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Dielectric breakdown properties of hot SF/He mixtures predicted from basic data

Physics of Plasmas, ISSN: 1070-664X, Vol: 20, Issue: 11
2013
  • 32
    Citations
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  • 19
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Metric Options:   Counts1 Year3 Year

Metrics Details

  • Citations
    32
    • Citation Indexes
      32
  • Captures
    19

Article Description

Sulfur hexafluoride (SF) gas has a quite high global warming potential and hence it is required that applying any substitute for SF gas. Much interest in the use of a mixture of helium and SF as arc quenching medium was investigated indicating a higher recovery performance of arc interruption than that of pure SF. It is known that the electrical breakdown in a circuit breaker after arc interruption occurs in a hot gas environment, with a complicated species composition because of the occurrence of dissociation and other reactions. The likelihood of breakdown relies on the electron interactions with all these species. The critical reduced electric field strength (the field at which breakdown can occur, relative to the number density) of hot SF/He mixtures related to the dielectric recovery phase of a high voltage circuit breaker is calculated in the temperature range from 300 K to 3500 K. The critically reduced electric field strength of these mixtures was obtained by balancing electron generation and loss mechanisms. These were evaluated using the electron energy distribution function derived from the Boltzmann transport equation under the two-term approximation. Good agreement was found between calculations for pure hot SF and pure hot He and experimental results and previous calculations. The addition of He to SF was found to decrease the critical reduced electric field strength in the whole temperature range due to a lack of electron impact attachment process for helium regardless its high ionization potential. This indicates that not the behaviour of dielectric strength but possibly the higher energy dissipation capability caused mainly by light mass and high specific heat as well as thermal conductivity of atomic helium contributes most to a higher dielectric recovery performance of arc interruption for SF/He mixtures. © 2013 AIP Publishing LLC.

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