• 한국데이터정보과학회:학술대회논문집
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• 2003.10a
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• pp.31-38
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• 2003

In this paper, we obtain the estimator of system reliability for the bivariate Pareto model with bivariate type 1 censored data. We obtain the estimators and approximated confidence intervals of the reliability for the parallel system based on likelihood function and the relative frequency, respectively. Also we present a numerical example by giving a data set which is generated by computer.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1999.05a
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• pp.375-381
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• 1999

In this study, turbine speed control algorithm is studied for Buk-Jeju steam turbine power plant and also digital governor system is designed for speed control of steam turbine in power plant. By using duplex I/O module, triplex CPU module, 2 out of 3 voting algorithm and adding self diagnostic ability, the reliability of the designed digital governor system can be acquired satisfactorily. Designed and manufactured digital governor system is implemented in a pilot steam turbine plant of 0.3kw output power Installed in Korea Maritime University. After a series of experiment the reliability and availability is confirmed and also stable operation is achieved.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.16 no.6
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• pp.1-7
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• 2016

As new information and communication technologies evolve, security threats are also becoming increasingly intelligent and advanced. In this paper, we analyze the time series data continuously entered through a series of periods from the network device or lightweight IoT (Internet of Things) devices by using the statistical technique and propose a system to detect abnormal behaviors of the device or abnormality based on the analysis results. The proposed system performs the first level abnormal detection by using previously entered data set, thereafter performs the second level anomaly detection according to the trust bound configured by using stored time series data based on time attribute or group attribute. Multi-level analysis is able to improve reliability and to reduce false positives as well through a variety of decision data set.

• Journal of Korean Physical Therapy Science
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• v.2 no.1
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• pp.383-392
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• 1995

The purpose of this investigation was to determine the intratester reliability of measurements obtained with 3 Dimensional Motion Analysis System(3DMAS) by tester on normal subject. Twenty subjects between the ages of 9 and 29(x=22) were evaluated with 3DMAS using a test-retest reliability procedure after a familiarization session. Computerized 3DMAS was done with 4 50 - Hz CCD cameras connected to the ELITE system(B. T. S., Italy) and kinetic data were collected from the AMTI force platform(AMTI., U. S. A). Data were analyzed by the Eliclinic software to obtain gait parameters, joint angles and joint internal moment and power. Test-retest revealed intraclass correlation coefficients from .80 to .99. A series of paired t-tests revealed no significant differences between test and retest values. Finally, it was concluded that tester with 3DMAS could obtain reliable measurements with 3DMAS for determining kinetic, kinematic and gait parameters in normal subjects.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.6
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• pp.743-749
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• 2010

This paper proposes a derating design method for improving system reliability by using a probabilistic approach. In the proposed design, the focus is upon system levels in determining derated levels of stresses such as temperature and current, unlike recent design approaches that focus on component levels. System reliability is evaluated using component reliability metrics that are given as functions of time and unknown stresses; this evaluation is based on a series system-reliability model. The variation in stress, which was not considered in previous derating designs, is introduced in the present design to account for the uncertainty in both environmental and operating conditions at the customer' hands. Optimization problems for system reliability improvement are formulated and solved using FORM to determine the best derating design. An example of a derating design for an electrical system shows the details of the proposed method and its applicability to systems design for reliability improvement.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.11
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• pp.1523-1529
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• 2018

Electric vehicles that are currently in operation are being produced domestically. Therefore, there is no great difficulty in receiving or repairing the failed parts or in the overall repair. On the other hand, most of the electric locomotives are manufactured by introducing the parts and technology of foreign vehicle manufacturers. In this paper, conducted a study about life cycle cost analysis of developed auxiliary power unit in 8200 series electric locomotive and suggested cost down method. This confirms the economic benefits of the developed products of the auxiliary power supply compared to the existing products. In addition, a sensitivity analysis of MTBF was conducted to suggest a life cycle cost down method.

