• Journal of Electrical Engineering and Technology
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• 제9권2호
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• pp.508-513
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• 2014

Heavy load start but light load operation is a common case in practical drive applications. When an induction motor is employed for such applications, its rated power is usually chosen according to the heavy load start. Then, during light load operation, its efficiency and power factor are low. To solve this problem, it is proposed to adjust the motor windings from the startup to the normal operation conditions. In this paper, arrangement of the adjustable windings is introduced, air gap field with different windings is investigated, and steady state operation performance under various loads is examined. It can be seen that by using proper winding arrangement both startup and operation performances are satisfactory.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.975-976
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• 2007

Thermal and mechanical stresses, caused by repetitive start and stop and load fluctuation during long time operation, on winding stator bars are one of the main causes for electrical degradation of insulating materials. To understand the degradation process, we manufactured bar specimens with the same processes that make generator winding stator bars and the specimens were subjected to various degrees of thermal cycling. Measurements of the insulation properties, such as dissipation factor, tip-up and partial discharge, for un-aged specimens and for specimens aged by thermal cycling at 50, 100, 250, 500 and 1000 thermal cycles were performed. Finally all specimens were tested to obtain electrical breakdown voltages. In this paper we present the data and electrical degradation analysis results obtained during this program.

• International Journal of Automotive Technology
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• 제7권5호
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• pp.527-534
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• 2006

Modern passenger cars with diesel engines are equipped with DOC(diesel oxidation catalyst) for the purpose of reducing HC and CO in the exhaust stream. Cold start exhaust emissions pose troubles here as on gasoline engine vehicles. As a result, some of the diesel passenger cars roll off todays the assembly lines with WCC(warm-up catalytic converter). Oxidation characteristics of the particulates in WCC is analyzed in this study by EEPS(engine exhaust particulate size spectrometer). The maximum number of PM is found to come out of WCC in sizes near 10nm when an HSDI diesel engine is operated under the conditions of high speed and medium to heavy load. When the temperature of the WCC exceeds $300^{\circ}C$, the number of PM smaller than 30 nm in diameter sharply increases upon passing through the WCC. Total mass of emitted PM gets reduced downstream of the WCC under low speed and light load conditions due to adsorption of PM onto the catalyst. Under conditions of high speed and medium to heavy load, the relatively large PM shrink or break into fine particles during oxidation process within the WCC, which results in more mass fraction of fine particles downstream of the WCC.

• 한국자동차공학회논문집
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• 제13권2호
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• pp.101-107
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• 2005

In this paper, optimized operating parameters were found using multi-dimensional engine simulation software (KIVA-3V) and micro-genetic algorithm for heavy duty diesel engine. The engine operating condition considered was at 1,737 rev/min and 57 % load. Engine simulation model was validated using an engine equipped with a high pressure electronic unit injector (HEUI) system. Three important parameters were used for the optimization - boost pressure, EGR rate and start of injection timing. Numerical optimization identified HCCI-like combustion characteristics showing significant improvements for the soot and $NO_X$ emissions. The optimized soot and $NO_X$ emissions were reduced to 0.005 g/kW-hr and 1.33 g/kW-hr, respectively. Moreover, the optimum results met EPA 2007 mandates at the operating point considered.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제35회 추계학술대회논문집
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• pp.331-334
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• 2010

두산중공업(주)에서 개발 중인 발전용 가스터빈 DGT-5 엔진의 작동 특성을 평가하였다. 다양한 연료 스케쥴과 여러 가지 조합의 bleed valve 개폐 제어에 대한 영향을 분석하기 위한 시험을 통해 시동 특성을 개선하였고, 시동부터 부하운전 전체 작동 영역에서 압축기에서의 불안정 현상 없이 엔진이 안정적으로 작동됨을 확인하였다. 순간적인 부하 변동과 load rejection에 대한 엔진의 동적 거동 분석을 통해 실제 계통 병입 조건에서 급격한 부하변동 시 엔진이 안정적으로 제어될 수 있음을 확인하였다.

