Mf. Frechette et al., BREAKDOWN BEHAVIOR OF SF6 GAS-INSULATED SYSTEMS AT LOW-TEMPERATURE, IEEE transactions on dielectrics and electrical insulation, 2(5), 1995, pp. 925-951
The controversy surrounding low-temperature SF6 breakdown is addressed
in detail. Earlier relevant studies are reviewed, some of the existin
g data is analyzed in a new light, and further theoretical considerati
ons are presented. These discussions served to outline an experimental
approach aimed at confirming or invalidating breakdown invariance at
subnormal temperatures. Low-temperature de breakdown of an SF6 gas-ins
ulated system was investigated experimentally for temperatures ranging
from -50 to 24 degrees C, using associated pressure values that had b
een selected carefully to avoid phase transition of the gas-insulating
medium. The context allowed experimentation under both uniform and no
nuniform field conditions; the nonuniformity was due to the active rol
e of the cathode-gas interface at high fields. The experiment was cond
ucted for molecular densities ranging from 2.596 to 16.43x10(19) cm(-3
) (equivalent to pressures of 105 and 624 kPa, respectively, at 24 deg
rees C) and for gap lengths starting at 0.5 mm and extending to 7 mm.
Data sets show consistency, low statistical scattering, and high repro
ducibility. Data analysis led to several major conclusions. At constan
t density, the breakdown of the SF6-insulated system is temperature de
pendent, which is responsible for a decrease in the electric strength,
by similar to 10%. This decrease occurs for uniform field conditions,
the effect being small if not negligible for nonuniform field conditi
ons, and is noted to appear at a threshold temperature (-25 to -30 deg
rees C), take a constant value, and be fairly independent of density.