Dielectric Properties and Electric Conductivity of Liquefied Insulating Gas C4-Fluoronitrile

For gas-insulated switchgear, an ecologically friendly candidate could be C4-Fluoronitrile, used in gas mixtures e.g. with CO2. Because of the relatively high dew-point of C4-Fluoronitrile, partial liquefaction could occur at very low operating temperatures. This would affect the electric field distribution and could lower the dielectric strength of the insulation system. Hence, the electric and dielectric properties of the liquid phase of the insulating gas C4-Fluoronitrile need to be studied. Liquefaction of gaseous C4-Fluoronitrile is achieved by cooling of an electrode inside of the test vessel at saturation vapour pressure at room temperature. The relative permittivity and the dielectric dissipation factor at 50 Hz of liquefied C4-Fluoronitrile are determined according to IEC 60247 with field strengths up to 400 V/mm in a plate-plate-electrode-Arrangement according to IEC 62631. Further, the electric conductivity is determined in steady-state condition with field strengths up to 500 V/mm, both at positive and negative DC voltage.