A Comparative Study for reduction of 3-phase short circuit current in chemical plant

학위논문(석사) -- 서울대학교대학원 : 공학전문대학원 응용공학과, 2024. 2. 서은석.본 연구에서는 대형 화공플랜트 수용가 전력 계통을 대상으로 단락전류 저감을 위해 계통 변경 검토를 수행 시 종합적인 계통 신뢰도 평가를 통해 최적 안을 선정하기 위한 평가 절차 및 평가지표를 새로이 제안하였다. 평가 대상으로 국내 화공플랜트 중 하나인 한화토탈에너지스 전력 계통을 선정하고, `모의 계통 작성을 위해 해당 계통에 적용 가능한 단락전류 저감방안 5가지 (모선 분리운전, 한류 리액터 설치, 변압기 임피던스 상향, 전압레벨 격상, 변전소 신설 및 부하이설)를 대책안으로 선정하였다. 그리고 산업용 플랜트 계통해석 시 일반적으로 사용되는 전력계통 해석 프로그램인 ETAP을 이용하여 대책안이 적용된 각 모의 계통을 제안된 평가 절차에 따라 시뮬레이션하였다. 그 다음으로는 제안된 기술적 평가지표를 통해 각 모의 계통의 전기적 신뢰도를 정량적으로 비교 평가하고, 추가적으로 경제성 비교분석을 실시하여 계통 상황별 적용 가능한 방안들을 선정하였다. 1970-1980년대에 준공된 국내외 여러 화공플랜트 전력계통은 지속된 공장 증설에 의한 계통 포화상태로 단락전류에 관해 유사한 문제점을 보유하고 있을 것으로 예상된다. 본 연구에서 수행된 단락전류 저감방안 선정을 위한 연구는 화공플랜트 실 계통을 대상으로 수행함으로써 현실적이고 유사한 계통을 보유 중인 여러 산업용 플랜트에서도 적용 가능할 것으로 생각된다 주요어 : 화공플랜트, 단락전류 저감방안, ETAP, 평가지표 학 번 : 2022-26064In this study, a new evaluation procedure and criteria for selecting the optimal solution through comprehensive power system reliability assessment were proposed when considering system modifications to reduce short-circuit currents in the power system of a large chemical plant customer. The power system of Hanwha Totalenergies, a major domestic chemical plant, was selected as the evaluation target. 5 possible measures for mitigating short-circuit currents in this system were chosen as countermeasures (separate bus operation, installation of current-limiting reactors, increase in transformer impedance, increase in voltage level, new substation and load relocation). Subsequently, each of these measures was simulated using the widely used power system analysis program ETAP, following the proposed evaluation procedure. Finally, through the proposed evaluation criteria, we quantitatively compared and evaluated the effectiveness of each alternative. As a result, we selected the optimal solution for the current system, which is the installation of a current-limiting reactor, as the preferred option. It is anticipated that power systems of various chemical plants commissioned domestically and internationally in the 1970s and 1980s are facing issues related to short-circuit currents due to sustained plant expansions, resulting in a saturated state of the power grid. The study conducted for the selection of measures to reduce short-circuit currents is considered to be realistic, as it was carried out on the actual system. And it is believed to be applicable to multiple customers that possess similar system as well.제 1 장 서론 . 1 제 1 절 연구배경 및 목적 1 제 2 절 논문 구성 및 연구 내용 7 제 2 장 고장전류 계산 및 저감방안 8 제 1 절 고장전류 계산 (IEC 60909) . 8 제 2 절 고장전류 저감 원리 20 제 3 절 모선 분리운전 22 제 4 절 한류 리액터 설치 24 제 5 절 변압기 임피던스 상향 27 제 6 절 계통 전압레벨 격상 30 제 7 절 변전소 신설 (New Substation) 32 제 3 장 평가지표 작성 34 제 1 절 ETAP 분석기능 검토 34 제 2 절 평가 절차 36 제 3 절 기술적 평가지표 39 제 4 절 기술적 평가지표의 적정성 49 제 4 장 계통 평가 (ETAP 시뮬레이션) 51 제 1 절 ETAP Modeling . 51 제 2 절 모선 분리운전 59 제 3 절 한류 리액터 적용 69 제 4 절 변압기 임피던스 상향 78 제 5 절 전압레벨 격상 89 제 6 절 변전소 신설 (New Substation) 99 제 7 절 평가결과 분석 110 제 5 장 결론 113 참고문헌 116 Abstract . 119 iii석

리스에 관한 實證分析 : 리스와 負債의 關係

학위논문(석사)--서울大學校 大學院 :經營學科 經營學專攻,1997.Maste

Frost formation on a flat horizontal plate under forced convection

학위논문(석사) - 한국과학기술원 : 화학공학과, 1985.2, [ v, 65 p. ]한국과학기술원 : 화학공학과

Endoscopic removal of the antral portion of antrochoanal polyp by powered instrumentation

Objectives: To introduce a new surgical technique for endoscopic removal of the antral portion of antrochoanal polyp (ACP) by powered instrumentation and to determine its efficacy by measures of relevant patient outcome. Study Design: Prospective study in 28 patients undergoing endoscopic sinus surgery for ACP by our surgical technique. Methods: Improvements of clinical symptoms and endoscopic and computed tomographic findings were evaluated post-operatively with a follow-up period ranging from 12 to 52 months. All symptom scores on a 100-mm visual analogue scale before operation were compared with those at the last visit after operation. Postoperative endoscopic and computed tomographic findings were graded using a three-point scale ranging from 0 to 2. In surgical technique, the antral portion of ACP was identified through the enlarged ostium under intranasal endoscopy and removed by a blade of powered instrumentation that was inserted through the canine fossa. Results: Symptom scores were all significantly reduced postoperatively. All but one patient showed improvement in clinical symptoms and endoscopic and computed tomographic findings during the follow-up period. There were no major complications specific to this technique. Conclusion: Our technique provides an attractive alternative to other methods for removing the antral portion of an ACP and is associated with excellent outcomes and minimal morbidities

New preamble structures for synchronization and cell searching in OFDM systems

학위논문(석사) - 한국정보통신대학교 : 공학부, 2005, [ vi, 44 p. ]This thesis proposes two new preamble structures for synchronization and cell searching in cellular based Orthogonal Frequency Division Multiplexing (OFDM) systems. The proposed preamble structures are to impose Pseudo Noise sequences (PN-sequences) on the OFDM transmitted signal in time-domain for time and frequency synchronization. This scheme make it possible to achieve a good performance at a low SNR, therefore, it can guarantee a reliable communication to a mobile located at the cell edge. Herein, the PN-sequences occupies the whole or part of the preamble according to the two different preamble structures. The proposed preamble structures are compared each other in terms of frame and frequency synchronization, cell searching and mean acquisition time. The simulation results elucidate that the proposed preamble structures are appropriate for cellular based OFDM systems.한국정보통신대학교 : 공학부