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ABCD 파라미터를 활용한 PT의 고주파 전달특성 측정 및 분석
나완수,김형주,김광호,박민혜,심선주,최종기 대한전기학회 2022 전기학회논문지 Vol.71 No.5
This paper presents a measurement setup and network parameter-based analysis methodology for high-frequency transmission characteristics analysis between the primary and secondary sides of a PT (potential transformer). The raw data was extracted by measuring a scattering parameter (S-parameter) using a vector network analyzer. ABCD parameters were obtained using the measurement data to analyze the transmission characteristics of the transformer, and the source-transformer-load model was introduced to define the voltage and current gains considering the terminating impedance and input impedance applied to the transformer. Representative sine wave and square wave was applied to analyze the high-frequency transmission characteristics. In order to analyze the surge transmitted to the secondary system when applied to the actual system, the waveform of the IEC standard was generated and applied. When the load resistance is 1 MΩ, the voltage gain converted from the ideal turns ratio is applied to the input signal was confirmed that the maximum value of surge corresponding to about 1.9 times was formed.
나완수 成均館大學校 科學技術硏究所 1996 論文集 Vol.47 No.2
Superconducting transformers are superior to conventional ones in many respects, such as in high efficiency, light weight, and low life-cycle cost. These advatages mainly come from high current density in supercondcuting windings. But, due to high resistivity of matrix around superconductors, this high current density could lead to high density of heat when quench occurrs in superconducting windings. Of course, quench protection scheme should be included in superconducting transformer system, but. the situation is different from DC superconducting magnet system, e.g. MRI magnet system, due to intrinsic AC operation of transformer. In this paper two essential quench protection schemes are studied and the protection principles are established for AC conditions. Finally a protection scheme without auxiliary windings is suggested, using derived equations in this paper.
永久電流 모드를 가지는 超傳導 MRI 마그네트의 勵磁에 대한 硏究
나완수 成均館大學校 科學技術硏究所 1996 論文集 Vol.47 No.1
Superconducting MRI(Magnetic Resonance Image) magnets have various shim coils for the uniform magnetic field, operating in persistent-current-mode. The shim coils, especially between the Z^2 shim and main coils, are magnetically strongly-coupled such as transformer, which disturbs the magnetic uniformities during energization. Since the resistances of the coils are absolutely zero (at DC current) in the superconducting state, the final target currents get contaminated by the magnetically-coupled--shim-coil energization. In this paper, the energization circuits for superconducitng MRI manget are analyzed and the effective way of energizations are proposed. Finally, distributions of magnetic fields after energizations are reported.
접지망에서의 과도 전위 변동으로 인한 2차 케이블의 전압변동 예측을 위한 등가 회로모델 개발에 대한 연구
나완수,최경륜,김광호,박민혜,심선주,최종기,김용상 대한전기학회 2022 전기학회논문지 Vol.71 No.10
In this paper, an equivalent circuit model of the surge transmission path was proposed to analyze the effect of potential fluctuations in the substation grounding grid on secondary cables. For the surge hitting the grounding grid, the surge waveform defined in the international standard surge immunity test standard IEC 61000-4-5 was referred to. Based on the FFT result of the surge waveform, the effective frequency band was set up to 20 MHz. In addition, an equivalent circuit model for each model was produced by dividing the structure of the substation into four parts, and the individual models were verified through comparison of the 3D EM simulation. Finally, the equivalent model of the complete system were verified by comparing the results from 3D simulation in the time domain, and the voltage induced at both ends of the secondary cable when the grounding network was struck was compared.