• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.2
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• pp.89-96
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• 2007

The bobbin probe examination is basic and the important method among other ECT techniques for the steam generator tube integrity assesment that is practiced during each plant outage. The bobbin probe is one of the essential components which consist of the whole ECT examination system, and provides us a decisive data for the evaluation of tube integrity in compliance with acceptance criteria described in specific procedures. The selection of examination probe is especially important because the quality of acquired ECT data is determined by the probe design characteristics, such as geometry and operation frequency, and has enormous effects on examination results. In this study, An optimal differential bobbin probe is designed for the steam generator tube inspection in nuclear power plants(NPPs). Based on the test results for electrical and ECT signal characteristics, the prototype bobbin probe satisfies all the criteria.

• The Pure and Applied Mathematics
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• v.17 no.2
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• pp.185-188
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• 2010

In this note the distribution of roots of cubic equations in contrast to 0 is given, which is useful to discuss eigenvalues for qualitative properties of differential equations.

• The Transactions of the Korean Institute of Power Electronics
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• v.21 no.2
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• pp.95-101
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• 2016

This paper proposed a high-power density bidirectional converter for hybrid electric vehicle high-voltage DC-DC converter(HDC). The conventional HDC has two disadvantages. First, large inductance is required to satisfy the ripple current of inductor by low switching frequency (<20 kHz). Second, large core size is required to prevent the saturation of inductor by high current. Compared with the conventional HDC, the proposed HDC can reduce inductance with SiC-FET for high frequency driving. High-power density of I/O capacitors can be achieved through two-phase interleaved method. The high-power density of inductors can be achieved because the offset current of magnetizing inductance is theoretically terminated by using the differential mode coupled inductor instead of using two single inductors. The validity of the proposed converter is proved through the 50 kW prototype.

• Journal of Electrical Engineering and Technology
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• v.12 no.2
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• pp.513-521
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• 2017

HVDC protection setting is difficult to be calculated analytically because of its strong nonlinearity. The currently used setting method is based on the empirical setting of previous projects and then verified by digital simulation. It entails a huge workload and low efficiency. To facilitate protection setting, this paper systematically summarizes the HVDC protection characteristics and then presents a classification of HVDC protections according to the protection principles. On the basis of the fault quantities, a novel setting procedure suitable for travelling wave protection, derivative and level protection, and differential protection is proposed. The proposed procedure is illustrated and verified in detail with the example of travelling wave protection. An HVDC protection setting system that has the functions of automatic protection setting and data management is developed utilizing the C# programming language.

• Proceedings of the KIEE Conference
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• 2008.05a
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• pp.183-184
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• 2008

The aim of this study is to find out the effects of thermal aging condition on dielectric strength and degree of crtstallinity of XLPE insulation. Thermal properties of XLPE insulation were investigated by DSC(differential scanning calorimetry) and dielectric strength were analyzed using AC BDV tester. Aging of XLPE samples were conducted through different four conditions. The degree of crtstallinity and AC BDV were changed by thermal history. From these results, it can be suggested that DSC and AC BDV test are suitable for diagnostic method of extra high voltage XLPE cable.

• Smart Structures and Systems
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• v.22 no.3
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• pp.327-334
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• 2018

In this paper, dynamic buckling of the smart subjected to blast load subjected to electric field is studied. The sandwich structure is rested on Pasternak foundation with springs and shear elements. Applying piezoelasticity theory and hyperbolic shear deformation beam theory (HSDBT), the motion equations are derived by energy method. For calculating the dynamic instability region (DIR) of the sandwich structure, differential quadrature method (DQM) along with Bolotin method is used. The aim of this study is to investigate the effects of applied voltage, geometrical parameters of structure and boundary conditions on the DIR of the structure. The results show that applying negative voltage, the DIR will be happened at higher excitation frequencies. In addition, the clamped-clamped beam leads to higher excitation frequency with respect to simply supported boundary condition.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.35 no.5
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• pp.199-204
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• 1986

The breakdown phenomena of N2 gas by 13.56MHz electric field are very different from those under steady field. In this paper we analyzed the breakdown phenomena by using electron distribution function and diffusion equation. The second-order differential equation derived from the Boltzmann equation is solved for the electron distribution function. The ionization rate and diffusion coefficient are calculated using kinetic theory formulas. The breakdown condition is that the number of electrons produced by ionization equal the number diffusing to the walls of the discharge chamber. Theses theoretical breakdown electric fields are calculated by the computer and compared with the experimental values.

• Proceedings of the KIEE Conference
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• 1998.07d
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• pp.1425-1427
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• 1998

The thermal history of XLPE insulated cable during heating cycle voltage test specified by IEC 840 was examined by DSC(differential scanning calorimetry) method, of which the principal is on the basis of the phenomenon that the crystals in polyethylene are rearranged as it is annealed near/below the melting temperature. From the result, it can be estimated that XLPE insulation near the conductor was exposed at the temperature of about $100^{\circ}C$ with the electrical stress through the test.

• Proceedings of the KIEE Conference
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• 1993.11a
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• pp.151-153
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• 1993

This paper proposes a novel motor drive system for the electric vehicle. In this paper, four-wheel-direct-drive type electric vehicle system is designed and the theoretical and experimental analysis of the system is investigated. The concept of steering not with steering the wheels but with the difference of the motor torque fives the flexibility of the vehicle design and, allows the omission of the differential gear, transmission gear, and drive axles. Thus the proposed system gives the space between wheels and improves the driver's steering performance.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.6
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• pp.751-755
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• 2011

Electric Parking Brake(EPB) is the system operated by electric control actuator. It differs from the mechanical parking brake system which is operated by lever and pedal in need of human power. The EPB system is composed of DC motor, helical and differential epicyclic gear, screw, cables, and sensor. This paper describes about the EPB system mathematically and constructs a modeling of the EPB system using MATLAB/SIMULINK. Especially, SimMechanics library in SIMULINK is used to make each parts of system a module. By made modeling of the friction torque between bolt and nut. Cable tension can be maintained after the motor operating stops.