Hiroshi Miyao

Influence of dc and dc/ac composite fields on the flow electrification characteristics of transformer oil

Flow electrification characteristics of transformer oil were investigated by applying dc and dc/ac composite fields to both bare and covered coaxial cylinder electrode systems. For the bare electrode system, flow electrification characteristics were almost the same between positive and negative dc voltage applications and negative charges were generated for both dc and dc/ac composite voltage applications at high dc fields. For the covered electrode system, the apparent flow electrification characteristics differed between positive and negative dc voltage applications. For the former, negative charges were generated at high dc fields for both dc and dc/ac composite voltage applications, and for the latter, positive charges were always generated for both voltage applications. However, negative charge generation for the positive voltage application was attributed to the influence of negative charge generation at the bare part of the covered electrode end; the fundamental charge generation characteristics of the covered electrode showed an increase of positive charge generation by dc voltage application, and positive charge generation was accelerated by a composite ac field.

Investigation of higher breakdown voltages of multi layer insulating films by voltage clamp phenomenon

The voltage clamp phenomenon was investigated by measuring the dielectric characteristics of Ta/sub 2/O/sub 5//SrTiO/sub 3/ and SiO/sub 2//Ta/sub 2/O/sub 5/ multilayer films. These films consist of alternating high- and low-dielectric-constant layers. It was attempted to raise the between voltage of the multilayer films by lowering the resistivity of the insulating film with the low dielectric constant in a high electric field to a value near its breakdown strength. In this way, applied voltages higher than the breakdown field strength of the low-dielectric-constant film can be applied to the high-dielectric-constant insulating, and shared voltages of the former can be kept constant, as if in a voltage clamp, during any further applied voltage rise. The Ta/sub 2/O/sub 5//SrTiO/sub 3/ film was found to exhibit voltage clamp, resulting in higher breakdown strengths, but the SiO/sub 2//Ta/sub 2/O/sub 5/ film did not, and it was necessary to improve the deposition method used for the SiO/sub 2/ film. A self-healing breakdown characteristic was found to be necessary for the multilayer insulating film to attain higher breakdown strengths due to the voltage clamp phenomenon.<<ETX>>