• Journal of Electrical Engineering and Technology
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• 제2권1호
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• pp.35-41
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• 2007

This paper presents the results of investigating harmonic levels on medium voltage motors at loading conditions in air separation plant. The essential results of the measurements of the medium voltage motor harmonics are summarized in the values for the total harmonic distortion (THD). Motors loading case is used to assess the current and voltage harmonic distortions. Proper system analysis is important when adding a new motor starting and controlling the equipment. With the result of the paper it is possible to suggest the most appropriate starting and control method. Two medium voltage motors of air separation unit measurement results and simulations are summarized. Both current and voltage harmonic distortions are fitted by using a linear and exponential regression model. The prediction of THD values can be used for this kind of process for future planning by utilities.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 추계학술대회 논문집 전력기술부문
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• pp.224-226
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• 2003

본 논문에서는 현장측정을 통하여 수용가별(업무용, 주택용, 산업용)로 발생하는 전압, 전류고조파의 특성을 비교분석하였다. 특히 국내에서 규정되어 있지 않은 전류 고조파 종합왜형률($THD_i$)과 더 향상된 방식인 전류 종합 부하왜형률($TDD_i$)을 제시하여 $THD_i$와 비교하였다. 또한 50조파까지의 측정을 통해 향후 국내의 실정에 맞는 고조파 한계 기준에 적합한 설정치를 제시하였다.

• Tribology and Lubricants
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• 제16권5호
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• pp.341-350
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• 2000

The study reported in this paper deals with the development for parametric investigation of the influence of the rheological properties of the lubricant in the thermohydrodynamic (THD) film conditions which occur in slider and journal bearings. A parametric investigation based on a Bingham model with a shear yield stress which best fit the experimental pressure is performed for predicting the thickness of the shear Bone in lubricating films with fixed geometry between the stationary and moving surfaces. The results suggest that the shear yield stress for the lubricating film is proportional to the pressure developed in the film within the range of the investigated cases and the shear zone thickness which is of the same order of magnitude as that obtained by the empirical formula is significantly smaller than the fluid film thickness in the lubrication zone.

• 드라이브 ㆍ 컨트롤
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• 제11권1호
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• pp.8-13
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• 2014

Hydraulic servo valves are widely used in various fluid power systems because of their fast response and precision control. In this paper, we studied the effect of metering notch shapes and amount of their openings on the flow characteristics within the spool valve using a computational fluid dynamic (CFD) code, FLUENT. To obtain the results for more realistic operating conditions, viscous heating due to the jet flow and viscosity variation of the hydraulic fluid with temperature were considered. For two types of notch shape, streamlines, oil temperature and viscosity distributions, and variations of flow and friction forces acting on spool were showed. The flow and friction forces affected by the metering notch shapes and their openings, and oil temperature rise near metering notch was significant enough to results in the jamming phenomenon. A thermohydrodynamic (THD) flow analysis adopted in this paper can be used in optimum design of hydraulic servo valves.

• Tribology and Lubricants
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• 제3권1호
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• pp.39-46
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• 1987

Frictional loss in turbulent regime is abnormally increased compared with in laminar regime. Thus the consideration of temperature rise across fluid film is significant in analysis and conventional isothermal theory loses its usefulness for performance prediction. This paper proposes to the three-dimensional thermohydrodynamic analysis of finite journal bearings operating under turbulent condition using two-equation model($\kappa-\varepsilon$ model) proposed by Hassid & Poreh. The equations are solved numerically by finite difference method. We make the analysis applicable even at large eccentricity when back flow of the lubricants occurs and axial flow is no longer ignored compared to circumferential flow.

• 한국산학기술학회논문지
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• 제19권5호
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• pp.72-81
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• 2018

본 논문에서는 영구자석형 동기전동기를 구동하는 인버터에서 사용할 수 있는 정현파 전류 운전 방식과 120도 운전 방식 및 150도 운전 방식에 대하여 각각 시뮬레이션을 수행하고 이것들의 운전 특성을 비교 분석한다. 이 운전 방식들은 통전각과 전동기의 상전류에 형태로 구분이 된다. 종래에는 인버터의 효율 향상을 위하여 정현파 전류 운전 방식과 120도 운전 방식 간의 전환 방법에 중점을 둔 연구가 많았으나, 본 논문에서는 이들 각각의 운전 방식에 대한 운전 특성을 비교 분석하여 그것들의 장점을 다양한 전환 방법으로 응용할 수 있도록 하는데 중점을 둔다. 이를 위하여 각각의 운전 방식에 대하여 전동기의 발생 토크, 속도 응답 특성, 상전류 THD에 대하여 시뮬레이션을 수행하였다. 그 결과로 정현파 전류 운전 방식이 3가지 운전 방식들 중에서 전체적으로 가장 좋은 성능을 보였고, 120도 운전 방식은 150도 운전 방식에 비하여 속도 응답 특성이 다소 우수하였으며, 150도 운전 방식은 120도 운전 방식에 비하여 상전류 THD가 낮은 것을 확인하였다.

