• The Transactions of the Korean Institute of Power Electronics
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• v.13 no.1
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• pp.33-40
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• 2008

This paper proposes a sensorless drive method that estimates the rotor position by analysing Back EMF of single-phase Switched Reluctance motor (SRM). The rotor position information is necessary required, because SRM's torque is generated by exciting a stator winding according to rotor position. In order to detect the position of the rotor, the various rotor position sensors have been used. However, most of the position sensors not only increase the construction cost and the volume of the motor but also decrease reliability of driving system with environment. This paper proposed the method using the Back EMF to solve such problems. When a rotor and stator are overlapped, the Back EMF is sharply changed. By detecting this point, the rotor position can be estimated. Thus SRM is driven by turn on and turn off switches at the proper position through speed calculation. The validity of proposed method is verified through simulation and experiment.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.23 no.12
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• pp.58-65
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• 2009

Recently, the Korea Tilting Express(TTX), "HANVIT 200", KRRI(Korea Railroad Research Institute) developed runs for test on the conventional railroad, Honam line, Center line, Chunk-buk line and Tae-baek line. In this paper, we measured the service voltage while TTX ran on the conventional railroad and analyzed the condition of voltage. For measuring voltage directly, we installed PT under the pantograph and measured the voltage of the primary winding. In addition, we record situations that other trains pass by TTX and environments while TTX ran. And then we analyzed the condition of voltage using the records and CBEMA curve. In result, over 110[%] voltage of rated voltage(25[kV]) often occurred and the voltage of some place continued over 110[%] for about 200[s]. Especially, the voltage condition of Tae-baek line is the worst. The results in this paper can help to stabilize the power device and power converter of TTX.

• International Journal of Highway Engineering
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• v.15 no.1
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• pp.23-36
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• 2013

PURPOSES: The problem under this circumstance is that the erosion not only drops strength of the steel dowel bar but also comes with volume expansion of the steel dowel bar which can reduce load transferring efficiency of the steel dowel bar. To avoid this erosion problem, alternative dowers bars are developed. METHODS: In this study, the bearing stresses between the FRP tube dowel bar and concrete slab are calculated and compared with its allowable bearing stress to check its structural stability in the concrete pavement. These comparisons are conducted with several cross-sections of FRP tube dowel bars. Comprehensive laboratory tests including the shear load-deflection test on a full-scale specimen and the full-scale accelerated joint concrete pavement test are conducted and the results were compared with those from the steel dowel bar. RESULTS: In all cross-sections of FRP tube dowel bars, computed bearing stresses between the FRP tube dowel bar and concrete slab are less than their allowable stress levels. The pultrusion FRP-tube dowel bar show better performance on direct shear tests on full-scale specimen and static compression tests at full-scale concrete pavement joints than prepreg and filament-winding FRP-tube dowel bar. CONCLUSIONS: The FRP tube dowel bars as alternative dowel bar are invulnerable to erosion that may be caused by moisture from masonry joint or bottom of the pavement system. Also, the pultrusion FRP-tube dowel bar performed very well on the laboratory evaluation.

• Journal of Advanced Navigation Technology
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• v.23 no.2
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• pp.172-178
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• 2019

This paper has designed, fabricated, and analyzed the passive devices realized using low temperature co-fired ceramic (LTCC) multi layer substrates by dividing into the shrinkage process and the non-shrinkage process. Using two types of ceramic materials with dielectric constant 7 or 40, we have fabricated the same shape of various elements in 2 different processes and compared the characteristics. For the substrate of dielctric constant 40, compared with the shrinkage process which has 17% shrink in the X and Y directions with 36% shrink in the Z direction, the non-shrinkage process has 43% shrink in the Z direction without shrink in the X and Y directions, so high dimensional accuracy and surface flatness can be obtained. The inductances and capacitances of the fabricated elements are estimated from measurement using empirical analysis equations of parameters and implemented as a design library. Depending on the substrate and the process, the inductance and capacitance depending on the turn number of winding and unit area have been measured, and empirical polynomials are proposed to predict element values.

• The Transactions of the Korean Institute of Power Electronics
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• v.26 no.6
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• pp.404-410
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• 2021

This paper proposes a high step-up converter with zero-voltage transition (ZVT) cell for fuel cell electric vehicle. The proposed converter applies a ZVT cell to a dual floating output boost converter (DFOBC) so that not only the main switch but also the ZVT switch can achieve full-range soft switching. The current rating of the ZVT switch is 17% of the main switch. The proposed converter has high reliability in that no timing issue occurs. Therefore, online calculation is not required. The minimum turn-on time of the ZVT switch that guarantees soft switching at all loads and input/output voltage is obtained by analysis. In addition, the proposed DFOBC allows the use of a 650 V device even at 800 V output and has the advantage of being able to boost the voltage by 3.5 times with 0.56 duty. Planar coupled inductor with PCB winding was successfully implemented with the converter operated at 300 kHz. The 25 kW prototype achieves peak efficiency of 99% and power density of 63 kW/L.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.22 no.5
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• pp.111-116
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• 2022

The causes of motor burnout include overload, phase loss, restraint, interlayer short circuit, winding ground fault, instantaneous overvoltage, and the rotor contacting the stator, leading to insulation breakdown, leading to breakdown or electrical accidents. Therefore, equipment failure causes not only loss due to cost required for equipment maintenance/repair, but also huge economic loss due to productivity decrease due to process stop because the process itself including the motor is stopped. The current level of technology for diagnosing motor failures uses vibration, heat, and power analysis methods, but there is a limit to analyzing the problems only after a considerable amount of time has passed according to the failure. Therefore, in this paper, a device and algorithm for measuring insulation resistance using DC AMP signal was applied to an industrial motor to solve this problem. And by following the insulation resistance state value, we propose a diagnosis of deterioration and failure of the motor that cannot be solved by the existing method.

