of the capacity for fault current limiting.

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.

A transformer type superconducting fault current limiter (SFCL) is one of the fault current limiters which have been proposed to reduce the fault current in the transmission lines. This paper proposes the new circuit configuration of a transformer type SFCL and also investigates the operating characteristics of the transformer type SFCL containig the resistor in the tertiary winding. The proposed SFCL contains the resistor in the tertiary winding. The newly inserted resistor can divert the power which the High-Tc superconducting has to bear. Because the resistor in the tertiary winding relieves the power of the High-Tc superconducting, it is possible that the proposed transformer type SFCL can decrease the more larger fault current than the conventional SFCL with the same High-Tc superconducting. And the cost of the proposed transformer type SFCL can be reduced.

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.

We have proposed a flux-coupling type superconducting fault current limiter (SFCL) using coils and analyzed its operating characteristics. The SFCL consisted of the primary and secondary coils, which were wound in series each other through an iron core. The superconducting unit, which was based on YBCO thin film, was connected with secondary coil in parallel. Meanwhile, the primary coil and secondary coil with serially connected superconducting unit were connected in parallel in a flux-lock type SFCL, which didn't permit the same inductances between the primary and secondary coils. The short-circuit currents were effectively limited by adjusting the numbers of winding turns of each secondary coil and the winding directions of the coils without a certain limitation in a flux-coupling type SFCL. The flux generated from a coil in normal operation is cancelled out by the direction of windings in the SFCL and the zero resistance behavior of the superconducting unit. In order to compare the influence by turn numbers between coils, the turn number of the secondary coil was varied from 21 to 84 while the turn number of the primary coil was 42 and 63. We confirmed that the flux-coupling type SFCL was significantly efficient in reducing the initial line current after fault initiation. The voltage generated in the superconducting unit was also lowered by reducing power burden of the YBCO thin film in the flux-coupling type SFCL. We considered that this was caused by mutual linkage of the flux between two coils. The current limiting behavior of the flux-coupling type SFCL was more effective for fault current limiting operation.

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.

Atomic force microscopy (AFM) has become an attractive technique to fabricate nano devices since the observing mechanism is different from fabricating one. We have fabricated the superconducting flux flow transistor (SFFT) with a serial-channel structure using the AFM lithography analyzed the modified surface by the AFM image. We investigated the induced voltage in a serial-channel terminals dependence on the gate current by the I–V measurement system. We performed the numerical simulation to get the theoretical characteristics of the SFFT controlled by the gate current via the modified channel. The transresistance was 0.006 Ω for Id=51 mA at Ig=5 mA. It is very low transresistance in comparison with SFFTs fabricated by the other processes, however our results show that the SFFT with a serial-channel structure is effectively fabricated by an AFM lithography method.

The flux-lock type superconducting fault current llmiter (SFCL) uses the magnetic coupling between two coils connected in parallel with each other. This SFCL has the merit that both the resistance of high-TC superconducting (HTSC) element and the limiting current capacity can be simultaneously increased through the application of magnetic field into HTSC element. However, like other type of SFCLs using an iron core, unless the saturation of the iron core in the design is considered, the actual limited fault currents can be higher than expected as the saturation of the iron core occurs, and can lead to damage the electrical equipment of the power system. To analyse the dependence of the fault current in the flux-lock type SFCL on the fault angles, its electrical equivalent circuit with the magnetization branch was derived. From the electrical equivalent circuit, the fault current and the inner magnetic flux considering the fault angles as well as the design parameters such as winding direction and inductance ratio of two coils were calculated. The analysis results were compared with the experimental ones, and both the results agreed.

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.

We investigated that the current limiting capability of the high- superconducting (HTSC) elements comprising the hybrid type superconducting fault current limiter (SFCL) could be improved with lower power burden for each HTSC element and higher limiting impedance of the SFCL by adjusting the number of turns of the secondary winding. As estimable parameters to confirm it, the resistance and the power loss generated in each HTSC element and the limiting impedance of the SFCL were derived from the electrical equivalent circuit. It was confirmed through the analysis based on the fault current limiting experiments that the power burden of HTSC element in the hybrid type SFCL could be decreased with higher limiting impedance of the SFCL by using a smaller number of turns of secondary windings.

Temperature rise characteristics of medium voltage class transformers and dielectric characteristics of its insulation oil according to the loading rate were investigated using the transformer that has thermocouples embedded in the windings. The hottest-spot of the transformer locates at about 2/3 height of the windings where they adjoin each other among the 3 phase windings. The temperature difference between the hottest-spot and top-oil is about and the value keeps uniformly in short time after changing the loading rate. Capacitance of the oil varies in inverse proportion to temperature and the inclination rate is about -0.0106 that is not dependent on the aging rate. On the other hand the capacitance is increased depending on the aging rate, so the capacitance characteristics of the oil could be applied to the diagnostic technique.

