This is a laboratory study on the aging of SIR and hydrophobicity recovery. UV radiation, corona discharges, acid rain, dry-band arcing are employed as sources of the aging. Chemical and morphological analysis is used to detect the surface chemical and structural changes derived from these stresses. The nature of highly mobile low molecular weight (LMW) chains achieving a quick recovery of the hydrophobicity is carefully examined. Their generation and extinction caused by these stresses are investigated. From this study, it is shown that oxidation that induces crosslinking, branching, interchanging and a formation of silanol groups are the most dominant chemical reactions during the aging of SIR. Furthermore, silanol groups that are byprodncts of oxidation restrict the diffusion of mobile LMw chains, which decreases the recovery speed of hydrophobicity and accelerates the aging. A typical aging scenario of SIR from the installation to the end of their life is drawn.

Electrical and environmental aging of silicone rubber used in outdoor insulation

Tracking and erosion of high temperature vulcanizing (HTV)-silicone rubber (SIR) and the suppression mechanism of alumina trihydrate (ATH) filler were investigated in the present study. The tracking and erosion resistance of HTV-SIR filled with 0 to 60%wt ATH was evaluated by employing an IEC 587 inclined plane (IP) tracking and erosion test, during which leakage current pulses on HTV-SIR were counted. Surface temperature distributions and the occurrences of thermal spots >400/spl deg/C also were observed by means of an infrared thermovision study. We employed thermogravimetry (TG)-differential thermal analysis (DTA)-mass spectrometer (MS) to observe the thermal degradation of unfilled and filled HTV-SIR in both air and argon. The test results indicate that 40%wt is a critical ATH level and whether tracking and erosion is allowed in the IP tracking and erosion test. Highly filling ATH (>40%wt) reduces the number of low unit silicone oligomer precursors which promote dry-band arcing as well as the presence of residual carbon which leads to carbonization. Chemical modifications of water vapor liberated from heated ATH to methyl groups, which occurs at the thermal decomposition temperature of silicone rubber, were found to result in the above process. The protection mechanisms of ATH for the tracking and erosion of HTV-SIR are formulated herein.

Tracking and erosion of HTV silicone rubber and suppression mechanism of ATH

It is of fundamental importance that appropriate oil purity be preserved for all applications in electrical equipment. Oil purity can be maintained if good oil handling and testing procedures are provided. Trace contaminants and very small particle contents have recently received more attention because of improved measurement techniques. As delivered, new oils require pre-treatment by the users, but most often this is only drying and filtering, although mixing and additive treatments are also used. Care has to be taken, as problems with the miscibility of the compounds can be experienced. >

Electrical insulating oils. I . Characterization and pre-treatment of new transformer oils

On the application of high electric fields to a dielectric fluid, a convective motion of the fluid is induced. By controlling the fluid motion in nonuniform dc fields, a new type of fluid motor is developed. An angular velocity of more than 15 s−1 (150 rpm) can be achieved at a dc voltage of 5 kV for a motor with a rotor radius of 10 mm. The efficiency of energy transformation from electric to kinetic energy is about 4%. Since magnetic fields and switching circuits are not required, the advantage of the fluid motor will be enhanced by size reduction. The dielectric fluid motor is attractive as a source of mechanical energy in a micromachine.

Dielectric fluid motors

The dielectric breakdown behavior of thin metalized PP films for use in HV capacitors was studied as function of temperature with and without rape-seed oil as impregnation medium. The impregnating oil penetrates into the amorphous regions of the dielectric. With oil impregnation, the dielectric breakdown strength of the PP film is increased by >25%. A correlation between the breakdown strength and the degree of impregnation was found. With increasing temperature the breakdown strength of PP films decreases. Moreover, the measurements showed abrupt changes of slope in the breakdown strength at defined temperatures. From these results a correlation was established between the dielectric breakdown strength of PP films and temperature induced structure changes. It was shown that the abrupt changes of slope in the breakdown strength occurring at defined temperatures are due to the additives contained in the PP capacitor films used. Finally, guidelines for further development of impregnated PP films as dielectrics for high power capacitor applications are presented.

