• 전기학회논문지
• /
• 제67권1호
• /
• pp.29-37
• /
• 2018

Inrush current and fault current in a transformer need to be distinguished from one another. In order to do this, KEPCO uses a 2nd harmonic restraint/block method. We use two setting values for 2nd harmonic restraint; 15% and 10%. We also apply per-phase blocking method among various harmonic restraint methods. If the transformer is located at the radial system, we adjust 10% in the 2nd harmonic restraint, but this method is not enough to prevent mal-operations of the current differential relay and let us spend more time to change setting value again as the power system changes. In this paper, a more reasonable setting value for a 2nd harmonic blocking scheme in KEPCO is proposed. To present a proposed method, the fault data of the current differential relays which have occurred since 2009 are analyzed. To evaluate the performance of the proposed method, the results of the RTDS test for the current differential relay of the transformer by KEPCO are analyzed.

• Steel and Composite Structures
• /
• 제19권5호
• /
• pp.1203-1219
• /
• 2015

'Distortional buckling' is one of the predominant buckling types that may occur in a steel-concrete composite box beam (SCCBB) under a negative moment. The key factors, which affect the buckling modes, are the torsional and lateral restraints of the bottom plate of a SCCBB. Therefore, this article investigates the equivalent lateral and torsional restraint rigidity of the bottom plate of a SCCBB under a negative moment; the results of which show a linear coupling relationship between the applied forces and the lateral and/or torsional restraint stiffness, which are not depended on the cross-sectional properties of a SCCBB completely. The mathematical formulas for calculating the lateral and torsional restraint rigidity of the bottom plate can be used to estimate: (1) the critical distortional buckling stress of SCCBBs under a negative moment; and (2) the critical distortional moment of SCCBBs. This article develops an improved calculation method for SCCBBs on an elastic foundation, which takes into account the coupling effect between the applied forces and the lateral and/or torsional restraint rigidity of the bottom plate. This article analyzes the accuracy of the following calculation methods by using 24 examples of SCCBBs: (1) the conventional energy method; (2) the improved calculation method, as it has been derived in this article; and (3) the ANSYS finite element method. The results verify that the improved calculation method, as it has been proved in this article, is more accurate and reliable than that of the current energy method, which has been noted in the references.

• 한국안전학회지
• /
• 제19권4호
• /
• pp.8-13
• /
• 2004

The purpose of this paper is to investigate the welding residual stress distribution according to the constraint or non-constraint welding condition with titanium commonly using power station, aircraft, and ship. The measuring method of the residual stress was applied stress release rating method with strain gages and a potable strain meter. The x direction residual stress generally showed the tensile residual stress in case of res03int welding. On the other hand, the x direction residual stress under non-restraint welding were changed tensile stress into compressive stress on 15mm away from welding bead center. Also, the y direction residual stress generally showed the tensile residual stress in case of non-restraint welding and the y direction residual stress under restraint welding were changed tensile stress into compressive stress about 60mm away from welding bead center.

• Steel and Composite Structures
• /
• 제18권2호
• /
• pp.325-344
• /
• 2015

Experimental tests on cellular beams with sinusoidal openings showed two main failure modes around the openings. They concern the formation of four plastic hinges and the local instability of the sinusoidal part of the opening. In parallel, numerical analysis of the sinusoidal part of the opening revealed the existence of an elastic rotational restraint between the intermediate web-post and the adjacent opening panel. The aim of the present study is to present an approach to quantify this rotational restraint. Through the response surface method, a mathematical model is proposed. It shows a great ability to predict the rotational restraint value as a function of the geometrical parameters of the opening. This model can be used to perform an extensive study with various geometrical configurations of beams with the aim to develop a reliable and realistic analytical model predicting the resistance of the sinusoidal openings.

