• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1996.11a
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• pp.306-310
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• 1996

In this paper a series of developing process for an insulator which can be employed in overhead distribution lines, using polymeric composite materials, is introduced. In order to design an insulator for heavily polluted area, weathershed of alternating type was adopted, which could have longer leakage distance. Modified EVA was used as surface material which has good electrical and mechanical characteristics as well as superior chemical stability. FRP core was covered with above surface material through heat shrinking process. By standardization of each process, higher productivity and lower production cost could be ensured. The developed insulator has been put under various tests including long-term field test and artificial aging test and satisfactory results were obtained.

• Proceedings of the KIPE Conference
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• 2005.07a
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• pp.408-410
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• 2005

Multilevel converters have emerged like a new strategy for energy conversion from medium power to high power. The main characteristic of the topologies classified as multilevel, is the use of commutation devices connected in series, allowing the distribution of the voltage and reducing stress in the commutation switches. Stacked Multicell Converter (SMC), is classified as single-phase voltage source inverter(VSI). Due to the fact, the SMC generates a signal of alternating current of several levels of voltage of direct current. The following work will demonstrate the flexibility of the above mentioned topology using a low cost control circuit architecture.

• Journal of Power Electronics
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• v.19 no.5
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• pp.1099-1107
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• 2019

A soft switching converter with wide voltage range operation is investigated in this paper. A series resonant converter is implemented to achieve a high circuit efficiency with soft switching characteristics on power switches and rectifier diodes. To improve the weakness of the narrow voltage range in LLC converters, an alternating current (ac) power switch is used on the primary side to select a half-bridge or full-bridge resonant circuit to implement 4:1 voltage range operation. On the secondary-side, another ac power switch is adopted to select a full-wave rectifier or voltage-doubler rectifier to achiever an additional 2:1 output voltage range. Therefore, the proposed resonant converter has the capacity for 8:1 (320V~40V) wide output voltage operation. A single-stage hybrid resonant converter is employed in the study circuit instead of a two-stage dc converter to achiever wide voltage range operation. As a result, the study converter has better converter efficiency. The theoretical analysis and circuit characteristics are verified by experiments with a prototype circuit.

• Macromolecular Research
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• v.9 no.2
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• pp.116-121
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• 2001

A series of poly(1,4-phenylenevinylene-alt-3-alkyl-2,5-thienylenevinylene)s (alkyl = hexyl [PPV-alt-6-TV] and octyl (PPV-alt-8-TV] group) have been synthesized by the Heck coupling reaction. These polymers were characterized using $^1$H-NMR, FT-IR spectroscopy, and thermogravimetric analysis (TCA). They are solvent processible and have obviously copolymeric structure. The photophysical properties of the polymers were investigated using UV-visible and steady-state photoluminescence(PL) spectroscopy. We studied the change of light-emitting properties by incorporating the thiophene group into the PPV polymer backbone using alternating copolymer system. The properties of two synthesized polymers are very similar, but they exhibited apparent changes of light-emitting properties compared with other PPV backbone based polymers. The broad absorption bands from 350 to 570 nm are due to $\pi$-$\pi$* transitions of the polyconjugated systems. The absorption maxima of the two polymers were found at about 452 and 448 nm for PPV-alt-6-TV and PPV-alt-8-TV, respectively. The copolymers showed broad PL spectra between 550 and 700 nm without vibronic bands and PL emission maxima of PPV-alt-6-TV and PPV-alt-8-TV are about 620 and 605 nm, respectively. The copolymers exhibited the red emission (PPValt-6-TV), but more red shifted emissions are needed to obtain real red color.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.14 no.4
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• pp.275-283
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• 2021

In this study, a driver IC for an AC-powered LED that can be manufactured with a low voltage semiconductor process is designed and the performances of the driver IC were simulated. In order to manufacture a driver IC that operates directly at AC 220V, a semiconductor manufacturing process that satisfies a breakdown voltage of 500V or higher is required. A semiconductor manufacturing process for a high-voltage device requires a much higher manufacturing cost than a general semiconductor process for a low-voltage device. Therefore, the LED driver IC is designed in series so that it can be manufactured with semiconductor process technology that implements a low-voltage device. This makes it possible to divide and apply the voltage to each LED block even if the input voltage is high. The LED lighting circuit shows a power factor of 96% at 220V. In the pnp transistor circuit, a very high power factor of 99.7% can be obtained, and it shows a very stable operation regardless of the fluctuation of the input voltage.

