We present a study of the performance of silicone oil as an environmentally friendly and flame retardant insulating medium for electric power equipment. We have investigated the streaming electrification characteristics for flowing silicone oil for cooling of electric power equipment. As the initial step, the electric charge density accumulated in silicone oil and on the surface of the insulator is investigated simultaneously. We have used 5 types of insulating material for the experiment, including aramid paper. Silicone oil becomes negatively charged by streaming electrification, in contrast to conventional mineral oil, and the magnitude of the electric charge density on the insulating material is influenced by the kind of insulating material. As the second step, the streaming electrification characteristics of silicone oil were further examined using an insulator for which the work function is known. Based on these results, streaming electrification for various kinds of insulator and silicone oil is evaluated with respect to the work function. We consider the optimum combination of silicone oil and insulating material.

This paper describes the surface breakdown characteristics of the silicone oil which has the possibility of the application to innovative switchgear as an insulating medium. At the first step, we have experimentally studied on the impulse breakdown characteristics of the configuration with a triple-junction where a solid insulator is in contact with the electrode. The test configurations consist of solid material (Nomex and pressboard) and liquid insulation oil (silicone and mineral oil). We have discussed the experimental results based on the maximal electric field at a triple-junction. As the second step, we have studied the configuration which may improve the surface breakdown characteristics by lowering the electric field near the triple-junction.

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A sudden capacity increase in demand during the summer peak, or in contingencies such as malfunctioning transformers, may cause an overload in normal transformers. In this paper, on the basis of overloaded transformer operation in distribution substations, thermal aging testing in oil was carried out under various overload patterns, such as short-term overload and long-term overload, but with the winding insulation paper's lifespan loss kept constant. From the results, various characteristics, such as the mean degree of polymerization and production of furfural and (CO 2 +CO), and their effects on the lifespan loss of the insulation paper, were obtained.

We report on compression behaviors of oil-immersed insulating pressed-boards used in transformers for analyzing the axial vibration of windings. We examined the compression stressstrain curves of oil-immersed pressed-boards. We found that compression behaviors depended on strain rates and temperatures, that is, viscoelastic behaviors were observed. By applying the time-temperature superposition principle to the pressed-boards' compression behaviors, we obtained the relationship between the modulus of compressive elasticity and strain rate. As a result, we were able to estimate the pressedboards' compression behaviors at high compression forces at high strain rates.