• 한국초전도ㆍ저온공학회논문지
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• 제16권2호
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• pp.29-32
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• 2014

The critical current, $I_c$ of HTS superconducting tapes can be measured by transport or contactless method. Practically, the transport method using the four-probe method is the most common. In this study, a simple test procedure by clipping the voltage lead taps have been introduced instead of soldering which reduces time and effort and thereby achieving a much faster measurement of $I_c$. When using a pair of iron clips, $I_c$ value decreased as compared with the measured one by standard method using soldered voltage taps and varies with the width of the clipped specimen part. However, when using a pure Cu clip, both by clipping and by soldering voltage taps give a comparable result and $I_c$ measured are equal and close to the samples specification. As a result, material to be used as voltage clip should be considered and should not influence the potential voltage between the leads during $I_c$ measurement. Furthermore, the simulation result of magnetic flux during $I_c$ measurement test showed that the decrease of $I_c$ observed in the experiment is due to the magnetic flux density, $B_y$ produced at the clipped part of the sample by the operating current with iron clips attached to the sample.

• 한국화재소방학회논문지
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• 제21권3호
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• pp.78-83
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• 2007

석유류 중에서도 차량, 선박, 보일러 등에 많이 사용되고 있는 디젤유는 휘발유나 등유보다도 연소시에 발열량이 높기 때문에, 화재 발생시에 큰 피해를 초래한다. 따라서 본 연구는 시중에 판매중인 디젤유을 이용하여 액면화재 실험을 하였으며, 연소시에 화염의 내부온도와 화염으로부터 발생되는 복사열에 대해서 측정하였다. 디젤유의 순간 최대화염온도는 $900^{\circ}C$ 이상되는 것으로 나타났으며, 평균 최대화염온도는 $800^{\circ}C$ 이상으로 나타났다. 또한 최대화염온도는 가연성 액체의 표면으로부터 5 H/D에서 나타났으며, 이 거리 보다 멀어질 수로 화염의 온도는 낮아졌다. 복사열의 경우 저장용기의 크기와 시료의 량에 따라서 크게 달라지는 것을 알 수 있었으며, 실험 용기의 크기가 0.5 m이고, 시료량이 13 mm와 20 mm에서는 각각 92.29 kW와 117.43 kW로 나타났으며, 크기가 1.0 m의 용기에서는 각각 364.35 kW와 405.88 kW로 나타났다.

• 설비공학논문집
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• 제16권9호
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• pp.845-854
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• 2004

The evaporation heat transfer coefficient for R-l34a, R-407C (a mixture of 23wt% R-32, 25 wt% R-125, and 52 wt% R-l34a) and R-410A (a mixture of 50 wt% R-32 and 50 wt% R-125) flowing in the oblong shell and plate heat exchanger were investigated experimentally in this study. Four vertical counterflow channels were formed in the exchanger by four plates of commercial geometry with a corrugated sinusoid shape of a chevron angle of 45 degree. The effects of the mean vapor quality, mass flux, heat flux, and saturation temperature of different refrigerants on the evaporation heat transfer were explored in detail. Similar to the case of a Plate heat exchanger, even at a very low Reynolds number, the flow in the oblong shell and plate heat exchanger remains turbulent. It is found that the evaporation heat transfer coefficient in the plates is much higher than that in circular pipes. The present data show that the evaporation heat transfer coefficients of all refrigerants increase with the vapor quality. At a higher mass flux h, is higher than for the entire range of the vapor quality. Raising the imposed wall heat flux was found to slightly improve h$_{r}$, while h$_{r}$ is found to be lower at a higher refrigerant saturation temperature. A comparison of the performance of the various refrigerants reveals that R-410A has the highest heat transfer performance followed by R-l34a, and R-407C had the lowest performance of the refrigerants tested. Based on the present data, empirical correlations of the evaporation heat transfer coefficient were proposed.sed.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2001년도 Proceedings ICPE 01 2001 International Conference on Power Electronics
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• pp.355-359
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• 2001

This paper presents an implementation of digital control system of speed sensorless for Reluctance Synchronous Motor (RSM) drives with DTC. The control system consists of stator flux observer, rotor position/speed/torque estimator, two hysteresis band controllers, an optimal switching look-up table, IGBT voltage source inverter, and TMS320C31 DSP controller by using fully integrated control software. The stator flux observer is based on the combined voltage and current model with stator flux feedback adaptive control that inputs are current and voltage sensing of motor terminal with estimated rotor angle for wide speed range. The rotor position is estimated by observed stator flux-linkage space vector. The estimated rotor speed is determined by differentiation of the rotor position used only in the current model part of the flux observer for a low speed operating area. It does not require the knowledge of any motor parameters, nor particular care for motor starting, In order to prove the suggested control algorithm, we have a simulation and testing at actual experimental system. The developed sensorless control system is shown a good speed control response characteristic results and high performance features in 50/1000 rpm with 1.0Kw RSM having 2.57 ratio of d/q reluctance.

