The establishment of lightning protection design of household electrical appliances has been an important subject with progress of a highly informative society. As examining lightning protection design of household electrical appliances, the individual measure for power equipment, communication equipment, and household electrical appliances is insufficient. And it is important to evaluate and examine these synthetically as one circuit (low voltage distribution system). This report describes the results of the study to lightning protection design for low-voltage distribution systems experimentally, and the results of the lightning hazard evaluation based on experiments.

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This paper presents numerical calculation method on the versatile spreadsheet software such as Microsoft® Excel® for instantaneous value of inrush current in three-phase transformers. This method was developed using the Ralston's Runge-Kutta method and φ-L magnetizing characteristics. Inrush current waveform calculated using this method was compared with them calculated by EMTP-ATP.

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There are growing concerns around the world about global warming issues, and the countermeasures to reduce global warming by greenhouse gases are proposed. In the transport sector, Electric vehicle (EV) is expected as one of solutions to reduce heavy dependence on oil and CO₂ emissions in Japan. In order to promote large-scale diffusion of EV, it is necessary to build charging infrastructures where EV can be charged rapidly. In this research, we firstly evaluated daily EV charging load taking account of rapid charging at charging stations by using the traffic simulator. As the result, it was found that there is a possibility of balancing uncontrollable EV charging load and Photovoltaic (PV) output. Finally, the reduction effect of annual fuel cost in power grid was evaluated by controlling EV charge. In optimal charging pattern, the annual fuel cost is reduced about 40 billion yen.

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This paper describes development of a unit commitment model with demand response and electric storage device for the integration of variable renewable energies by considering forecast outputs and errors for photovoltaic and wind power generations. We analyze operation plans for power systems in Tokyo area and Tohoku area where a large amount of variable renewable energies are introduced in 2030. We estimate curtailment of wind power for Tohoku area in 2030 because the power system in Tohoku area can not integrate wind power generation planned to be installed in 2030. Then this paper shows that the integrated operation of the two power systems can integrate both photovoltaic and wind power generations planned to be installed in 2030. Finally we evaluate economic efficiency for the integrated operation of the two power systems.

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Whenever a power transformer under no load condition is manually tripped, residual flux appears in the transformer core which vitally causes inrush current when the transformer is later reenergized. However real aspects of residual fluxes in relation with the tripping time have not yet been experimentally cleared. The authors established their interpretation of residual flux as of the ending states of transient phenomena after tripping, and they executed experimental proof test. By the authors' interpretation, three phase balanced transient phenomenon of voltage, current and core-flux is caused immediately after the transformer is tripped at t_op0, and it continues until time t_op1. The real aspect of the residual flux should be the core flux φ_a(t_op1), φ_b(t_op1), φ_c(t_op1) at t_op1. Further such residual flux as well as voltages and currents during the transient interval are practically three phase balanced so that they can be expressed as three phase balanced equilateral triangle phasors. By the way, the core flux values and the waveforms can not be directly measured while they can be digitally generated as integration of voltage waveform. So, the proof test of the residual flux by the above interpretation can be executed indirectly by preparing (a) measured voltage waveforms just after transformer tripping, (b) mathematically generated flux waveforms by voltage integration just after tripping and (c) measured transient inrush current i_{rush a}, i_{rush b}, i_{rush c} caused immediately after the transformer is reenergized at timing θ_cl, and then by comparing all these three data as the characteristics on the 3-D coordinates of [θ_op0, θ_cl, i_rush] and of [θ_op1, θ_cl, i_rush].
The authors executed experimental proof test using a mimic-test-circuit where large number of on-off-switching tests of a transformer were conducted. The test result clearly indicated that inrush current becomes the largest whenever θ_cl is reverse angular timing toward θ_op1 (in stead of θ_op0), and it becomes the smallest whenever θ_cl is in-phase with θ_op1. All these test results satisfied the authors' interpretation of real aspect of the transient phenomena and the residual flux after tripping. The test results suggest essential algorisms of inrush current restraining control in order to appropriately restrain inrush current phenomena.

