Considering the high Global Warming Potential (GWP) and the long residence-time of sulfur hexafluoride (SF₆), it is urgent to seek the potential for alternative insulation gases used in gas-insulated electric equipment. Recently, HFO-1336mzz(E), a new eco-friendly insulation medium to SF₆, has been triggered much attention from engineering staff due to its environmental friendliness and excellent insulating properties. The decomposition characteristics can provide a significant reference for its engineering application, whereas it is unclear at present. The AC breakdown experiments were performed in a designed steel chamber. The needle-plate electrode was set in the gas chamber filled with HFO-1336mzz(E)/air mixture. Then the power frequency AC voltage was put on the chamber by a power supply. The test gas was taken every 10 times breakdown. Then the sample gas was detected by the GC-MS. The experimental results showed that the main decomposition compounds mainly include CF₄, C₂F₆O₃, C₂F₄, CHF₃, C₃F₈, CF₃CN, C₂HF₅, C₄F₆, C₃HF₃, C₃H₂F₄(E), C₃H₂F₄(Z), and C₅F₈, etc. Physic-chemistry properties indicated that CF₃CN is a highly toxic gas, which may be a potential threat to the operation and maintenance personnel. Therefore, sufficient attention should be triggered when the gas is detected. The content of most decomposition products is low and the insulation property of the HFO-1336mzz(E)/ buffer gas mixture does not have a prominent decline. Of course, effective absorbents for the toxic gaseous products are prospected to be developed before the engineering application in the electric industry.

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