• 전력전자학회:학술대회논문집
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• 전력전자학회 2003년도 춘계전력전자학술대회 논문집(2)
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• pp.644-647
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• 2003

The predictive maintenance can help to avoid the serious plant breakdowns and catastrophies. This paper deals with the fault diagnosis of the rotor of the induction motor which is widely used in the plants. In order to detect the broken bar, the Extended Kalman Filter is adopted to estimate the rotor resistance on the base of model-based method. The proposed estimation method is simulated with the aid of Matlab.

• 대한수학교육학회지:학교수학
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• 제1권2호
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• pp.451-459
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• 1999

The teaching through the graphics in the newspaper which students look at easily, will encourage the student's interest and make them learn the principle of representing the statistics graphics. In this paper, we analyzed the cases of the bar chart and the graph of broken lines which is seen many in the newspaper. Through showing the good point and fault of the graphic cases, we intend that students know the principle of analyzing or making the statistics graphics.

• Journal of Biosystems Engineering
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• 제28권1호
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• pp.19-26
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• 2003

An oscillating digger mechanism was designed, constructed. and tested. The mechanism is consisted of a six-bar linkage, one four-bar linkage was fer the digger blade and the other one fur variable soil-crop separation. Experimental variables were amplitude(3, 6, 9 mm). frequency(11.2, 14.9. 17.0 Hz), and forward speed of tractor(0.91, 1.13, 1.56 km/h). Each combination of these variables was replicated three times to measure the draft and torque for power requirement evaluation. and the broken-up soil height on the soil separation sieve mechanism. Four parameters λ(the ratio of vibration speed to forward velocity), p(the ratio of vibration acceleration to forward velocity), K(the ratio of vibration acceleration to gravitational acceleration), and T(the product of λ and K) were induced from three experimental variables: amplitude, frequency, and tractor speed. And the power requirement and soil separation ability were analyzed by regression. Though λ and K were known to be the representative parameters. T was the most moderate one to explain draft. torque. and soil separation in this study. It was estimated that the T equal to or greater than 2.4 was the minimum recommended value. Figure 18 would be useful fir the selection of amplitude. frequency, or operating tractor speed once any two variables are known.

• 대한토목학회논문집
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• 제5권1호
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• pp.141-148
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• 1985

본(本) 연구(硏究)는 현존(現存)하는 백제시대(百濟時代)의 두 석탑(石塔)인 미륵사지(彌勒寺址) 석탑(石塔)과 정림사지(定林寺址) 오층석탑(五層石塔)의 조형(造形)에 관한 기하학적(幾何學的) 해석(解析)이다. 두 석탑(石塔)을 지상측정용(地上測定用) Camera P31과 정밀입체도화(情密立體圖化)에 A-10을 이용하여 현존(現存) 복발(覆鉢)부분까지 남아있는 정림사지(定林寺址) 오층석탑(五層石塔)과 손상부분이 많은 미륵사지(彌勒寺址) 석탑(石塔)을 비교고찰(比較考察)한 결과 같은 조형원리(造形原理) 즉, 기준면(基準面)(module)으로부터 정삼각형을 작도하고 그 정삼각형의 정점(頂點) 윗부분에 있는 옥개석폭(屋蓋石幅)의 비(比)가 9 : 8 : 7 : 6 : (5)로 체감(遞減)되어 나가는 것을 알 수 있었고, 손상되기전의 복발(覆鉢)부분까지의 높이를 추정(推定)할 수 있었다.

• 한국주조공학회지
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• 제20권2호
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• pp.110-115
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• 2000

In this study, the powders of Mg-3wt%Al-1wt%Zn-1wt%MM alloy were produced under vacuum condition by the inert gas atomization and the rapidly solidified powders were consolidated by the vacuum hot extrusion. Then the structural change of powders during extrusion was investigated. The effects of misch metal addition to AZ31 on mechanical properties of extruded bars were also examined. During extrusion of the rapidly solidified powders, their dendrite structure was broken into fragments and remained as grains of 2 ${\mu}m$ size in extruded bar. The Mg-Al-Ce intermetallic compounds formed in the interdendritic regions of powders were broken finely, too. The yield stress, tensile strength and ductility obtained in as-extruded Mg-3wt%Al-1wt%Zn-1wt%MM alloy were ${\sigma}_{0.2}=325$ MPa, ${\sigma}_{T.S.}=417$ MPa and ${\varepsilon}=16.8%$. All of these improvements on mechanical properties result from the refined micostructure and second-phase dispersions.

