Alternative SF_6 insulation by deposition of amorphous CxFy film on electric machine conductors

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In order to reduce the usage of SF_6 insulation gas with a high GWP (global warming potential) value, the present project proposed to use a-C : F film coated conductor prepared by RF C_8F_<18> vapor plasma method for electric power system insulation as alternatives to SF_6 gas. This project was motivated because we had experienced very high deposition rates in RF plasma if per-fluorocarbon vapors were used. The main results are summarized as follows.1.The deposition rate on Si and Al substrates was about 100-200nm/min, which is a few tens times higher than those obtained by conventional CF_4 and C_2F_6 gases.2.The a-C : F film, which is composed of C-C and C-F bonds, was excellent insulation properties (dielectric constant【approximately equal】2) with high density and good thermal strength.3.The breakdown voltages V_s of N_2, Ar and He gases between the a-C : F film coated Al electrodes were 3 times larger than those between Al ones in low p d (pressure x gap length) region. For pd<20 Torr/cm the V_s was rather higher than that of SF_6 gas.4.The decomposed species of C_8F_<18> were observed using Photo Multiple Analyzer and Quadra Pole Mass Analyzer. It was found that C_2, CF, CF_2, CF_3 and CF_5 were produced significantly. These species could contribute the chemical and electrical properties of a-C : F film, e.g.C/F ratios. Then the dielectric constant value may be changed.The present results suggest that coating of the a-C : F film on electric conductor enhances the dielectric strength of a gas insulation system.