• The Transactions of the Korean Institute of Electrical Engineers P
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• v.59 no.4
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• pp.477-480
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• 2010

Fault current in power system is expected to increase by demand of power capacity. Therefore, when the fault occurred, fault current was increased in the power system. Many studies have been progressed to limit the fault current. Superconducting fault current limiter (SFCL) is one of them which has been studied in worldwide. In this paper, we will analyze characteristics of a transformer-type SFCL by reclosing operation when the voltage increases. Twice opening times in the reclosing of circuit breaker were set as the 0.5 and 15 seconds, respectively. Turn's number of primary and secondary coils set 4:2 and we increased voltages from 120V to 280V for each experiment. By the current waveform, maximum fault current in second and third cycles was lowered when the voltage was increased. In the recovery waveform, recovery time was increased as the voltage was increased. The reason was that power burden of the SFCL increased when consumption power was increased, so the time to get back to SFCL took longer. We compared the characteristics of a resistive-type and transformer-type SFCL. As a result, we found that the fault current of a transformer-type was lower than resistive-type and recovery time of the SFCL was shorter. Consequently, transformer-type SFCL was more profitable for limitation of fault current and recovery time under the same condition for reclosing operation.

• Journal of radiological science and technology
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• v.24 no.2
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• pp.5-11
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• 2001

Most of X-ray generator had used rectifier type transformer with high tension generator which is supplied in a clinical diagnosis. Because the ripple rate of tube voltage is high, X-ray generating efficiency is very low. In these days, high tension generator for inverter type X-ray generator is being supplied from a broad which uses semi-conductor switching element for the electric power that have a high speed switching ability to solve these problem. But, semi-conductor element with large capacity is used with X-ray tube's large consumption power and diffusion is difficult in the small size hospital because production cost is going up by doing digital control through DSP. Therefore, this paper designed and manufactured CR type voltage divider for feedback control of tube voltage with high frequency resonance type inverter and for high tension transformer with high frequency. It was to make economical diffusion type X-ray generator which has wide output voltage and load extent. It was preyed that the X-ray generator had the stability of X-ray tube's output characteristics.

• Journal of Electrochemical Science and Technology
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• v.10 no.1
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• pp.1-13
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• 2019

Na-ion batteries are being considered as promising cost-effective energy storage devices for the future compared to Li-ion batteries owing to the crustal abundance of Na-ion. However, the large radius of the Na ion result in sluggish electrode kinetics that leads to poor electrochemical performance, which prohibits the use of these batteries in real time application. Therefore, identification and optimization of the anode, cathode, and electrolyte are essential for achieving high-performance Na-ion batteries. In this context, the current review discusses the suitable high-voltage cathode materials for Na-ion batteries. According to a recent research survey, sodium vanadium fluorophosphate (NVPF) compounds have been emphasized for use as a high-voltage Na-ion cathode material. Among the fluorophosphate groups, $Na_3V_2(PO_4)_2F_3$ exhibited the high theoretical capacity ($128mAh\;g^{-1}$) and working voltage (~3.9 V vs. $Na/Na^+$) compared to the other fluorophosphates and $Na_3V_2(PO_4)_3$. Here, we have also highlighted the classification of Fluorophosphates, NVPF composite with carbonaceous materials, the appropriate synthesis methods and how these methods can enhance the electrochemical performance. Finally, the recent developments in NVPF for the application in energy storage devices and its outlook are summarized.

• Journal of Power Electronics
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• v.19 no.1
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• pp.89-98
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• 2019

This paper analyzes the input side performance of a conventional three-phase to single-phase matrix converter (3-1MC). It also presents the input-side waveform quality under this topology. The suppression of low-frequency input current harmonics is studied using the 3-1MC plus capacitance compensation unit. The constraint between the modulation function of the output and compensation sides is analyzed, and the relations among the voltage utilization ratio and the output compensation capacitance, filter capacitors and other system parameters are deduced. For a 3-1MC without large-capacity energy storage, the system performance is susceptible to input voltage imbalance. This paper decouples the inner current of the 3-1MC using a Lyapunov function in the input positive and negative sequence bi-coordinate axes. Meanwhile, the outer loop adopts a voltage-weighted synthesis of the output and compensation sides as a cascade of control objects. Experiments show that this strategy suppresses the low-frequency input current harmonics caused by input voltage imbalance, and ensures that the system maintains good static and dynamic performances under input-unbalanced conditions. At the same time, the parameter selection and debugging methods are simple.

• Journal of IKEEE
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• v.23 no.1
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• pp.99-106
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• 2019

This paper propose a new form of UPQC (Unified Power Quality Compensator) to compensate the current and voltage quality problems of nonlinear loads. The conventional UPQC system consists of a series inverter, a parallel inverter, and a common DC link. A new type of UPQC proposed is a parallel compensator with SVC (Static Var Compensator) added to compensate for the wide compensation range and low DC link voltage. The parallel inverter compensates the reactive power generated by the nonlinear load, and the series inverter compensates the sag and swell generated at the power supply side.

