• 대한용접접합학회:학술대회논문집
• /
• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
• /
• pp.361-365
• /
• 2002

Advancements in silicon phase control (SCR) technologies provide an arc welding power supply that has the capability to allow the alteration of the Alternating Current (AC) welding output. These technologies provide a square wave output involving sixteen frequency selections and multiple balance selections. While an AC out put is known to minimize magnetic disturbances associate with Direct Current (DC), the potentials of a non-sinusoidal waveform have not been explored. The focus of the paper is to determine the effects that the frequency and balance of an AC wave form output will have upon a high speed Submerge Arc (SAW) application. The test matrix of the project includes welding .250" steel plate. Joint type is square groove with a travel speed of 65 IPM. Each of the weld parameters was held constant, only the frequency and/or balance were altered between welds. Each frequency/balance combination involved three-gap spacing. Upon completion of the welds the bead profiles were measured and recorded. A relationships/trends were observed with various frequency and balance values. Optimum frequency and balance values were found for the .250" square groove application which permit consistent weld sizing, ease of slag removal, and minimal plate distortion.

• Journal of Electrical Engineering and Technology
• /
• 제11권3호
• /
• pp.662-669
• /
• 2016

In this work, nonlinear control of a three-phase shunt active power filter (SAPF) has been studied and compared to classical control based on proportional integral regulator. The control strategy is based on the direct current method using sliding mode control (SMC), where the aim is to regulate the average voltage across the dc bus of the inverter. Details are given for the control algorithm; the controller is comprised of a current loop which utilizes a hysteresis controller to generate the gating signals for the switching devices, and a nonlinear controller based on SMC law which is different from classical laws based on error between reference and measured output voltage of the inverter. Sliding surface applied in this work contains the whole of state variables, in order to ensure full control of the system behavior in the presence of disturbances that affect the supply source, the load parameters or the reference value. The designed controller offers advantage that it can gives the improvement of dynamic and static performances in cases of large disturbances. A comparison of the effects of PI control and SMC on the APF response in steady stat, under line variations, load variations, and different component variations is performed.

• Journal of Plant Biology
• /
• 제29권1호
• /
• pp.1-10
• /
• 1986

Intra- and inter-specific protoplast fusion of tobacco (Nicotiana tabacum cv. Virginia 115) and pea (Pisum sativum cv. Sparkle) were carried out in highly inhomogeneous alternating electric fields. Under the electric field of alternating current (AC, sine wave), 600 V/cm and 800 kHz for tobacco protoplast, and 600 V/cm and 700 kHz for pea protoplasts, the protoplasts were aggregated in pearl chains. Intra-specific protoplast fusions were most effectively induced within the aggregates of tobacco and pea, respectively, by the additional application of a single high field pulse of direct current (DC, square wave) at 1 kV/cm for 50 $mutextrm{s}$. Inter-specific fusions between protoplasts of the two plants were most effectively induced in the electric field of 600 V/cm and 700 kHz, and square wave pulse at 1 kV/cm for 50 $mutextrm{s}$. The duration of the pulse over the electrical breakdown voltages was simulated from 1 to 100 $mutextrm{s}$ in both tobacco and pea protoplast. The yield of the electrofusion products was significantly high (above 60%), compared with that (20%) of the standard fusion method by polyethylene glycol (PEG) 4,000, and the viability of electrofused protoplasts was above 70%, but that of PEG-fused protoplasts 8~16%, when determined by Evan's blue staining method.

• Journal of Electrical Engineering and Technology
• /
• 제9권5호
• /
• pp.1501-1510
• /
• 2014

Low voltage direct current (LVDC) distribution system is a suitable techno-economic candidate which can create an innovative solution for distribution network development with respect to rural electrification. This research focuses on the use of LVDC distribution system to replace some of KEPCO's existing traditional medium voltage alternating current (MVAC) distribution network for rural electrification in South Korea. Considering the technical and economic risks and benefits involved in such project, a comparative techno-economic analysis on the LVDC and the MVAC distribution networks is conducted using economic assessment method such as the net present value (NPV) on a discounted cash flow (DCF) basis as well as the sensitivity analysis technique. Each would play a role in an economic performance indicator and a measure of uncertainty and risk involved in the project. In this work, a simulation model and a computational tool are concurrently developed and employed to aid the techno-economic analysis, evaluation, and estimation of the various systems efficiency and/or performance.

