A compact 154-kV superconducting fault current limiters (SFCL) system has been developed by Korea Electric Power Corporation and led to a primary prototype being tested for three months at Gochang Power Test Center. Due to the fact that the volume of the primary model was still relatively large for application to substations, a compact system was designed. To reduce the volume of the SFCL system, electric field analyses were performed. By carrying out a fine modification of the shape, the design of a compact system was completed, and the volume and footprint of the compact cryostat were 65% and 77% of the primary model, respectively. Following that, a single-phase compact model was fabricated and installed on a dedicated test site at Gochang Power Test Center. Several tests were then performed on the SFCL system, which led to a single-phase voltage of 154 kV being applied to the system. The period covered by the long-term test lasted for one year. This paper presents the results of the one-year testing.

Supercapacitor, especially electrical double-layer capacitance(EDLC), have many advantage that can operate at very high charge and discharge rates and have lifetimes of over a million cycles [1]. Furthermore, supercapacitor can complement batteries to reduce the size of batteries using with frequency regulation. Their utilization in a system can potentially eliminate the need for frequent replacement as required by batteries, hence, saving the resources invested in the upkeep of the whole system in the long run of power grid. However, supercapacitor are still far from being able to replace batteries and struggle in meeting the demand for a high energy density [2]. Since electrode material is the main key to improve the energy density, today, graphene considered as an attractive material because graphene has excellent conductivity, stability, and high surface area [3]. However, many aspects of the electrochemical behaviour of electrode still need to be examined closely in order to apply for electrode for commercial use, and there is another issue that graphene production methods are easy to aggregate or stack and lead to reduce surface area. In this reason, it is very difficult to maintain an outstanding graphene property for electrode production in case of large scale area for mass production. In this study, in order to practical application, we compared various electrode properties of activated carbon and activated graphene. To demonstrate the electrochemical performance of the activated carbon and graphene electrode, we manufactured a series of supercapacitor on CR2032 coin cells. The samples were punched into round

Korea Electric Power Corporation has developed a 154-kV superconducting fault current limiter (SFCL). This report is a part of the design process of the SFCL, particularly for fixation of posts supporting the superconducting element on the cryostat wall side. For supporting the superconducting element, the use of a post insulator is inevitable; however, the post insulator and cryostat with liquid nitrogen (L-N2) during operation of the SFCL form three junction points where electric field is intensified. In this study, we aim to design the metal shield in order to relax the electric field intensity at triple points (TPs) through numerical analysis of electric field distribution. For the electric field distribution analysis, a commercial software based on the finite-element method was employed. Each design for the metal shield was checked whether it makes the electric field intensity at the TP sufficiently lower than dielectric strength in L-N2 for 750-kV input and whether there is any electrically weak point on the metal. The designs of the metal shields were improved through four critical steps where thermal contraction, manufacture tolerance, and insulation distance in L-N2 were considered. It was experimentally verified that there was no electric breakdown in L-N2 between the metal shield and the fiber-reinforced plastic post insulator for the lightning impulse test and the ac breakdown voltage test according to the IEC 60137 standard.

The superconducting fault current limiter (SFCL) is an electric power device that limits the fault current immediately in a power grid. Korea Electric Power Corporation (KEPCO) has been developing a 154 kV, 2 kA SFCL since 2011 to protect power grids from increasing fault current and improve the stability and quality of electric power. This SFCL adopts 2G YBCO wires and operates at 71 K and 5 bars. In this paper, a cooling system for the 154 kV SFCL and its cooling test results are reported. This cooling system uses a Stirling-type cooler to make sub-cooled liquid nitrogen (LN2), which cools the superconductor modules of the SFCL. The LN2 is circulated between the cooler and the cryostat that contains superconductor modules. The LN2 also plays the role of a high voltage insulator between the modules and the cryostat, so the pressure was maintained at 5 bars for high insulation performance. After installation in a test site, the cooling characteristics of the system were tested. In this operation test, some important data were measured such as temperature distribution in LN2, pressure change, performance of the heat exchanger, and cooling capacity of the total system. Consequently, the results indicate that the cooling system operates well as designed.

Development and grid operation of superconducting fault current limiters (SFCLs) have been carried out in Korea Electric Power Corporation (KEPCO), as a possible measure to handle the increasing fault current in Korea. A 22.9 kV SFCL has been successfully operated unmanned on a distribution line of Icheon Substation. It has been very stable throughout the operation of more than 1.5 year. Temperatures and level of liquid nitrogen that cools the superconducting element have been maintained constant. Performance of the SFCL maintained the initial level. The SFCL was modified so that it can limit the fault current within the first half cycle. A short-circuit test on the modified SFCL showed it started limiting the current within 2 ms. In parallel, a 154 kV SFCL has been also developed. A superconducting element was designed and fabricated. A short-circuit test was performed on a superconducting unit module, and showed that the module limited the current effectively. The element is planned to be integrated into a single-phase 154 kV SFCL together with the cooling system and other components, and tested soon.

