Critical Electric-Field Strength of High-Temperature SF6 Mixture Gas with Ablated PTFE/BN Vapor at Temperatures of 300–4000 K

Concerning the dielectric breakdown phenomena occurring in a high-voltage SF
₆
circuit breaker, the present paper describes theoretical calculation results for a critical reduced electric-field strength E
_cr
in a temperature range of 300-4,000 K at 1.0 MPa. This paper focuses especially on the high-temperature SF
₆
admixed with the vapor of nozzle material (90mass% PTFE (Polytetrafluoroethylene or C
₂
F
₄
)-10mass% BN), because some of the circuit breakers employ nozzles made from these materials. The calculation result for a concentration of the nozzle-material vapor, e.g. 50%, shows that the admixture of the vapor into the SF
₆
gas causes E
_cr
to be 70-150 Td in a temperature range of 2,000- 4,000 K. However, this strength is about twice E
_cr
for a pure SF
₆
gas. The calculation result for the same concentration also reveals that E
_cr
is 150-220 Td at 300-2,000 K. This strength is be about half of that for the pure SF
₆
gas.