• Transactions on Electrical and Electronic Materials
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• v.18 no.2
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• pp.97-102
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• 2017

A current transformer (CT) is a type of sensor that consists of a combination of electric and magnetic circuits, and it measures large ac currents. When a large amount of current flows into the primary winding, the alternating magnetic flux in the iron core induces an electromotive force in the secondary winding. The characteristics of a CT are determined by the iron core design because the iron core is saturated above a certain magnetic flux density. In particular, when a large current, such as a current surge, is input into a CT, the iron core becomes saturated and the induced electromotive force in the secondary winding fluctuates severely. Under these conditions, the CT no longer functions as a sensor. In this study, the characteristics of the secondary winding were investigated using the time-difference finite element method when a current surge was provided as an input. The CT was modeled as a two-dimensional analysis object using constraints, and the saturation characteristics of the iron core were evaluated using the Newton-Rhapson method. The results of the calculation were compared with the experimental data. The results of this study will prove useful in the designs of the iron core and the windings of CTs.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.66 no.4
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• pp.200-205
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• 2017

In this paper, we propose a technique to determine the normal and arc of an alternating current using a mixed filter composed of an average filter and a band-pass filter and a frequency analysis. The proposed method uses the moving average filter of the FIR filter structure for noise removal and the band-pass filter of the IIR filter structure for detecting only specific frequency components after normalizing the measured current signal based on the maximum value. After performing Fast Fourier Transform (FFT) using the band-pass filtered signal, the total energy is calculated using the magnitude component of the frequency, and the arc is detected using the magnitude of the calculated energy. In order to show the validity of the proposed method, we experimented with various data and found that arc and steady state can be easily discriminated by calculating spectral energy. Therefore, it is considered that the proposed method can be applied to arc diagnosis of low voltage electric wire.

• Journal of Mechanical Science and Technology
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• v.19 no.11
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• pp.1988-1997
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• 2005

This study is concerned with structural integrity evaluations for the interference-fit flywheels in reactor coolant pumps (RCPs) of nuclear power plants. Stresses in the flywheel due to the shrinkage loads and centrifugal loads at the RCP normal operation speed, design overspeed and joint-release speed are obtained using the finite element method (FEM), where release of the deformation-controlled stresses as a result of structural interactions during rotation is considered. Fracture mechanics evaluations for a series of cracks assumed to exist in the flywheel are conducted, considering ductile (fatigue) and non-ductile fracture, and stress intensity factors are obtained for the cracks using the finite element alternating method (FEAM). From analysis results, it is found that fatigue crack growth rates calculated are negligible for smaller cracks. Meanwhile, the material resistance to non-ductile fracture in terms of the critical stress intensity factor (K$_{IC}$) and the nil-ductility transition reference temperature (RT$_{NDT}$) are governing factors for larger cracks.

• Bulletin of the Korean Mathematical Society
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• v.57 no.1
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• pp.207-218
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• 2020

Some modular representations of reflection groups related to Weyl groups are considered. The rational cohomology of the classifying space of a compact connected Lie group G with a maximal torus T is expressed as the ring of invariants, H*(BG; ℚ) ≅ H*(BT; ℚ)^W(G), which is a polynomial ring. If such Lie groups are locally isomorphic, the rational representations of their Weyl groups are equivalent. However, the integral representations need not be equivalent. Under the mod p reductions, we consider the structure of the rings, particularly for the Weyl group of symplectic groups Sp(n) and for the alternating groups A_n as the subgroup of W(SU(n)). We will ask if such rings of invariants are polynomial rings, and if each of them can be realized as the mod p cohomology of a space. For n = 3, 4, the rings under a conjugate of W(Sp(n)) are shown to be polynomial, and for n = 6, 8, they are non-polynomial. The structures of H*(BT^n-1; 𝔽_p)^A_n will be also discussed for n = 3, 4.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.7
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• pp.679-686
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• 2002

Based on the alternating series expansion of error probability function due to phase noise in PSK systems, the performance evaluations for Tikhonov and Gaussian probability density functions were performed in this paper. The range of the signal-to-noise ratio of recovered carrier signal which provides the same dependency between the error performances by Tikhonov function and Gaussian function was analyzed via loss evaluation due to phase noise. The phase noise with 1/f$^2$ characteristic was generated based on the relationship of the phase noise spectral density and the modulation index for frequency modulation signal. Using the generated phase noise as the input signal for digital satellite communication receiver, the performance losses due to the phase noise were measured and evaluated with the analyzed performance characteristics.