• 플랜트 저널
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• 제17권2호
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• pp.48-53
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• 2021

900 MW 복합화력발전소의 경우 소내 부하의 대부분은 회전기기이며 저역률로 운전되고 있고 역률 저하는 무효전력을 증가시켜 기기의 효율 저하 및 불필요한 소내 전력을 소비하는 원인이 된다. 본 연구에서는 이러한 문제점을 해결할 수 있는 방안인 무효전력을 흡수 및 제거하는 무효전력보상장치를 6.9 kV 소내 모선에 설치하여 운전함으로써 그에 대한 결과를 제시하고자 한다. 본 시스템의 적용 결과 우선 회전기기의 역률이 0.22로 개선 및 소내 부하전력량 1.4% 감소됨을 확인하였고 발전기 열효율 0.1%, 발전출력810 kW 증가함을 알 수 있었다. 다음으로 투자비 1.5억 원 대비 소내 전력손실비용 2억 원/년 감소 및 매출액 10억 원/년 증가로 경제성 있음으로 분석되었고 향후 건설 및 운영 시 비용절감이 가능함을 확인하였다.

• 전기학회논문지P
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• 제54권1호
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• pp.41-46
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• 2005

Most of LV customer have applied the 3-phase four wire system distribution system because it has advantage of supplying both of 1-phase & 3-phase loads simultaneously. Due to its structural simplicity, it is more convenient for use rather than the conventional separated scheme. But voltage unbalance more commonly emerges in individual customer loads due to phase load unbalance, especially where, single-phase power loads are used. Voltage unbalance factor(VUF) represents the loss of symmetry in the supply(magnitude and angle). It leads some problems such as de-rating or power losses. In this paper, voltage and current waveform in the actual fields have been measured and analyzed in relation with internationally allowable voltage unbalance limits.

• Tribology and Lubricants
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• 제32권4호
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• pp.132-139
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• 2016

The piston of a marine diesel engine works under severe conditions, including a combustion pressure of over 180 bar, high thermal load, and high speed. Therefore, the analyses of the fatigue strength, thermal load, clamping (bolting) system and lubrication performance are important in achieving a robust piston design. Designing the surface profile and the skirt ovality carefully is important to prevent severe wear and reduce frictional loss for engine efficiency. This study performs flexible multi-body dynamic and elasto-hydrodynamic (EHD) analyses using AVL/EXCITE/PU are performed to evaluate tribological characteristics. The numerical techniques employed to perform the EHD analysis are as follows: (1) averaged Reynolds equation considering the surface roughness; (2) Greenwood_Tripp model considering the solid_to_solid contact using the statistical values of the summit roughness; and (3) flow factor considering the surface topology. This study also compares two cases of skirt shapes with minimum oil film thickness, peak oil film pressure, asperity contact pressure, wear rate using the Archard model and friction power loss (i.e., frictional loss mean effective pressure (FMEP)). Accordingly, the study compares the calculated wear pattern with the field test result of the piston operating for 12,000h to verify the quantitative integrity of the numerical analysis. The results show that the selected profile and the piston skirt ovality reduce friction power loss and peak oil film pressure by 7% and 57%, respectively. They also increase the minimum oil film thickness by 34%.

• 전자공학회논문지
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• 제53권7호
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• pp.121-127
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• 2016

본 논문에서는 고조파로 전압과 전류가 왜곡된 상황에서 정확하게 기본파의 역률을 측정할 수 있는 방법을 제안한다. 제안한 역률 계측 방법에서는 전압과 전류를 DQ회전좌표계로 변환한 후 유효전력과 무효전력을 계산하여 역률값을 구하게 된다. 기존의 역률 계측방법과 제안한 방법을 수식적으로 비교하여 제시하고, 제안한 방법은 전압과 전류 모두 고조파 왜곡된 상황에서도 기본파의 역률을 정확하게 계측할 수 있는 것을 MATLAB을 이용한 모의실험에서 확인한다. 제안한 역률 계측방법을 자동역률제어장치에 적용할 경우 고조파 왜곡 환경에서 역률 보상 성능을 최대화 할 수 있다. 그 결과 수용가에서는 역률 개선을 통한 전기료 감소, 선로손실 감소, 부하 용량 증대 효과가 기대된다. 특히 발전 사업가 측에서는 역률 보상 성능의 향상으로 송전 여유 용량 확보와 발전량 절감이 가능하다.

• 전자공학회논문지
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• 제54권8호
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• pp.107-114
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• 2017

본 논문에서는 3상 4선식 전력계통에서 새로운 전압제어 방식의 역률보상시스템을 제안한다. 제안하는 전압제어 방식의 역률보상시스템은 슬라이닥을 이용하여 가변되는 출력전압을 커패시터에 인가하는 것으로 보상에 필요한 무효전력을 생성한다. 기존의 커패시터 뱅크 방법을 이용하는 역률보상시스템은 선택 가능한 커패시터 용량이 한정되어 있어 부하 상황에 따라 역률보상 오차가 발생하지만, 제안 시스템은 변화하는 부하를 추종하여 오차 없이 역률을 100%까지 보상할 수 있다. 본 논문에서는 3상 4선식 전력계통에서 전압제어 방식의 역률보상시스템과 제어 알고리즘을 개발하였고 모의실험과 실험을 통해 성능을 확인한다. 제안 시스템을 수용가에 설치할 경우 역률 개선을 통한 전기료 감소, 선로손실 감소, 부하 용량 증대 효과가 기대된다. 특히 발전 사업가 측에서는 역률 보상 성능의 향상으로 송전 여유 용량 확보와 발전량 절감이 가능하다.

