During the high economic growth period when electric power demand was continuously growing, installation and renewal of electric power equipment were actively conducted. Therefore, facility failures owing to aging were restrained. However, the increase in recent electric power demand slows down, and the capital investment decreases. This situation has stimulated concern over the increase of equipment failures owing to aging. To maintain and update a lot of electric power equipment facing aging, various investigations from viewing points such as rationalization of maintenance and equipment development are required.

In this paper, we show the estimated number of electric power facilities after 20 years and describe a fundamental way of thinking of equipment renewal. Finally, required future measures are mentioned.

We have proposed a concept model of emergency islanded operation by using distributed generators (DGs) such as PVs, EVs or batteries which can provide power to customers via undamaged distribution network in order to develop the resilient power system against large disasters, and it is named Islanded Distribution Network (IDN). Since there is no guarantee that the three-phase generation system is interconnected to the IDN, the single-phase DGs which are installed in the distribution network may be treated as main generators in the IDN operation. If the IDN has only single-phase DGs, it is difficult to regulate the three-phase voltage within the allowable range and to compensate the unbalance voltage. The aim of this study is to develop the method to supply three-phase balanced voltage by single-phase generators in the IDN. First, the operating condition of the generators is proposed for the supply of three-phase balanced voltage in the IDN model by algebra calculation. The control method for three single-phase generators has been developed by using the conditions obtained from the derivation of the generators conditions.

The increasing introduction of photovoltaic (PV) units into low voltage distribution system causes serious power quality issues, e. g. voltage variation and three phase voltage unbalance (VU) which limit the rating and number of further connections. Some conventional countermeasures such as on load tap changer, step voltage regulator, etc. have been applied to mitigate the voltage problems. However, these methodologies might not be enough to cope with PV output fluctuation due to the limitation in the number of tap changing operations or slow response of tap changers. On the other hand, it seems promising to use PV inverter control to solve the problems when PV units are allowed to inject or absorb reactive power. In particular, there is a possibility that PV inverter control can contribute to VU problem even if they are connected with low voltage single phase networks. This paper proposed a comprehensive inverter control strategy consisting of both reactive power control and active power curtailment to improve the operation performance of VU in medium voltage distribution network with high penetration of residential PV systems by minimizing network losses and active power curtailment with voltage quality constraints. The effectiveness of the proposed method was evaluated in consideration of solar insolation level which affects active power generation of PVs.

The power grid model, which represents the state of the power grid connection and characteristics of grid components such as loads and generators, is utilized for the fault analysis of the power grid and the necessary calculation in power grid stabilization systems. From the viewpoint of increasing the calculation time due to the increasing scale of the power grid, and the viewpoint of the difficulty of the information acquisition from the outer grid, the power grid reduction, which aggregates the full detailed power grid model into the small-scale reduced grid model, becomes necessary. The reduced grid model needs to duplicate the feature of the full detailed power grid model to the utmost, and minimize the error of the necessary amount of generator shedding as to the power grid stabilization. With this background, we have developed the power grid reduction method (DE method) which can reduce the error of power oscillation waveform, and improved DE method so that the error of the necessary amount of the generator shedding can be also reduced. For evaluating general-purpose properties of DE method, the accuracy of DE method has been evaluated not only in the standard model of IEEJ, but also in the actual system grid model of TEPCO. In this paper, from the view point of recent large-scale and rapid growth of renewables, DE method was applied and evaluated under the condition of large-scale renewables deployment in the future in consideration of the renewable's rapid fluctuation.

The DC series arc-faults lead a risk due to an aging of photovoltaic system components enhanced by environmental factors and high DC voltages in already existing photovoltaic systems. Until recently, many research activities have focused on the detection of DC series arc-faults by current signature analysis. However, DC arc detector has two problems. Firstly, it is difficult to distinguish arc noise and switching noise of power conditioner by circuit current in photovoltaic system. Secondly, when a DC series arc fault occurs in the photovoltaic system, DC series arc-fault string cannot be specified because the arc noise is propagated in the circuit. In this paper, we propose two novel techniques for the DC series arc-fault detection and identification of faulty strings. Experiments were performed by generating DC series arc in the field. The proposed technique is investigated based on the experimental results in the terms of effectivity and applicability.