The integration of the intermittent renewable energy sources has a significant impact on the power system stability such as short-term voltage stability, short-term frequency stability, and transient stability. This paper describes several factors that deteriorate each stability and the promising approaches to improve the stability in the emergency state along with the author's previous works including the use of distributed energy resources, grid-forming converters, and wide-area control systems.

The fault point prediction and detection method on electric power distribution system before and after power outage have been developed. Subject of this study is to collect and visualize disaster information of distribution system and to complete recovery plan within one hour after the disaster occurs.

As far as fault point prediction method before power outage, the problem is parameter selection of zero-phase current signals of high-voltage consumer's incoming facilities. Real-scale ATP analysis model based on IEEE 123 test feeder has been created and I₀ signals of high-voltage consumer's incoming facilities were analyzed.

It was confirmed that the ratio of the first peak value and the third peak value of the I₀ signals was the most suitable parameter to predict ground fault location. And the ground fault location in the distribution system can be predicted by about 137m error, based on correlation coefficient between “the ratio of the first peak value and the third peak value of I₀ signals vs the high-voltage consumer ID” distributions.

In order to achieve carbon neutrality by 2050, introduction of photovoltaic power generators (PVs) msut be increased in the distribution system. But reverse power flow from PVs may become issues such as violation of the appropriate voltage and over current. Conventionally, installing voltage regulating equipment and replacing the lines with thicker lines are implemented as countermeasures with high expense.

Therefore, from the perspective of reducing countermeasure costs, measures have been implemented to avoid voltage increases due to reverse power flow by injecting reactive power from PVs. Constant power factor control, in which a certain amount of reactive power is injected according to the amount of power generated, has been adopted for both high and low voltage, but these data have not been shown on actual distribution lines.

This paper confirms that power factor constant control is in operation by measuring the characteristics of active and reactive power when reverse power flow occurs during PVs, and shows that there is no discrepancy between the measured values on the actual distribution lines and the operational values with power factor constant control.

A model expressing beams, pillars, and electrical wiring in a building for lightning surge simulation by circuit analysis method is proposed in this paper. The proposed model expresses the self-surge impedance of the electrical wiring as a function of the distance between conductors and the radius of the electrical wiring. The mutual impedance is expressed by the distance between the surfaces of a structure and a nearby wire instead of the distance between the conductor centers. In the case of two conductors having far different radii in proximity, the distribution of electromagnetic fields around the two conductors is similar in horizontal and vertical arrangements. Thus the electrical wiring nearby pillars can be treated as a horizontal conductor. The circuit analysis results show that the voltage difference generated between the structure and the electrical wiring is calculated more precisely by the proposed model than by the conventional model.