• Journal of Electrical Engineering and Technology
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• 제10권1호
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• pp.261-270
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• 2015

In this paper, the Optimal Harmonic Stepped Waveform (OHSW) method is proposed in order to eliminate the selective harmonic orders available at the output of cascaded multilevel inverter (CMLI) fed by solar photovoltaic (SPV). This technique is used to solve the harmonic elimination equations based on stepped waveform analysis in order to obtain the optimal switching angles which in turn reduce the Total Harmonic Distortion (THD). The OHSW method considers the output voltage waveform as four equal symmetries in each half cycle. In the proposed method, a solar fed fifteen level cascaded multilevel is considered where the magnitude of six numbers of harmonic orders is reduced. A programmable pulse generator is developed to carry the switching angles directly to the semiconductor switches obtained as a result of OHSW analysis. Simulations are carried out in MATLAB/Simulink in which a separate model is developed for solar photovoltaic which serves as the input for cascaded multilevel inverter. A 3kWp solar plant with multilevel inverter system is implemented in hardware to show the effectiveness of the proposed system. Based on the observation the OHSW method provides the reduced THD thereby improving power quality in renewable energy applications.

• Journal of Electrical Engineering and Technology
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• 제8권6호
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• pp.1380-1388
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• 2013

The conventional graphical representation of the instantaneous compensation power flow for single-phase active power filters(APFs) simply represents the active power flow and the reactive power flow which flowing between the power source and the active filter / the load. But, this method does not provide the information about the rectification mode and the compensation mode of APFs, especially, the loss for each mode was not considered at all. This is very important to understand the compensation operation characteristics of APFs. Therefore, this paper proposes the graphical representation of the instantaneous compensation power flow for single-phase APFs considering the instantaneous rectification mode and the instantaneous inversion mode. Three cases are verified in this paper - without compensation, with compensation of the active power 'p' and the fundamental reactive power 'q', and with compensation of only the distorted power 'h'. To ensure the validity of the proposed approach, PSIM simulation is achieved. As a result, we could confirm that the proposed approach was easy to explain the instantaneous compensation power flow considering the instantaneous rectification mode and the instantaneous inversion mode of APFs, also, Total Harmonic Distortion(THD)/Power Factor (P.F) and Fast Fourier Transform(FFT) analysis were compared for each case.

• Journal of Power Electronics
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• 제10권1호
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• pp.85-90
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• 2010

In this paper the effects of a Static Synchronous Series Compensator, which is constructed with a 48-pulse inverter, on the power demand from the grid are studied. Extensive simulation studies were carried out in the MATLAB simulation environment to observe the compensation achieved by the SSSC and its effects on the line voltage, line current, phase angle and real/reactive power. The designed device is simulated in a power system which is comprised of a three phase power source, a transmission line, line inductance and load. The system parameters such as line voltage, line current, reactive power Q and real power P transmissions are observed both when the SSSC is connected to and disconnected from the power system. The motivation for modeling a SSSC from a multi-pulse inverter is to enhance the voltage waveform of the device and this is observed in the total harmonic distortion (THD) analysis performed at the end of the paper. According to the results, the power flow and phase angle can be controlled successfully by the new device through voltage injection. Finally a THD analysis is performed to see the harmonics content. The effect on the quality of the line voltage and current is acceptable according to international standards.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 B
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• pp.1209-1210
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• 2006

This paper presents a single phase high power factor PWM boost rectifier featuring soft commutat -ion of the active switches at zero current. It incorporates the most desirable properties of conventional PWM and soft switching resonant techniques. The input current shaping is achieved with average current mode control and continuous inductor current mode. This new PWM converter provides zero current turn on and turn off of the active switches, and it is suitable for high power applications employing IGBT's. The principle of operation, the theoretical analysis, a design example, and experi -mental results from a laboratory prototype rated at 1.6[kW] with 400[Vdc] output voltage are presented. The measured efficiency and the power factor were 96.2[%] and 0.99[%], respectively, with an input current THD equal to 3.94[%], for an input voltage with THD equal to 3.8[%], at rated load.