DEVELOPMENT OF POLTRATION-FREE INSULATING OILS AND UTILIZATION TO ENVIRONMENT FRIENDLY POWER APPARATUS

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The properties of electrohydrodynamic (EHD) pumping and dielectric strength were examined for two insulating oils, rapeseed ester oil and silicone oil, which were denatured by a bonding of hydrofluorocarbon (HFC134a) gas components decomposed using a barrier discharge reactor. The results obtained from this study are as follows.1. By taking the difference between spectrums of standard oil and denatured oil using a FT-IR ATR method, it was found that C-F and C-O radicals and C-H and C-O radicals were formed respectively in the denatured rapeseed ester oil and silicone oil.2. The electrical pumping ability in denatured oils was reinforced significantly compared with standard oils by a slight addition of ionic components. In the electrode geometry (quasi-doughnut to plane type) used in the experiment, the current level was less than 1 μA for the applied voltage up to 20 kV. The potential distribution measured at parallel plane electrodes in denatured oils also showed that there existed a … More heterocharge layer near the electrodes, which suggested that the powerful pumping was attributable to the pure conduction pumping mechanism.3. Impulse creeping discharges were affected sensitively by the ionic component in denatured oils. In denatured oils, the streamer propagated longer compared to standard oils, but the lengths of positive streamer did not exceed±15% of those in standard transformer oil. The ac breakdown voltage in denatured oils also reduced compared to those of standard oils. The dielectric strength of denatured rapeseed ester oil, however, was comparable to that of standard transformer oil.On the other hand, the coaxial cone to rod electrode assembly was devised newly and the properties of the liquid jet were experimentally examined. When a positive dc voltage was applied to the rod electrode, the liquid spouted forcibly from the glass tube outlet installed in the top of grounded conical electrode. This EHD pumping comes from the accumulation of ionic charges in the vicinity of rod electrode. It is also shown that a partial insulator coating of rod electrode surface leads to a rising of the pumping pressure and a reduction of the conduction current. An EHD pumping is expected largely as a new cooling technique in the oil-filled power apparatus, but there is need to take into consideration a reciprocal relation between the EHD mechanism and the electrical insulation. Less