Seok-Cheol Ko

Analysis on Magnetizing Characteristics Due to Peak Fault Current Limiting Operation of a Modified Flux-Lock-Type SFCL With Two Magnetic Paths

The advantage of the flux-lock-type superconducting fault current limiter (SFCL) is that the operational current of the SFCL can be easily adjusted by the winding ratio and the winding direction between two windings. Furthermore, the peak fault current limiting operation according to the transient initial fault current was reported to be performed by adding the third winding and another superconducting element into the flux-lock-type SFCL with either one or two magnetic paths. In this paper, the magnetizing characteristics of the modified flux-lock-type SFCL, due to its peak fault current limiting operation, which another superconducting element and the third winding were added into the E-I iron core structure with two magnetic paths, were analyzed. To analyze the dependence of its magnetizing characteristics on the peak fault current limiting operation of the SFCL, the peak fault current limiting tests of the SFCL due to the fault angle were carried out. With the measured voltage and the current values, the flux linkage and the magnetization current derived from the equivalent magnetization circuit were calculated and compared, at each fault angle, together with the magnetizing power related with the accumulated magnetic energy in the iron core during the fault period.

Effect of Peak Current Limiting in Series-Connection SFCL With Two Magnetically Coupled Circuits Using E-I Core

In this paper, we proposed a series-connection-type superconducting fault current limiter (SFCL) that can prevent the internal magnetic flux generation of cores during normal operation and prevent the saturation of cores due to a sudden magnetic flux generation at the initial stage of fault occurrence while limiting the peak current. The proposed SFCL does not mediate two cores, as previously reported, but mediates a single E-I core having a configuration of two magnetically coupled circuits using the first, second, and third windings. The other magnetic path is formed by the third coil and the other superconducting element isolated from two coils. Through a short-circuit experiment, we analyzed the operating status of the two superconducting elements and peak current limiting properties according to the amplitude of the fault current before and after the failure. Furthermore, the peak current limiting characteristics according to the winding directions, as well as the current and the voltage of each coil, were compared and analyzed.

Improvement of Current Limiting and Recovery Characteristics of Flux-Lock Type SFCL with Series Connection of Two Coils Using Its Third Coil

In this work, the current limiting and recovery characteristics of a flux-lock type superconducting fault current limiter (SFCL) with series connection of two coils were effectively improved by adding a third winding into the conventional flux-lock type SFCL with series connection of two coils. To confirm the contribution of the third winding to the current limiting and recovery characteristics of this type of the SFCL, short-circuit testing was carried out with consideration of the third winding, and the effect of the third winding on the current limiting and recovery characteristics was examined by comparative analysis of the amplitude of the limited fault current and the power burden of the high-TC superconducting (HTSC) element comprising the SFCL. Through the analysis of both the limiting impedance and the operational current as the main design parameter of the SFCL, the improved current limiting and recovery characteristics of the flux-lock type SFCL using the third winding could be verified.

Comparison of Peak Current Limiting in Two Magnetically Coupled SFCLs Using Dual Iron Cores

In this paper, the peak current limiting characteristics of a superconducting fault current limiter (SFCLs) using dual iron cores were compared with each other. Two magnetically coupled SFCLs were connected in parallel or series between the two coils. The peak current limiting and the recovery characteristics of these SFCLs could be varied depending on design conductions such as the winding direction and the inductance ratio between the two coils. Through the fault current limiting and the recovery experiment, the peak current limiting effect and the recovery characteristics for these SFCLs were definitely explained.

Reliability Testing and Materials Evaluation of Si Sub-Mount based LED Package

The light emitting diodes(LED) package of new structure is proposed to promote the reliability and lifespan by maximize heat dissipation occurred on the chip. We designed and fabricated the LED packages mixing the advantages of chip on board(COB) based on conventional metal printed circuit board(PCB) and the merits of Si sub-mount using base as a substrate. The proposed LED package samples were selected for the superior efficiency of the material through the sealant properties, chip characteristics, and phosphor properties evaluations. Reliability test was conducted the thermal shock test and flux rate according to the usage time at room temperature, high-temperature operation, high-temperature operation, high-temperature storage, low-temperature storage, high-temperature and high-humidity storage. Reliability test result, the average flux rate was maintained at 97.04% for each items. Thus, the Si sub-mount based LED package is expected to be applicable to high power down-light type LED light sources.

