The Criterion of Conductor Surface Roughness in Environment-friendly C4F7N/CO2 Gas Mixture

The discharge characteristics of strong electronegative gases are sensitive to non-uniform electric field distribution. However, it is difficult to make the electrode surface smooth of high-voltage electrical equipment completely. There are usually rough protrusion, causing local electric field distortion, thus reducing the gas insulation performance. In order to study the influence of local non-uniform electric field induced by rough electrode surface on gas discharge in the new environment-friendly C
₄
F
₇
N/CO
₂
gas mixtures to replace SF
₆
, the control value of electrode surface roughness of environment-friendly gas equipment was obtained. In this paper, the mechanism of electronegative gas discharge caused by electrode surface roughness is theoretically analyzed. And the merit of C
₄
F
₇
N/CO
₂
gas mixtures and its relationship with electrode surface roughness were proposed. The discharge tests of SF
₆
and C
₄
F
₇
N/CO
₂
were carried out, and the gas merits and discharge voltage curves with different C
₄
F
₇
N contents were obtained. The results show that as the content of C
₄
F
₇
N is less than 20%, the sensitivity of C
₄
F
₇
N/CO
₂
to the uneven electric field is similar to that of SF
₆
. When the content of C
₄
F
₇
N is in the range of 4%~20%, the control value of electrode surface roughness is consist with that in SF
₆
gas of 6.3μm. The experimental results verify that the theoretical analysis method is feasible and effective, and the proposed control value of electrode surface roughness in the C
₄
F
₇
N/CO
₂
equipment provides the guide for equipment design and development