• 대한용접접합학회:학술대회논문집
• /
• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
• /
• pp.396-401
• /
• 2002

A practical method for evaluating the possibility of the occurrence of cracking in actual thick-plate T-joint weldments is presented in this study. Systematic experiments based on the method of the design of experiment are conducted in order to investigate the crack tendency in relation to typical welding parameters such as diffusible hydrogen, restraint intensity, preheating temperature and so on. The elastic analysis using the [mite element techniques is employed to quantify the restraint intensities of the specimens. The defined restraint intensities are treated in numerical way for the sake of considering the most uncertain factor among some major factors that govern the cracking phenomena due to welding. The critical plane for judgment of the crack occurrence or crack density is presented as a function of typical welding parameters including determined restraint intensities. The results of numerical estimation by the proposed method for the experimental specimens show the usefulness as a practical tool in welding induced crack problem having extensive uncertainties.

• International Journal of Korean Welding Society
• /
• 제4권1호
• /
• pp.38-45
• /
• 2004

A practical method for evaluating the possibility of the occurrence of cracking in actual thick-plate T-joint weldments is presented in this study. Systematic experitrients based on the method of the design of experiment are conducted in order to investigate the crack tendency in relation to typical welding parameters such as diffusible hydrogen, restraint intensity, preheating temperature and so on. The elastic analysis using the fmite element techniques is employed to quantify the restraint intensities of the specimens. The defined restraint intensities are treated in numerical way for the sake of considering the most uncertain factor among some major factors that govern the cracking phenomena due to welding. The critical plane for judgment of the crack occurrence or crack density is presented as a function of typical welding parameters including determined restraint intensities. The results of numerical estimation by the proposed method for the experimental specimens show the usefulness as a practical tool in welding induced crack problem having extensive uncertainties.

• 한국해양공학회지
• /
• 제17권2호
• /
• pp.14-20
• /
• 2003

In this paper, a practical design criteria for judgement of crack occurrence in weldments is presented as a function of typical welding parameters, such as diffusible hydrogen, restraint intensity, and preheating temperature. The elastic analyses using the finite element techniques are employed in order to quantify the restraint intensities, numerically. Systematic experiments are also conducted in order to investigate the propensity of crack to typical welding parameters. The results of numerical estimation using the proposed method for the experimental specimens show the usefulness as a practical tool in welding induced crack problems with extensive uncertainties. Systematic experiments are also conducted in order to investigate the propensity of crack to typical welding parameters. The results of numerical estimation using the proposed method for the experimental specimens show the usefulness as a practical tool in welding induced crack problems with extensive uncertainties.

• 대한수의사회지
• /
• 제27권2호
• /
• pp.109-114
• /
• 1991

In the experiment of shoulder lockup restraint method for the 6 groups of Korean cattle that mean body weights were 155.3kg(Group 1), 275.3kg(Group 2), 301.3kg(Group 3), 342kg(Group 4), 384.Ok9(Group 5) and 446.3kg (Group 6), respectively, the obtained re

• 대한용접접합학회:학술대회논문집
• /
• 대한용접접합학회 2004년도 춘계 학술발표대회 개요집
• /
• pp.288-289
• /
• 2004

In this report, stress analysis of restraint specimen was done by numerical method (finite element method). Calculations were done by elastic-plastic analysis and thermo-elastic-plastic analysis. The results showed similarities for both cases, and by thermo-elastic-plastic analysis transient characteristics of welding could be found.

• 한국자동차공학회논문집
• /
• 제14권6호
• /
• pp.179-183
• /
• 2006

Whiplash injuries of the neck are one of the most common injuries reported from automotive rear impacts. Whiplash injuries can be reduced by changing geometry of head restraint. Therefore, geometries of head restraint were evaluated according to the test procedures of the Korea New Car Assessment Program(KNCAP) to improve safety of head restraint. In this study, nine vehicle's head restraints were tested. As the test results, one head restraints is rated at "Marginal", three head restraints are rated at "Acceptable" level, and the last five head restraints are rated at "Good" level.