• 설비공학논문집
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• 제26권2호
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• pp.67-71
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• 2014

In this study, a fan coil unit with an oval-type heat exchanger has been developed. The performance of the present fan coil unit has been investigated, by comparison with the previous fan coil unit with a circular-type heat exchanger. For the fan coil unit with circular- and oval-type heat exchangers, the heat flux and pressure loss through the heat exchangers were measured at standard operating conditions. In addition, the wind speeds exhausted from the fan coil units were compared, for the same fan motor operation. The experimental results show that the average wind speed of the oval-type heat exchanger is 20 percent higher than that of the circular-type heat exchanger. The heat flux in the oval-type heat exchanger is enhanced by 40% or more, over the circular-type heat exchanger.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 추계학술대회 논문집 Vol.17
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• pp.61-64
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• 2004

In this paper, we investigated the variations of initial fault current limiting instant according to fault angles in the flux-lock type SFCL. The flux-lock type SFCL consists of the coil 1 and the coil 2 that are wound in parallel each other through an iron core. The operation of the flux-lock type SFCL can be divided into the subtractive polarity winding and the additive polarity winding operations according to the winding directions between the coil 1 and coil 2. The subtractive polarity winding operation could be analyzed with three modes. On the other hand, the additive polarity winding operation could be analyzed with five modes. The variations of initial fault current limiting instant in two winding directions were dependent on the fault angles. It was confirmed from experiment that the fault current limiting instant was getting faster and the magnitude of fault current at the initial fault time was getting higher for higher fault angle.

• 한국안전학회지
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• 제21권2호
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• pp.52-56
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• 2006

This paper describes the methods for the detection of shorted-turn in the rotor of a cylindrical synchronous generator. A search coil is installed in the air-gap to detect the shorted-turn. The occurrence of a fault in the rotor winding results in a decrease of the induced voltages in the stator. And the magnitude of the rotor flux can be estimated by using the search coil and the estimated stator voltages respectively. And the magnitude of the estimated rotor flux is used for discriminating the rotor windings short or not by detecting the magnitude of the rotor flux. The method using a search coil located in the air-gap can detect not only the occurrence of a turn fault but also its position in the rotor winding. But the method using the estimated stator voltages gives the magnitude of the rotor flux, and only the number of a short-turn.

• 한국정밀공학회지
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• 제18권12호
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• pp.73-81
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• 2001

The MIAB welding uses a rotating arc as its heat source and is known as an efficient method fur pipe butt welding. The arc is rotated around the weld line by the electro-magnetic force resulting from the interaction of arc current and magnetic field. The electro-magnetic force is affected by magnetic flux density, arc current, and arc length. Especially, the magnetic flux density is an important factor on arc rotation and weld quality. This paper presents a 2D finite element model for the analysis of magnetic flux density in the actual welding conditions. The magnetic flux density is mainly dependent on gap between two pipes, the position of coil from gap center, exciting current, and relative permeability. Thus, the relations between magnetic flux density and main factors were investigated through experiment and analysis. Experiments were performed for the steel pipes(48.1mm O.D and 2.0mm thickness). The analysis results of magnetic flux density reveal that it increases with increasing exciting current, increasing relative permeability, decreasing distance from gap center to coil, and decreasing gap size. It is considered that the results of this study can be used as important data on the design of coil system and MIAB welding system.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제53권12호
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• pp.732-738
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• 2004

In this paper, we constructed 13 turns pancake coil and solenoid coil with HTS tape and measured AC losses of the pancake coil. The critical current of the pancake coil and the solenoid coil were 80A and 109A, respectively. To compare measured AC losses of the two coils, we carried out numerical analysis using 2-D FEM program for manufactured coils. This paper presents current density distribution, flux density distribution and AC losses of the pancake coil and the solenoid. As a result, we obtained that current density distribution was closely related to the orientation of magnetic field and distribution of AC losses were also closely related to the perpendicular component of flux density distribution in coil. The calculated AC losses of the two coils showed good agreement with measured AC losses and AC losses of the pancake coil was about 9 times bigger than that of the solenoid coil under the same turns and length.

• 한국초전도ㆍ저온공학회논문지
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• 제12권2호
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• pp.13-16
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• 2010

The superconducting synchronous motor or generator mostly has high permeability iron only around outer yoke portion. Therefore, if excitation voltage (Back E.M.F) is calculated from 2 dimensional magnetic field distributions, it can be largely different from actual value due to additional voltage originated from end coils. In order to calculate the excitation voltage more accurately, 3 dimensional magnetic field calculation is necessary for including the end coil effect from large air-gap structure. The excitation voltage can be calculated by stator (armature) coil linkage flux originated from rotor (field) coil excitation, but it is difficult to calculate the flux linkage exactly because of complicated structure of the stator coil. This paper shows a method to calculate the excitation voltage from 3 dimensional magnetic energy that can be calculated directly from volume integration of magnetic flux density and field intensity scalar product through FEM (Finite Element Method) analysis software.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.1
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• pp.601-604
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• 2003

The magnetic field generated in the iron core, which is required for the magnetic field to link each coil of the flux-lock type reactor, affects the fault current limiting characteristics of the flux-lock type high-Tc superconducting fault current limiter(SFCL). By applying numerical analysis for equivalent circuit of flux-lock type SFCL, the magnetic field induced in the iron core including currents of each coil was investigated. Through the analysis of magnetic field, we have analyzed that the magnetic field linked the 3rd coil, which is wound in the iron core, prevents the saturation of the iron core, but decreases the impedance of the flux-lock type SFCL.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 하계학술대회 논문집 B
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• pp.580-582
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• 2001

In moving coil LOA, the variation of mover position and the consequent changes of coil flux path affect the coil inductance because of unbalanced magnetic circuit. Furthermore, the armature field shifts and distorts the airgap flux density distribution due to the magnet alone by a certain amount, which cause the unbalanced reciprocating force. In this paper, we propose the reduction method of armature reaction and coil inductance. The proposed LOA has the shorted ring the saturated core, the double coil, and Halbach array.

• Journal of Magnetics
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• 제15권3호
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• pp.143-147
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• 2010

Rotary-type voice coil motors are widely used as actuators in hard disk drives. The recent trend toward higher density and smaller form factors in data storage devices requires performance improvement of the voice coil motor. In this study, we introduce a Halbach magnet array to the voice coil motor in order to increase the force generation. The Halbach magnetic circuit outperforms the conventional magnetic circuit due to the confined magnetic flux. To investigate the performance of the Halbach magnetic circuit, we analyze air gap flux density with the various shapes and thickness of the magnets using 3-dimensional finite element analysis. Consequently the optimum shape of the Halbach magnetic circuit is proposed. Simulations and experimental results proved effectiveness of the proposed magnet array in the voice coil motor for a commercial hard disk drive.

• 열처리공학회지
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• 제26권5호
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• pp.233-240
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• 2013

Rapid and homogeneous heating in heat treatment has been a challenging engineering issue throughout a heating temperature over $1,000^{\circ}C$. Induction heating has been widely used in field of heat treatment compared with conventional heating system. Advantages in homogeneous heating, simple fabrication, and repeatable use can be efficiently made with the induction heater. In this paper, numerical analysis of an induction coil system for heat flux gauge heating is performed. The effect of configuration on the heating performance was considered in various cases of the coil radius, distance between the winding, relative height difference between the heat flux gauge and the coil, and the applied current frequency. Temperature distribution within the heat flux gauge at frequency-steady state was calculated with a finite element method. Sensitivity analysis was also performed and the relative importance of 2 key parameters; coil radius, distance between the winding, were taken as main contributors for induction heating.