• Transactions on Electrical and Electronic Materials
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• 제6권4호
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• pp.159-163
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• 2005

We analyzed the fault current limiting characteristics of a flux-lock type $high-T_c$ super­conducting fault current limiter (HTSC-FCL) using series resonance between capacitor for series resonance and magnetic field coil which was installed in coil 3. The capacitor for the series resonance in the flux-lock type HTSC-FCL was inserted in series with the magnetic field coil to apply enough magnetic field into HTSC element, which resulted in higher resistance of HTSC element. However, the impedance of the flux lock type HTSC-FCL has started to decrease since the current of coil 3 exceeded one of coil 2 after a fault accident. The decrease in the impedance of the FCL causes the line current to increase and, if continues, the capacitor for the series resonance to be destructed. To avoid this operation, the flux-lock type HTSC-FCL requires an additional device such as fault current interrupter or control circuit for magnetic field. From the experimental results, we investigated the parameter range where the operation as mentioned above for the designed flux-lock type HTSC-FCL using series resonance occurred.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 하계학술대회 논문집 A
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• pp.633-635
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• 2004

The current limiting characteristics of the flux-lock type superconducting fault current limiters(SFCLs) were investigated. The flux-lock type SFCL consists of a flux-lock reactor and high-T_c superconducting (HTSC) element. In this SFCL the initial limiting current level can be controlled by adjusting the inductances of two coils. In this paper, the operational characteristics of the flux-lock type SPCL were analyzed and the current Limiting characteristics of it were investigated through the experiments.

• 한국전기전자재료학회논문지
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• 제30권2호
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• pp.96-100
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• 2017

In this paper, the flux-lock type superconducting fault current limiter (SFCL) using double quench was suggested and its transient current limiting characteristics were analyzed. The suggested flux-lock type SFCL using double quench consists of two magnetically coupled windings and two $high-T_{c}$ superconducting (HTSC) elements connected in series with each winding. To analyze the transient current limiting characteristics of the flux-lock type SFCL using double quench, the short-circuit tests according to the fault angles, which affect the transient component of the fault current right after the fault occurs, were executed. From the comparative analysis for the short-circuit tests at both $0^{\circ}$ and $90^{\circ}$ fault angles, the useful transient current limiting operations of the suggested flux-lock type SFCL through the double or the single quench occurrence were confirmed.

• 열처리공학회지
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• 제23권5호
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• pp.249-256
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• 2010

Water jet impingement cooling has been widely used in a various engineering applications; especially in cooling of hot steel plate of steelmaking processes and heat treatment in hot metals as an effective method of removing high heat flux. The effects of cooling water temperature on water jet impingement cooling are primarily investigated for hot steel plate cooling applications in this study. The local heat flux measurements are introduced by a novel experimental technique that has a function of high-temperature heat flux gauge in which test block assemblies are used to measure the heat flux distribution during water jet impingement cooling. The experiments are performed at fixed flow rate and fixed nozzle-to-target spacing. The results show that effects of cooling water temperature on the characteristics of jet impingement heat transfer are presented for five different water temperatures ranged from 5 to $45^{\circ}C$. The local heat flux curves and heat transfer coefficients are also provided with respect to different boiling regimes.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 학술대회 논문집 전문대학교육위원
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• pp.47-52
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• 2001

This paper presents a high-performance control system for Reluctance Synchronous Motor (RSM) drives with direct torque control (DTC). The system consist of stator flux observer, rotor position/speed estimator, torque estimator, two hysteresis band controllers, an optimal switching look-up table, IGBT voltage source inverter, and F240/C31DSP controller by using fully integrated control software. The stator flux observer is based on the combined voltage and current model with stator flux feedback adaptive control that inputs are current and voltage sensing of motor terminal with estimated rotor angle for wide speed range. The rotor position is estimated by the observed stator flux-linkage space vector. The estimated rotor speed can be determinated by differentiation of the rotor position used only in the current model part of the flux observer for a low speed operating area. To prove the suggested control algorithm, we have a simulation and testing at actual experimental system. The developed digitally high-performance position sensorless control system are shown a good motion control response characteristic results and high performance features using 1.0Kw RSM.

• 동력기계공학회지
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• 제11권1호
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• pp.121-126
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• 2007

This study aims at investigating the effect of heat treatment conditions on the dry sliding wear behavior of thermally sprayed Ni-based self-flux alloy coatings. Ni-based self-flux alloy powders were sprayed onto a carbon steel substrate and then heat-treated at 700, 800, 900 and $1000^{\circ}C$ for 30 minutes in a vacuum furnace. Dry sliding wear tests were performed using sliding speed of 0.4 m/s and applied load of 6 N. AISI 52100 ball(diameter 8 mm) was used as counterparts. Microstructure and wear behavior of both as-sprayed and heat-treated Ni-based self-flux alloy coatings were studied using a scanning electron microscope(SEM), energy dispersive X-ray spectroscopy(EDX), electron probe micro-analysis(EPMA) and X-ray diffraction(XRD). It was revealed that microstructure and wear behavior of thermally sprayed Ni-based self-flux alloy coatings were much influenced by heat treatment conditions.