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Large penetration of wind power generation makes transmission line power flow more fluctuate. This study proposes novel AR (area requirement) allocation method to suppress transmission power flow fluctuation in coordination with battery. This coordination method between thermal generating units and batteries enables the proposed method to suppress power flow fluctuation. Compared with the existing method, the proposed method has been proven to be effective by numerical simulation.

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When a configuration of distribution system is radial, a load of every customer is served from single distribution substation. Therefore, a fault that takes place at the distribution substation causes every load in the system out of electricity. Then, it is required to supply electricity from the neighboring distribution networks to the faulted network by modifying the on/off status of circuit breakers (CB) within the faulted network and tie-lines that can connect the faulted system and the neighboring networks. For finding a new configuration of distribution system, following constraints should be checked: a configuration of distribution system must be radial, no overload in any line occurs, every customer should be supplied electricity or the number of customers without electricity should be minimized. In order to find the most desirable configuration, many cases of combinations of the on/off status of CBs are formed as candidates that should be checked if they satisfy the aforementioned constraints. Since many numbers of CBs are implemented in actual distribution system, it may be impossible to check every candidate because it takes very long computation time. In order to shorten the computation time, this paper proposes approaches with some criteria by which procedures checking the constraints is terminated during processing for finding solutions and also the number of candidates to be checked if they satisfy the constraints is reduced. Numerical examples carried out for a system with 30CBs. The total number of candidates that will be formed by using every combination of CBs is 2³⁰ (≒ 1.0 × 10⁹). The number of candidates that are checked by the proposed method is 6158 that is about 1/180000 of the total number of candidates. In addition, solutions obtained by the proposed method accorded with those obtained by using every combination of CBs. This shows that the number of candidates that can be checked within a limited time will be increased greatly by using the proposed method.

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Large penetration of photovoltaic (PV) generation systems into power system will cause surplus power of whole power system, which will be caused by that the sum of the generated power of PVs and minimal output power of generators operating in power system exceed the total electricity demand of whole power system. One of the measures for suppressing the surplus power is using electric energy storage system. However, when the surplus energy exceeds the storage capacity of electric energy storage system, it would be necessary to suppress the output power of PV by setting the output power limit on PV. In order to utilize the surplus power, authors have proposed the daytime operation of heat pump hot water heaters (HPWHs). By considering the customer's convenience, the operation schedules of each customer are varied because of the difference of hot water demand of each customer, and there is possibility to utilize the surplus power more effectively by considering operation schedules of all customers and setting output power limit to appropriate level. This paper proposes the method to determine the appropriate level of the output power limit of PV based on operation patterns of HPWHs of each customer. The proposed method considers the operation of electric energy storage system installed in power system by keeping the integral of the sum of the reverse power flow from each customer in daytime to be constant. The simulation results shows that proposed method reduce the suppressed output power energy of PV effectively compared with the case that determined the output power limit of PV without considering the operation schedule of HPWHs of all customers.

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This paper describes on a diagnostic method using gas analysis for terminals in aged 66-77kV XLPE cable lines. It was revealed from fundamental experiments and gas analysis of 45 terminals in actual XLPE cable lines that acetylene was particular gas produced by discharge at interface areas in terminals and the most suitable gas for diagnosis. It was cleared from the results of gas analysis and dismantlement carried out for another 96 terminals that a large amount of brownish-red deposits including black ones were observed at the interface area between XLPE and pre-molded insulations for terminals with high concentrations of acetylene gas, which strongly suggested the generation of partial discharge at that area. It was also found from the correlation between gas-analysis and dismantlement results that concentration of acetylene gas increased rapidly with degree of aging degradation, which showed that acetylene gas analysis was applicable to deterioration diagnosis for aged terminals in actual XLPE cables. In addition, easy and safe on-site gas sampling was established with the installation of a gas cock in metal casing of the terminal.

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