Experiences on maintenance and operation of the 125 MVA flywheel motor generator facility at the National Institute for Fusion Science

Some problems have appeared during maintenance and operation of the 125 MVA flywheel motor generator facility in the 254 thousand accumulated shots during the past 15 years. Prior to commissioning, we had an initial accident in which the bearing metal of the flywheel motor generator melted. After this accident, the control system was improved and redundancy was added to the lubricating oil supply system with a new safety philosophy of direct participation by the human operators controlling these enormous energy-storage devices. After commissioning, problems which have appeared are lubricating oil pump noise, drive motor end ring cracking, abrasion of the anti-corona coatings on the generator stator windings, excessive main shaft vibration, etc. We report on some of the countermeasures used to solve these problems. We also report on the annual number of fault occurrences and shots. Finally, we remark on the importance of human operators in the maintenance and operation of the facility. (orig.)