Gas decomposition and electrode degradation characteristics of a 20% C ₃ F ₇ CN and 80% CO ₂ gas mixture for high voltage accelerators

Abstract

Sulphur hexafluoride (SF 6 ) is a potent greenhouse gas used in high voltage accelerators. As a promising alternative to SF 6 , the C 3 F 7 CN/CO 2 gas mixture and its by-products are of great interest to ensure the safe operation of accelerators that will adopt any SF 6 -free solution. This work experimentally examines the electrical ageing characteristics of a 20% C 3 F 7 CN/80% CO 2 gas mixture tested using spark gaps under a pressure of 7.2 bar (abs.). Gas samples were collected after 1000 DC breakdowns and analysed using gas chromatography mass spectrometry (GC-MS) with an estimated toxicity value of 54,459 ppm v , which indicates the aged mixture to be non-toxic. Subsequent investigation was conducted on the gas-solid interface after 500 breakdowns for both SF 6 and the 20% C 3 F 7 CN/80% CO 2 gas mixture. Aged electrodes were analysed using X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) techniques. Electrode surface analysis revealed the formation of metal fluorides on the electrode surface tested using the 20% C 3 F 7 CN/80% CO 2 mixture, whereas metal fluorides and sulphides were detected for electrodes tested with SF 6 . The findings provide a reference on the toxicity and gas-solid interaction of the electrically aged 20% C 3 F 7 CN/80% CO 2 gas mixture for potential retro-fill application in high voltage accelerators.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Mitigation of Aging Product Generation in C4F7N-Based SF6 Alternatives: A Holistic Approach

“…), small fluoronitriles (CF 3 CN, C 2 F 5 CN, etc. ), and C 2 N 2 . − The generation of these aging products not only compromises the equipment integrity but also presents hazards to personnel safety in power grid operations, as some of them potentially have considerable toxicity.…”

Multidimensional coupled structure‐activity relationship models for replacement of SF6

“…C4), hydrofluorocarbons (HFO-1234ze), CF 3 I etc. [5][6][7][8][9]. The emergence of SF 6 -free alternatives for an increasing number of applications leads a foreseeable decrease of SF 6 emissions in the near future.…”

“…Subsequently, Rabie and Franck screen out 7 preliminary candidates for their suitability as high voltage insulation gases by integrating the SAR models of dielectric strength and boiling point [16]. On the basis of the SAR models for dielectric strength and boiling point using the statistical electrostatic potential descriptors [9], Yu and coworkers proposed a hybrid protocol to design the environmentally sustainable perfluorinated molecules for dielectric use in contrast to the conventional physical mixing of two or three individual gases [17].…”