• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.918-920
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• 2006

Metal sulfide powders such as MnS, $MoS_2$ and FeS are simply used to the machinery processing improvement agent and solid lubricant in powder metallurgy industrial. And then, metal sulfide powders have received relatively little attention from powder metallurgy. Recently, the portable machine is one of the important interfaces between human or human and electronic machine. With the increase of the intelligent activity, the social and industrial demands for information display device and power source are increasing. The transition metal sulfide materials (FeS, ZnS) have received considerable attention due to the large variety of its electric, optical and magnetic properties. Among the metal sulfide, $FeS_2$ is appealing superior material for applications in $Li-2^{nd}$ battery because of high capacity. ZnS is also a famous phosphor material with various luminescence properties, such as photoluminescence (PL) and electroluminescence (EL). So generally used in the fields of display, sensors and laser. Metal sulfide materials, therefore, are provided for most widely application in all industries. In recent years, material researchers have become increasingly interested in studying with synthesis of metal sulfide.

• Journal of the Korean Ceramic Society
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• v.13 no.4
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• pp.5-8
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• 1976

Both oriented and non-oriented ferroxplana $Co_{1-x}Zn_xZ(Ba_3Co_{2(1-x)}Zn_{2x} Fe_{24}O_{41})$ with x=0.00, 0.45 were prepared by conventional ceramic method. The magnetostrictions of thus prepared specimens were measured by use of the three terminal capacitor device at room temperature. The magnitude of measured values was approximately five times greater than that of ZnY ferroxplana. The easy-magnetization plane at room temperature of both CoZ and Co0.55 $Zn_{0.45}$Z was their basal plane. The magentostrictions in the basal plane and the other planes showed saturated values at magnetic field intensity of about 2Koe and 4Koe, respectively. The magnetostriction constants $K_1, \; K_2, \;K_3\; and\; K_4$ for CoZ were -2.4, -10.5, -5.9 and -45.2$\times10^{-6}$ , while those for $Co_{0.55}Zn_{0.45}Z$ were +0.1, -1.2, -6.3 and -39.0$\times$10^{-6}, , respectively.

• Proceedings of the KIEE Conference
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• 1998.07a
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• pp.104-106
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• 1998

For the development of the 0.7 MJ small-sized superconducting magnetic energy storage (${\mu}$SMES) device, quench currents of a kA class superconducting cable were tested for various winding tensions because a dry superconducting coil is usually quenched by an abrupt heat pulse due to strand motions. The test coil similar to parameters of the optimally designed 0.7 MJ ${\mu}$SMES except a stored energy and a size was fabricated based on the test results of the kA class superconducting cable and tested. These experimental results show that the highly prestressed test coil has an excellent DC performance in spite of a dry type coil but its quench current is much degraded even at the low field ramping rate of about 0.4 T/s.

• The Transactions of the Korean Institute of Power Electronics
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• v.17 no.1
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• pp.77-84
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• 2012

This paper describes the process of optimal resonant frequency design with full-bridge series-loaded resonant dc-dc converter in a high efficiency 3.3 kW on-board battery charger application for Electric Vehicles and Plug-in Hybrid Electric Vehicles. The optimal range of resonant frequency and switching frequency used for ZVS are determined by considering trade-off between loss of switching devices and resonant network with size of passive/magnetic devices. In addition, it is defined charging region of battery, the load of on-board charger, as the area of load by deliberating the characteristic of resonant. It is verified the designed frequency band by reflecting the defined area on resonant frequency.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.48 no.11
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• pp.646-654
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• 1999

This paper deals with PWM patterns for harmonic reduction in inverter fed traction motors and the gear changing techniques for the variable speed drive of traction motor. GTOs are used as switching device of inverter because traction motor is a large load. To derive PWM rattern which can minimize the harmonics with the limited switching frequency, the output current and torque characteristic of SPWM and SHE PWM was analyzed. GTO inverter used for traction motor drive includes harmonics in the output current and torque by the limitation of switching frequency. However, the hybrid PWM method that adopt SPWM in the range of low frequency and SHE PWM in upper frequency range can achieve less harmonic characteristics in GTO inverters. If the traction motor is driven in variable speed by the proposed PWM pattern, 7 times of gear changing is needed. At the instant of the mode change, magnetic flux and torque may be altered and the large current flow. To reduce such an undesirable transient behavior, it is also presented the technique for the gear changing of inverter fed traction motor drive operated with the hybrid PWM. The results are verified by simulations and experiments.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1984-1986
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• 2000

