In response to environmental demands, inverter-driven motors are increasingly used in industry and mobility. This has raised expectations for higher motor performance and reliability. Recent advances in power electronics have led to higher frequency and faster slew rates of inverter output pulse voltages. As a result, insulation degradation due to inverter surges has become a concern. These surges, caused by impedance mismatches at motor terminals, can trigger PD (partial discharge) within insulation materials. PD can degrade insulation and eventually lead to breakdown. To improve the reliability of inverter-driven motors, understanding PD characteristics and insulation lifetime under repetitive surge voltages is important. This paper proposes a computational algorithm to estimate insulation lifetime under repetitive surge voltages. The algorithm is based on experimental results under AC voltage. The estimated insulation lifetime of twisted pair samples was compared with experimental data, confirming the algorithm's validity.

We investigated penetration probability in order to clarify threshold of surface resistivity that can prevent breakdown of insulating film by discharge. Insulating films were polyethylene terephthalate films that were coated by a conductive carbon-nanotube-added ink to modify surface resistivity, and we applied discharge to the insulating film. As a result, it was found that penetration probability due to discharge was 0% when surface resistivity of insulating film was 8.10×10³ Ω/sq. or lower. Furthermore, it is considered that potential propagates due to time constant calculated by surface resistivity and capacitance between insulating film and ground. When surface resistivity is 8.10×10³ Ω/sq. or lower, time constant is 4.0 ns or less, which is shorter than propagation time of creeping discharge. Because electric field at tip of discharge is relaxed, it is difficult to penetrate insulating film.

With the increasing functionality of mobile devices, their components are required to operate reliably at high frequencies. Consequently, the selection of materials for printed circuit boards has become limited, and polytetrafluoroethylene (PTFE) has emerged as a promising candidate due to its low dielectric loss. In this study, we investigated the surface chemical state affecting the adhesion between PTFE and Cu thin films by varying the irradiation angle and dose of H₃⁺ ion beams to PTFE. The ion irradiation was performed at incident angles of 0°, 45°, and 60° with an acceleration voltage of 10 kV. The primary objective of this work was to examine the surface morphology and chemical states of PTFE after irradiation, which are closely related to its adhesion properties. At irradiation angles of 45° and 60°, temporary surface smoothing was observed at specific irradiation dose. XPS measurement also revealed a decrease in water contact angle, indicating increased hydrophilicity associated with the formation of surface C-H bonds.

To develop a magnetic field heat treatment technique using induction heating for Fe-based amorphous (Fe-Si-B), we studied the effects of induction heating on these materials. Heat treatment was carried out selected wound model cores using an induction heating system. To achieve effective induction heating, the magnetic excitation frequency was set to 20 kHz during the heating phase, while DC excitation was applied during the cooling phase. After heat treatment by the induction heating, the magnetic properties of the wound model cores were measured using the exciting current method. The effects and remaining issues of heat treatment under the magnetic field on amorphous wound cores using induction heating were clarified.

For the self-inductance of single-layer regular polygonal coils, an exact formula already exists. However, obtaining the exact value requires cumbersome and skillful work for numerical integration, as the formula involves a double infinite integral. If a simpler, faster and highly accurate calculation method for determining the inductance value could be found, its utility in coil design would be extremely high. In this technical note, we introduce a new “shape coefficient” and tabulate its exact values, similar to the Nagaoka coefficient. Then using shape coefficients read from the numerical table, we have proposed a simplified calculation method that quickly determines inductance through basic arithmetic operations. We have also verified the validity and usefulness of this simplified calculation method by applying it to three types of coils (equilateral triangle, regular pentagon and regular hexagon). Ultimately, by utilizing the shape coefficient determined by the coil specifications, it is possible to easily obtain accurate inductance values.

This letter introduces a categorical framework in which electrical quantities are modeled as elements of a fixed D-graded commutative ℝ-algebra, and concrete unit systems are realized as choices of homogeneous base quantities in a corresponding T_D-algebra. Within this framework, changes of unit system for a fixed dimension group D are represented by graded T_D-algebra automorphisms that capture SI-CGS conversions such as the MKSA-rCGS-emu current transformation. As a practical contribution to electrical engineering, we derive a dimensionless relation between MKSA and rCGS-emu current units that ensures the invariance of all dimensionless electrical observables under SI-CGS unit changes.