• Proceedings of the KIEE Conference
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• 2015.07a
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• pp.944-945
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• 2015

Many sensitive loads always rely on UPS systems to maintain continuous power during abnormal utility power conditions. As any disturbance occurs at the utility side, an off-line UPS system takes over the load within a quarter cycle to avoid a blackout. However, the starting of the inverter can root the momentous inrush current for the transformer installed before the load, due to its magnetic saturation. The consequences of this current can be a reduction of line voltage and tripping of protective devices of the UPS system. Furthermore, it can also damage the transformer and decrease its lifetime by increasing the mechanical stresses on its windings. To prevent the inrush current, and to avoid its disruptive effects, this paper proposes an off-line UPS system that eliminates the inrush current phenomenon while powering the transformer coupled loads, using a current regulated voltage source inverter (CRVSI) instead of a typical voltage source inverter (VSI). Simulations have been performed to validate the operation of proposed off-line UPS system.

• Journal of Industrial Technology
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• v.14
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• pp.89-100
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• 1994

The effects of transient inrush currents on the dynamic characteristics of percentage differential relays are studied when the power transformers are reenergized. An algorithm of estimation the nonlinear magnetic property of power transformer and current trnasformer core are developed. Using this method, we can analyze the effect of inrush currents on the trip region of the percentage differential relays corresponding to the variation of the phase angle and the residual magnetism at the instant of switch closing. Test results are used to verify the availibility of the proposed algorithm. Finally a case study is performed to the 110 MVA main transformer in hydraulic power station.

• Proceedings of the KIEE Conference
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• 1999.07a
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• pp.315-317
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• 1999

This paper presents a method for determining of the equivalent d-q model parameters of three-phase squirrel cage induction motors. The method is based on the use of a finite-element field calculation which enables the precise slot geometry to be modelled accurately, and includes the effects of magnetic saturation of iron core. The proposed method can reduce computational costs compared with the method that needs the iterative field analysis to obtain the impedance. It is verified that the circuit inductances are shown as functions of the current.

• Journal of Magnetics
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• v.15 no.4
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• pp.169-172
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• 2010

The coercivity mechanism in permanent magnets was analyzed according to the effects of domain nucleation and domain wall pinning. The coercivity mechanism of a TbCo thin film with high perpendicular magnetic anisotropy was considered in terms of the local inhomogeneity in the thin film. The initial magnetization curves of the TbCo thin films demonstrated domain wall pinning to be the main contributor to the coercivity mechanism than domain nucleation. Based on the coercivity model proposed by Kronmuller et al., the inhomogeneity size acting as a domain wall pinning site was determined. Using the measured values of perpendicular anisotropy constant ($K_u$), saturation magnetization ($M_s$), and coercivity ($H_c$), the inhomogeneity size estimated in a TbCo thin film with high coercivity was approximately 9 nm.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.38 no.1
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• pp.1-9
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• 1989

In this paper, an efficient method of a hybrid stepping motor is proposed using permeance method. To be specific, hybrid stepping motor is modelled firstly as an equivalent nonlinear magnetic circuit including the saturation effects of iron parts, and then the static holding torque of the motor is calculated as a function of each design factor via Newton-Raphson's method. To show the validities of the proposed method, a prototype of hybrid stepping motor for 5 1/4 inches FDD header drive is made and tested in laboratory. As a result, the experimental data for the static holding torque is shown to be within 10% error compared with that of the simulated results.

• Proceedings of the KIPE Conference
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• 2007.07a
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• pp.211-213
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• 2007

The electrical parameters are used to calculate gains in the current regulator as well as to determine the reference currents of speed controller in various control strategies of Synchronous Reluctance Motors (SynRMs). Many methods of measuring or estimating the electrical parameters of SynRM have been proposed by other authors. But almost papers only measure or estimate in the limited conditions without fully considering the effects of inverter, connecting wire and magnetic saturation. The parameter results are usually different from the real system parameters. The drive performance, therefore, can not be good if using inaccurate parameters. In this paper, several methods used to measure the electrical parameters are introduced. The first method is LCR meter. And then, a method determining inductances by measuring AC current and voltage from AC power supply is presented. A new method with high reliability is proposed to measure the electrical parameters of SynRM. The experiment results verify the effectiveness of the new proposed method.