In this study we investigated ac transport current losses in the face to face stack for the anti-parallel current flow, and compared the electromagnetic properties with those of the single SC tape as well as those of the same stack for the parallel current path. The gap between the SC tapes in the stack varied in order to verify the electromagnetic influence of the neighbors when current flows in opposite direction, and the model was implemented in the finite element method program by the commercial software, COMSOL Multiphysics 4.2a. Conclusively speaking, the loss was remarkably decreased for the anti-parallel current case, which is attributed the magnetic flux compensation between the SC layers due to the opposite direction of the current flows. As the gap between SC tapes was increased, the loss mitigation became less effective. Besides, the current density distribution is very flat cross the sample width for the narrower gap case, which is believed to be benefit for the power electric system. These results are all in good agreement with those predicted theoretically for an infinite bifilar stack.

We experimentally investigated the correlation between the high-temperature superconducting (HTS) wires configuration in an HTS element and recovery time after quench in a resistive superconducting fault current limiter. The variables of the configuration are horizontal and vertical gap distances between HTS tapes in an element. Eight samples were made with different gap distances and tested. A SUS-stabilized YBCO tape with 4.4 mm width had been used in the experiment. It was cooled by LN2 in a cryostat under the pressure of 1 bar, saturated state. In the short-circuit test, the temperature of the wire's surface was measured. Recovery time of the HTS sample increased with decreasing horizontal and vertical gap distance due to stagnation of bubbles. When the gap distance was larger than a size of a bubble, the effect of gap distance was ignorable. Considering a volume and recovery time, the sample that has narrower gap distance was favorable.

A 22.9 kV superconducting fault current limiter (SFCL) has been in operation in a real grid in Korea. The SFCL is of hybrid type, in which the fault current is detected by a superconductor and bypassed by a high-speed switch to a reactor in a parallel circuit for current limitation. It has a current rating of 630 A, and has been operated in a distribution line in Icheon Substation, which is located in a suburban area with moderate loads. The SFCL has been operated very stably with no degradation in performance. Temperatures and level of the liquid nitrogen cooling the superconductors have been maintained within 0.1 K and 0.3 cm, respectively, under large daily load variation of about 100 A. Performance of the SFCL was tested by measuring minimum limitation current and impedance of the SFCL, and was proved to maintain the initial level of performance. There was a single line-to-ground fault event in the distribution line where the SFCL has been operated, and the SFCL limited the fault current successfully. Data analysis showed that the SFCL limited the current as designed. These results proved reliability and performance of the SFCL.

A 22.9 kV/630 A-class superconducting fault current limiter (SFCL) was installed on a distribution line in Icheon Substation for real-grid operation. The substation is located in a semi-urban area with moderate loads. The SFCL is of hybrid type. After installation it was subjected to a series of on-site tests. Test procedures were determined by following convention in testing both superconductivity-related and not-related specifications of the SFCL. Tests performed were minimum limiting current test, temperature test, dielectric test, and impedance measurement. After successfully passing the tests, the cooling system of the SFCL was operated for more than 5 months under various load conditions to optimize the operation condition. During that period, temperatures, liquid nitrogen level, and internal pressure remained within ±0.1 K, ±0.5 cm, and ±0.5 bar range, proving stability in cooling superconducting elements. The SFCL was then energized and went into real-load operation successfully.

This paper presents the results of short-circuit tests with a 22.9 kV hybrid superconducting fault current limiter (SFCL) on the KEPCO test grid. The hybrid SFCL we used for the test had suffered from lots of field tests including a long term operation and it is still in working order. We have already proved that the SFCL showed high reliability as well as feasibility through a long term operation and short-circuit tests performed before. In this paper, we tried to study a dynamic characteristics of the same SFCL on the distribution power grid through short-circuit tests with a circuit breaker and a reclosing relay. An artificial fault generator (AFG) was used to generate fault currents in the KEPCO power test center. The two objectives of the tests are (1) verifying a precise reaction of the SFCL to reclosing operation and (2) a study for protection coordination with SFCL. The test results showed that the SFCL worked precisely with a fast recovery of the superconducting elements when we applied a one-time reclosing operation with the interval of 0.6 second. We also suggested a proper manipulation of the coordination of the protection system in distribution networks with the SFCL in the paper.

