Brushless excitation systems are widely used in marine synchronous generators due to their high reliability and reduced maintenance requirements. In these systems, the rotating rectifier converts the three-phase AC output of the exciter into DC current for the main field winding. However, faults in the rotating rectifier, particularly a single diode open-circuit fault, can degrade excitation performance without immediately triggering protective devices, making early detection difficult. This paper experimentally investigates the effects of a single rotating rectifier diode open-circuit fault on the excitation system and voltage formation of a brushless synchronous generator under no-load operating conditions. The no-load condition minimizes the influence of armature reaction and load current, allowing fault-induced excitation behavior to be clearly isolated. A brushless excitation system was implemented using three synchronous machines of identical rating, and a single diode open-circuit fault was intentionally introduced in the rotating rectifier. Excitation-related electrical quantities related to the excitation system, including DC excitation current and voltage, exciter armature currents, and generator terminal voltage, were measured and compared before and after the fault. Experimental results demonstrate that the single diode open-circuit fault causes reduction in the average excitation current and introduces low-frequency ripple components in the excitation current waveform while the terminal voltage reduction remains limited under no-load conditions. These results indicate that excitation-related electrical signals can serve as effective indicators for the detection of rotating rectifier diode faults in brushless synchronous generators.

서 론
재료 및 방법
    선박용 3상 발전기 전압 형성과 여자 시스템 개요
    실험의 조건 및 범위
    실험의 구성 및 계측 방법
결과 및 고찰
    실험 구성 및 시험 조건
    단일 다이오드 개방 고장 분류
    정상운전 상태
    다이오드 단일 개방 고장 상태
결 론
References

• 류기탁(한국해양수산연수원 해양기술교육팀 교수) | Ki-Tak RYU (Professor, Ocean Technology Training Team, Korea Institute of Maritime and Fisheries Technology, Busan 48562, Korea)
• 이윤형(한국해양수산연수원 해양기술교육팀 교수) | Yun-Hyung LEE (Professor, Ocean Technology Training Team, Korea Institute of Maritime and Fisheries Technology, Busan 48562, Korea) Corresponding author
• 이주연(한국해양과학기술원 연구원) | Joo-Yeon LEE (Research Scientist, Korea Institute of Ocean Science and Technology, Busan 49111, Korea)
• 김종필(한국해양수산연수원 오션폴리텍해운팀 교수) | Jong-Phil KIM (Professor, Ocean Polytech Maritime Team, Korea Institute of Maritime and Fisheries Technology, Busan 48562, Korea)
• 김홍중(한국해양수산연수원 오션폴리텍해운팀 교수) | Hong-Jung KIM (Professor, Ocean Polytech Maritime Team, Korea Institute of Maritime and Fisheries Technology, Busan 48562, Korea)
• 안종갑(경상국립대학교 실습선운영관리센터 교수) | Jong-Kap AHN (Professor, Training Ship Operation Center, College of Marine Science, Gyeongsang National University, Tongyeong 53064, Korea)