A fire occurred inside a control panel at the Hamaoka Nuclear Power Station’s 275kV switchyard on 15 September 2026. The likely cause was prolonged energisation while the stopper was engaged during the closing operation of the grounding switch, and recurrence-prevention measures are reported to have been disclosed.
Based on the site investigation and fact-finding, the reported sequence of events was as follows: during inspection work on power transmission equipment, an operator closed the grounding switch in the 275kV switchyard. This energised the coil, and because the stopper was engaged, the switch remained in the closed position. Prolonged energisation caused abnormal overheating, leading to the fire.
The direct cause identified in the investigation was that the operator referred only to the adjustment procedure and did not check the operating procedure. The investigation also pointed to an operational misunderstanding linked to the fact that, for other grounding switches, the stopper was not operated in the open position.
Recurrence-prevention measures include enforcing the use of the operating procedure and clarifying procedure categories, standardising stopper operation and eliminating its use in the open position, training shift supervisors, and planning replacement of the coil with a view to improving the resistance of circuits similar to that of the coil that ignited.
Regarding disclosure, the information released on the fire at the Hamaoka Nuclear Power Station’s 275kV switchyard is reported to be the primary information disclosed to date, and supplementary information is also reported to have been made public.