The short circuit analysis of the integrated three phase flux-lock type superconducting fault current limiter (SFCL), which consisted of three-phase flux-lock reactor wound on an iron core with the same turn's ratio between coil 1 and coil 2 for each single phase, was performed. In a normal time, the flux generated in the iron core is zero because the flux generated between two coils of each single-phase is canceled out. In a fault time, the integrated three-phase flux-lock type SFCL showed the different fault current limiting characteristics from other three-phase SFCLs with the separated three iron cores. Through the computer simulation for the three-phase circuit with its equivalent circuit, the current limiting characteristics of the integrated three-phase flux-lock type SFCL were analyzed

The fault current limiting characteristics of DC dual reactor type superconducting fault current limiter (SFCL) using switching operation of high-TC superconducting (HTSC) elements were analyzed. The suggested SFCL consists of a diode bridge, DC dual reactor with magnetic coupling and HTSC elements. Unlike the conventional bridge type SFCL, which requires the controller for the operation of the interrupter to prevent the continuous increase of fault current after a fault happens, this SFCL can be operated without the interrupter and the controller for its operation. In addition, despite different critical currents after a fault accident, the balanced power burden between HTSC elements can be achieved by the magnetic coupling between two coils of DC dual reactor. It was confirmed through the experiments for the fault current limiting characteristics that the suggested SFCL performed the advantageous current limiting operations compared to the conventional bridge type SFCL using HTSC coil

The quench characteristics of high-TC superconducting (HTSC) tape for alternating over-current applications have been investigated at various amplitudes of the over-current and its quench developments have been analysed by applying discrete Fourier transform (DFT) for the voltage and the current waveforms of HTSC tape. Generally, the HTSC tape shows a broad superconducting and normal transition region above its critical current due to the metal sheath unlike HTSC thin film or HTSC bulk. Moreover, the voltage-current characteristics of HTSC tape are complicated because the quench and the recovery between the superconducting state and the normal state are repeated. In this paper, the alternating over-current experiments for the HTSC tape were performed to analyse its quench developments. The fundamental frequency components for the current and the voltage waveforms of the HTSC tape were abstracted by applying DFT. From those fundamental frequency components, the numerical formula for HTSC tape's resistance has been derived. By applying its numerical formula into circuit equation, the quench developments of HTSC tape dependent on alternating over-current have been estimated and the agreement with the experimental results has been found

Needle coke, the remaining material after refining petroleum, is used as an anode of a lithium-ion secondary battery. Sulfur is separated from the needle coke to below 0.1 wt.% using the molten caustic leaching (MCL) method developed at the Korea Institute of Energy Research. The needle coke with high-purity is carbonized at various temperatures, namely 0, 500, 700 and 900 °C. The coke treated at 700 °C gives a first and second discharge capacity of more than 560 and 460 mAh g−1, respectively, between 0 and 2.0 V. By contrast, the first and second discharge capacity of untreated coke is over 420 and 340 mAh g−1, respectively, between 0.05 and 2.0 V.The first discharge capacity of 560 mAh g−1 is beyond the theoretical maximum capacity of 372 mAh g−1 for LiC6. Though the cycle efficiency is not consistent, the needle coke heat-treated at 700 °C persistently maintains an efficiency of over 90% until the 50th cycle, except on the first cycle. This study demonstrates that the needle coke with high-purity could be a good candidate for an anode material in fabricating high-capacity lithium-ion secondary batteries.

We investigated fault current limiting characteristics of the flux-lock type superconducting fault current limiter (SFCL), which consisted of a primary winding and several secondary windings connected in series between superconducting (HTSC) thin films. Each YBCO thin film has a 2 mm wide and 42 cm long meander line with 14 stripes of different length. The power imbalance due to the slight difference of Ie between YBCO current limiting elements causes the significant power burden on YBCO element with lower . We confirmed from our experiments that the mutual coupling between the primary winding and secondary windings of the flux-lock type SFCL reduced the power imbalance between YBCO current limiting elements compared with the resistive type SFCL connected in series.

In this paper deals with the frequency control of the HVDC scheme linking Haenam to Cheju Island. The primary aim of the study is to develop and evaluate a new frequency control that can be employed without having to utilise the existing Synchronous Compensators(Gas Turbines). Transient condition studies are performed utilising the detailed control strategies for the HVDC link, implemented in PSCAD/EMTDC. Study cases are completed involving synchronous compensators trip and load ripping events and study plots presented. It is demonstrated that the existing frequency measurement can be replaced by one derived from the AC network alone, incorporated into a new frequency control algorithm and gives effective frequency control and dynamic performance.

A flux-lock type SFCL consists of two coils, which are wound in parallel each other through an iron core, and a HTSC thin film connected in series with coil 2. If the current of the HTSC thin film exceeds its critical current by the fault accident, the resistance generated of the HTSC thin film, and thereby the fault current can be limited by the impedance of the flux-lock type SFCL. The amplitude of fault current can be set by the impedance of the flux-lock type SFCL. In this paper, we investigated the variance of the limiting current due to the ratio of inductances between coil 1 and coil 2 in the flux-lock type SFCL through the computer simulations and short circuit tests. In addition, both the simulation results and experimental ones were compared each other. From the comparison of both the results, the simulation results agreed well with the experimental ones.