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박우진(Woo-Jin Park),김일현(Il-Hyun Kim),조해용(Hae-Yong Jo),김영근(Young-Guen Kim),안길영(Kil-Young Ahn) 대한전기학회 2019 전기학회논문지 Vol.68 No.12
A low voltage DC(Direct Current) circuit breaker is an electric control device that interrupts the abnormal currents which result from the over-loads or short-circuits in a low voltage(less than 1,500Vdc) distribution line. Recently, higher current breaking performance has become crucial in providing the reliability for the modern devices requiring small scale and high performance. When a short circuit occurs, a fault current flows between contacts of DC circuit breaker even though they are separated by the protective control system. Arc voltage between contacts of circuit breaker should generate as high as possible during breaking phase. High arc voltage could lead the main circuit to zero arc current so that arc plasma is eliminated. Based on this behavior, arc extinction system of a circuit breaker should be designed for increasing arc voltage during breaking period of the current. Since DC does not have current zero point, it can be more difficult and important to secure the breaking performance. There are conventional methods that are widely known as arc extinction methods and most of them involve method for increasing arc voltage. In this paper, experiments and CAE analysis were carried out to find out the criteria of the arc extinction and to verify the validity of methods of extinguishing an electric arc.
조해용,정석영,김명한,조창용,이제훈,서정 한국레이저가공학회 2001 한국레이저가공학회지 Vol.4 No.1
Simulation on the electron beam welding of Al 2219 alloy was carried out by using commercial FEM code MARC, which encounters moving heat sources. Due to axisymmetry of geometry, a half of the cylinder was simulated. A coupled thermo-mechanical analysis was carried out and subroutine for heat flux was substituted in the program. The material properties such as specific heat, heat transfer coefficient and thermal expansion coefficient were given as a function of temperature and the latent heat associated with a given temperature range is considered. As a result, the proper beam power is 60kVX60mA and welding speed is 1~1.5 m/min. The residual stress in the heat-affected zone as well as the fusion zone does not increase. It is necessary to use jigs for preventing distortion of cylinder and improving weld quality.