• 동력기계공학회지
• /
• 제18권1호
• /
• pp.22-31
• /
• 2014

This paper introduced the new calibration algorithm of a straight-type five-hole pressure probe necessary for calculating three-dimensional flow velocity components. The new velocity data reduction method using both a commercial two-dimensional curve-fitting program and the zone partition method of a calibration map was firstly introduced in this study. This new calibration method can be applied up to the wide flow angle of ${\pm}80^{\circ}$ despite of using a five-hole pressure probe because this data reduction method showed a comparatively good performance in calculating yaw and pitch angles from the calibration map.

• KIEE International Transactions on Power Engineering
• /
• 제2A권4호
• /
• pp.131-135
• /
• 2002

This paper describes a new ultra-fast contingency screening algorithm for on-line TSA without time simulation. All machines are represented in a classical model and the stability index is defined as the ratio between acceleration power during a fault and deceleration power after clearing the fault. Critical clustering of machines is done based on the stability index, and the power-angle curve of the critical machines is drawn assuming that the angles of the critical machines increase uniformly, while those of the non-critical ones remain constant. Finally, the critical clearing time (CCT) is computed using the power-angle curve. The proposed algorithm is tested on the KEPCO system comprised of 900-bus and 230-machines. The CCT values computed with the screening algorithm are in good agreement with those computed using the detailed model and the SIME method. The computation time for screening about 270 contingencies is 17 seconds with 1.2 GHz PC.

• Journal of Electrical Engineering and Technology
• /
• 제8권6호
• /
• pp.1345-1351
• /
• 2013

Variable iron loss as function of current phase angle of Interior Permanent Magnet Synchronous Motor(IPMSM) was calculated through Curve Fitting Method(CFM). Also, a magnetic flux density distribution of iron core according to current phase angle was analyzed, and an iron loss calculation was performed including harmonic distortion. The experiment was performed by production of non-magnetizing model for the separation of mechanical loss, and the iron loss was calculated by the measurement of input using power analyzer and output power using dynamometer. Some error was generated between experimental results and calculation value, but an iron loss diminution according to current phase angle followed a same pattern. So, errors were generated by measurement, vibration, noise, harmonic distortion loss, etc.

• 한국전기전자재료학회논문지
• /
• 제17권2호
• /
• pp.207-211
• /
• 2004

We have performed computer simulation to obtain a globa1 optimization of power consumption and viewing angle characteristic of reflective twisted nematic (R-TN) mode liquid crystal display (LCD) with sin81e polarizer and λ/4 plate. Our studies shout that with increasing the twist angle, a steepness of reflectance-voltage curve increase, operation voltages decreases, the region where contrast ratio (CR) greater than 10 increases but the reflectance of the white state starts to decrease at above the twist angle of 75$^{\circ}$. Above the twist angle of 90$^{\circ}$, the R-TN mode LCD shows the most favorable combination of low consumption and good viewing angle characteristic.

• 대한정형도수물리치료학회지
• /
• 제9권1호
• /
• pp.29-38
• /
• 2003

The purpose of this study was to investigate relationship of lumbar extensor muscle power & spinal column curve for old female patients with LDK(Lumbar degenerative kyphosis). Subjects were composed of 37 old female with LDK. The subjects were tested in their spinal segment movement and spinal column curve with Spinal-$Mouse^{\leq}$ in $1^{st}$ loaded test and $2^{nd}$ loaded test and then tested lumbar extensor muscle power with $Medx^{\leq}$ lumbar extension machine. The results of this study, were as follow; There were statistically significant difference $1^{st}$ loaded test and $2^{nd}$ loaded test in upright position increase spinal column forwardly(p<0.01) and decrease lumbar lordosis angle(p<0.01), but no statistically significant difference $1^{st}$ loaded test and $2^{nd}$ loaded test thoracic and hip & sacrum curve angle. Their lumbar extensor muscle poser is very weakness, 61.4% of normal people.

