• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.5
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• pp.17-26
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• 2018

If a photovoltaic (PV) system is installed in a primary feeder interconnected with the PV system, bi-directional power flow can occur, and then, the magnitude and direction of the fault current can change, depending on the fault location and point of common coupling (PCC) of the PV system, and the time current curve (TCC) cannot be properly coordinated between protection devices. Also, it is difficult to obtain a proper time interval for protection devices because the conventional setting approach is applied, even though the PV system is installed and operating. Therefore, this paper presents three operation modes considering the operational conditions of the PV system to obtain setting values for protection devices. Based on the mode, this paper proposes an algorithm to calculate the optimal protection coordination time interval according to the introduction capacity of the PV system. In addition, this paper performs modelling of a distribution system with the PV system and protection devices by using Off-DAS S/W, and analyzes the characteristics of the time interval between the protection devices, such as substation relays, reclosers, customer relays, and PV customer relays. The simulation results confirmed that the proposed operational modes and setting-value algorithms are useful and effective for protection coordination in a distribution system for a PV system.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07b
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• pp.976-979
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• 2002

A focusing grating coupler (FGC) was not fabricated by the 'Continuous Path Control' writing strategy but by an electron-beam lithography system of more general exposure mode, which matches not only the address grid with the grating period but also an integer multiple of the address grid resolution (5 nm), To more simplify the fabrication, we are able to reduce a process step without large decrease of pattern quality by excluding a conducting material or layer such as metal (Al, Cr, Au), which are deposited on top or bottom of an e-beam resist to prevent charge build-up during e-beam exposure. A grating pitch period and an aperture feature size of the FGC designed and fabricated by e-beam lithography and reactive ion etching were ranged over 384.3 nm to 448.2 nm, and $0.5{\times}0.5mm^2$ area, respectively, This fabrication method presented will reduce processing time and improve the grating quality by means of a consideration of the address grid resolpution, grating direction, pitch size and shapes when exposing. Here our investigations concentrate on the design and efficient fabrication results of the FGC for coupling from slab waveguide to a spot in free space.

• Transactions on Electrical and Electronic Materials
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• v.3 no.1
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• pp.30-37
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• 2002

A focusing grating coupler (FGC) was not fabricated by the 'Continuous Path Control'writing strategy but by an electron-beam lithography system of more general exposure mode, which matches not only the address grid with the grating period but also an integer multiple of the address grid resolution (5 nm). To more simplify the fabrication, we are able to reduce a process step without large decrease of pattern quality by excluding a conducting material or layer such as metal (Al, Cr, Au), which are deposited on top or bottom of an e-beam resist to prevent charge build-up during e-beam exposure. A grating pitch period and an aperture feature size of the FGC designed and fabricated by e-beam lithography and reactive ion etching were ranged over 384.3 nm to 448.2 nm, and 0.5 $\times$ 0.5 mm$^2$area, respectively. This fabrication method presented will reduce processing time and improve the grating quality by means of a consideration of the address grid resolution, grating direction, pitch size and shapes when exposing. Here our investigations concentrate on the design and efficient fabrication results of the FGC for coupling from slab waveguide to a spot in free space.

• Korean Journal of Optics and Photonics
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• v.17 no.6
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• pp.556-563
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• 2006

We present a comprehensive study of a chirped pulse Ti:sapphire regenerative amplifier system operating at 1 kHz. Main constituents of the system are described in detail. The amplifier stage was first converted to a repetition rate-tunable kHz gain-switched nanosecond Ti:sapphire laser. Operation characteristics at different repetition rates such as build-up times of laser pulses, pump power-dependent output powers and pulse durations, damage thresholds, and tunability ranges were studied. Based on the results achieved, the switching time of the Pocket's cell used and the round trip numbers in the regenerative amplifier were optimized at 1 kHz. The output pulses with a pulse width of 50fs from a home-made Ken lens mode-locked Ti:sapphire oscillator were used as seed pulses. The pulses were expanded to 120ps in a grating stretcher prior to coupling into the 3-mirror amplifier cavity. After amplification and recompression, a stable 1kHz Ti:sapphire regenerative amplifier system, which delivers 85-fs, $320-{\mu}J$ pulses, was fully constructed.

