• Title/Summary/Keyword: weibull distribution

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A Study for Reliability Improvement of Passenger Service Equipment using Failure Analysis (고장 분석을 통한 승객서비스 장치의 신뢰성 향상방안 연구)

  • Roh, Bumtaek;Chung, Kwangwoo
    • Journal of the Korean Society for Railway
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    • v.19 no.5
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    • pp.609-616
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    • 2016
  • The Passenger Service Equipment(PSE) provide various train operation data such as flag station data. When PSE incur service failures or errors, passengers who use the train feel great inconvenience. In this paper, I have chosen PSE that were important to passengers and have applied Reliability Centered Maintenance(RCM), deviating from the existing perspective that operators have taken to perform RCM. FMEA/FMECA was performed for reliability analysis of the PSE. The highly critical device among the PSE is defined as the Passenger Information Control System(PICS), which is used to control the automatic announcement and signaling board. Through Weibull distribution of the PICS, failure analysis was performed. Based on the analyzed results, I have proposed a solution that will minimize service failure of PICS.

Application of Judgement Criteria to Measure Deterioration and to Judge Insulation Resistance in High-Power Live XLPE Cables (고전력 활선 XLPE 케이블의 열화를 측정하기 위한 판정기준의 적용 및 절연상태 판정)

  • Um, Kee-Hong
    • The Journal of the Institute of Internet, Broadcasting and Communication
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    • v.17 no.2
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    • pp.239-244
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    • 2017
  • The demand for electric power is increasing every year. All facilities operating at power stations and all facilities used in transmitting high volumes of electric power are therefore expected to operate with a high degree of reliability. 6.6 kV XLPE 100 SQ 1C cables are used to deliver high levels of generated electric power. Depending on the method of manufacture, installation environment, and usage conditions, the deterioration processes of power cables start from the instant of operation. Cable junctions may break down in three years from the start of operation due to manufacturing or construction defects. We have invented the first device in Korea to monitor the status of live cables and installed these at Korea Western Power Co., Ltd.. We have set the criteria to determine deterioration status and specified the degree of deterioration at which one should replace the cables. In this paper, we present the effect of insulation layer and sheath on the insulation resistance status in cables.

Optimal Inspection Policy for One-Shot Systems Considering Reliability Goal (목표 신뢰도를 고려한 원-샷 시스템의 최적검사정책)

  • Jeong, Seung-Woo;Chung, Young-Bae
    • Journal of Korean Society of Industrial and Systems Engineering
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    • v.40 no.4
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    • pp.96-104
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    • 2017
  • A one-shot system (device) refers to a system that is stored for a long period of time and is then disposed of after a single mission because it is accompanied by a chemical reaction or physical destruction when it operates, such as shells, munitions in a defense weapon system and automobile airbags. Because these systems are primarily related with safety and life, it is required to maintain a high level of storage reliability. Storage reliability is the probability that the system will operate at a particular point in time after storage. Since the stored one-shot system can be confirmed only through inspection, periodic inspection and maintenance should be performed to maintain a high level of storage reliability. Since the one-shot system is characterized by a large loss in the event of a failure, it is necessary to determine an appropriate inspection period to maintain the storage reliability above the reliability goal. In this study, we propose an optimal inspection policy that minimizes the total cost while exceeding the reliability goal that the storage reliability is set in advance for the one-shot system in which periodic inspections are performed. We assume that the failure time is the Weibull distribution. And the cost model is presented considering the existing storage reliability model by Martinez and Kim et al. The cost components to be included in the cost model are the cost of inspection $c_1$, the cost of loss per unit time between failure and detection $c_2$, the cost of minimum repair of the detected breakdown of units $c_3$, and the overhaul cost $c_4$ of $R_s{\leq}R_g$. And in this paper, we will determine the optimal inspection policy to find the inspection period and number of tests that minimize the expected cost per unit time from the finite lifetime to the overhaul. Compare them through numerical examples.