In pulsed-power techniques. Marx generator is generally used for the high-power device. but this generator has insulation and spatial problems. So we will suggest a pulse transformer that has a small size to generate the high voltage pulse instead of Marx generator. In this paper, Pulse duration is 4 [${\mu}s$] and the ratio of input and output voltage is 40[kV]/200[kV](step-up ratio=5). The output voltage and the process of pulse compression for pulse circuit are simulated by EMTP (Electro-Magnetic Transient Program). The secondary voltage of pulse transformer is about 200[kV] and pulse width is 4[t/s]. When the secondary winding of the pulse transformer is saturated. the pulse width is 1.25[${\mu}s$]. We selected dummy load 50[$\Omega$] for impedance matching. The pulse voltage of dummy load is 100[kV] and pulse width is 500[ns].

• Proceedings of the KIEE Conference
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• 2000.07b
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• pp.919-921
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• 2000

This paper considers the research of the hybrid interrupter which adopts both rotating arc and thermal expansion technology. The operating principle of this device depends on rapid arc rotation due to the magnetic field created by the fault current through a coil which is mounted on contacts and also relies on the principle of thermal expansion created by arc energy in extinguishing chamber and finally causes pressure rise in expansion volume. In this research, the principle of the interrupting techniques are given and experimental results of hybrid interrupter which is developed by new technology is introduced.

• Proceedings of the KIEE Conference
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• 1998.07a
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• pp.224-227
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• 1998

Linear motors are increasingly employed as direct actuators replacing the more conventional systems composed by a rotating motor and a mechanical device. Linear DC motor is useful in a high speed and high accuracy positioning system with a feedback controller. Because of these advantages, linear DC motors have already been used as motors of pen recorders and magnetic disk storage devices, these are moving coil type linear DC motors as these movers are light. Moving magnet type linear DC motor has advantages at long stroke motors because its mover's feeding wires for driving is not necessary. This paper is concerned with the analysis of linear DC motor that is moving magnet type with unipolar. In order to analyze the dynamic behaviour a mathematical model based on a simplified field analysis developed. A two dimensional finite element field solution is employed in order to illustrate the effect of yoke saturation and motor performance. It is deduced the relation between the limit value of the thrust of the linear DC motor and the dimension of the yokes.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.672-675
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• 2010

Spray characteristics for the modulation with a pulsed spray in low-frequency region were investigted by performing with additional internal pulsed injection. The 1st perturbative flow was generated by rotating-type pulsed device and the 2nd pulse source generated by the magnetic valve was used to modulate the 1st flow. A pattern of the modulated spray was observed through FFT result and visualization. In case of modulated spray with the 2nd pulse control, the width of up and down motion of the modulated spray is smaller than that of the spray without the 2nd pulse. Also, the depth of penetration of the down stream is higher than that of spray without the 2nd pulse.

• Proceedings of the KSR Conference
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• 2005.11a
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• pp.356-361
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• 2005

Earth brush for electrical multiple units(EMUs) is a device through which the current of the EMU load's consumed power fed from the DC 1,500V overhead line (or from the AC 25.000V catenary) flows via axle to the rail(ground) and which prevents the electric corrosion of the axle bearings by preventing the current flow to the axle bearings caused by electric potential from the magnetic field when the bearings rotate together with the earthing function when a thunderbolt falls or a surge comes. The earth brush wear rates among cars, however, shows quite differences when the earth brushes after being separated from the holders are measured with vernier callipers every 6 months of maintenance period. Main causes of the earth brush wear are divided as mechanical, electric arc and electrical one, and the factors can be running speed, current, harmonics, connection state. spring tension, earth brush material, lubricant and so on. but only the earth brushes of the motor(M1) car show the highest wear rate and moreover maintenance difficulty occurs because of the wear rate differences among e earth brushes in one holder. The reason for these preponderant wear comes from the design concept of making preponderant current flow to some particular earth brushes and moreover the heat generated by the harmonics when the inverter starts to operate accelerate the wear. By defining these causes through experiments. I hope that the found results would be helpful for the future EMU design, safety, economy and maintenance.