• 대한기계학회논문집B
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• 제24권6호
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• pp.753-759
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• 2000

Photoelectric charging is a very efficient way of charging small particles. This method can be applied to combustion measurement, electrostatic precipitator, metal separation and control of micro-contamination. To understand the photoelectric charging mechanism, particle charging of silver by exposure to ultraviolet is investigated in this study. Average charges and charge distributions are measured at various conditions, using two differential mobility analyzers, a condensation nucleus counter, and an aerosol electrometer. The silver particles are generated in a spark discharge aerosol generator. After that process, the generated particles are charged in the photoelectric charger using low-pressure mercury lamp that emits ultraviolet having wavelength 253.7 nm. The results show that ultra-fine particles are highly charged by the photoelectric charging. The average charges linearly increase with increasing particle size and the charge distribution change with particle size. These results are discussed by comparison with previous experiments and proposed equations. It is assumed that the coefficient of electron emission probability is affected by initial charge. The results also show that the charge distribution of a particle is dependent on initial charge. Single changed particle, uncharged particle and neutralized particle are compared. The differences of charge distribution in each case increase with increasing particle size.

• Journal of Power Electronics
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• 제17권1호
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• pp.127-135
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• 2017

Recently the researches on modular multi-level converter (MMC) are being highlighted because high quality and efficient power transmission have become key issues in high voltage direct current (HVDC) systems. This paper proposes an improved pre-charging method for the sub-module (SM) capacitor of MMC-based HVDC systems, which operates in the nearest level control (NLC) modulation and does not need additional circuits or pulse width modulation (PWM) techniques. The feasibility of the proposed method was verified through computer simulations for a scaled 3-phase 10kVA MMC with 12 SMs per each arm. Hardware experiments with a scaled prototype have also been performed in the lab to confirm the simulation results.

• 한국전기전자재료학회논문지
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• 제36권5호
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• pp.474-481
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• 2023

This paper is an experimental study on the optimal operating conditions of direct charging type electrospray for particulate matter collection. To perform the research, a direct charging type electrospray visualization system was configured to photograph the spray shape of microdroplets, and experiments were performed with varying electrode distance, flow rate, and applied voltage, which are the main factors affecting the particulate matter collection efficacy. Through image processing, the total number of microdroplets according to each condition was analyzed, and the number of microdroplets with a diameter of 1.5 mm or less was confirmed. In addition, by calculating the number of microdroplets per power consumption according to the applied voltage, the optimal operating conditions were derived in terms of energy consumption efficacy, and the microdroplet size distribution was analyzed under the optimal operating conditions. As a result of the experiment, it was confirmed that the optimal operating condition was at a flow rate of 10 mL/min and a voltage of -20 kV in case of 5 mm electrode distance, and at a flow rate of 15 mL/min and a voltage of -30 kV in case of 100 mm electrode distance.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2005년도 추계학술대회 논문집
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• pp.736-741
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• 2005

This paper presents electric characteristics analysis and safe configuration for extension power supply between existent 6.6kV ungrounded distribution system and establishment and improvement 22.9kV direct grounding distribution system. For this, we model 6.6kV ungrounded and 22.9kV direct grounding distribution system of urban underground, ground region. and rural electrical, unelectrical region using PSCAD/EMTDC and analyze voltage drop, charging current, ground and short fault through simulation. To analyze electric characteristics of extension power supply, we simulate extension power supply of overhead line of 6.6kV ungrounded system and underground line of 22.9kV direct grounding system of rural electrical region and propose operation condition for safe extension power supply through result of analysis. Characteristics of voltage drop, charging current, ground and short fault appear almost similarly with electrical characteristic of direct power supply. However, because unbalance of phases may cause relay's malfunction of ungrounded system and ground fault current of direct grounding system may demage facilities of ungrounded system, we propose safe system configuration such as impedance grounding system of neutral point.

• 전기학회논문지
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• 제65권10호
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• pp.1655-1663
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• 2016

Recently the researches on Modular Multi-level Converter (MMC) are being highlighted because high quality and efficient power transmission are key issues in the High Voltage Direct Current (HVDC) transmission system. This paper proposes an improved pre-charging method for the sub-module capacitors in MMC that operates in Nearest Level Control (NLC) modulation. The proposed method does not require additional circuits or Pulse Width Modulation (PWM) techniques. The feasibility of proposed method was verified through computer simulations for a scaled 3-phase 10kVA MMC with 12 sub-modules per each arm. Hardware experiments with a scaled prototype were performed in the lab to confirm the simulation results.