A Study on the Electrical Breakdown Characteristics of Air according to Electrode Gap (전극 간격에 따른 공기의 절연파괴 특성에 관한 연구)

  • Kang, Jong O;Lee, Onyou;Kim, Junil;Bang, Seungmin;Lee, Hongseok;Lee, Jong Doug;Kang, Hyoungku
    • The Transactions of the Korean Institute of Electrical Engineers P
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    • v.63 no.4
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    • pp.301-306
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    • 2014
  • Recently in accordance with the rapid development of the industrial society, the accidents caused by dielectric breakdown have been increasing in power grid. It is important to prevent the dielectric breakdown of a high voltage apparatus to reduce the damage from electrical hazards. To establish an electrically reliable database of insulation design criteria for high voltage apparatus, a study on dielectric characteristics test is indispensable. In this study, dielectric characteristics according to field utilization factors (${\xi}$) which are represented as the ratio of mean electric field to maximum electric field are investigated. the dielectric breakdown experiments by using several kinds of electrode systems made with stainless steel are performed by AC breakdown voltage under air-insulation. Also, the experimental results are analyzed by the Weibull distribution. As a result, it is found that the dielectric characteristics of air-insulation are determined by ${\xi}$ as well as arrangement of electrode systems. It is considered that the results of this study would be applicable to designing the air-insulated high voltage apparatuses.

Characteristics of Ultimate Load in a Wind Turbine for IEC 61400-1 DLC1.1 and DLC1.3 (IEC 61400-1 DLC1.1과 DLC1.3에 대한 풍력터빈의 극한하중 특성)

  • Kim, Chung-Ok;Nam, Hyun-Woo;Eum, Hark-Jin;Kim, Gui-Shik
    • Journal of the Korean Solar Energy Society
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    • v.32 no.1
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    • pp.15-24
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    • 2012
  • IEC 61400-1 requires design lifetime of wind turbines at least 20 years, thus wind turbine should be assured for structural safety through load assessment. DLCs have been defined with respect to the load assessment in IEC 61400-1. In addition, if the extreme design values for DLC1.3 are equal or exceed the extreme design value for DLC1.1, DLC1.1 may be omitted. To omit DLC1.1, scale factor (c) will be increased in DLC1.3. However, this particular adjustment is not specified guidelines. Thus, this study was conducted. DLC1.1 was calculated for extrapolation of 50 years-extreme events using several probability distribution functions and fitting methods. And DLC1.3 was calculated for up to seven different values of scale factor (c) with $2{\leq}c{\leq}5$ in steps of 0.5. Finally, in this study, scale factor (c) that was the value of 4.51 was determined.

Offshore Wind Resource Assessment around Korean Peninsula by using QuikSCAT Satellite Data (QuikSCAT 위성 데이터를 이용한 한반도 주변의 해상 풍력자원 평가)

  • Jang, Jea-Kyung;Yu, Byoung-Min;Ryu, Ki-Wahn;Lee, Jun-Shin
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.37 no.11
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    • pp.1121-1130
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    • 2009
  • In order to investigate the offshore wind resources, the measured data from the QuikSCAT satellite was analyzed from Jan 2000 to Dec 2008. QuikSCAT satellite is a specialized device for a microwave scatterometer that measures near-surface wind speed and direction under all weather and cloud conditions. Wind speed measured at 10 m above from the sea surface was extrapolated to the hub height by using the power law model. It has been found that the high wind energy prevailing in the south sea and the east sea of the Korean peninsula. From the limitation of seawater depth for piling the tower and archipelagic environment around the south sea, the west and the south-west sea are favorable to construct the large scale offshore wind farm, but it needs efficient blade considering relatively low wind speed. Wind map and monthly variation of wind speed and wind rose using wind energy density were investigated at the specified positions.

The Electrical Insulation Characteristics of HTS SMES (초고온초전도 SMES의 절연특성)

  • Cheon, Hyeon-Gweon;Choi, Jae-Hyeong;Kim, Hae-Jong;Seong, Ki-Chul;Kim, Sang-Hyun
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2005.07a
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    • pp.623-626
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    • 2005
  • Toward the practical applications, on operation of conduction-cooled HTS SMES at temperatures well below 77 K should be investigated, in order to take advantage of a greater critical current density of HTS and considerably reduce the size and weight of the system. Recently, research and development concerning application of the conduction-cooled HTS SMES that is easily movement are actively progressing in Korea. Electrical insulation under cryogenic temperature is a key and an important element in the application of this apparatus. Using multi wrapped copper by polyimide film for HIS SMES, the breakdown characteristics of models for turn-to-turn, that is surface contact model, were investigated under ac and impulse voltage at 77 K. A material that is Polyimide film (Kapton) 0.025 mm thickness is used for multi wrapping of the electrode. Statistical analysis of the results using Weibull distribution to examine the wrapping number effects on breakdown voltage under ac and impulse voltage in $LN_2$ was carried.

