Technologies concerning lightning, thermal plasma, and arc discharge are required to properly protect systems and equipment used in the power and energy field. In the industrial application field and the environmental field and so on, these technologies are also used for building a more comfortable society through an active utilization of the high energy state. Moreover, these technologies are hoped to take on an important role in a next-generation society. In this review paper, we introduce the latest trends of these technologies about a protection of the electrical power system, an evaluation of the electrical installation performance for fault arcs, and the arc plasma applications.

While wind turbine generators have widely spread as one of the renewable energy sources, lightning protection for the wind turbine generators has been becoming a very important issue because lightning damages of them may cause the economic losses and the public disaster. As one of the studies for such lightning protection, internal arc tests for wind turbine blade models, which simulates the lightning penetration into a wind turbine blade, were carried out using a short-circuit generator. On these tests, length of the wind turbine blade model and waveform of the arc current are dominant test parameters because they are thought to be influential factors related to the pressure rise in a wind turbine blade. In this paper, the CFD calculations of pressure rise due to a DC arc in a closed space are conducted, where the closed space is a long cylinder as simplifying the inside of a wind turbine blade. From a result of the CFD calculations, we clarified a dependence of the internal pressure rise not only on the length of cylindrical space, which varies from 2 to 40m, but also on the waveform of direct current, which varies from 2 to 8kA with a constant electric charge of 100C.

This paper describes a basic mechanism of Ag contact erosion by DC arc at the beginning of the contact break in low-voltage switch. We focused on the relationship between the contact erosion and the arc duration, and found that there is the contact erosion M_b, which is generated immediately after the start of break and does not depend on the arc duration but depends on approximately square of the current at the start of break. We considered that the M_b is the contact erosion due to the bridge formation at the beginning of the break, and the bridge formation depends on electrode heating at the final contact point. We also clarified the rate of the contact erosion at the beginning of the break is large against the total contact erosion. Especially, this rate reaches 90% in maximum case of this paper.

For an experimental DC motor equipment immersed in ethanol and gasoline, commutator currents were measured at various rotational speeds to find out an arc duration time during commutation process and a residual current. The result revealed that the arc duration time for the ethanol was 3-6 µsec and this duration time was longer than that for the gasoline. The residual current in the ethanol also proved to be 2-3A and to be about twice higher than that in the gasoline. Subsequently these results were discussed on the basis of contact resistance just before brush-commutator separation. As a result, the contact resistance was found to be 0.6 times lower in the ethanol than in the gasoline. A novel approach was lastly made to the contact state of the brush on the commutator in view of mechanical properties: coefficient of friction, lubrication, contact load. This approach achieved successful explanation of the phenomena above.

The vacuum arc cathode spot can be applied to pretreatment of thermal spray because it can remove oxide layer on the metal surface. However, the cathode spot affected by the oxide layer remains unclear. Few studies have examined movement of the cathode spot with the oxide layer and theoretically estimated energy density. In this paper, energy balance on current density distribution of cathode spot in vacuum arc is calculated by the 3D electromagnetic thermal fluid simulation. As a result, in the case without considering metal vapor, the ratio of heat input to the cathode increases with increasing the current. On the other hand, in the case of considering metal vapor, it decreases with increasing the current. This reason is that current density and arc temperature decrease with increasing the ratio of metal vapor. Consequently, energy balance on current density distribution of cathode spot in vacuum arc is elucidated.

The arc affected by the lateral gas is deflected to leeward, and the problem of heat transfer decrement occurs in the base metal at the arc welding. The elucidation of arc deflection is necessary with the lateral gas. It has been researched that the heat transfer decreases with increasing the arc deflection length. However, the measurement of arc pressure is difficult because the plasma jet affected by lateral gas flows to leeward. For this reason, the arc stiffness has not been elucidated at the only experiment with lateral gas. The understanding of correlation between the plasma jet and heat transport affected by the convective heat transfer is necessary using 3-D numerical analysis for the elucidation of the arc stiffness. In this paper, the contribution of axial arc pressure gradient near cathode on the enthalpy flow of arc to axial direction with the lateral gas was elucidated. As a result, the mean convective force in arc periphery part increased a bit and the axial arc pressure gradient did not change in the case of the low lateral gas flow velocity. The total heat transfer derived from the enthalpy flow to axial direction did not change because the axial arc pressure gradient was higher than the convective force of lateral gas. In contrast, the mean convective force in arc periphery part increased and the axial arc pressure gradient decreased in the case of the high lateral gas flow velocity. The total heat transfer derived from the enthalpy flow to axial direction decreased because the plasma jet affected by the convective force of lateral gas move to leeward direction. Therefore, the axial arc pressure gradient plays an important role for the prevention of arc deflection.

Since waste to energy (WTE) can't generate power for a long period due to unexpectable failure, periodical maintenance etc., WTE network, that exchanges electric power between incineration plants is one of the most realistic solutions. In this study, robust WTE network is proposed and its risk against failures has been assessed.