• 한국산업융합학회 논문집
• /
• 제24권4_1호
• /
• pp.377-385
• /
• 2021

High voltage direct current(HVDC) systems has been an alternative method of a power transmission to replace high voltage alternate current(HVAC), which is a traditional AC transmission method. Due to technical limitations, Line commutate converter HVDC(LCC-HVDC) was mainly used. However, result from many structural problems of LCC-HVDC, the voltage source converter HVDC(VSC-HVDC) are studied and applied recently. In this paper, after analyzing the reactive power and output voltage ripple, which are the main problems of LCC-HVDC, the characteristics of each HVDC are summarized. Based on this result, a new LCC-HVDC structure is proposed by combining LCC-HVDC with the MMC structure, which is a representative VSC-HVDC topology. The proposed structure generates lower reactive power than the conventional method, and greatly reduces the 12th harmonic, a major component of output voltage ripple. In addition, it can be easily applied to the already installed LCC-HVDC. When the proposed method is applied, the control of the reactive power compensator becomes unnecessary, and there is an advantage that the cut-off frequency of the output DC filter can be designed smaller. The validity of the proposed LCC-HVDC is verified through simulation and experiments.

• 한국진공학회지
• /
• 제10권3호
• /
• pp.356-360
• /
• 2001

다음극 DC PACVD법에서 합성된 직경 80 mm, 두께 900 $\mu\textrm{m}$ ~ 950 $\mu\textrm{m}$의 자유막 다이아몬드웨이퍼의 특성을 분석하였다. 광투과현미경으로 결함의 분포를 관찰하고, Raman 및 IR 장치로 결정성을 분석하였다. 결함은 결정입계 부위에서 많이 관찰되었다. 또한 하나의 결정립에서 (111)면이 (100)면에 비해 상대적으로 많은 결함을 함유하였다. Raman 다이아몬드 peak의 FWHM 및 10.6 $\mu\textrm{m}$ 파장에서의 IR 투과도는 각각 4.6 $\textrm{cm}^{-1}$ /~5.3 $\textrm{cm}^{-1}$및 51.7% ~ 61.9%로, 두 값의 웨이퍼 내에서 균일성은 $\pm$7% 및 $\pm$9%이었다. 다이아몬드 웨이퍼의 결정성은 가운데에서 가장자리로 갈수록 저하되었다.

• 한국표면공학회지
• /
• 제38권5호
• /
• pp.202-206
• /
• 2005

Nitriding treatments were conducted on tool steel (SKD 61) at a temperature of $500^{\circ}C$ for 5 hr using high vacuum direct current (DC) plasma, with ammonia and argon as source gases. The structural and compositional changes produced in the nitrided layers by applying different ratios of Ar to $NH_{3}\;(n_{Ar}/n_{NH3}) were investigated using glancing x-ray diffraction (GXRD), optical microscopy, atomic force microscopy (AFM), micro-Vickers hardness testing, and pin-on-disc type tribometer. Nitriding case depths of around of $50{\mu}m$ were produced, varying slightly with different ratios of $n_{Ar}/n_{NH3}. It was found that the specimen surface hardness was 1150 Hv with $n_{Ar}/n_{NH3}=1, increasing to a maximum value of 1500 Hv with $n_{Ar}/n_{NH3}=5. With a further increase in ratio to $n_{Ar}/n_{NH3}=10, the surface hardness of the specimen reduced slightly to a value of 1370 Hv. These phenomena were caused by changes of the crystallographic structure of the nitride layers, i.e the $\gamma'-Fe_{4}N$ phase only was observed in the sample treated with $n_{Ar}/n_{NH3}$=1, and the intensity of the $\gamma'-Fe_{4}N$ phase were reduced but new phase of $\varepsilon'-Fe_{3}N$, which was known as a high hardness, with increasing $n_{Ar}/n_{NH3}. Also, the relative weight loss of counterface of the pin-on-disc with unnitrided steel was 0.2. And that of nitrided steel at a gas mixture ($n_{Ar}/n_{NH3}) of 1, 5, 7, and 10 was 0.4, 0.7, 0.6, and 0.5 mg, respectively. This means that the wear resistance of the nitrided samples could be increased by a factor of 2 at least than that of unnitrided steel.

