Technical Viability of Retro-filling C3F7CN/CO2 Gas Mixtures in SF6-designed Gas Insulated Lines and Busbars at Transmission Voltages

Loizos Loizou, Tony Chen, Qiang Liu, Ian Cotton, Mark Waldron, John Owens

Research output: Contribution to journalArticlepeer-review

Abstract

Sulphur hexafluoride (SF6), the most popular dielectric medium adopted in compressed gas insulated equipment, has been identified as a highly potent greenhouse gas. This has led to increased interest in finding a more environmentally friendly replacement candidate. In this paper, the technical viability of C3F7CN/CO2 gas mixtures was assessed as a potential retro-fill solution for existing SF6-filled gas insulated lines (GIL) and busbars (GIB). A reduced-scale coaxial prototype was developed to establish the breakdown strength of 20% C3F7CN / 80% CO2 and 16% C3F7CN / 84% CO2 gas mixtures in direct comparison with pure SF6 under the standard lightning impulse (1.2/50 μs). Breakdown results demonstrate that a mixture of 20% C3F7CN / 80% CO2 exhibits comparable insulation capability to pure SF6 in coaxial geometries with similar field uniformity to GIL / GIB. This initial finding has led to the construction of a full-scale GIB demonstrator rated for 420/550 kV. Type tests according to IEC 62271-204 showed that the 20% C3F7CN / 80 % CO2 gas mixture has passed all the required voltage levels as SF6. The research findings in this paper are an encouraging step towards a technically viable SF6-free retro-fill solution for existing GIL / GIB installed for the 400 kV transmission network in the UK.
Original languageEnglish
Article number9019889
Pages (from-to)2394-2402
Number of pages9
JournalIEEE Transactions on Power Delivery
Volume35
Issue number5
DOIs
Publication statusPublished - 2 Mar 2020

Keywords

  • Heptafluoro-iso-butyronitrile (C3F7CN)
  • gas insulation
  • gas insulated lines and busbars
  • lightning impulse breakdown
  • sulphur hexafluoride (SF6)

Fingerprint

Dive into the research topics of 'Technical Viability of Retro-filling C3F7CN/CO2 Gas Mixtures in SF6-designed Gas Insulated Lines and Busbars at Transmission Voltages'. Together they form a unique fingerprint.

Cite this