• Journal of Welding and Joining
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• v.23 no.6
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• pp.61-66
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• 2005

A probabilistic approach for evaluating failure risk is suggested in this paper. Probabilistic fracture analyses were performed for a pressurized pipe of a Cr-Mo steel reflecting variation of material properties at high temperature. A crack was assumed to be located along the weld fusion line. Probability density functions of major variables were determined by statistical analyses of material creep and creep crack growth data measured by the previous experimental studies by authors. Distributions of these variables were implemented in Monte Carlo simulation of this study. As a fracture parameter for characterizing growth of a fusion line crack between two materials with different creep properties, $C_t$ normalized with $C^*$ was employed. And the elapsed time was also normalized with tT, Resultingly, failure probability as a function of operating time was evaluated fur various cases. Conventional deterministic life assessment result was turned out to be conservative compared with that of probabilistic result. Sensitivity analysis for each input variable was conducted to understand the most influencing variable to the analysis results. Internal pressure, creep crack growth coefficient and creep coefficient were more sensitive to failure probability than other variables.

• Journal of Institute of Control, Robotics and Systems
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• v.9 no.10
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• pp.755-767
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• 2003

This paper proposes a robust fault-tolerant control framework for robot manipulators to maintain the required performance and achieve task completion in the presence of both partial joint failures and complete joint failures and uncertainties. In the case of a complete joint failure or free-swinging joint failure causing the complete loss of torque on a joint, a fully-actuated robot manipulator can be viewed as an underactuated robot manipulator. To detect and identify a complete actuator failure, an on-line fault detection operation is also presented. The proposed fault-tolerant control system contains a robust adaptive controller overcoming partial joint failures based on robust adaptive control methodology, an on-line fault detector detecting and identifying complete joint failures, and a robust adaptive controller overcoming partial and complete joint failures, and so eventually it can face and overcome joint failures and uncertainties. Numerical simulations are conducted to validate the proposed robust fault-tolerant control scheme.

• Proceedings of the KIEE Conference
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• 2005.10b
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• pp.421-423
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• 2005

Power transmission lines have been playing a key role as the mainstay of national industry. When a power failure occurs, it can have severe effects on national security as well as national industry and economy. In this paper, we consider an insulator failure, which is one of the main causes of such a power failure. In spite of its importance, however, a shortage of manpower in the insulator maintenance field is getting more serious due to working environments with a high voltage and a high place. For this reason, a new active maintenance technique using a robot system is required to prevent such an insulator failure. In this paper, a new robot mechanism for insulator cleaning and inspection was developed. We confirmed its effectiveness through experiments.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.157-160
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• 1999

The paper provides the results of failure analysis for the porcelain suspension insulators. The comparisons of characteristics were made as a function of failed and unfailed isulators which had been used in real distribution line. This paper also described the failure modes which could be occurred in the fields. The cracks inside cap were detected though measuring the resistance or the leakage current. The ratio of open porosity was calculated from the Archimedes Method. The failure analyses of porcelain suspension insulators were conducted from the various analysis method.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.335-336
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• 2008

Overhead transmission lines are mainly crossing mountainous area. They are easily affected in weathers like typhoon, strong wind, lightning, heavy rain, or heavy snow. Sometimes these weathers cause transmission line faults. A lightning flashover is most often fault. Nowadays lightning density in KOREA is growing high and lightning flashovers occur more often. A lightning flashover on transmission line is mostly cleared by momentary operation of a circuit breaker, so power failure happens rarely. However, when both circuits trip simultaneously due to the lightning flashovers on double circuit transmission line, short time power failure and voltage drop happen. KEPCO has used transmission line arresters to avoid double circuit simultaneous trip out since 2003. And transmission line arresters cannot be installed with KEPCO's present metal fittings, so various fittings have been used for each transmission line arrester manufacturer. This paper introduces development and standardization of arc-horn and metal fittings for transmission line arrester which can be used for both existing lines and new lines in KEPCO.