• 대한화학회지
• /
• 제33권6호
• /
• pp.614-622
• /
• 1989

0.1M LiCl의 ethanol 용액에서 ${\alpha},{\beta}$-dibenzyl N-benzylidene L-aspartate의 전기화학적 환원을 direct current, differential pulse polarography, cyclic voltammetry 그리고 controlled potential coulometry 방법으로 연구하였다. ${\alpha},{\beta}$-dibenzyl N-benzylidene L-aspartate의 환원과정은 1단계(-0.92 volts vs. Ag-AgCl)에서 양성자 첨가와 2전자이동에 의한 완전 비가역의 CEC 혹은 CE 반응기구로 진행되었으며 ${\alpha},{\beta}$-dibenzyl N-benzyl L-aspartate가 생성되었다. 계면활성제가 포함된 용액에서 polarography 환원파는 전체적으로 약간 억제되었으며 Triton X-100의 농도가 진해질수록 비가역성을 증가시키는 것으로 나타났다. 생성물 분석과 pH 변화에 따른 전극환원과정에 대한 고찰로 전기화학적 반응기구를 제안하였다.

• 대한화학회지
• /
• 제32권3호
• /
• pp.186-194
• /
• 1988

계면활성 micelle을 형성하는 acetonitrile 용액을 O,O-dimethyl-O-(3-methyl-4-nitrophenyl)-phosphorothioate (Fenitrothion)의 전기화학적 환원을 direct current 및 differential pulase polarography, cyclic voltammetry 그리고 controlled potential coulometry 방법으로 연구하였다. Fenitrothion의 환원과정은 1단계로 4 전자 이동에 의한 부분 가역적 전자이동 화학반응(EC, EC)기구로 O,O-dimethyl-O-(3-methyl-4-hydroxyaminophenyl)-phosphorothioate를 형성하고, 더 높은 음전위에서 2 전자 이동에 따른 양성자 반응으로 phosphorus 원자와 phenoxy group의 단일 결합이 끊어지면서 주 생성물인 p-amino-m-cresol과 dimethyl thiophosphinic acid를 생성하였다. Sodium lauryl sulfate micelle 용액에서 polarography 환원파는 전체적으로 억제 되었으며 특히 1차 환원파는 음이온 micelle의 선택적 작용으로 2단계로 분리되었다.

• 마이크로전자및패키징학회지
• /
• 제17권3호
• /
• pp.71-77
• /
• 2010

마그네슘 합금은 낮은 밀도를 가지는 장점을 이용하여 자동차, 항공, 이동전화, 컴퓨터 등에 많이 쓰이고 있으나 기계적 강도가 낮고 내부식성이 좋지 않아 사용이 제한되었다. 마그네슘 합금 표면에 내식성 산화층을 형성하기 위하여 환경 친화적인 전해 플라즈마 산화법(PEO)을 연구에 사용하였다, PEO법은 수용약 중에서 플라즈마를 발생시켜 전기화학적 산화막을 형성시키는 방법이다. 인가전압과 전휴가 산화피마에 미치는 영향에 대하여 고찰하였다, 또한, 직류와 펄스전류를 사용하여 결과를 분석하였다. 펄스전류를 사용하고 정전류법을 사용한 경우에 치밀한 산화막을 얻을 수 있었다, 부식특성 분석을 위하여 양극산화분극방법을 이용하였다. 표면의 강도는 처리전의 AZ9ID에 비하여 5배 이상 증가하였다.