• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.8
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• pp.651-658
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• 2014

Notification 2013-611 of MOLIT has come into effect. It relates primarily to new standard impact source. In this study, an in-depth experimental analysis of the difference between a bang machine and an impact ball was performed via field testing of shear wall and flat plate structure at 51 sites. This paper focuses on the difference in single number quantities between a bang machine and an impact ball. At wall thicknesses of 180 and 210 mm in shear wall structure, the single number quantities exhibited differences of 3.1 and 4.5 dB, respectively, and at thicknesses exceeding 250 mm in flat plate structure, the difference was constant at 4.6 dB. With regard to flat plate structures, the single-index difference increased up to 11 dB as the thickness of the floor slab increased. In general, the highest level of contribution for the bang machine was 63 Hz, irrespective of thickness determining bandwidth. The highest level for the impact ball were 63 Hz and 125 Hz. In future research, when reviewing additional field performance measurement data, it will be necessary to consider a detailed examination instead of the current method of uniformly adding 3 dB for all thicknesses and types of structures.

• Journal of Power Electronics
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• v.11 no.2
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• pp.194-201
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• 2011

The air flow supplied to a fuel cell system is one of the most significant factors in determining fuel efficiency. The conventional method of controlling the air flow is to fix the oxygen supply at an estimated constant rate for optimal efficiency. However, the actual optimal point can deviated from the pre-set value due to temperature, load conditions and so on. In this paper, the maximum efficiency point tracking (MEPT) algorithm is proposed for finding the optimal air supply rate in real time to maximize the net-power generation of fuel cell systems. The fixed step MEPT algorithm has slow dynamics, thus it affects the overall efficiency. As a result, the variable step MEPT algorithm is proposed to compensate for this problem instead of a fixed one. The complete small signal model of a PEM Fuel cell system is developed to perform a stability analysis and to present a design guideline. For a design example, a 1kW PEM fuel cell system with a DSP 56F807 (Motorola Inc) was built and tested using the proposed MEPT algorithm. This control algorithm is very effective for a soft current change load like a grid connected system or a hybrid electric vehicle system with a secondary energy source.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.16 no.5
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• pp.53-60
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• 2002

This paper presents exact autotransformer-fed AC electric railroad system modeling using constant current mode, and single-phase STATCOM(Static Synchronous Compensator) which has an effect on electric railroad system. An AC electric railroad is rapidly changing single-phase feeding electric power. To avoid voltage fluctuation under single phase loads, electric power should be received from a large source. The system modeling theory is based on the solution of algebraic. The AC electric railroad load model is nonlinear. Therefore this paper is considered nonlinear load using PSCAD/EMTDC. And the proposed modeling method is considered the line self-impedances and mutual-impedances that techniques for the AC electric railroad system modeling analysis, and that single-phase STATCOM can reliably compensate the voltage drop. In the case study, the allowance range of feeding voltage is 22.5∼27.5 kV, AT-fed AC electric railroad system circuit is analyzed by loop equation both normal and extension modes. The simulation objectives are to calculate the catenary and rail voltages with respect to ground, as the train moves along a section of line between two adjacent ATs. The results show that single-phase STATCOM can reduce the voltage drop in the feeding circuit and improve the power quality at AC electric railroad system by compensating the reactive power.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.2
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• pp.147-152
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• 2012

This paper dealt with the frequency component analysis of acoustic signals produced by corona and series-arc discharges as a diagnostic technique for closed-switchboards. Corona and series-arc discharge were simulated by a needle-plane electrode and an arc generator specified in UL1699, respectively. Acoustic signal was detected by a wideband acoustic sensor with a frequency bandwidth of 4 Hz~100 kHz (-3 dB). We analyzed frequency spectrums of the acoustic signals detected in various discharge conditions. The results showed that acoustic signals mainly exist in ranges from 30 kHz to 60 kHz. From the experimental results, an acoustic detection system which consists of a constant current power supply (CCP), a low noise amplifier (LNA) and a band pass filter was designed and fabricated. The CCP separates the signal component from the DC source of acoustic sensor, and the LNA has a gain of 40 dB in ranges of 280 Hz~320 kHz. The high and the low cut-off frequency are 30 kHz and 60 kHz, respectively. We could detect corona and series-arc discharges without any interference by the acoustic detection system, and the best frequency is considered in ranges of 30 kHz~60 kHz.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.11
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• pp.755-761
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• 2017

In railways powered by AC power, the main circuit breaker (MCB) is used for supplying the electric power to the catenary of the vehicle. Generally, the main circuit breaker is located between the pantograph and the main transformer, and the phase of the power applied to the vehicle changes according to the operation timing of the main circuit breaker. The operation of the main circuit breaker should be actively controlled according to the phase of the power source, since the phase of the power causes unintended transient states in the vehicle's electrical system in the form of an inrush current and surge voltage. However, the MCB has a delay time when it operates which is not constant. Therefore, an intelligent controller is needed to predict the operation delay time and control the opening and closing of the MCB.

