• Journal of IKEEE
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• v.24 no.1
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• pp.354-359
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• 2020

DGA(Dissolved Gas Analysis) is regularly performed to detect internal defects of power transformers and prevent failures. The overheating or discharging in the transformer can be confirmed by DGA but the defective parts should be identified by internal inspection. However, winding or iron core defects cannot be checked by internal inspection, so it is impossible to establish actions by DGA alone. In this paper, the internal defect mode is analyzed and presented based on the transformer internal inspection reports, and the internal defect can be predicted by considering DGA.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.4
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• pp.391-397
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• 2011

Conventional film radiographic test has been generally and widely used in the inspection on the weldment for quality assurance. On the other hand, since the analog RT is well known for typical time and cost consuming method with complex process of inspection, the industry has researched various ways how to improve radiographic test technology. In this study, we verified the fact that digital RT provides a lot more benefit in effectively detecting defects, ever film details, through digital processing of image enhancement, compared to film RT. As a result, we reached conclusion that digital RT is positively able to replace the film RT in industry in part or in whole.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.1116-1120
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• 2004

In the nuclear power plant, there are several cylindrical vessels such as reactor vessel, pressuriser and so on. The vessels are usually constructed by welding large rolled plates, forged sections or nozzle pipes together. In order to assure the integrity of the vessel, these welds should be periodically inspected using sensors such as ultrasonic transducer or visual cameras. This inspection is usually conducted under water to minimize exposure to the radioactively contaminated vessel walls. The inspections have been performed by using a conventional inspection machine with a big structural sturdy column, however, it is so huge and heavy that maintenance and handling of the machine are extremely difficult. It requires much effort to transport the system to the site and also requires continuous use of the utility's polar crane to move the manipulator into the building and then onto the vessel. Setup beside the vessel requires a large volume of work preparation area and several shifts to complete. In order to resolve these problems, we have developed an underwater mobile robot guided by the laser pointer, and performed a series of experiments both in the mockup and in the real reactor vessel. This paper introduces our robotic inspection system and the laser guidance of the mobile robot as well as the results of the functional test.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.6
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• pp.738-744
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• 2011

The reliability of blade root fixing section is required to endure the centrifugal force and vibration stress for the last stage blade of steam turbine in thermal power plant. Most of the domestic steam turbine last stage blades have finger type roots. The finger type blade is very complex, so the inspection had been performed only on the exposed fixing pin cross-section area due to the difficulty of inspection. But the centrifugal force and vibration stress are also applied at the blade root finger and the crack generates, so the inspection method for finger section is necessary. For the inspection of root finger, inspection points were decided by simulating ultra-sonic path with 3D modeling, curve-shape probe and fixing jig were invented, and the characteristics analysis method of ultrasonic reflection signal and defect signal disposition method were invented. This invented method was actually executed at site and prevented the blade liberation failure by detecting the cracks at the fingers. Also, the same type blades of the other turbines were inspected periodically and the reliability of the turbine increased.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.7 no.3
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• pp.8-14
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• 2011

The clogging of the flow area at the tube support plates(TSPs), especially at the upper TSPs results in the water level oscillation of a steam generator during normal operation. A reduction of the TSP flow area causes to increase in pressure drop within the two-phase flow zone, which destabilizes the boiling flow through the tube bundle. This phenomenon was occasionally observed at a few domestic and foreign nuclear power plants. One of the methods for defining the flow area clogging is visual inspection, which is the most effective inspection method. The results of the visual inspection for TSPs' flow area are clogging images on TSPs' quartrefoil lobes. These images are complexly distorted due to lens aberration and external factors like the distance to a subject and angle etc. In this work, we developed the analysis algorithm for clogging image of the TSP flow area of steam generators. For this purpose, we designed an image verification device applicable to the camera employed in the field for visual inspection and then, we demonstrated the validity of image analysis algorithm by using this device and commercial autoCAD program.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.4
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• pp.77-83
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• 2016