Plastic Liquid Crystal Display with Polarizers Integrated Inorganic Conducting and Alignment Layers

We investigated polarizer integrated conducting and alignment functions SiO2/ ITO/SiO2 films on polarizer films for the high transmittance and contrast ration of liquid crystal (LC) cell. SiO2/ITO/SiO2 films were directly deposited on polarizer films using r. f. magnetron sputtering system at room temperature, which are used as substrates for plastic liquid crystal displays. To align LC molecules, we exposure on SiO2 film surfaces with low-energy ion beam. Transmittance of twisted nematic (TN) and electrically controlled birefringence (ECB) cell with SiO2/ITO/SiO2/polarizer was higher by 3%∼5% than those of SiO2/ITO/glass/polarizer in average visible wavelength.

Current Limiting Characteristics of a SFCL with Two Triggered Current Limiting Levels in a Simulated Power Distribution System

When the accident occurred in power distribution system, it needs to control efficiently the fault current according to the fault angle and location. The flux-lock type superconducting fault current limiters (SFCL) can quickly limit when the short circuit accidents occurred and be made the resistance after the fault current. The flux-lock type SFCL has a single triggering element, detects and limits the fault current at the same time regardless of the size of the fault current. However, it has a disadvantage that broken the superconductor element. If the flux-lock type SFCL has separated structure of the triggering element and the limiting element, when large fault current occurs, it can reduce the burden of power and control fault current to adjust impedance. In this paper, this system is composed by triggering element and limiting element to analyze operation of limiting current. When the fault current occurs, we analyzed the limiting and operating current characteristics of the two triggering current level, and the compensation characteristics of bus-voltage sag according to the fault angle and location.

Analysis on Current Limiting Characteristics of Series Connection-type SFCL with Two Magnetically Coupled Circuits Applied into a Simulated Power System

The series connection-type superconducting fault current limiter (SFCL) with two magnetically coupled circuits was suggested and its effectiveness through the analysis on the current limiting and recovery characteristics was described. The fault current limiting characteristics of the proposed SFCL as well as the load voltage sag compensating characteristics according to the winding direction were investigated. To confirm the fault current limiting and the voltage sag suppressing characteristics of the this SFCL, the short-circuit tests for the simulated power system with the series connection-type SFCL were carried out. The series connection-type SFCL designed with the additive polarity winding was shown to perform more effective fault current limiting and load voltage sag compensating operations through the fast quench occurrence right after the fault appears and the fast recovery operation after the fault removes than that with the subtractive polarity winding.

Current Limiting and Voltage Sag Compensation Characteristics of Flux-Lock Type SFCL Using a Transformer Winding

The superconducting fault current limiter (SFCL) can quickly limit the fault current shortly after the short circuit occurs and recover the superconducting state after the fault removes and plays a role in compensating the voltage sag of the sound feeder adjacent to the fault feeder as well as the fault current limiting operation of the fault feeder. Especially, the flux-lock type SFCL with an isolated transformer, which consists of two parallel connected coils on an iron core and the isolated transformer connected in series with one of two coils, has different voltage sag compensating and current limiting characteristics due to the winding direction and the inductance ratio of two coils. The current limiting and the voltage sag compensating characteristics of a SFCL using a transformer winding were analyzed. Through the analysis on the short-circuit tests results considering the winding direction of two coils, the SFCL designed with the additive polarity winding has shown the higher limited fault current than the SFCL designed with the subtractive polarity winding. It could be confirmed that the higher fault current limitation of the SFCL could be contributed to the higher load voltage sag compensation.

Characteristics of Insulation Degradation in Epoxy Mold Type BCT

Various stresses (such as electrical stress, mechanical stress, environmental and electrochemical stress, and defects of structure) result in insulation degradation of epoxy mold type insulators. Since the insulation degradation of BCT(Bushing Current Transformer) and bushing proceeds during fabrication process or operation time due to these causes, various methods to reduce the degradation in their insulation ability have been suggested. In this paper, we investigated surface temperature increment of these insulators due to PD(partial discharge). After the voltage applied into the insulator to generate the artificial PD, the surface temperature of the insulator was measured with non-contact thermometer using infrared rays. It was confirmed through the analysis based on PD experiments that the procession in the insulation degradation of the insulator could be estimated through the measurement of the surface temperature in the insulator.