• Korean Journal of Radiology
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• v.21 no.8
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• pp.967-977
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• 2020

Objective: To evaluate the effects of tube voltage on image quality in coronary CT angiography (CCTA), the estimated radiation dose, and DNA double-strand breaks (DSBs) in peripheral blood lymphocytes to optimize the use of CCTA in the era of low radiation doses. Materials and Methods: This study included 240 patients who were divided into 2 groups according to the DNA DSB analysis methods, i.e., immunofluorescence microscopy and flow cytometry. Each group was subdivided into 4 subgroups: those receiving CCTA only with different tube voltages of 120, 100, 80, or 70 kVp. Objective and subjective image quality was evaluated by analysis of variance. Radiation dosages were also recorded and compared. Results: There was no significant difference in demographic characteristics between the 2 groups and 4 subgroups in each group (all p > 0.05). As tube voltage decreased, both image quality and radiation dose decreased gradually and significantly. After CCTA, γ-H2AX foci and mean fluorescence intensity in the 120-, 100-, 80-, and 70-kVp groups increased by 0.14, 0.09, 0.07, and 0.06 foci per cell and 21.26, 9.13, 8.10, and 7.13 (all p < 0.05), respectively. The increase in the DNA DSB level in the 120-kVp group was higher than those in the other 3 groups (all p < 0.05), while there was no significant difference in the DSBs levels among these latter groups (all p > 0.05). Conclusion: The 100-kVp tube voltage may be optimal for CCTA when weighing DNA DSBs against the estimated radiation dose and image quality, with further reductions in tube voltage being unnecessary for CCTA.

• Proceedings of the KIEE Conference
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• 2002.07b
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• pp.1149-1151
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• 2002

In this paper, an auxiliary winding driving system of single-phase induction motors is described. Starting charateristics variations are obtained by controlling the auxiliary winding voltage magnitude and phase angle, while the motor's main winding is directly connected to the local utility. A variable auxiliary winding voltage phase angle is shown to yield significant torque control, providing starting and braking torque. The analysis includes the determination of the relationship between the auxiliary winding voltage phase angle and the phase angle difference between the main and auxiliary winding current. The paper proposed for adjusting an auxiliary winding voltage magnitude and phase angle. Experimental results of motor's starting characteristics with using the DC-AMP and PWM inverter for auxiliary winding power supply are shown. The drive is tested using a dynamometer to experimentally verify the results of the theory.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.54 no.11
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• pp.503-507
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• 2005

Both ratio error and phase angle error in voltage transformer(VT) depend on values of VT burden used. Thus, precise measurement of burden is very important for the evaluation of VT. A method of evaluation for VT burden has been developed by employing the portable decade resistor, with AC-DC resistance difference less than 10-3. The burden value(value and power factor) can be obtained by conductance and susceptance, obtained by measuring the change of ratio error and phase angle error caused by the resistance change of decade resistor. The burden value and power factor obtained by the method are consistent with those obtained using power analyzer within corresponding uncertainties.

• Journal of Electrical Engineering and Technology
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• v.12 no.2
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• pp.549-558
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• 2017

DC distribution has several differences compared to AC distribution. DC distribution has a higher efficiency than AC distribution when distributing electricity at the same voltage level. Accordingly, power can be transferred further with low-voltage DC. In addition, power flow in a DC grid system is produced by only a voltage difference in magnitude. Owing to these differences, operation of a DC grid system significantly differs from that of an AC system. In this paper, the power flow problem in a bipolar-type DC grid with unbalanced load conditions is organized and solved. Control strategy of energy storage system on a slow time scale with power references obtained by solving an optimization problem regarding the DC grid is then proposed. The proposed strategy is verified with computer simulations.

• Proceedings of the KIPE Conference
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• 2004.07a
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• pp.406-410
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• 2004

Generally, a voltage difference exists between the reference and the output voltagesin a pulse width modulated (PWM) voltage source inverter (VSI). In this paper, the nonlinearity in a PWM VSI is analyzed and a new on-line estimation method in consideration of parameter variations for a permanent magnet synchronous motor (PMSM) is proposed to compensate the time varying voltage distortion.

• Proceedings of the KIEE Conference
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• 2005.07a
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• pp.172-174
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• 2005

Recently, a concern of power qualify increases because of electronic device development and well-being generation. Power quality problems such as voltage sag, harmonics, flicker etc. have adverse effects on electric devices. Therefore, power quality problems have been monitored. This paper studies a detection of voltage sag that is more severer than the others. A voltage sag has been monitored using rms or wavelet method. This paper proposes an advance detection method using wavelet. An error Of Start Point differs error of ending point. We use this difference. So, we respectively revise detection error. Also, we revise multiplying average error rate.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.1374-1377
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• 2006

The voltage distribution of an external electrode fluorescent lamp(EEFL) having a gas pressure of 50 torr and a gas composition of Ne:Ar with a ratio of 90:10 has been estimated by varying the distance between the two external electrodes and monitoring the change of the lamp voltage. The estimated voltage gradient, which represents the electric field in the positive column of the EEFL, was very sensitive to the electrode area of EEFL and was in the range of $13\;{\sim}\;27\;V/cm$ at the electrode length of $15\;{\sim}\;31\;mm$. Changing the lamp current in the range $3\;{\sim}\;5\;mA$ did not make noticeable difference in the electric field of the positive column. Theses results may serve as basic data for the optimization of electric and optic characteristics of EEFL.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.7
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• pp.559-563
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• 2002

A threshold voltage model of SiC N-channel MOSFETs for high-temperature and hard radiation environments has been developed and verified by comparing with experimental results. The proposed model includes the difference in the work functions, the surface potential, depletion charges and SiC/$SiO_2$acceptor-like interface state charges as a function of temperature. Simulations of the model shoved that interface slates were the most dominant factor for the threshold voltage decrease as the temperature increase. To verify the model, SiC N-chnnel MOSFETS were fabricated and threshold voltages as a function of temperature were measured and compared wish model simulations. From these comparisons, extracted density of interface slates was $4{\times}10^{12}\textrm{cm}^{-2}eV^{-1}$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.05c
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• pp.233-236
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• 2002

This paper describes the properties of between the residual voltage for ${\gamma}$-irradiated in electric power cable using in nuclear power generating station. As these properties related with ${\gamma}$-irradiation dose, it is suggested that these properties can be utilized as a index of irradiation degradation. From theory and experiment We found the residual voltage is not influenced by cable length. We found that residual voltage of basic composite and practical composite have not a difference an occasion be the same cable length. As the ratio of degradation increases, the residual voltage in the initial time range increases and the peak moves to the shorter time. Therefore, We can know the degree of radiation degradation from the position of the peak.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.9 no.5
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• pp.41-50
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• 1995

Single-phase induction motors are widely used in many light duty applications, especially in home and office. many applications which use these motors require adjustable speed control continuously. In general, the speed control of single-phase induction motor is accomplished at a few discrete speeds by using tapped-windings, pole switching or gear. These techniques are inefficient and complicated. In this paper, Torque controller which adjusts a generating torque using phase difference between main winding voltage and auxiliary winding voltage is proposed. The analysis includes the determination of the relationship between the auxiliary winding voltage is proposed. The analysis includes the determination of the relationship between the auxiliary winding voltage phase angle and torque. Simulation results of the torque-speed characteristics using the controlled auxiliary winding supply are shown and discussed. and the drive is tested experimentally to verify the results of the theory by using a dynamometer.