In this paper, electric leakage and overcurrent are a cause of power outages in the home. When a power outage occurs, the supply of electricity to the home may be stopped for a long time, which hinders daily life. In addition, it is assumed that many damages due to electric leakage have occurred due to recent typhoons and heavy rains.

Therefore, the authors propose measures to reduce the power outage time due to electric leakage and overcurrent in the house and the power outage section after restoration. In order to reduce the power failure section, we propose a method in which the wiring from the circuit breaker is divided by the division switch and the divided section is interconnected with the adjacent section by the interconnection switch. By applying this method, the power failure section can be limited to the minimum section to be divided by the division switch at the minimum, and the power failure section can be reduced.

Large-scale introduction of electric vehicles puts an electric load to the power system. Recently, the capacities of on-board batteries and the outputs of quick chargers have been increasing. Increase in battery capacity allows EV owners to charge more freely; however, the charging may concentrate at a certain time such as on Friday afternoon before a weekend, because EVs travel relatively long distance on weekend. Therefore, we evaluate the impact on the peak load, under large capacity batteries, high power quick chargers, and simultaneous charging. Charging threshold is defined as follows: when a state of charge (SOC) of an EV falls below the charging threshold, the EV goes to a quick charging station to charge. We set up cases that the charging thresholds are raised on Friday afternoon to prepare for EV use on a weekend.

Through the analysis targeting Osaka Prefecture, we obtained following findings: (1) the differences in battery capacity and charger output have a small impact on the peak loads; (2) as for the charging threshold, the value itself has a small impact on the peak load, but if the charging threshold changes at a specific time, the impact is large; (3) the larger the charge threshold is raised on Friday afternoon, the larger the peak load.

Efforts to minimize power outage caused by natural disasters receive much attention. In that context, contingency plan in pre-incident is expected to be effective for reducing potential disaster damage and realizing quick recovery. Existing contingency planning schemes are usually designed as model-based approach to prevent either the worst-case scenario or a few typical scenarios. However, the effectiveness and adaptability of these schemes can be reduced in the long-term disaster such as a typhoon; there are an enormous number of risk scenarios caused by cascading accidents over time. In this paper, we propose a policy-based planning approach based on reinforcement learning for pre-allocation of power-supply cars and re-scheduling generator operation. By learning effective policies via simulations of various disaster scenarios in advance, the model can instantly output plans tailored to the disaster situation even for an enormous number of disaster scenarios. Therefore, the derived plan can follow the progress of the disaster dynamically. The practicality of proposed method is evaluated via numerical experiments based on the original grid simulating Eastern Japan and Typhoon No. 15 in 2019. The result shows the reduction of power outage by the proposed method compared to the existing method under multiple faults in transmission lines.

In this paper, a new method is proposed for distribution system static state estimation with low redundant measurements. It is different from transmission system static state estimation because the distribution system static state estimation has low redundancy of measurements while the transmission system static state estimation has enough redundancy. This paper makes use of the nest structure of DistFlow of the distribution system power flow calculation to transform the formulation into evaluating the state variable vector at distribution substations. In other words, the distribution state estimation problem may be expressed as an optimization problem. As the optimization method, PPBSO (Predator-Prey Brain Storm Optimization) of evolutionary computation is proposed to solve the problem. The proposed method is successfully applied to a sample system.

A short-term solar irradiance forecasting method has been developed to provide highly accurate prediction, using satellite image prediction model in combination with numerical weather prediction model. This method was applied and evaluated using the solar irradiance observational site at the CRIEPI Akagi Testing Center (Gunma Prefecture, Japan).

Based on historical forecasting and observation datasets at JMA observation sites in the computational domain, the best blending ratio between the satellite image prediction model and the numerical weather prediction model was selected and used. The developed method has shown high accuracy. Compared to satellite image forecasting, accuracy results averaged between three and six hours of lead-time showed improvements in the RMSE by 44% for the before-sunrise case, 20% for the after-sunrise case, and 8% for the noon to sunset case.

Because of the global warming, low cabonization has been received attention from all over the world. In Japan, efforts are being made to build the power system with realization of low carbonization because it is nesesarry to reduce CO2 emissions in electric power sector which has the highest rate of CO2 emission. As ammonia and hydrogen is known as carbon-free fuels, it has been paid attention for the use as a fuel. Another issue in Japan is the low energy self-sufficiency ratio. Although the introduction of renewable energy has improved the energy self-sufficiency rate, it is necessary to store surplus power of renewable energy because renewable energy sources do not have a supply-demand adjustment function. In this study, we propose the model which can optimize the operating status of power plants when giving value to domestic manufacturing rate of ammonia. To verify the proposed model, we performed the numerical simulation in four cases.

Some 6.6kV XLPE Power Cables are E-T type with the external semi-conductive layer wrapped with tape. In the E-T type cables, there have been many dielectric breakdown accidents due to water-tree degradation. The cables with dielectric breakdown were investigated. As a result, the unbridged water-tree was the cause of the breakdown. All of those cables were less than ten years old. In other words, the process of dielectric breakdown and the speed at which the water-tree develops were different from the knowledge of the water-tree. In the knowledge, first, the time to dielectric breakdown is at least 10 years due to the water-tree degradation. Second, the water-tree does not causes dielectric breakdown immediately even if it is bridged. Finally, the bridged water-tree causes dielectric breakdown due to the subsequent abnormal voltage. Therefore, in this study, the factors that accelerate the growth of the water-tree and the dielectric breakdown process were investigated. As a result, the acceleration factor was confirmed to be the ion products from the materials in the semi-conductive tape. Moreover, the dielectric breakdown process was considered through the shape of the water-tree and the aspect of the electrical-tree generated at the origin of the water-tree.

