原子力発電所の非常用所内電源系統の外部電源変圧器の一相欠相時のEMTPによる応答解析

摘要

The emergency power supply systems of nuclear power plants for the object of this research are critical to supply stable electric power to such systems as the emergency core cooling system (ECCS) ， and to maintain the safety of the nuclear power reactor; this was apparent from the accident at Fukushima Daiichi Nuclear Power Plant. USNRC issued regulatory documents (BL 2012-01,IN 2012-03) ， and has commenced to review the problem which cannot be detected by degraded-voltage protection relays such as new design vulnerability of the power supply systems that are certain kind of winding structures and iron core structures when the one phase open fault occurred without a ground fault of the transformer connected to the offsite power supply system including when the offsite power supply side is a wye connection and load side is a delta connection etc.. This research used simulation by the electro-magnetic transients program (EMTP) and obtained findings that clearly specified the response at the time of power supply side one phase open without ground fault of various winding structures and various iron core structures of the three phase transformer and identified the important issue for the response of emergency power supply systems and the safety related components of representative domestic PWR plants when one phase open fault occurred without ground fault.%研究対象の原子力発電所の非常用電源系統は,福島第一原子力発電所事故に見られるように，非常用炉心冷却系統（ECCS)等に安定した電力を供給し，原子炉の安全を維持するうえで極めて重要な電源である.米国NRCは，規制文書BL 2012-01,IN 2012-03を発行し,外部電源側がY結線，負荷側が⊿結線の変圧器など，ある種の巻線構成や鉄心構成では，外部電源系統に接続された変圧器の一相が，地絡のない欠相故障した場合に，低電圧保護リレーによる検出ができない問題を，電源系統の設計上の新たな脆弱性として検討を開始している.本研究は,三相変圧器の種々の巻線構成や鉄心構成の地絡のない電源側一相欠相時の応答および国内代表PWRプラントの地絡のない外部電源一相欠相時の非常用電源系統および安全関連機器の応答に係る安全上の重要な問題点を,EMTP電気過渡応答解析コードによるシミュレーションを用いて明確に特定した.