• Restorative Dentistry and Endodontics
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• v.24 no.3
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• pp.473-481
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• 1999

This study evaluated the shear bond properties of IPS Empress glass ceramic to enamel and dentin surfaces with three ceramic surface treatments, and three resin cements. The influence of thermocycling was also investigated. The purpose of this study was to investigate the influences of resin cements, ceramic surface treatments, and thermocycling on shear bond properties. Ninety freshly extracted, noncarious human molars were selected for this study. The surface treatments of ceramic were etching <5.0% hydrofluoric acid, application of silane coupling agents(Tokuso Ceramic Primer, Clearfil porcelain bond, Monobond-S), and the combination of the two methods. Empress cylinders were bonded to enamel and dentin surfaces with three kinds of resin cements(Bistite resin cement, Panavia 21, Variolink). The specimens were aged in $37^{\circ}C$ distilled water for 24 hours. Half of the specimens were then thermocycled 500times between $5^{\circ}C$ and $55^{\circ}C$ with a dwell time of 15 seconds. Each specimen was debonded in shear mode and measured shear bond properties by using the universal testing machine(Zwick 020, Germany). The data were analyzed by SPSS/PC+(one-way ANOVA, Scheffe' s test and t-test). The results were as follows : 1. Without thermocyling, there was significant difference of shear bond strength to enamel surface between Bistite Resin Cement and Panavia 21 in case of etched and silane-treatment(p<0.05). 2. Without thermocyling, the shear bond strength of a group treated with silane and etching was significantly higher than that of a group treated with silane or etching with the application of Panavia 21 and Variolink(p<0.05). 3. A group treated with etching with the application of Variolink only showed a decrease of shear bond strength after thermocycling(p<0.05).

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1996.06a
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• pp.179-200
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• 1996

The intrinsic instabilities of fluid flow occurred in the melt of the Czochralski crystal growth system Czochralski method, asymmetric flow patterns and temperature profiles in the melt have been studied by many researchers. The idea that the non-symmetric structure of the growing equipment is responsible for the asymmetric profiles is usually accepted at the first time. However further researches revealed that some intrinsic instabilities not related to the non-symmetric equipment structure in the melt could also appear. Ristorcelli had pointed out that there are many possible causes of instabilities in the melt. The instabilities appears because of the coupling effects of fluid flow and temperature profiles in the melt. Among the instabilities, the B nard type instabilities with no or low crucible rotation rates are analyzed by the visualizing experiments using X-ray radiography and the 3-D numerical simulation in this study. The velocity profiles in the Silicon melt at different crucible rotation rates were measured using X-ray radiography method using tungsten tracers in the melt. The results showed that there exits two types of fluid flow mode. One is axisymmetric flow, the other is asymmetric flow. In the axisymmetric flow, the trajectory of the tracers show torus pattern. However, more exact measurement of the axisymmetrc case shows that this flow field has small non-axisymmetric components of the velocity. When fluid flow is asymmetric, the tracers show random motion from the fixed view point. On the other hand, when the observer rotates to the same velocity of the crucible, the trajectory of the tracer show a rotating motion, the center of the motion is not same the center of the melt. The temperature of a point in the melt were measured using thermocouples with different rotating rates. Measured temperatures oscillated. Such kind of oscillations are also measured by the other researchers. The behavior of temperature oscillations were quite different between at low rotations and at high rotations. Above experimental results means that the fluid flow and temperature profiles in the melt is not symmetric, and then the mode of the asymmetric is changed when rotation rates are changed. To compare with these experimental results, the fluid flow and temperature profiles at no rotation and 8 rpm of crucible rotation rates on the same size of crucible is calculated using a 3-dimensional numerical simulation. A finite different method is adopted for this simulation. 50×30×30 grids are used. The numerical simulation also showed that the velocity and flow profiles are changed when rotation rates change. Futhermore, the flow patterns and temperature profiles of both cases are not axisymmetric even though axisymmetric boundary conditions are used. Several cells appear at no rotation. The cells are formed by the unstable vertical temperature profiles (upper region is colder than lower part) beneath the free surface of the melt. When the temperature profile is combined with density difference (Rayleigh-B nard instability) or surface tension difference (Marangoni-B nard instability) on temperature, cell structures are naturally formed. Both sources of instabilities are coupled to the cell structures in the melt of the Czochralski process. With high rotation rates, the shape of the fluid field is changed to another type of asymmetric profile. Because of the velocity profile, isothermal lines on the plane vertical to the centerline change to elliptic. When the velocity profiles are plotted at the rotating view point, two vortices appear at the both sides of centerline. These vortices seem to be the main reason of the tracer behavior shown in the asymmetric velocity experiment. This profile is quite similar to the profiles created by the baroclinic instability on the rotating annulus. The temperature profiles obtained from the numerical calculations and Fourier transforms of it are quite similar to the results of the experiment. bove esults intend that at least two types of intrinsic instabilities can occur in the melt of Czochralski growing systems. Because the instabilities cause temperature fluctuations in the melt and near the crystal-melt interface, some defects may be generated by them. When the crucible size becomes large, the intensity of the instabilities should increase. Therefore, to produce large single crystals with good quality, the behavior of the intrinsic instabilities in the melt as well as the effects of the instabilities on the defects in the ingot should be studied. As one of the cause of the defects in the large diameter Silicon single crystal grown by the