• KSTLE International Journal
• /
• 제1권2호
• /
• pp.101-106
• /
• 2000

Variable displacement axial piston pumps are widely used for raising the energy level of the fluid in hydraulic systems. And the regulator is the device which regulates the discharge flow of the piston pump by controlling the swivel angle. The regulator receives the hydraulic pilot pressure and controls the pump output flow depending on the machine load and engine speed. This work deals with constant power control (horsepower control) in the design of a regulator by using a bent-axis type piston pump. In order to effectively use engine power, we must keep the horsepower from the engine to the pump constant. Therefore the regulator operates the constant power control. As a result, optimum power usage is obtained by accurately following the power hyperbola. This study focused on developing a simulation model of a regulator. First, the governing equations of the regulator are derived, and analysis is performed by computer simulation, which can identify significant parameters of regulator. As a result, the variation of the swivel angle, flow rate, hyperbolic curve, inner leakage and responsibility are simulated, and significant parameters of a regulator are identified.

• Journal of Electrical Engineering and Technology
• /
• 제9권5호
• /
• pp.1527-1536
• /
• 2014

This paper investigates the optimal values of turn-on and turn-off angles, and ratio of flux linkage at turn-off angle and peak phase current positions of optimal control for accomplishing maximum output power in an 8/6 Switched Reluctance Generator (8/6 SRG). Phase current waveform is analyzed to determine optimal excitation angles (optimal turn-on and turn-off angles) of the SRG for maximum output power which is applied from a nonlinear magnetization curve in terms of control variables (dc bus voltage, shaft speed, and excitation angles). The optimal excitation angles in single pulse mode of operation are proposed via the analytical model. Simulated and experimental results have verified the accuracy of the analytical model.

• 한국태양에너지학회 논문집
• /
• 제29권5호
• /
• pp.73-80
• /
• 2009

A tidal current turbine is designed and analyzed numerically by using blade element momentum theory. The rated power has a limitation because the diameter of the tidal current turbine cannot exceed the depth of sea water. This study investigates a horizontal axis tidal-current turbine with a rated power of 500 kW. NACA-6 series laminar foil shape is used for basic airfoil along the blade span. The distributions of chord length and twist angle along the blade span are obtained from the hydrodynamic optimization procedure. Prandtl's tip loss correction and angle of attack correction considering the three-dimensional effect are applied for this study. The power coefficient curve shows maximum peak at the rated tip speed ratio of 6.0, and the maximum torque coefficient is developed at the tip speed ratio of 4. The drag coefficient reaches about 0.85 at the design tip speed ratio.

• 조명전기설비학회논문지
• /
• 제21권5호
• /
• pp.112-119
• /
• 2007

가공송전 도체는 정상 동작조건 하에서 전력회사의 선로 설계지침에 규정된 지상고를 안정범위 내에서 항상 유지할 수 있어야 한다. 따라서 새로운 선로를 건설하거나 노화도체의 장력을 다시 조정하거나 또는 전력용량을 최대화하기 위해 동적송전용량을 모니터링하는 경우에, 도체 이도를 측정/또는 모니터링하는 것은 매우 중요하다. 본 연구에서는 도체의 카테너리 각도로 이도 및 장력을 추정하기 위한 새로운 방법을 제안한다. 가공송전선로의 대부분의 도체들은 전형적인 카테너리 곡선을 나타내므로 철탑 측의 카테너리 각도로부터 도체의 카테너리 곡선을 유일하게 결정할 수 있다. 이 카테너리 곡선을 토대로 도체의 이도나 수평장력을 쉽게 추정할 수 있다. 몇 가지 시뮬레이션과 간단한 실험 결과를 통하여 제안된 방법이 가공송전선의 도체 이도와 장력을 측정/또는 모니터링하는데 효과적으로 사용될 수 있음을 확인하였다.

• Journal of Electrical Engineering and Technology
• /
• 제10권4호
• /
• pp.1518-1526
• /
• 2015

For now, there are some low frequency oscillations in the power system which feature low frequency oscillation with positive damping and cannot be explained by traditional low frequency oscillation mechanisms. Concerning this issue, the dynamic damping effect is put forward on the basis of the power-angle curve and the study of damping torque in this article. That is, in the process of oscillation, damping will dynamically change and will be less than that of the stable operating point especially when the angle of the stable operating point and the oscillation amplitude are large. In a situation with weak damping, the damping may turn negative when the oscillation amplitude increases to a certain extent, which may result in an amplitude-increasing oscillation. Finally, the simulation of the two-machine two-area system verifies the arguments in this paper which may provide new ideas for the analysis and control of some unclear low frequency phenomena.