• Journal of Electrical Engineering and Technology
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• 제9권6호
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• pp.1967-1977
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• 2014

In this paper, for the development of a safe and reliable DC home appliance suitable for DC home power supply system, we classified a number of inherent problems with help of the comparative analysis of existing AC and new DC home appliance. Several new technical problems of DC home appliances are mainly linked to the DC transient state. Among them, this paper concentrates on start-up inrush current problem, uni-polarity problem, and heavy DC load control problem. And to address these problems, we herein present an implementation of robust safety circuits for DC home appliances. Specifically, we investigate several multi-circuit countermeasures and select the best among them through comparative evaluation, based on theoretical, simulational, and experimental results.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.847-852
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• 2001

A thorough understanding of the transient behavior during load following and start-up is essential in the design and operation of an heat recovery steam generator(HRSG). During this period of time, material that is exposed to high temperature and experiences a large temperature variation is subject to high thermal stress. APESS(Advanced Plant Engineering & Simulation System) is a dynamic simulation software for power plant which is under being developed by Doosan Heavy Industries & Construction Co., Ltd. This paper present the introduction of APESS and the result of simulation for an heat recovery steam generator.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 추계학술대회 논문집 학회본부
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• pp.544-549
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• 1997

Injector of high voltage or linear ion accelerator is intended to generate, extract and form beam of certain species with required parameters at the entrance of accelerating structure or, for low energy case, directly in the processing chamber (end station). Injector is the main part defining the ion accelerator performance and reliability. Its power supply and control system (PSCS) features are conditioned by placing the injector equipment at high voltage potential and by complexity of the plasma-beam load. The injector's PSCS should provide: - Transmission of electric power onto high voltage (h/v) terminal; - Obtaining of required output characteristics for injector equipment operation; - Transmission of the operational data and start/stop signals from h/v terminal to control cabinet; - Rremote control of injector; - Withstanding the high voltage breakdowns and X-ray radiation; - Compatibility with other equipment. The paper is concerned with analysis of injectors' PSCS structure and description of the system developed for 50 keV, 20 mA heavy ion injector.

• 한국기계기술학회지
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• 제13권4호
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• pp.85-91
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• 2011

Experimental analysis has been carried out to investigate thermal characteristics of hydraulic system in special vehicles. Hydraulic system performance is largely influenced by oil temperature, and there are considerable performance decline and malfunctions in the system for high temperature conditions caused by heavy load and continuous operation. Transient oil temperature and pressure variation are analyzed and heat generation rates in the several main system parts are compared for various flow rates. With the start of system operation oil temperature gradually increases, and viscosity deceases by about 70% as temperature increases from $20^{\circ}C$ to $80^{\circ}C$. Operation pressure in the hydraulic system decreases with oil temperature, and its variation rate becomes less steep as oil temperature increases. Heat generation rate in hydraulic pump also depends on the oil temperature, and it reaches maximum near $50^{\circ}C$. These results in this study can be applied to optimal design of efficient hydraulic system in special vehicles.

• 한국통신학회논문지
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• 제40권9호
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• pp.1693-1698
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• 2015

본 논문은 이중 펄스 폭을 지닌 PFM(Pulse-Frequency Modulator) 부스트 변환기를 제안한다. 부스트 변환기의 구동 회로 구조는 밴드 갭 기준 전압 발생 회로와 이를 이용해 여러 가지의 기준 전압을 생성하는 기준 전압 발생 회로, 소프트 시동 회로, 에러 증폭기, 고속 전압 비교기, 인덕터 전류 센싱 회로, 펄스 폭 발생 회로로 구성되어있다. 변환기는 부하 전류 상태에 따라 서로 다른 최대 인덕터 전류 값을 갖도록 구성해 부하 범위를 넓히고, 출력 전압 리플을 감소하도록 했다. 제안된 PFM 부스트 변환기는 입력 전압으로 3.7V를 받고, 18V의 출력 전압을 생성한다. 구동 가능한 부하 전류는 0.1~300mA의 범위를 가진다. 모의실험 결과 저 부하 전류 동작 구간에서 0.43%, 고 부하 전류 동작 구간에서는 0.79%의 출력 전압 리플을 보였다. 변환기는 저 부하 구간에서 85%의 효율을 나타내며 20mA에서 86.4%로 최대의 효율을 나타냈다.