• 한국산업융합학회 논문집
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• 제24권6_1호
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• pp.669-681
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• 2021

As the supply of xEV in Korea is rapidly increasing, the amount of waste batteries is expected to increase rapidly, but the current recycling system for waste xEV batteries is very insufficient. In order to properly utilize the xEV reusable battery module, it is essential to classify it into a type that has similar discharge characteristics to the current state of health(SOH), which is the discharge capacity of the battery. This paper proposes a system that can minimize the exchange of energy with the KEPCO system by using the charging/discharging method by circulating power between batteries in order to minimize the power consumption when charging and discharging waste batteries. In the proposed system, a function to measure parameters during the charging/discharging test of the waste battery was implemented to build a customized big date for the test waste battery. In addition, the dynamic characteristics of the proposed circuit were analyzed using PSIM, which is useful for power electronics analysis, and the validity of the proposed circuit was verified through experiments.

• 한국자동차공학회논문집
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• 제12권1호
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• pp.10-16
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• 2004

The Homogeneous Charge Compression Ignition (HCCI) engine has advantage for reducing the NOx and P.M. simultaneously. Therefore, HCCI engine is receiving attention as a low emission diesel engine concept. This study was carried out to investigate the characteristics of combustion and exhaust emission for operating conditions in a direct injection type of HCCI engines such as supercharged and naturally aspirated using diesel fuel and additive. From the experimental result, we found that cool flame was always appeared and also it was difficult to control combustion characteristics by changing the injection timing in HCCI. In addition, at the lean air-fuel ratio and high speed range, it was observed that charging air pressure, additive or increasing intake air temperature is effective to increase combustion performance and reduce exhaust emission. We concluded that chemical reaction by the increasing intake air temperature or additive without physical improvement has limitation for reduction of exhaust emission.

• 화약ㆍ발파
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• 제24권2호
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• pp.1-8
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• 2006

본 연구는 규석광의 터널 굴착시 굴진장 향상과 사압현상 및 소결현상을 예방하기 위해 모든 장약공의 장약밀도를 다르게 적용하였다. 이 때 심발공은 동일 장약공내에 2개의 뇌관을 이용한 정기폭과 역기폭의 복합기폭방식을 도입하였다. 자유면 형성이 어려운 공저부분은 높은 장약밀도로 장전하고, 주상부분은 공저보다 낮은 장약밀도로 장전함으로써 폭약의 위력이 효과적으로 암반에 대응할 수 있는 공법인 복합장약기폭시스템을 개발하였다. 그 결과 경암이나 장공발파에서 흔히 발생되는 사압현상 및 소결현상 등을 방지할 수 있었다. 또한 1회 천공장 대비 굴진장을 95% 이상 증대시킴으로써 약 15% 정도의 시공능율이 향상되고 비장약량이 20% 정도 감소되었다.

• 전기의세계
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• 제18권4호
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• pp.7-15
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• 1969

In this method the condenser excite winding has the phase angle of 90 electrical degree, with the load winding in stator. The condenser excite wing is connected with the condenser while the load winding is with the full rectifer. Direct and quardrature axis components of rotating field winding are composed, of balanced two phase winding, and each one of them is connected with half wave rectifiers. Initically, small amount of lead current can be induced at the condenser excite winding by residual magnetism of rotor. The induced lead current forces the rotating field winding to be excited by synchronous alternating magnetic field. The speed electromotive force, there for, induced in rotating field winding shall electro magnetize the rotating field pole by rotating half wave rectifiers. In the case of the charging generator directly coupled with engines at the operation of wide range speed, the generated region, such as vehicles, aircraft, ships etc, is occured. In conclusion, we can take the advantage of, omitting of voltage regurator and current limiter for charging load and reducing the consumption of fuel using the generated region which can be devided in to Impossible generated region, Generated region, and suspension generated region.

• 에너지공학
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• 제10권4호
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• pp.357-362
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• 2001

충진농도, 냉매 팽창밸브 개도, 그리고 약용액의 유량 변화에 따른 벤치타입 암모니아-물 흡수식 열교환 사이클에 대한 실험을 수행한 결과 시스템의 충진농도가 증가할수록 냉방능력이 증가하였으며, 최적의 충진농도가 존재함을 알았다. 그리고 냉매 팽창 밸브의 개도는 응축기 출구의 직접적인 영향을 주고 있으며 최적의 과냉도가 0~4$^{\circ}C$임을 알았다. 또한 약용액의 유량이 증가시킬수록 증발압력과 강용액의 농도가 즐어들었으며, 냉방능력과 COP가 최대가 되는 최적의 약용액 유량이 존재하였다.