• Progress in Superconductivity and Cryogenics
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• v.24 no.4
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• pp.40-45
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• 2022

The electrical/thermal stabilities and magnetic field controllability of a no-insulation (NI) high-temperature superconducting magnet are characterized by contact resistance between turn-to-turn layers, and the contact resistance characteristics are determined by properties of conductor surface and winding tension. In order to accurately predict the electromagnetic characteristics of the NI coil in a design stage, it is necessary to control the contact resistance characteristics within the design target parameters. In this paper, the contact resistance and critical current characteristics of a rare-earth barium copper oxide (REBCO) conductor were measured to analyze the effects of surface treatment conditions (roughness and oxidation level) of the copper stabilizer layer in REBCO conductor. The test samples with different surface roughness and oxidation levels were fabricated and conductor surface analysis was performed using scanning electron microscope, alpha step surface profiler and energy dispersive X-ray spectroscopy. Moreover, the contact resistance and critical current characteristics of the samples were measured using the four-terminal method in a liquid nitrogen impregnated cooling environment. Compared with as-received REBCO conductor sample, the contact resistance values of the REBCO conductors, which were post-treated by the scratch and oxidation of the surface of the copper stabilizer layer, tended to increase, and the critical current values were decreased under certain roughness and oxidation conditions.

• Progress in Superconductivity
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• v.3 no.1
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• pp.130-133
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• 2001

A multifilamentary Bi-2223 HTS tape for superconducting power applications was studied through the fabrication of 250-meter long tapes by the PIT(powder in tube) process. To fabricate continuous long wire, a drawing machine, a two-drum bull block and a rolled tape winding machine were developed. Especially, 250-meter long tapes were heat treated in the shape of pancake coil to reduce the heat affect zone and to achieve the high critical current. Engineering critical current density was improved through both the enhancements of critical current density by control of thermal process and the increase of filling factor by using thin Ag alloy sheath tubes less than 1.5 mm in thickness. We have made successfully 250-meter long 37 filamentary tapes with high filling factor up to 31 % employing the modified drawing and rolling technique. The critical current of 250-meter long tapes with pancake coil type was measured by transport method at self-field up to 250 gauss of center field. The measured values, based on the transport critical current at self-field, $I_{c}$ -B characteristics and magnetic field analysis, are 34 A of I$_{c}$ and 4.0 $kA/\textrm{cm}^2$ of $J_{e}$ at 250 m, 77 K, and 0 T. We also have achieved the 56 A of I$_{c}$ and 7.0 $0 kA/\textrm{cm}^2$ of$ J_{e}$ in short tapes at 77K, self-field, and 1$mutextrm{V}$/cm.

• Journal of the Korean Society of Safety
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• v.38 no.1
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• pp.25-33
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• 2023

In this study, we determined the failure rate and fire status of electric motors widely used in domestic and industrial devices and analyzed the associated fire risks by identifying the electrical and temperature characteristics of electric motors under the normal and restrained operation modes in industrial sites and laboratories. A 2.2kW motor used for driving a conveyor during the vulcanization process in a rubber product manufacturing plant was employed as the study object and was exposed to a high- temperature environment as this motor is widely used in industrial sites. The current amplitude was 4.45-4.50 A during normal operation and 38.2-41.5 A during restrained operation due to the pinching of products and semi-finished products (i.e., 8.5 times higher than that during normal operation). The leakage current amplitude was 0.33 mA during both operation modes. The temperature of the workplace in summer was 42.38℃, indicating a poor environment for the installed motor. In the laboratory, the current and temperature of the coil inside a 3.7kW motor were measured under the restrained operation mode as performing measurements of the coil inside the motor in industrial sites is challenging. The current amplitude during normal operation was 3.5 A, whereas that during restrained operation for 30 s was 51.7-58.6 A, which is 14.8-16.7 times higher than that of normal operation. Moreover, the temperature of the motor coil increased from 22.9℃ to 101℃. Based on the experimental data, we derived the temperature increase formula according to the restrained operation time by performing a regression analysis and verified the time at which the temperature exceeded the stipulated limit for the insulation grade. The findings presented in this paper can be utilized to establish fire-prevention measures and perform safety management of motors of the same type or with a similar capacity.

• Composites Research
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• v.36 no.2
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• pp.80-85
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• 2023

A cylindrical composite lattice structure is manufactured by filament winding. The distribution of nonuniform fiber volume fraction induced by the manufacturing process can be observed. The stiffness and buckling characteristics can be influenced by non-uniform fiber volume fraction. In this paper, the effect of non-uniform fiber volume fraction through thickness direction on the torsional buckling load of the cylindrical composite lattice structure was examined. The stiffness variation induced by the non-uniform fiber volume fraction was applied to the finite element model, and buckling analysis was performed. The variations of buckling load with variations of fiber volume fraction were compared. The non-uniform fiber volume fraction reduced the torsional buckling load of the composite lattice structure.