• Journal of Electrical Engineering and Technology
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• v.11 no.4
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• pp.869-877
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• 2016

Necessity has compelled man to improve upon the art of tapping wind energy for power generation; an apt reliever of strain exerted on the non-renewable fossil fuel. The power generation in a Wind Farm (WF) depends on site and wind velocity which varies with time and season which in turn determine wind power modeling. It implies, the development of an accurate wind speed model to predict wind power fluctuations at a particular site is significant. In this paper, Box-Jenkins ARIMA (Auto Regressive Integrated Moving Average) time series model for wind speed is developed for a 99MW wind farm in the southern region of India. Because of the uncertainty in wind power developed, the economic viability and reliability of power generation is significant. Life Cycle Costing (LCC) method is used to determine the economic viability of WF generated power. Reliability models of WF are developed with the help of load curve of the utility grid and Capacity Outage Probability Table (COPT). ARIMA wind speed model is used for developing COPT. The values of annual reliability indices and variations of risk index of the WF with system peak load are calculated. Such reliability models of large WF can be used in generation system planning.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.60 no.2
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• pp.94-98
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• 2011

Electrolytic power capacitors today form essential components for virtually any power electronic system such as DC/DC converter or UPS. Frequently, electrolytic capacitors for DC link voltage smoothing are the key components which determine the life cycle of the whole unit and often are responsible for converter breakdown failures. In this paper, ethernet-based remote diagnosis system for DC voltage smoothing capacitor using DSP control board is developed. To estimate the status of the capacitor, the equivalent series resistor(ESR) of the component has to be determined. The ESR detection scheme is based on the determination of the capacitor ripple power losses calculated from DC link voltage/current measurement. Experimental results show the veridity and reliability of the proposed ethernet-based remote on-line capacitor diagnosis system.

• International Journal of Reliability and Applications
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• v.15 no.1
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• pp.51-64
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• 2014

This paper develops a warranty cost model for complex systems with imperfect repair within a warranty period by addressing a practical case that the first inter-failure interval is longer than any other inter-failure intervals. The product is in its best condition before the first failure if repair is imperfect. After the imperfect repair, other inter-failure intervals which are explained by renewal processes, are stochastically smaller than the first inter-failure interval. Based on this idea, we suggest the failure-interval-failure-criterion model. In this model, we consider two random variables, X and Y where X represents failure intervals and Y represents failure criterion. We also obtain the distribution of the number of failures and conduct the warranty cost analysis. We investigate different types of warranty cost models, reliabilities and other measures for various systems including series-parallel configurations. Several numerical examples are discussed to demonstrate the applicability of the methodologies derived in the paper.

• Journal of Electrical Engineering and Technology
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• v.3 no.2
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• pp.224-234
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• 2008

Multi-phase machines can be used in variable speed drives. Their applications include electric ship propulsion, 'more-electric aircraft' and traction applications, electric vehicles, and hybrid electric vehicles. Multi-phase machines enable independent control of a few numbers of machines that are connected in series in a particular manner with their supply being fed from a single voltage source inverter(VSI). The idea was first implemented for a five-phase series-connected two-motor drive system, but is now applicable to any number of phases more than or equal to five-phase. The number of series-connected machines is a function of the phase number of VSI. Theoretical and simulation studies have already been reported for number of multi-phase multi-motor drive configurations of series-connection type. Variable speed induction motor drives without mechanical speed sensors at the motor shaft have the attractions of low cost and high reliability. To replace the sensor, information concerning the rotor speed is extracted from measured stator currents and voltages at motor terminals. Open-loop estimators or closed-loop observers are used for this purpose. They differ with respect to accuracy, robustness, and sensitivity against model parameter variations. This paper analyses operation of an MRAS estimator based sensorless control of a vector controlled series-connected two-motor five-phase drive system with current control in the stationary reference frame. Results, obtained with fixed-voltage, fixed-frequency supply, and hysteresis current control are presented for various operating conditions on the basis of simulation results. The purpose of this paper is to report the first ever simulation results on a sensorless control of a five-phase two-motor series-connected drive system. The operating principle is given followed by a description of the sensorless technique.