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Classification of Wind Sector in Pohang Region Using Similarity of Time-Series Wind Vectors (시계열 풍속벡터의 유사성을 이용한 포항지역 바람권역 분류)

  • Kim, Hyun-Goo;Kim, Jinsol;Kang, Yong-Heack;Park, Hyeong-Dong
    • Journal of the Korean Solar Energy Society
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    • v.36 no.1
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    • pp.11-18
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    • 2016
  • The local wind systems in the Pohang region were categorized into wind sectors. Still, thorough knowledge of wind resource assessment, wind environment analysis, and atmospheric environmental impact assessment was required since the region has outstanding wind resources, it is located on the path of typhoon, and it has large-scale atmospheric pollution sources. To overcome the resolution limitation of meteorological dataset and problems of categorization criteria of the preceding studies, the high-resolution wind resource map of the Korea Institute of Energy Research was used as time-series meteorological data; the 2-step method of determining the clustering coefficient through hierarchical clustering analysis and subsequently categorizing the wind sectors through non-hierarchical K-means clustering analysis was adopted. The similarity of normalized time-series wind vector was proposed as the Euclidean distance. The meteor-statistical characteristics of the mean vector wind distribution and meteorological variables of each wind sector were compared. The comparison confirmed significant differences among wind sectors according to the terrain elevation, mean wind speed, Weibull shape parameter, etc.

Prediction of Crack Growth Lives of an Aged Korean Coast Guard Patrol Ship based on Extended Finite Element Method(XFEM) J-Integral (확장 유한 요소법(XFEM) J-적분을 이용한 노후 순시선의 균열 성장 수명 예측)

  • Kim, Chang-Sik;Li, Chun Bao;Kim, Young Hun;Choung, Joonmo
    • Journal of the Society of Naval Architects of Korea
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    • v.54 no.4
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    • pp.335-343
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    • 2017
  • The Newman-Raju formula and contour integral-based finite element analyses(FEAs) have been widely used to assess crack growth rates and residual lives at crack locations in ships or offshore structures, but the Newman-Raju formula is known to be less accurate for the complicated weld details and the conventional FEA-based contour integral approach needs concentrated efforts to construct FEA models. Recently, an extended finite element method(XFEM) has been proposed to reduce those modeling efforts with reliable accuracy. Stress intensity factors(SIFs) from the approaches such as the Newman-Raju formula, conventional FEA-based J-integral, and XFEM-based J-integral were compared for an infinitely long plate with a propagating elliptic crack. It was concluded that the XFEM approach was far reliable in terms of prediction ability of SIFs. Assuming a 25 year-aged coast guard patrol ship had the prescribed cracks at the bracket toes attached to longitudinal stiffeners in way of deck and bottom, SIFs were derived based on the three approaches. To obtain axial tension loads acting on the longitudinal stiffeners, long term hull girder bending moments were assumed to obey Weibull distribution of which two parameters were decided from a reference (DNV, 2014). For the complicated weld details, it was concluded that the XFEM approach could cost-effectively and accurately estimate the crack growth rates and residual lives of ship structures.

Failure Mechanism and Long-Term Hydrostatic Behavior of Linear Low Density Polyethylene Tubing (선형저밀도 폴리에틸렌 튜빙의 파손 메커니즘과 장기 정수압 거동)

  • Weon, Jong-Il;Chung, Yu-Kyoung;Shin, Sei-Moon;Choi, Kil-Yeong
    • Polymer(Korea)
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    • v.32 no.5
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    • pp.440-445
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    • 2008
  • The failure mechanism and failure morphology of linear low density polyethylene (LLDPE) tubing under hydrostatic pressure were investigated. Microscopic observations using video microscope and scanning electron microscope indicate that the failure mode is a brittle fracture including cracks propagated from inner wall to outer wall. In addition, oxidation induction time and Fourier transform infrared spectroscopy results show the presence of exothermic peak and the increase in carbonyl index on the surface of fractured LLDPE tubing, due to thermal-degradation. An accelerated life test methodology and testing system for LLDPE tubing are developed using the relationship between stresses and life characteristics by means of thermal acceleration. Statistical approaches using the Arrhenius model and Weibull distribution are implemented to estimate the long-term life time of LLDPE tubing under hydrostatic pressure. Consequently, the long-term life time of LLDPE tubing at the operating temperature of $25^{\circ}C$ could be predicted and also be analyzed.