Recent policy and regulatory developments in Japan—such as revisions to the Electricity Business Act, power system reforms, and the Cabinet decision on the Act for Strengthening Energy Supply Resilience—are increasing the importance of strengthening the resilience of power distribution equipment. General transmission and distribution operators have implemented diverse measures to ensure stable supply during major natural disasters, yet related technologies and knowledge have not been comprehensively organized in a systematic manner. To address this gap, the IEEJ Technical Report surveys practices and challenges with a focus on large-scale disasters, including typhoons, earthquakes, heavy snow, and volcanic eruptions. In addition, initiatives in other critical infrastructure sectors, such as telecommunications and railways, are reviewed to clarify disaster response approaches considering sector-specific equipment characteristics. This section outlines the survey scope and key findings of the report.

This study proposes an optimal design for a 100% renewable, off-grid electrical system for Namie Town, Fukushima, a region promoting local energy independence after the 2011 disaster. The town has rich solar, wind, and biomass potential and hydrogen infrastructure, but a quantitative analysis of an isolated system integrating these four elements—renewables, biomass power, hydrogen storage, and an off-grid configuration—has not been fully conducted. We developed an energy optimization model using linear programming with 8760-hour time-series data to minimize the total annual cost. The model compares a photovoltaic (PV) and wind system (PW case) with a system that also includes biomass (PWB case). Results show that adding biomass reduces the electricity cost by 2.20JPY/kWh (from 19.08 to 16.88JPY/kWh) by lowering the required capacity of PV, batteries, and hydrogen storage. The energy curtailment rate dropped from 19.2% to 8.7%, and overall system efficiency improved from 63.3% to 77.1%. This indicates biomass can function as a key dispatchable power source, improving stability and cost-effectiveness for an isolated renewable electrical system.

Changes in the characteristics of the insulating materials that compose the Capacitor Voltage Transformers (CVT) or insulation abnormalities in the oil-impregnated paper capacitors in the CVT are manifested as changes in the CVT transformation ratio. In this paper, a diagnostic method based on the measurement of CVT secondary voltage was investigated. The change in the CVT secondary voltage (calculated value) in the event of a single element breakdown of oil-impregnated paper capacitors is sufficiently large compared to the dispersion in the secondary voltage (measured value) of actual CVTs used in the substation. It was shown that CVT diagnosis is possible by comparing the secondary voltages of CVTs connected to the same bus bar in the substation with each other. A concrete example of the CVT diagnosis flow when applied to an actual substation is also presented.