• International Journal of Concrete Structures and Materials
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• v.2 no.1
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• pp.57-62
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• 2008

When the yield line theory is used to estimate the ultimate strength of a concrete barrier, it is of primary importance that the correct assumption is made for the failure mode of the barrier. In this study, a static test was performed on two full-scale concrete barrier specimens of Korean standard shape that simulate the actual behavior of a longitudinally continuous barrier. This was conducted in order to verify the failure mode presented in the AASHTO LRFD specification. The resulting shape of the yield lines differed from that presented in AASHTO when subjected to an equivalent crash load. Furthermore, the ultimate strengths of the specimens were lower than the theoretical prediction. The main causes of these differences can be attributed to the characteristics of the barrier shape and to a number of limitations associated with the classical yield line theory. Therefore, a revised failure mode with corresponding prediction equations of the strength were proposed based on the yield lines observed in the test. As a result, a strength that was more comparable to that of the test could be obtained. The proposed procedure can be used to establish more realistic test levels for barriers that have a similar shape.

• Proceedings of the KIEE Conference
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• 2003.10a
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• pp.151-159
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• 2003

According to the records, approximately 50 percent of power failure were caused by lightning. Conventional fault preventive measures against lightning include reduction of the footing resistance of the tower, multiplication of overhead ground wires and unbalanced insulation of the double circuit transmission tower. In addition to these, transmission line arresters have been recently appeared as an alternatives. In this paper an unbalanced insulation method with transmission line arrester was assumed as another countermeasure against simultaneous double circuit trip of 154 kV transmission line by lightning strike. The lightning performance of line arrester was compared with conventional insulation concept using different numbers of porcelain and glass insulator. Larger numbers of insulator simply increase flashover current level by lightning but the lightning performance doesn't proportional to it. EMTP simulation and predictive calculation of lightning failure rate were carried out to evaluate the performance.

• Proceedings of the KIEE Conference
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• 2002.07c
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• pp.1623-1627
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• 2002

If the ambient temperature rises in AC PDP, some of the discharged cells arc turned off because of the addressing failure. Particularly, the addressing failure at the last scan line is more serious than at the first scan line. The failure is accompanied with delay of the address discharge and reduction of total charge involved. In order to compensate this kind of misfiling, the progressively increasing address voltage waveform is used instead of constant one. In this method, we found that the total charge and address time at the last scan line are similar to those of the first line. As a result, we can have stable discharge without misfiring even at the high ambient temperature.

• Structural Engineering and Mechanics
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• v.71 no.3
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• pp.305-315
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• 2019

Extremely long-span transmission tower-line system is an indispensable portion of an electricity transmission system, and its failures or collapse can impact on the entire electricity grid, affect the modern life, and cause great economic losses. It is therefore imperative to investigate the failure and safety of the transmission tower subjected to ground motions. In the present study, a detailed finite element (FE) model of a representative extremely long-span transmission tower-line system is established. A segmental damage indicator (SDI) is proposed to quantitatively assess the damage level of each segment of the transmission tower under earthquakes. Additionally, parametric studies are conducted to investigate the influence of different ground motions and incident angles on the ultimate capacity and weakest segment of the transmission tower. Finally, the collapse fragility curve in terms of the maximum SDI value and PGA is plotted for the exampled transmission tower. The results show that the proposed SDI can quantitatively assess the damage level of the segments, and thus determine the ultimate capacity and weakest segment of the transmission tower. Moreover, the different ground motions and incident angles have a significant influence on the SDI values of the transmission tower, and the collapse fragility curve is utilized to evaluate the collapse resistant capacity of the transmission tower subjected to ground motions.

• Journal of the Korea Concrete Institute
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• v.14 no.1
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• pp.110-117
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• 2002

In a strengthened bridge deck which received increased service loads, failure patterns of bridge deck vary depending on deck thickness, compressive strength of concrete, yielding strength of reinforcement, reinforcement ratio and additional strengthening ratio. General failure pattern that is most commonly reported as punching shear failure after the main rebar yields, followed by yielding of distributing rebar. In this paper, by Proposing a limit to the amount of strengthening material, a brittle failure can be prevented and a ductile failure mode similar to that developed in unstrengthened deck is derived. In order to calculated the limit strengthening ratio, the yield line theory and previously proposed plastic punching shear model have been used