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Ansan, South Korea

Park D.,Korea Advanced Institute of Science and Technology | Heo S.,Korea Advanced Institute of Science and Technology | Cho H.,VitzroTech | Kwon S.,Korea Advanced Institute of Science and Technology
Transactions of the Japan Society for Aeronautical and Space Sciences | Year: 2015

A gas-turbine-driven pump system was designed and tested. Pump systems are generally driven by an electric motor, but a gas turbine is occasionally used as the power source for high power and performance; for example, the turbopump of a liquid rocket propulsion system. For research on turbopumps, a gas generator, turbine, and pump are developed. After each component is developed, the performance should be confirmed with a link test. In the case of a turbopump, an axial turbine is applied to generate huge torque, but a radial inflow turbine was used in this research. A radial inflow turbine can be obtained easily and mass-produced. System analysis was conducted using a link test with all components at once. The turbine generated shaft power under steady operation of the gas generator, and the pump performance was measured using a stepped closing valve at the pump exit. Turbine heat loss was considered and a slip factor was applied to the impeller design to modify performance. This research shows the feasibility of developing a pump system operated by a radial inflow turbine and its application to a small turbopump for a hybrid rocket propulsion system and an air-independent system. © 2015 The Japan Society for Aeronautical and Space Sciences. Source


Joo Y.,Pohang Accelerator Laboratory | Park Y.,Pohang Accelerator Laboratory | Heo H.,Pohang Accelerator Laboratory | Hu J.,Pohang Accelerator Laboratory | And 8 more authors.
Journal of the Korean Physical Society | Year: 2014

The 3-dB power splitter to be used in the Pohang Accelerator Laboratory X-ay Free-electron Laser (PAL XFEL), which have been under construction since 2011, must operate at a peak power of 400 MW and a repetition rate of 120 Hz. For these operational conditions of the PAL XFEL, the old 3-dB power splitter that was originally designed to be used in the PLS LINAC will most suffer from RF breakdown. Therefore, for the new 3-dB power splitter, the original design has been modified to reduce the field gradient and the surface current. The new 3-dB power splitter is designed by using a finite-difference time-domain (FDTD) simulation. We have fabricated a prototype, and the result of a high-power test indicates that the RF performance of the new 3-dB power splitter satisfies the specifications of the PAL XFEL S-band LINAC RF system. © 2014 The Korean Physical Society. Source


Joo Y.,Pohang Accelerator Laboratory | Park Y.,Pohang Accelerator Laboratory | Heo H.,Pohang Accelerator Laboratory | Hu J.,Pohang Accelerator Laboratory | And 8 more authors.
Journal of the Korean Physical Society | Year: 2013

The directional coupler to be used in the Pohang Accelerator Laboratory X-ray free electron laser (PAL XFEL) under construction since 2011 must satisfy the conditions for operating at a peak power of 400 MW and a repetition rate of 120 Hz. In these operational conditions of the PAL XFEL, the old Bethe-hole directional coupler that was originally designed to be used in the Pohang Light Source linac is more likely to inflict damages on the ceramic window that cause vacuum leaks. Therefore, for the new Bethe-hole directional coupler, the original design has been modified to use a conventional N-type RF vacuum feedthrough for vacuum sealing instead of the ceramic window. The new Bethe-hole directional coupler is designed by using a finite-difference time-domain simulation. We have fabricated a prototype, and the result of a high-power test indicates that the RF performance of the new DC satisfies the specifications of the PAL XFEL S-band Linac RF system. © 2013 The Korean Physical Society. Source


Heo H.,Pohang University of Science and Technology | Joo Y.-D.,Pohang University of Science and Technology | Park Y.-J.,Pohang University of Science and Technology | Kang H.-S.,Pohang University of Science and Technology | And 4 more authors.
Journal of the Korean Physical Society | Year: 2015

We developed an S-band traveling-wave accelerating structure for the Pohang Accelerator Laboratory’s X-ray free-electron laser (PAL-XFEL), and we fabricated and tested a full-scale prototype. In order to reduce the field asymmetry inside the coupler cavity, we used the SUPERFISH code and the CST MWS electromagnetic field solvers to design the constant-gradient traveling-wave accelerator to use quasi-symmetric single-feed racetrack couplers. The RF measurement results indicate that the accelerating gradient of the prototype structure is as high as 27 MV/m for an input RF power of 65 MW. © 2015, The Korean Physical Society. Source


Kang H.-G.,VitzroTech | Song U.-S.,VitzroTech | Kim J.-H.,VitzroTech | Kim S.-C.,VitzroTech | And 2 more authors.
Journal of Electrical Engineering and Technology | Year: 2014

The digital substations are being built based on the IEC 61850 network. The cooperation and protection of power system are becoming more intelligent and reliable in the environment of digital substation. This paper proposes a novel method to prevent the malfunction caused by the Transformer Magnetizing Inrush Current(TMIC) using the IEC 61850 based data sharing between the IEDs. To protect a main transformer, the current differential protection(87T) and over-current protection(50/51) are used generally. The 87T IED applies to the second harmonic blocking method to prevent the malfunction caused by the TMIC. However, the 50/51 IED may malfunction caused by the TMIC. To solve that problem, the proposed method uses a GOOSE inter-lock signal between two IEDs. The 87T IED transmits a blocking GOOSE signal to the 50/51 IED, when the TMIC is detected. The proposed method can make a cooperation of digital substation protection system more intelligent. To verify the performance of proposed method, this paper performs the real time test using the RTDS (Real Time Digital Simulator) test-bed. Using the RTDS, the power system transients are simulated, and the TMIC is generated. The performance of proposed method is verified in real-time using that actual current signals. The reaction of simulated power system responding to the operation of IEDs can be also confirmed. Source

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