• Korean Journal of Materials Research
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• v.5 no.1
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• pp.3-11
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• 1995

$(TiO_{2})$ thin films were deposited on p-Si(100) substrate by APMOCVD using titanium isopropoxide as a source material. The deposition mechanism was well explained by the simple boundary layer theory and the apparent activation energy of the chemical reaction controlled process was 18.2kcal /mol. The asdeposited films were polycrystalline anatase phase and were transformed into rutile phase after postannealing. The postannealing time and the film thikness as well as the postannealing temperature also affected the phase transition. The C-V plot exhibited typical charateristics of MOS diode, from which the dielectric constant of about 80 was obtained. The capacitance of the annealed film was decreased but those of the Nb or Sr doped films were not changed. I-V characteristics revealed that the conduction mechanism was hopping conduction. The postannealing and the doping of Nb or Sr cause to decrease the leakage current and to increase the breakdown voltage.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.51-51
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• 2008

Carbon nanotubes (CNTs) have long been reported as an ideal material due to their excellent electrical conductivity and chemical and mechanical stability as well as their high aspect ratios for field emission devices. CNT emitters made by screen printing the organic binder-based CNT paste may act as a source to release gases inside a vacuum panel. These residual gases may cause a catastrophic damage by electrical arcing or ion bombardment to the vacuum microelectronic devices and may change their physical or electrical properties by adsorbing on the CNT emitter surface. In this study, we analyzed the composition of residual gases inside the vacuum-sealed panel by residual gas analyzer (RGA), investigating the effects of individual gases of different kinds at several pressures on the field emission characteristics of CNT emitters. The residual gases included $H_2$, CO, $CO_2$, $N_2$, $CH_4$, $H_2O$, $C_2H_6$, and Ar. Effect of residual gases on the field emission was studied by observing the variation of the pulse voltages with the duty ratio of3.3% to keep the constant emission current of $28{\mu}A$. Each gas species was introduced to a vacuum chamber up to three different pressures ($5\times10^{-7}$, $5\times10^{-6}$, and $5\times10^{-5}$ torr) each for 1 h while electron emission was continued. The three different pressure regions were separated by keeping a high vacuum of $\sim10^{-8}$ torr for a 1 h. The emission was terminated 6 h after the third gas exposure was completed. Field emission characteristics under residual gases will be discussed in terms of their adsorption and desorption on the surface of CNTs and the resultant change of work function.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.12
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• pp.2446-2452
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• 2009

A Ceramic Metal-halide lamp is achieved by adding multiple metals to a basic mercury discharge. Because the vapor pressure of most metals is very much lower than mercury itself, metal-halide salts of the desired metals, having higher vapor pressures, are used to introduce the material into the basic discharge. The metal compounds are usually polyatomic iodides, which vaporize and subsequently dissociate as they diffuse into the bulk plasma. Metals with multiple visible transitions are necessary to achieve high photometric efficiency and good color. Compounds of Sc, Dy, Ho, Tm, Ce, Pr, Yb and Nd are commonly used. The maximum visible efficacy of a Ceramic Metal Halide lamp, under the constant of a white light source, is predicted to be about 450lm/W. This is controlled principally by the chemical fill chosen for a particular lamp. Current these lamps achieve 130lm/W and these life time are the maximum 16,000[hr]. So factors of performance lower are necessary to improve lamp performance. In this paper, we analyzed factors of performance lower by accelerated deterioration test. The lamp was operated with short duration turn-on/turn-off procedure to enhance the effect due to electrode sputtering during lamp ignition. The tested lamp that was operated with a longer turn-on/off(20/20 minutes) showed blackening, changed distance between electrodes and lowered color rendering & color temperature by losses of Dy at 421.18nm, I at 511nm, T1 at 535nm and Na at 588nm compared with the new lamp.

• Journal of Power Electronics
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• v.16 no.2
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• pp.464-472
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• 2016

This study applies the selective harmonic elimination (SHE) technique to design and operate a regulated AC/DC/AC power supply suitable for maritime military applications and underground trains. The input is a single 50/60 Hz AC voltage, and the output is a 400 Hz regulated voltage. The switching angles for a multi-level inverter and transformer turns ratio are determined to operate with special connected transformers with equal power ratings and produce an almost sinusoidal current. As a result of its capability of directly controlling harmonics, the SHE technique is applicable to apparatus with congenital immunity to specific harmonics, such as series-connected transformers, which are specially designed to equally share the total load power. In the present work, a single-phase 50/60 Hz input source is rectified via a semi-controlled bridge rectifier to control DC voltage levels and thereby regulate the output load voltage at a constant level. The DC-rectified voltage then supplies six single-phase quazi-square H-bridge inverters, each of which supplies the primary of a single-phase transformer. The secondaries of the six transformers are connected in series. Through off-line calculation, the switching angles of the six inverters and the turns ratios of the six transformers are designed to ensure equal power distribution for the transformers. The SHE technique is also employed to eliminate the higher-order harmonics of the output voltage. A digital implementation is carried out to determine the switching angles. Theoretical results are demonstrated, and a scaled-down experimental 600 VA prototype is built to verify the validity of the proposed system.

• Steel and Composite Structures
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• v.19 no.6
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• pp.1549-1560
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• 2015

This paper presents the characterization of fatigue crack in the A283 Grade C steel using the MMM method by identifying the effects of magnetic flux leakage towards the crack growth rate, da/dN, and crack length. The previous and current research on the relation between MMM parameters and fatigue crack effect is still unclear and requires specific analysis to validate that. This method is considered to be a passive magnetic method among other Non-Destructive Testing (NDT) methods. The tension-tension fatigue test was conducted with a testing frequency of 10 Hz with 4 kN loaded, meanwhile the MMM response signals were captured using a MMM instrument. A correlation between the crack growth rate and magnetic flux leakage produces a sigmoid shape curve with a constant values which present the gradient, m value is in the ranges of 1.4357 to 4.0506, and the y-intercept, log C in the ranges of $4{\times}10^{-7}$ to 0.0303. Moreover, a linear relation was obtained between the crack length and magnetic flux leakage which present the R-Squared values is at 0.830 to 0.978. Therefore, MMM method has their own capability to investigate and characterize the fatigue crack effects as a main source of fracture mechanism for ferrous-based materials.