To decrease lightning damages on wind turbines and keep public safety around the wind turbines, it is very important to improve the wind-turbine performance related on lightning protection and minimize the damage of the wind turbine. In this paper, latest trend in technologies for sound operation of wind turbines against lightning is summarized.

Recently, residential solid oxide fuel cell cogeneration system (SOFC CGS) has been put to the practical use. Considering this fact, in the present study, the authors evaluated the energy saving performance of the residential SOFC CGS. At first, the authors discussed what type of the back-up boiler is suitable for the residential SOFC CGS, and decided to focus on the heat pump water heater. Next, the authors carried out simulations of the operation pattern and performance of the residential SOFC CGS with heat pump water heater (SOFC/HP system) by using the measured results of the electric and hot water loads of an apartment in Fukuoka. As the nominal electric efficiency (LHV base) of the SOFC CGS, two cases of 50% and 60% were supposed. Performance simulations of the actually used residential systems of the conventional system with gas water heater, the all-electric system with heat pump water heater and the SOFC CGS with gas water heater (SOFC/GS system) were also carried out for comparison, It was made clear that the SOFC CGSs generally exhibit very high annual total energy efficiency. It is worthy of special mention that the total energy efficiency of the residential SOFC/HP system with the nominal electric efficiency of the SOFC CGS of 60% reaches one step higher level among them and exceeds the highest level of that of the SOFC/GS system.

Recently, a multi area system operation utilized a tie-line has been verified to resolve a shortage of a control capacity of frequency control generators output due to a widespread penetration of renewable energy systems (RES). In order to determine the proper dispatch of the generators output to compensate RES fluctuation in the multi area system operation, the power system operators should consider power flow constrains and indexes of power system conditions such as the speed of dispatch, the balance of reserved control capacity in each area and the stability of power supply. In this paper, we propose a methodology to determine multi-objective dispatch candidates of frequency control generators output to compensate RES fluctuation in multi area system operation considering three indexes, a speed of dispatch, a reserved control capacity and a transient stability based on OPF and MOPSO. The methods determine the dispatch based on Euclidean norm of the indexes in the calculated candidates in order to consider all indexes well-balanced. The effectiveness of the proposed methodology is verified by a numerical simulation used IEEJ EAST 30-machine system model with much RES, and the effectiveness of the dispatch minimized Euclidean norm is confirmed by comparison to single-objective solution in each index among the calculated candidates.

This paper describes a simple determination method of the optimal operating threshold in step voltage regulators (SVRs) that allow us to avoid hunting operations even if multiple SVRs are installed in a distribution line, to which photovoltaic (PV) inverters are connected. The SVRs dealt with in this paper have either time integral action type or voltage integral action type. In the case of voltage integral action type, the response time varies according to the PV output fluctuation. In the proposed method, the average response time of voltage integral action type is first estimated with the facility information on the distribution line. Second, the operating threshold of multiple SVRs including voltage integral action type is decided based on the average response time of voltage integral action type. Simulation results showed the method can effectively reduce the number of hunting operations by 75% on average in an example distribution line with PVs.

Increases in the proportion of variable renewable energy sources (var-RES) in electrical power networks are accompanied by increased fluctuations in the conductor currents and an increased risk of conductors exceeding their thermal ratings. Dynamic line ratings, which use real-time loading and weather information to continuously adjust the thermal ratings of conductors, are one of the measures that has been applied to increase the loadability while addressing the challenges caused by increased current fluctuations. However, the mathematical models that have been developed based on the empirically observed conductor thermal dynamics show that the relationships between the conductor temperature and both the current and ambient weather conditions are nonlinear. This makes it difficult to incorporate the conductor electro-thermal characteristics when specifying the line ratings. This paper presents numerical approximations of the various components used in the International Council on Large Electric Systems (CIGRE) physical model in order to simplify estimations of the temperature of overhead conductors under dynamic line ratings regimes. The resulting simple equations can be used to directly estimate the conductor temperature without the need for iterative calculations, which are required in the full CIGRE model. Comparisons between the simplified model and the full CIGRE model are provided for validation purposes.

Electric field analysis is one of the most important tools for the insulation design of high voltage power apparatus. The efficient method of electric field analysis is required for the insulation design and its optimization processes. In this paper, we made basic study for a process on electric field calculation with the aid of a machine learning technique. A lot of data by electric field analysis are used for the machine learning process. The machine learning is carried out before the analyzed configuration are determined. As a result, it is expected to obtain the electric field analysis results with less calculation time. As a first step, the basic availability of the process is confirmed by using the calculation examples.

Generation cost of renewable energy is decreased under 3 cents/kWh in some cases. Thermal energy storage becomes economic technology under this condition since storage cost occupies major part of the cost to stabilize the intermittent renewable energies. Thermal energy storage station and wind power utilize this thermal energy storage is described. Electric-heat generator, which can absorb surplus energy in the grid as the additional function, is also described and test and simulation results are presented.