Wind turbines at the coast of Sea of Japan are often exposed to energetic upward lightning flashes in winter, and it is essential to obtain the dataset of parameters for such lightnings for effective operations or inspections. Currently, the height of wind turbines are becoming taller for higher power generation, and this may change lightning performances such as the escalation of frequency of the lightning strikes. However, there are few studies of current observations for upward lightning flashes hitting wind turbines which height are over 100m. In addition, the variation of the characteristics of upward lightning flashes currents depends on observation areas and the effect of the global warming remains unclear. Thus, the observation of upward lighting current has started at the Kashiwazaki-Kariwa power plant since 2020. This paper reports the summary of the observation system and observed data as of March 2022.

Screening is key technology for renewable energy development using 2nd life battery which has a performance variation. Proposal method, which includes multi-layer AI analysis and MT system based on Taguchi method, determine whether the capacity, as the measure of battery performance, exceeds the threshold. The method analyzing internal impedance of 2nd life battery was able to select about 30 times faster than conventional method using discharge and as high accuracy as conventional one.

The frequency response analysis (FRA) of transformer has been expected to be a good method for diagnosing the transformer condition. The special measuring instrument is usually used for the FRA measurement. So, in this paper, a new method of FRA measurement using a general-purpose square wave voltage and the oscilloscope is proposed.

FRA of this method is evaluated with the frequency response characteristic of the transformer input impedance.

The procedures of this method are as follows. First, the square wave voltage is applied to a transformer and the input voltage and the input current at that time are measured with the oscilloscope. Next, the high order frequency components of voltage and current are calculated by Fourier series expansion. At last, high order transformer input impedance is calculated by doing division of the high order frequency component of the input voltage and the input current. Frequency response characteristics of the input impedance of the transformer are provided in the above-mentioned procedure.

We report that we have experimentally confirmed that winding turn-to-turn short circuit, winding displacement and core defect of three phase transformer can be detected by FRA using square wave voltage.

The isolated power system (off-grid) using only PCS (Power Conditioning Subsystem) resources is studied. On the other hand, the off-grid of the Japanese general transmission and distribution company using only PCS resources has not been realized. To realize and clarify the safety operation of off-grid, in this paper, fault aspects of off-grid were simulated easily. After the simulation, small experiments of off-grid using only PCS resource were carried out.

Information about forecasting errors of photovoltaic power generation (PV) output is useful in daily supply and demand operation of power systems for large-scale integration of PV. In the conventional error analyses, average is generally used which implies the summary of errors in a certain period. It does not represent actual transitions of errors that occurred every day and hence likelihood of future transitions with time cannot be grasped in the forecasting error. In this paper, we propose an error analysis method for PV output forecasting to grasp characteristics of error transitions such as the shapes and their occurrence probabilities. We enable such an analysis by extracting representative patterns in shape of error transitions in the following way. All the days are classified to some clusters by using a clustering method based on a similarity of shape of the error transition in that day, and then representative patterns are obtained by averaging the error transitions for each cluster. The numerical result shows that the k-means method, which is one of the clustering methods, is suitable for helping understand annual trends of error transitions. We also clarify how we should estimate the appropriate number of patterns of error time transitions.

In order to realize the carbon neutral society, it is essential to replace the legacy thermal power plants using fossil fuels by alternative sources. The authors investigate a potential of a microgrid for electricity, heat and hydrogen supply, in generation and balancing capacities perspective. Contributions by a microgrid are measured in terms of the amount of electricity purchased from the grid, the variation of im- and exporting power, and the available demand-supply balancing capacity. This paper estimates the additional cost for securing demand-supply balancing capacity in a microgrid, based on an optimal capacity design considering annual operation. The estimation results shows that the additional cost is enough comparable to the current balancing cost. In other words, the balancing power currently secured mainly by thermal plants could be replaced by microgrids at a lower cost. Especially, the introduction of hydrogen supply facilities is effective for both generation capacity measured in the amount of electricity purchased, and balancing capacity.

As installation of lightning protection devices on pole-mounted distribution transformers has been progressing, the number of lightning failure of the transformers has been decreasing. However, some lightning failure of the transformers has occurred even though lightning protection devices have been installed. Specifically, the number of lightning failure in the primary bushings has been decreasing, but lightning failure in the primary windings has still occurred. Several transformer models have been proposed for electromagnetic transient studies. However, these models cannot calculate lightning overvoltages which generate in the transformer windings. In this paper, first, we explain differences in lightning failure aspects of the transformers by dismantling investigation. Then, we present experimental results of lightning overvoltages which generate in the primary windings. Finally, based on the lightning failure aspects of the transformers and the experimental results, we propose a transformer model which can calculate lightning overvoltages in the transformer windings, and show validity of this model by comparisons between experimental and calculated results.

The scope of application of vacuum circuit breakers is being expanded as an environment-friendly electric power device for carbon neutrality. Since the energy of the actuator increases as with the breaking capacity increases, it is important to properly evaluate the mechanical durability due to the switching operation impact in order to improve the reliability of the product. Accordingly, this research devised a method for evaluating component damage due to switching operation impact. It is necessary to evaluate the influence of switching operation impact on component damage by considering the frequency of the impact acceleration not only by the peak value of the acceleration. Evaluation by the damage boundary curve defined by the maximum acceleration and the velocity change of the component is applicable. By applying this method, it is possible to prevent damage to circuit breaker components and avoid cost increase due to overdesign.

The Power and Energy Society Annual Conference was held at University of Fukui on September 7-9, 2022. Total number of papers was 327, and sessions were 45. A panel discussion and two special lectures were also organized during the conference period. The number of participants reached 1012. The conference was successfully completed with great contribution from all the participants. This report summarizes the conference.