• Journal of IKEEE
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• v.24 no.4
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• pp.1129-1135
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• 2020

The effects of battery aging limit the rechargeable capacity, State of Health(SoH). It is very important to estimate the SoH in the battery monitoring system(BMS) and many algorithms of measuring the internal resistance of the battery were proposed. A method is used by applying a current source of a specific frequency to the battery and measuring the voltage response. When charging harmonic noise is generated in the voltage response, it results in poor resistance measurement accuracy. In this paper, a robust battery internal resistance measurement algorithm is proposed to eliminate the effect of charging noise by integrating the current source and voltage response signals for a certain period. It showed excellent accuracy and stable measurement results. Applying to the BMS for uninterruptible power supply, the usefulness of the proposed method is verified.

• KEPCO Journal on Electric Power and Energy
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• v.7 no.2
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• pp.317-321
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• 2021

As the large-scale renewable energy power plant increases, the high-capacity and compact Energy Storage System (ESS) is required. However, this trend could reduce the insulation reliability of ESS. In this study, the surface flashover characteristics for four types of solid insulators are investigated in the uniform electric field with AC and Lightning Impulse (LI) voltage waveforms under various contamination levels. In addtion, insulator surfaces are compared based on the contact angle before and after surface flashover. The experimental results show that AC flashover voltage is dependent on the materials and the contamination level, but LI flashover voltage is only associated with the contamination level. Especially, AC flashover voltage of PC (PolyCarbonate) is higher than that of other insulators, which is associated with the unique and sequential creepage discharge propagation pattern of PC. The localized discharges on the surface of PC form corresponding tracking points. Then, the interconnected trackings result in the complete flashover. This flashover patterns degrade the surface of PC much more than that of epoxy and Bulk Molding Compoud (BMC). Thus, the contact angle of PC is significantly reduced compared to that of other insulators. The increased hydrophilicity in the surface of PC enhances the insulator surface conductivity.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.35 no.1
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• pp.66-71
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• 2022

The insulator used for the transmission line is a device that is bonded with a cap, pin, ceramic, and cement to withstand insulation capacity and mechanical load. The insulator design can help to reduce the dispersion of the electric field; thus, the optimization of today's design, especially as demanded power grows, is critical. The designs of four manufacturers were used to perform a comparative analysis. Under dry circumstances of the new product, an electric field distribution study was done with no pollutants attached. Manufacturer D's design has the best voltage uniformity of 24.33% and the arc length of 500 mm or more. Manufacturer C's design has an equalizing voltage of more than 2% higher than that of other manufacturers. The importance of the design of the insulator and the number of connections according to the installation conditions is very efficient for transmission lines that will increase in the future.

• Progress in Superconductivity and Cryogenics
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• v.8 no.2
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• pp.20-24
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• 2006

Recently, utility network is becoming more and more complicated and huge due to IT and OA devices. In addition to, demands of power conversion devices which have non-linear switching devices are getting more and more increased. Consequently, because of the non-linear power semiconductor devices, current harmonics are unavoidable. Sometimes those current harmonics flow back to utility network and become one of the main reasons which can make the voltage distortion. Also, it makes noise and heat loss. On the other hands, voltage sag from sudden increasing loads is also one of the terrible problems inside of utility network. In order to compensate the current harmonics and voltage sag problem, AF(active filter) systems could be a good solution method. SMES is a very good promising source due to it's high response time of charge and discharge. Therefore, the combined AF and SMES system can be a wonderful device to compensate both harmonics current and voltage sag. However, SMES needs a superconducting magnetic coil. Because of using this superconducting magnetic coil, quench problem caused by unexpected reasons have always been unavoidable. Therefore, to solve out mentioned above, this paper presents a decisive method using shunt and series active filter system combined with SMES. Especially, authors analyzed the change of original energy capacity of SMES regarding to the size of resistance caused by quench of superconducting magnetic coil.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2002.09a
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• pp.396-399
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• 2002

Intense quasi-monochromatic x-ray irradiation from the linear plasma target is described. The plasma x-ray generator employs a high-voltage power supply, a low-impedance coaxial transmission line, a high-voltage condenser with a capacity of about 200 nF, a turbo-molecular pump, a thyristor pulse generator as a trigger device, and a flash x-ray tube. The high-voltage main condenser is charged up to 55 kV by the power supply, and the electric charges in the condenser are discharged to the tube after triggering the cathode electrode. The x-ray tube is of a demountable triode that is connected to the turbo molecular pump with a pressure of approximately 1 mPa. As electron flows from the cathode electrode are roughly converged to the molybdenum target by the electric field in the tube, the weakly ionized plasma, which consists of metal ions and electrons, forms by the target evaporating. In the present work, the peak tube voltage was almost equal to the initial charging voltage of the main condenser, and the peak current was about 20 kA with a charging voltage of 55 kV. When the charging voltage was increased, the linear plasma x-ray source grew, and the characteristic x-ray intensities of K-series lines increased. The quite sharp lines such as hard x-ray lasers were clearly observed. The quasi-monochromatic radiography was performed by a new film-less computed radiography system.