This paper reports on the operation test of a 22.9 kV hybrid superconducting fault current limiter (SFCL) in the KEPCO test grid. The SFCL works at a rated voltage and current of 22.9 kV and 630 A, respectively. There are two major objectives of the operation test: (1) long-term operation and (2) fault tests for protection coordination study. The operation lasted for more than a year. We experienced several times of cryostat suspension due to blackouts and false alarms due to sensor failures during the operation. We also carried out short circuit tests in the test grid, equipped with circuit breakers and a recloser. An artificial fault generator was used to generate fault currents. The tests showed that the SFCL, together with the recloser, functioned reliably under repeated faults. We also confirmed the reclosing capability of the SFCL. We have presented herein the operation details, cost of operation, short-circuit test results, and our plans for further tests for protection coordination.

YBCO coated conductor (CC) wires has many advantages for resistive superconducting fault current limiters (SFCLs). Especially, the 344S manufactured by AMSC CC clad with stainless steel can reduce fault current to lower temperature because stainless steel stabilizer roles as higher resistant shunt. Multi parallel structure is inevitable for SFCLs with large current capacity. The two layered with four parallel paths non-inductive wound solenoid coils were fabricated. The inductances of inner and outer layers were calculated using finite element method (FEM) tool. These results were compared with measured values. In this paper, the current distribution characteristics of coils were measured when 240 Apeak was applied. From the experiments, the results show that more large current flows into inner layers by difference in inductance. Therefore, the two solenoid coils was transposed to reduce of non-uniform current distribution between inner and outer layers by electrical inductance. The experimental results provide to suitable design parameters and showed technical feasibility of multi parallel structure.

High temperature superconducting (HTS) magnets have been studied for insert coils of high field nuclear magnetic resonance (NMR) magnets but the temporal stability required for NMR is hard to achieve due to low index value and high joint resistance. In this research, the HTS power supply with magnets using coated conductor (CC) was investigated and tested in helium cryogenic system. All joints were conducted by soldering after etching stabilizer of the CC to minimize joint resistance. The pumping rate was determined by current amplitude and timing sequential control of heaters and the electromagnet. Operating characteristics were analyzed to enhance charging efficiency and the feasibility of temporally stable CC magnet during persistent mode was studied.

Superconducting fault current limiters (SFCLs) have been developed in many countries, and they are expected to be used in the recent electric power systems, because of their great efficiency for operating these power system stably. It is necessary for resistive FCLs to generate resistance immediately and to have a fast recovery characteristic after the fault clearance, because of re-closing operation. Short-circuit tests are performed to obtained current limiting operational and recovery characteristics of the FCL by a fault controller using a power switching device. The power switching device consists of anti-parallel connected thyristors. The fault occurs at the desired angle by controlling the firing angle of thyristors. Resistive SFCLs have different current limiting characteristics with respect to the fault angle in the first swing during the fault.This study deals with the short-circuit characteristic of FCL coils using two different YBCO coated conductors (CCs), 344 and 344s, by controlling the fault angle and experimental studies on the recovery characteristic by a small current flowing through the SFCL after the fault clearance. Tests are performed at various voltages applied to the SFCL in a saturated liquid nitrogen cooling system. (C) 2007 Elsevier B.V. All rights reserved.

This paper deals with the short-circuit characteristics, including current limiting and current distribution characteristics of non-inductive superconducting coil wound with stainless steel-stabilized coated conductor (CC). From the tests of current limiting characteristics, we concluded that:(1) stainless steel-stabilized CC is efficient in the reduction of the wires required and volume of bobbin. However, its current limitation was not as efficient due to its high resistivity;(2) proper thickness and intermediate resistivity between copper and stainless steel can be an optimal specification of stabilizer for resistive SFCLs.From current distribution measurement tests, we concluded that contact resistance, impedance and cooling condition plays a dominant role in the current distribution characteristics before the fault, during the fault and during the recovery, respectively. (C) 2007 Elsevier B.V. All rights reserved.

Recent development of CC, usually called second generation (2G) HTS, is actively in progress. Because of its higher critical current density as well as higher n-value, 2G HTS is feasible for the applications such as superconducting fault current limiter and superconducting cable. For operating the HTS equipment stably, it needs to investigate the characteristics of normal zone propagation occurred by quench. Investigations on the fundamental characteristics can be one of the indispensable foundations for research and development of power equipments.In this paper, normal zone propagation (NZP) characteristics according to various insulation materials are researched. By heating with NiCr heater and insulating with epoxy, we applied the operating current with respect to the critical current for calculation of minimum quench energy (MQE) and measurement of NZP. (C) 2007 Elsevier B.V. All rights reserved.