• 전력전자학회논문지
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• 제20권1호
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• pp.65-71
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• 2015

This paper presents the efficiency analysis of a critical current mode interleaved PFC rectifier, in which each of three different semiconductor switches is employed as the active switch. The Si FET, SiC FET, and GaN FET are consecutively used with the prototype PFC rectifier, and the efficiency of the PFC rectifier with each different semiconductor switch is analyzed. An equivalent circuit model of the PFC rectifier, which incorporates all the internal losses of the PFC rectifier, is developed. The rms values of the current waveforms main circuit components are calculated. By adapting the rms current waveforms to the equivalent model, all the losses are broken down and individually analyzed to assess the conduction loss, switching loss, and magnetic loss in the PFC rectifier. This study revealed that the GaN FET offers the highest overall efficiency with the least loss among the three switching devices. The GaN FET yields 96% efficiency at 90 V input and 97.6% efficiency at 240 V, under full load condition. This paper also confirmed that the efficiency of the three switching devices largely depends on the turn-on resistance and parasitic capacitance of the respective switching devices.

• Journal of Electrical Engineering and Technology
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• 제12권1호
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• pp.126-133
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• 2017

This paper deals with the effects of welding, which is done to fix the stator stack, on a motor in case of fabricating a prototype motor that is manufactured in a small quantity. In the case of a small motor, the stator is designed and fabricated with the segmented core as a way to raise the fill factor of winding wire to the utmost within a limited size. In case of fabrication by welding both inside and outside of the stator in order to fix the segmented-core stator, the effects of stack are ignored, and the eddy current loss occurs. This paper performed the no-load test on an IPM-type BLDC motor for driving the suction fan of a vacuum cleaner, which was manufactured by using a segmented-core stator. As a result of the test, it was found that input power more than expected was supplied. To analyze the effects of welding by using the finite element analysis method and verify them experimentally, a stator was re-manufactured by bonding, and input power supplied during the no-load test was compared.

• 한국자동차공학회논문집
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• 제11권2호
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• pp.203-210
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• 2003

A simulation study was carried to analyze the vehicle fuel consumption on component basis. Experiments was also carried out to identify the simulation results, under FTP-75 Hot Phase driving conditions. and arbitrary driving conditions. A good quantitative agreement was obtained. Based on the simulation, fuel energy was used in pumping loss(3.7%), electric power generation(0.7%), engine friction(12.7%), engine inertia(0.7%), torque converter loss(4.6%), drivetrain friction(0.6%), road-load(9.2%), and vehicle inertia(13.4%) under FTP-75 Hot Phase driving conditions. Using simulation program, the effects of capacity factor and idle speed on fuel consumption were estimated. A increment of capacity factor of torque converter resulted in fuel consumption improvement under FTP-75 Hot Phase driving conditions. Effect of a decrement of idle speed on fuel consumption was negligible under the identical driving conditions.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2002년도 전력전자학술대회 논문집
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• pp.723-726
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• 2002

In this paper, a high efficiency leakage transformer for neon tube is developed to improve its power factor, to reduce its core loss and weight by using a technique of shape optimization and direction of grain-oriented silicon steel sheet. A protection circuit is designed for all types of neon transformer loaded with one or more neon lamps. Whenever the neon tube fails to be started up or comes to the life end, or encounters faults with open-circuits at the output terminals of the neon transformer, the protection circuit will be initiated to avoid more critical hazards. These neon transformers need a protection circuit to prevent from current stresses on circuit components by neon tube fail. The input of the transformer is automatically cut off when the abnormal condition occurs, preventing waste of no-load power. As the results of the study, the core weight is reduced by $11\%$, the power factor improved by $5\%$ and the efficiency increased by $6\%$ compared with the conventional type due to the employment of the grain-oriented steel sl)eel and the optimized core shape.

• 조명전기설비학회논문지
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• 제19권8호
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• pp.62-69
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• 2005

본 논문에서는 보조 스위치의 하드 스위칭 문제를 개선한 AC/DC PFC(Power-Factor-Correction) ZVT(Zero-Voltage-Transition) Boost 컨버터에 관하여 논하였다. 기존의 AC/DC PFC ZVT Boost 컨버터는 주 스위치 턴온 시 보조 스위치를 함께 동작시켜 경부하시에도 강제적으로 영전압 스위칭이 가능하게 함으로써 전 부하범위에서 주 스위치 손실을 저감하였다. 그러나 보조 스위치에서의 손실이 크며 주 스위치의 턴온시 역방향 전류가 증가하는 문제점을 지닌다. 따라서 본 연구에서는 기존의 ZVT 컨버터에 단지 하나의 다이오드를 추가함으로써 보조 스위치의 전류 스트레스 및 주 스위치의 턴온시 역방향 전류를 감소시키게 되어 효율 향상을 기할 수 있었다. 본 논문에서는 MOSFET를 사용하여 640[W]급 시작품을 제작, 100[kHz]에서 실험하였다.