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삼출성 중이염 환아군과 구개열소아군의 측두골 함기화 정도에 대한 비교분석
박철원,정연기,정진석,지용배,이승환 대한이비인후과학회 2002 대한이비인후과학회지 두경부외과학 Vol.45 No.9
Background and Objectives:A number of studies have documented that the incidence of otitis media with efusion (OME) is greater than 90% in children with cleft palates. The purpose of this study was to evaluate the correlation of OME and mastoid pneumatization in children with cleft palate. Subjects and Method:We studied 175 ears in 95 patients. They were categorized into thre groups according to otologic finding:normal children (38 ears) (89 ears), children with cleft palates (38 ears). The mastoid pnuematization was graded into 5 groups. Results:The masoid pneumatization was relatively good in 76.3% of normal children. The mastoid pneumatization was poor in 40.4% of the children with OME. All children with cleft palate had OME in both ears and their mastoid pneumatizations were very poor, with 16.7% of grade IV and 83.3% of grade V. Conclusion:cleft palate. We believe that mastoid pneumatization was influenced by the disease of middle ear and mastoid, environmental factors. Special consideration is neded to deal with otologic problems in children with cleft palate. (Korean J Otolaryngol 2002;45:862-5)
3권선 전력용 변압기 시스템의 주 보호기법에 관한 연구
박철원 한국조명.전기설비학회 2023 조명·전기설비학회논문지 Vol.37 No.4
Recently, the fault characteristics of inverter-based VRE (Variable Renewable Energy) power supplies, which are increasing, are different from those of synchronous power sources. The concerns have been raised about malfunctions of existing protection methods. The detailed transient analysis such as FFT (Fast Fourier Transform), waveform identification, and fault type classification considering the characteristics of the future hybrid power grid should be preceded. In this paper, as a preceding study for a power system in which an inverter-based power source is connected, the main protection method of IED (Intelligent Electronic Device) for three-winding transformer is analyzed. First, the modeling is performed using the PSCAD platform using field system data for a three-winding power transformer of 600MVA 345/161/23kV. After the steady state simulation, the transient state of excitation inrush, ground fault and short fault are analyzed. Finally, the performance of the percentage differential relay method with 2nd harmonic restraint is verified using the PSCAD library.
박철원,안준영,이종수,이상성,신명철 대한전기학회 2006 대한전기학회 학술대회 논문집 Vol.2006 No.11
In this paper, we simulated transient-state under fault in stator windings of synchronous generator. The fault types are line to ground fault, line to line short fault, and three phase short fault. For fault analysis of generator system, the voltage equation of a synchronous machine using the two-axis theory was used. It can be used to analyze important features of faults and to develope enhanced protection methods.
765kV 모델링 데이터에 의한 개선된 주파수 추정기법의 성능 평가
박철원 대한전기학회 2010 전기학회논문지 P Vol.59 No.3
The frequency is an important operation parameter for the control, protection, and stability of a power system. The frequency as a key index of power quality can be indicative of system abnormal conditions and disturbances. Due to the sudden change in generation and loads or faults in power system, the frequency is supposed to deviate from its nominal value. It is essential that the frequency must be maintained very close to its nominal frequency. An accurate monitoring of the power frequency is essential to optimal operation and prevention for wide area blackout. As most conventional frequency estimation schemes are based on DFT filter, it has been pointed out that the gain error could cause defects when the frequency is deviated from nominal value. This paper presents an advanced frequency estimation technique using gain compensation to improve the performance of DFT filter based techniques. To evaluate performance of the proposed algorithm, the 765kV T/L system in Korea is simulated by EMTP-RV software. The proposed technique can reduce the gain error caused when the power system frequency deviates from nominal value.