• Korean Journal of Metals and Materials
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• v.47 no.6
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• pp.378-382
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• 2009

We investigated the effects of deposition conditions on the fabrication of $Fe_{3}O_{4}$ thin films using a reactive DC magnetron sputtering at room temperature. The structural, electrical, and magnetic properties of Fe oxide films dependence on the film thickness, oxygen flow rate, and the substrate crystallinity were also studied. We have successfully fabricated $Fe_{3}O_{4}$ film with thickness of about 10 nm under optimal reactive sputtering conditions. The saturation magnetization, resistivity, and Verwey transition of the $Fe_{3}O_{4}$ film were298 emu/cc, $4.0{\times}10^{-2}{\Omega}cm$, and 125 K, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.06a
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• pp.375-377
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• 1998

The magneto-optical properties of Co/Co$_2$TiSn two-phase magnet films were studied. These films show that relatively large Kerr rotations which are -0.4 deg. at the wavelength of 400 nm, compared to that of pure Co. It is conceivable that the magneto-optical effects may be due to both contributions of ferromagnetic Co matrix and ferromagnetic Co$_2$TiSn Heusler alloy precipitate. The perpendicular magnetization curve domonstrates a typical bubble domain hysteresis loop. the saturation magnetization change of the annealed film is less sensitive to temperature in the low temperature region and the Curie temperature of Co$_2$TiSn Heusler alloy precipitate is a little higher in the annealed film. These can be explained by the increase of the number of Co-Co exchange interaction in Heusler alloy structure resulting from the change of chemical ordering by annealing.

• Journal of the Korean Magnetics Society
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• v.5 no.4
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• pp.275-280
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• 1995

The sites for $Fe^{+3}$ are partly substituted by $Co^{+2}$ and $Ti^{+4}$ cations to control coercivity of Ba-ferrite particles for use in high density magnetic recording. The substituted $Co^{+2}$ cation has very much different effects on magnetic properties and particle characteristics from that $Ti^{+4}$ cation has. The decrease in the coercivity with the $Co^{+2}$ substitution is attributed to the formation of excessive spinel-block(S-block) in pure Ba-ferrite crystal, while saturation magnetization is increased and the distributions of coercivity and particle size become broad. The substitution with the $Ti^{+4}$ decreases the sauration magnetization, but has less effect on a change in coercivity than the $Co^{+2}$. The $Ti^{+4}$ acts as a nucleation agent in amorphous phase of formulated compound, and consequently particle size and aspect ratio are decreased. Furthermore, the enhancement of substitution of the $Co^{+2}$ for the $Fe^{+3}$ sites in rhombohedral-block(R-block) by the $Ti^{+4}$ retards the nucleation of spinel phase of Ba-ferrite, which results in uniform magnetic properties of Ba-ferrite particles. It is suggested that the contents of the cations to be substituted for the $Fe^{+3}$ sites are optimized on the bases of magnetic properties and particle characteristics rather than on the base of electrical charge balance.

• Journal of the Korean Magnetics Society
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• v.8 no.1
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• pp.13-20
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• 1998

The crystallographic and high frequency characteristics of $Fe_{73.9}Cu_{1.0}Nb_{3.5}Si_{14.0}B_{7.6}$ soft magnetic alloys were investigated under the magnetic field annealing. As-cast ribbon with which already imbedded nanocrystalline Fe-Si phase on the surface have a preferred orientation with (400) plane to surface and also with the [011] direction parallel to the ribbon length. The extra nanocrystalline Fe-Si phase appeared throughout at 45$0^{\circ}C$ in samples with or without the longitudinal magnetic field. However the formation of nanocrystalline phase does not appear on the suface layer until 50$0^{\circ}C$ annealing temperature under the transverse field. The cryststallization fraction of annealed samples with longitudinal magnetic field is higher than that of samples without magnetic field. When the transverse magnetic field is applied, the crystallization fraction does not increases but decreases until 50$0^{\circ}C$. However the crystallization of internal regions can be confirmed by X-ray diffraction measurement via tilting the sample. It was found that for all samples, the saturation induction were all same with 1.3 T. The coercive field of as-cast sample was 1.06 A/cm, but in annealed samples it decrease from 0.56 to 0.1 A/cm with increasing annealing temperature from 400 and 55$0^{\circ}C$, respectively. The squareness of annealed samples under transverse magnetic field has a small value than that of both without field and with longitudinal field annealing.