Breakdown behavior of oil-impregnated polypropylene as dielectric in film capacitors

We have investigated the synthetic oil-impregnated power capacitor insulation system of all polypropylene film dielectrics which is currently used in company products. The results of dielectric measurements in low electric fields can be interpreted by chemical interaction of the polypropylene film with the aromatic synthetic fluid. These investigations' have proved to be quite helpful in the manufacture of power capacitors with superior dielectric properties for service over a wide range of applied voltages.

Dielectric Properties of Oil-Impregnated all Polypropylene Film, Power Capacitor Insulation System

Electric conduction phenomena and carrier mobilitybehavior in mineral base electrical insulating oiland various kinds of synthetic base dielectric fluidshave been investigated in the low voltage region andhave been compared with our results in these fluidscontaining various kinds of oil-soluble impurities.It was shown that the impurities bring about someionic conduction in the fluids, and that the carriermobilities of the fluids containing the impuritiesnot necessarily seem to be governed by Walden's rule,depending on the types of the fluids and the impurities.In contrast, the fluids with industrial puritiesobey the rule. Furthermore, it was suggestedthat an electric conduction mechanism in the fluidscontaining the impurities seems to be closely relatedto a carrier mobility mechanism in these fluids.Thus, it appears advisable that the electricalbehavior of the artificial impurities dissolved in thedielectric fluids should be dealt with apart fromthat of the natural impurities.

Electric Conduction Phenomena and Carrier Mobility Behavior in Dielectric Fluids

Phenyl methyl silicone fluids of low phenyl radical concentrations and low viscosities are characterized by their extraordinary gasabsorbing property in high electric fields. Their physical, chemical and electrical properties were investigated and compared with those of dimethyl silicone fluids. The corona resistant characteristics and applied voltage vs. life expectancy relationships were studied, using model capacitors consisting of the silicone fluid and polypropylene film capacitor paper insulation system, and heatresistant transformer models consisting of the silicone fluid and Nomex Aramid paper. It was found that the phenyl methyl silicone fluids greatly improve the corona resistance property and the life expectancy in high voltage fields over the dimethyl silicone fluids, although both fluids are similar in their general characteristics. As a result, it is suggested that the phenyl methyl silicone fluids can be used to construct reliable high voltage stationary apparatus which is small in size.

Phenyl Methyl Silicone Fluid and Its Application to High-Voltage Stationary Apparatus

The chemical interaction between biaxially-oriented polypropylene film and diarylalkane has been investigated by studying the dielectric properties of the polypropylene film impregnated by the fluid. It was found that the s dispersion in its dissipation factor-temperature relationship is related to the segmental motion of the amorphous phase existing in the film, and that the a dispersion is connected with the Maxwell-Wagner type dielectric polarization at the surface of the crystalline phase in the film. Furthermore, it was demonstrated that the dissipation factor at the s dispersion temperature correlates well with the dissolution of the film into the fluid, and that the dissipation factor at the a dispersion temperature correlates closely with the oil absorption of the film immersed in the fluid.

Maxwell-Wagner Dielectric Polarization in Polypropylene Film/Aromatic Dielectric Fluid System for High Voltage Capacitor Use

A mineral oil and a synthetic oil consisting of aromatic constituents were each irradiated by ?rays at both room temper-ature ture and abo°t 70OC; the degree of the degradation was analyzed by means of gas chromatograms. The results showed that synthetic oil consisting of diarylalkane hydrocarbons has superior radiation-resistant properties. In addition, when mineral oil containing sulfur compounds was irradiated by ?-rays in the presence of copper strips, the observed copper corrosion was slightly more rapid than that observed without irradiation.

Sachio Yasufuku

Papers

Dielectric Properties of Oil-Impregnated all Polypropylene Film, Power Capacitor Insulation System

Electric Conduction Phenomena and Carrier Mobility Behavior in Dielectric Fluids

Phenyl Methyl Silicone Fluid and Its Application to High-Voltage Stationary Apparatus

Maxwell-Wagner Dielectric Polarization in Polypropylene Film/Aromatic Dielectric Fluid System for High Voltage Capacitor Use

Radiation-Induced Degradation Phenomena in Electrical Insulating Oils