This article outlines the current state of international regulations on SF₆ gas and the development and application of equipment using SF₆-alternative gases, based on domestic and overseas trends related to SF₆ alternatives. It then compares, in terms of the basic properties and performance of SF₆-alternative gases and the advantages and disadvantages of their application to switchgear and substation equipment and explains the applicability of each type of SF₆-alternative gas equipment.

To realize a decarbonized society, the introduction of electric vehicles (EVs) is currently being promoted in the transportation sector. Commercial vehicles account for about 40% of CO₂ emissions in the transport sector, so electrification of these vehicles is especially important for decarbonization. Although the number of commercial vehicles is small, the electricity consumption when converted into EVs is large because of the long mileage; thus, the CO₂ reduction potential by charging from the renewable energy such as PVs is large. In this paper, we developed an EV traffic simulator for commercial vehicles, targeting the last one mile of home delivery, and evaluated the CO₂ reduction effect by EV delivery vehicles. Through an analysis targeting the cities of Takasaki and Maebashi in Gunma Prefecture, we obtained the following findings: (1) Increasing the charger output alone had a limited effect on CO₂ reduction, whereas combining a higher charger output with SOC control increased daytime charging and improved the CO₂ reduction effect. (2) Combining a higher charger output, SOC control, and charging schedule management further enhanced the CO₂ reduction effect. (3) By introducing a battery swap station, approximately 80% of the energy consumed for vehicle travel could be supplied by surplus PV electricity.

Synchronous machines for large-capacity turbine generators generally have a solid-steel rotor structure. In power system dynamic analysis, it is known that the synchronous generator model considering quadrature axis transient reactance x_q' is more accurate than a model that neglects x_q' for a synchronous machine with a solid-steel rotor. However, in Japan, synchronous machine models neglecting x_q' appears to be widely used for turbine generators. This is primarily because there is no significant difference between considering x_q' and neglecting it in rotor angle stability analysis of synchronous generator (SG). On the other hand, the introduction of synchronous condenser (SC) is one measure to maintain system stability. SC may have solid-steel rotor structure, similar to that of large-capacity turbine generators, but it is not clear whether there is significant difference in rotor angle stability analysis between considering x_q' and neglecting it. In this paper, the impacts of x_q' of the SC on the rotor angle stability analysis are investigated. The results of the simulations show that there is a clear difference in rotor angle stability analysis of SC between considering x_q' and neglecting it.

This paper proposes a new protection method for offshore terminals in HVDC transmission systems connecting offshore wind farms to onshore ac grids, specifically focusing on dc faults. The conventional single-arm short protection method allows a half-bridge modular multilevel converter (HB-MMC) to suppress the fault current to zero without external devices. However, this method is effective only for pole-to-ground faults in symmetrical monopole configurations and cannot handle pole-to-pole faults in asymmetrical monopole or bipolar configurations. The proposed method employs an HB-MMC with arm inductors consolidated into a single arm. By performing the single-arm short protection, this converter can suppress fault currents to zero for both pole-to-pole and pole-to-ground faults. Therefore, it is applicable to asymmetrical monopole and bipolar configurations. The validity of the proposed method is verified by simulations.

The high penetration of renewable energy sources raises concerns about decreasing power system inertia. To prepare for system separation events, continuous area-based inertia monitoring is desirable. To achieve continuous monitoring of area inertia, it is essential to accurately estimate area inertia using a limited number of measurement devices. In this paper, we propose a method to select effective measurement device placement for area inertia estimation. The effectiveness of the method is also verified by simulations using the IEEJ WEST 30-machine system model.