Atsushi Ohtake

Study on downsizing techniques for conventional motor with solid insulation system

This paper describes a feasibility study of a solid insulation system applied downsized motor. A large amount of insulation resin was employed to replace structural metal materials used in conventional motors. The optimal heat design, mechanically stable structure, and proper insulation resin are proposed and discussed. A prototype motor was manufactured, and results of a basic insulation test, temperature rise test and noise test are presented.

Development of discharge inception simulator considering environmental factors using advection-diffusion model

Insulation design with discharge simulation based on physical phenomena is used in designing electrical instruments to facilitate their miniaturization and obtain high insulation reliability. We developed a model to calculate partial discharge inception in a non-uniform air gap by considering how environmental factors, especially humidity, affect insulation performance. We upgraded the calculation model that built in the distribution of negative ion density using the amount of moisture on the electrodes. As a result, we can estimate the discharge inception voltage with high accuracy. Additionally, we attempted to extend the simulator for three-dimensional creep analysis.

Development of simulation techniques for mechanical strength of nanoconposite insulating materials

Mechanical strength simulation techniques for nanocomposite resins have been developed. Coarse grained molecular dynamics are used to calculate the nanofiller distribution in resin and the stress-strain curve (S-S curve) of nanocomposite resin. A molecular orbital method based on density functional theory in which the electrical fields from a large region (um-mm) of surrounding resin are taken into consideration to obtain the inter-molecular forces for molecular dynamics. In addition, present simulations were applied to silica/epoxy nanocomposite resins and the following results were obtained. 1) While hydrophilic silica is uniformly distributed, hydrophobic silica forms a network in epoxy. These results agree with an experimental observation using scanning electron microscope. 2) The maximum level of stress of the calculated S-S curves of resin with hydrophobic silica is greater than that with hydrophilic silica. This result qualitatively agrees with the fracture-toughness measured by using a three-point bending test.

Development of a Nonperiodic Boundary Practical Simulator for Oxide and Shallow Trench Isolation Chemical Mechanical Polishing Processes

We developed a fast simulator for the chemical mechanical polishing (CMP) process that works in nonperiodic boundary conditions. Since periodic boundary conditions are not used, it can calculate anywhere on a wafer, such as the wafers edge. Additionally, we enhanced the simulator to calculate the shallow trench isolation (STI)-CMP process. In the STI-CMP simulation method, additionally required simulation parameters are only one, under the assumption that dishing reaches steady state in enough short time relative to total polishing time. We found that the simulation results could match experimental film thicknesses with an error range of about 10-20 nm and that the calculation time was reduced to 1/20 relative to when the acceleration method was not introduced.