An installation of solar power generation system was limited to places with good sunshine conditions, but it tends to be built in various places and areas. Generated electric power is influenced by various factors such as weather condition and installation environment, and it depends greatly on performance of power conditioners (PCSs) cooperating with a grid. For the PCS conversion efficiency, measurement of static conversion efficiency and MPPT efficiency under certain conditions is specified by IEC and UL. However, the factors such as change of weather conditions and installation environment, the methods of performance evaluation corresponding to dynamic change which changes with every moment are not clear, and comprehensive evaluation including static evaluation is difficult. For this reason, we proposed a method to obtain step response of solar irradiance as a performance evaluation by analysis which can be comprehensively evaluated as a power generation amount of photovoltaic power generation systems.

This paper proposes dependable Multi-population Improved Brain Storm Optimization with Differential Evolution (MP-IBSODE) for optimal operational planning of energy plants. The problem can be formulated as a mixed-integer nonlinear programming (MINLP) problem and various evolutionary computation techniques such as particle swarm optimization (PSO), differential evolutionary PSO (DEEPSO), multi-population DEEPSO (MP-DEEPSO), and brain storm optimization (BSO) have been applied so far. When optimal operational planning of numbers of energy plants are calculated simultaneously in a data center, a challenge is to generate optimal operational planning as rapidly as possible considering control intervals and numbers of treated plants. One of the solutions for the challenge is speeding up by parallel and distributed computing. It utilizes numbers of processes and countermeasures for various faults of the distributed processes should be considered. Moreover, successive calculation at every control interval is required for keeping customer services. Therefore, sustainable (dependable) calculation keeping appropriate solution quality are required even if some of the calculation results cannot be returned from distributed processes. It is verified that total energy cost by the proposed dependable MP-IBSODE based method is lower than those by the compared methods, and higher quality of solutions can be kept even with high fault probabilities.

In this paper, photovoltaics (PV) outputs are not only limited constantly but also controlled by bidirectional communications to compensate short period power fluctuations. In this case, if qualities of communication systems are not high, communication failure may not be ignored. The effect of communication failure is evaluated. If communication failure are not very small, tracking performance receives a bad influence. Then, a compensation method of it is proposed. The compensation method uses an adaptive control. It is found that the proposed method can compensate communication failure to some extent by simulation. Short period power fluctuation may be reduced by the compensation method of communication failure.

This paper investigates a critical condition of transient stability that holds on critical trajectory at the stability boundary. While the conventional BCU theory states that critical trajectory converges an unstable equilibrium point (UEP), this paper shows a different aspect of critical trajectory and critical condition. A generalized critical condition is investigated and formulated for the computation of the critical trajectory.

Loss-of-load probability (LOLP) and expected unserved energy (EUE) are common as the power supply reliability indices based on probabilistic theory from the view point of the adequacy. These conventional indices are expected values of the annual blackout duration and unserved energy calculated by Monte Carlo method or state enumeration. Since these indices evaluate the probability distribution of blackout risk with only the expected value, it is possible to evaluate improperly because the information possessed by the probability distribution is ignored. In this paper, risk measure which is used in Economics is applied to supply reliability indicator. Since blackout is considered as the risk for the consumers, Risk Sensitive Value Measure (RSVM) is studied, that is a risk measure based on expected utility theory. The essence of RSVM is the weighting of the risk by the utility function for the probability distribution. Numerical simulations using IEEE-reliability test system are executed and the results clarify the effectiveness and natures of the proposed method.

This paper presents economic evaluation of storage battery systems which increase the self-use of PV output at houses and buildings. The selling price of PV generated energy is decreasing. Battery energy storage systems (BESS) can increase the self-use of PV output, and decrease the volume of buying electric power. So, the introduction of BESS to houses and buildings equipped with PV systems will be economical when the price of BESS is decreased enough. Authors investigated the optimum BESS capacity and hourly charge-discharge pattern for a year, then evaluated annual cost. Daily load pattern of each house and building, and time-of-use electric rates affect the conditions to make BESS cost-effective. Such conditions are shown in this paper.

In Japan, in order to improve supply reliability and power quality, distribution automation system has been widely introduced. However, automation equipment such as automation switch and its controller consists of many low-voltage devices, and therefore, vulnerability against lightning surge is a concern. From the survey results of lightning damaged automation equipment, it has shown that the main lightning damage factor is the energy of the lightning current passing through the automation equipment. In this paper, we experimentally examined lightning current distribution inside the automation equipment by direct lightning strike test using an actual-scale test distribution line. We found from experiment results that the lightning current distribution depends on the grounding system of automation equipment. To reduce the lightning current passing through the automation equipment, it is important to connect grounding conductors of the automation equipment, the surge arresters and the pole-mounted transformers at the single point.

Natural disasters, 2011.3.11 tremendous Earthquake M9·Tsunami, and 2018.9.6 Earthquake M6.7 etc. have changed conventional sense of electric power. Learning from disasters, this paper describes electric power elapsed over seven years and 9 months for thermal, solar power generation, reopen and accident phenomena of nuclear power plants and economical conditions.