High voltage research (breakdown strengths of gaseous and liquid insulators). Semiannual report, October 1, 1977--March 31, 1978. [Summaries of research activities at Oak Ridge National Laboratory]

The work on gas mixtures is focused on combinations of gases consisting of strongly electron-attaching components and one or more electron slowing-down components. Hypotheses based on the positions of electronically excited states are borne out experimentally in the low pressure (<1000 torr) breakdown measurements. The high pressure work shows dramatically the importance of the electron scattering cross section on breakdown strength by comparing Ar with Ne as single gases and in mixtures with SF/sub 6/. Although the ionization cross section for Ar is very much greater than that for Ne, Ar is a superior buffer gas. A theoretical discussion is given which describes the relation between the dielectric strength of a gas to its physical parameters including the electron attachment cross section, the ionization cross section, the ionization potential, and the electron energy distribution function. Also discussed is the importance of perfluorination in hydrocarbons to effect an increase in the electron attachment cross section and electron affinity and a decrease in the ionization cross section, and hence an increase in dielectric strength. Attachment rates were measured as a function of the mean electron energy for a comprehensive list of perfluorocarbons. Breakdown voltages were determined for SF/sub 6/ and for SF/sub 6/ (20%)/N/sub 2/(80%) as a function of temperature from -15/sup 0/C to 85/sup 0/C. Environmental aspects of gas dielectrics pertaining to gas decomposition and toxicity were studied

High voltage research (breakdown strengths of gaseous and liquid insulators) and environmental effects of dielectric gases. Semiannual report, April 1, 1979-September 30, 1979. [Health and Safety Research Div. , ORNL]

A number of gas mixtures are suggested for industrial-scale testing. Electron attachment rates were measured and unfolded to give attachment cross section functions for CCl/sub 3/F, CCl/sub 2/F/sub 2/, and CClF/sub 3/ each in N/sub 2/, and for CCl/sub 3/F in Ar. Electron attachment rates were measured also for n-C/sub 6/F/sub 14/ in both Ar and N/sub 2/. The effects of molecular structure on energy, cross section, and lifetime of negative ion states of organic molecules were considered. A study was made of the potential role of electron detachment in breakdown. The role of dipolar scattering of electrons in inhibiting breakdown was investigated. The nature of synergisms among constituents of a gas dielectric mixture is discussed. Examples are cited from recent breakdown measurements. Breakdown measurements in plane-plane geometry were made for CF/sub 4/, 1,1,1-CH/sub 3/CF/sub 3/, and CHF/sub 3/. Similar measurements were conducted with binary mixtures containing one of (c-C/sub 4/F/sub 8/, SF/sub 6/) and one of (CF/sub 4/, CH/sub 2/F/sub 2/, 1,1,1-CH/sub 3/CF/sub 3/, CH/sub 2/F/sub 2/). Of special interest in these results were observed synergisms and the effect of dipole moment on the breakdown strengths. The initial fragmentation of 1,1,2-C/sub 2/Cl/sub 3/F/sub 3/ under electron impact was studied. Final decomposition products of sparked SF/sub 6//2-C/sub 4/F/sub 6/ mixtures were identified and quantified. The breakdown products of SF/sub 6/ were studied. Impulse measurements concentrated on c-C/sub 4/F/sub 8//SF/sub 6/ mixtures. Values of V/sub 50/, V/sub NO/, and V/sub 10x/ were obtained and evaluated. In the practical conditions of cylindrical geometry with and without surface roughness, many multicomponent mixtures of the gases SF/sub 6/, c-C/sub 4/F/sub 8/, 2-C/sub 4/F/sub 8/, N/sub 2/, and 1,1,1-CH/sub 3/CF/sub 3/ were tested, at both 1 and 4.4 atmospheres. The electric fields were calculated. In the study of liquid dielectrics n-hexane and perfluoro-n-hexane were tested. 35 figures, 20 tables

High voltage research (breakdown strengths of gaseous and liquid insulators) and environmental effects of dielectric gases. Semiannual report, October 1, 1978--March 31, 1979

Progress in research on the breakdown strengths of gaseous dielectrics, on the environmental effects of gaseous dielectrics breakdown products, and on measurements of breakdown voltages of liquid n-hexane are reported. A short discussion of transmission losses in EHV AC gas-insulated and oil-filled cable transmission lines is included. (LCL