• 한국지능시스템학회:학술대회논문집
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• 한국퍼지및지능시스템학회 2003년도 ISIS 2003
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• pp.539-542
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• 2003

A motor is the workhorse of our industry. The issues of preventive and condition-based maintenance, online monitoring, system fault detection, diagnosis, and prognosis are of increasing importance. Different internal motor faults (e.g., inter-turn short circuits, broken bearings, broken rotor bars) along with external motor faults (e.g., phase failure, mechanical overload, blocked rotor) are expected to happen sooner or later. This paper introduces the fault detection technique of induction motors based upon the stator current. The fault motors have rotor bar broken or rotor unbalance defect, respectively. The stator currents are measured by the current meters and stored by the time domain. The time domain is not suitable to represent the current signals, so the frequency domain is applied to display the signals. The Fourier Transformer is used for the conversion of the signal. After the conversion of the signals, the features of the signals have to be extracted by the signal processing methods like a wavelet analysis, a spectrum analysis, etc. The discovered features are entered to the pattern classification model such as a neural network model, a polynomial neural network, a fuzzy inference model, etc. This paper describes the fault detection results that use wavelet decomposition. The wavelet analysis is very useful method for the time and frequency domain each. Also it is powerful method to detect the features in the signals.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 춘계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.182-184
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• 2006

A down-scaled simulator is developed to simulate typical faults in induction motor such as short-turn stator winding, broken rotor bar, dynamic and static air-gap eccentricity, bearing trouble, and mechanical unbalance. The simulator is used as an initial builder to develop design algorithm for real-time faults detecting system by processing an abnormal signal and characteristics in each fault.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2009년도 제40회 하계학술대회
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• pp.638_639
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• 2009

The motors faults including mechanical rotor imbalances, broken rotor bar, bearing failure and eccentricities problems are reflected in electric, electromagnetic and mechanical quantities. This paper presents a study and the practical implementation of an induction motor for reactor containment fan cooler in nuclear power plant with Electric Signature Analysis(ESA). The results obtained present a good degree of reliability hence; the ESA predictive maintenance tools enable a pro-active evaluation of induction motors performance prior to failure.

• Journal of Advanced Marine Engineering and Technology
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• 제31권1호
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• pp.95-102
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• 2007

The issues of preventive and condition-based maintenance, online monitoring, system fault detection, diagnosis and prognosis are of increasing importance. This study introduces a technique to detect and identify faults in induction motors. Stator currents were measured and stored by time domain. The time domain is not suitable for representing current signals, so wavelet transform is used to convert the signals onto frequency domain. The raw signals can not show the significant feature, therefore difference values between the signal of the health conditions and that of the fault conditions are applied. The difference values were transformed by wavelet transform and the features are extracted from the transformed signals. The dynamic time warping method was used to identify the fault type. This study describes the results of detecting fault using wavelet analysis.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.1057-1058
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• 2007

This paper proposes an alternative vibration detection method in a squirrel-cage induction motor using flux sensors. The air-gap flux will be changed when mechanical vibration occurs by bearing fault as well as broken rotor bar and air-gap eccentricity. For detecting those flux variations due to vibration, search coils are installed at stator slots. The induction motor with 380 [V], 7.5 [kW], 4 [Poles], 1,760 [rpm] ratings is used. Magnitudes and distortion of the induced voltage from flux sensors are used to discriminate faulted types. As a result, the flux sensor has been proven to be useful for vibration detection. It is compared to the result with vibration sensor as well.