Investigation of the insulation performance of a new gas mixture with extremely low GWP

Since several decades SF₆ plays a dominant role for insulation and switching in transmission and distribution equipment due to its superior insulation and arc quenching capabilities. Leakage rates of modern SF₆ switchgear are extremely low and careful handling processes ensure minimum SF₆ emissions during operation. In the past several attempts have been made with different gases and gas mixtures to find alternatives with lower global warming potential, all of them showing severe drawbacks that restricted their implementation. This paper presents a new gas mixture for insulation with limitations within an acceptable range. Composed of perfluorinated ketones with technical air or CO₂ it shows a comparable insulation capability to SF₆, where this mixture has a very short atmospheric lifetime with a global warming potential of approximately one and zero ozone depletion potential. Measurements of the dielectric strength of the new mixtures and reference gases are done in a principle test device under homogeneous electrical field conditions over a wide pressure range. Synergistic effects similar to SF₆/N₂ mixtures are observed between the perfluorinated ketones and background gases used. It is found, that the AC and lightning impulse performance of the investigated mixtures can approach SF₆ values at increased total filling pressures.