Recently, interests for maintenance of transmission tower are increasing to extend life of structures and reduce maintenance cost. However, existing classical diagnosis method of corrosion deteriorated degree on the transmission tower steel members, visual inspection, has a problem that error often due to difference of inspector's individual knowledge and experience. In order to solve the problem, this study carried out to develop the corrosion deterioration inspection tool for transmission tower steel members. This tool is composed of camera equipment and computer-aided diagnosis system. We standardized the photographing method by camera equipment to obtain suitable pictures for image processing. Diagnosis system was designed to evaluate automatically degree of corrosion deterioration for member of transmission tower on the basis of the RGB color image processing techniques. It is anticipated that developed the corrosion deterioration inspection tool will be very helpful in decision of optimal maintenance time for transmission tower corrosion.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.10
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• pp.1291-1296
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• 2013

Risk-based inspection (RBI) is a well-known method that is used to optimize inspection activities based on risk analysis in order to identify the high-risk components of major facilities such as power plants. RBI, when implemented and maintained properly, improves plant reliability and safety while reducing unplanned outages and repair costs. Risk is given by the product of the probability of failure (POF) and the consequence of failure (COF). A semi-quantitative method is generally used for risk assessment. Semi-quantitative risk assessment complements the low accuracy of qualitative risk assessment and the high expense and long calculation time of quantitative risk assessment. The first step of RBI is to identify important failure modes and causes in the equipment. Once these are defined, the POF and COF can be assessed for each failure. During POF and COF assessment, an effective inspection method and range can be easily found. In this paper, the calculation of the POF is improved for accurate risk assessment. A modified semi-quantitative risk assessment was carried out for boiler facilities of thermal power plants, and the next maintenance schedules for the equipment were decided.

• Journal of the Korean Society of Safety
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• v.14 no.2
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• pp.155-162
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• 1999

reliability from components reliability. In this case, it assumes that components failure is mutually independent, but it may not true in real systems. In this study, the mean cost per unit time is computed as the ratio of mean life to the mean cost. The mean life is obtained by the reliability function under power rule model. The mean cost is obtained by the mathematical model based on the inspection interval. A heuristic method is proposed to determine the optimal number of redundant units and the optimal inspection interval to minimize the mean cost per unit time. The assumptions of this study are as following : First, in the load-sharing k-out-of-n:G system, total loads are applied to the system and shared by the operating components. Secondly, the number of failed components affects the failure rate of surviving components as a function of the total load applied. Finally, the relation between the load and the failure rate of surviving components is set by the power rule model. For the practical application of the above methods, numerical examples are presented.

• 제어로봇시스템학회:학술대회논문집
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• 2002.10a
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• pp.96.4-96
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• 2002

Thermal infrared imaging is a highly promising technology for condition monitoring and predictive maintenance of electronic, electrical and mechanical elements in nuclear power plants. However, conventional low-cost infrared imaging systems suffer from poor spatial resolution compared to commercial CCD cameras. This paper describes an approach to enhance inspection performances for calandria reactor area of Wolsung nuclear power plant through the technique of superimposing thermal infrared image into real CCD image. In the occurrence of thermal abnormalities on observation points and areas of calandria reactor area, unusual hot image taken from thermal infrared camera is mapped upon re...

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.11a
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• pp.106-107
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• 2005

Small vessels of less then 20 tonnage and leisure boats such as motor boats, sailing yachts, water motorcycle, etc have been excluded from the rules and regulations such as Marine Leisure Safety Act, Ship Act and Ship Safety Act for a long time in Korea. As a result, these small vessels and leisure boats have remained within the blind area of maritime safety and environment protection. Among these vessels and boats, some leisure boats such as motor boats of 20 horse power or more(excluding motor boats equipped with engine inside the vehicles), water motorcycles and rubber boats of 30 horse power or more are incorporated into the Marine Leisure Safety Act through the registry, safety inspection, insurance early 2005 in Korea. In relation to the scope of application of the national Acts concerned, I consider the conflicts between Acts and suggest the subordinate enforcement ordinance and regulations.