COMPACT AND HIGH DIELECTRIC STRENGTH OF ELECTRIC MACHINES WITH a-C:F FILM COATING OF LOW-DIELECTRIC CONSTANT AND HIGH DIELECTRIC STRENGTH DEPOSITED IN PLASMA

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SF_6 gas shows excellent properties as an electric insulating material, however as it's global warming factor is extremely big, the gas is now forbidden to be exhausted outdoors. The present research is, in place of SF_6 gas usage, to propose an alternative technique that conductor parts, which are coated by amorphous carbon-fluoride (a-C:F) film processed in plasma, are introduced in a gas insulation system. Then, the air breakdown voltage between the coated electrodes was shown to be the same level or even higher than that of SF_6 gas between the conventional electrodes.The main results are summarized as follow, 1) a-C:F film with a few hundred nanometers thickness was coated, in a chemically and physically stable condition, on the surface of spherical metal electrodes, 2) the present film was shown to be a tetrafluoroethylene (PTFE) like film with a low dielectric constant and high breakdown strength as a result of the analyses by SEM, XPS, FTIR and others, 3) the gas breakdown voltage in the Paschen curve, in which the breakdown voltage is given as a function of pd (p: gas pressure and d: gap length), in the present electrodes was the same level as the case of SF_6 in the conventional electrode system, 4) the surface condition of a-C:F film depended on the amount of buffer gases (Ar, He) in the RF plasma. In addition, assuming breakdown of a part of the film, re-deposition of a-C:F film was tried on the original surface, then, 4) double layers and triple layers, in the case of second and third times deposition, were clearly obtained. And in the case of the third times deposition, on the surface an interesting regularly patterned figures appeared.