Measurement of Ionization and Attachment Coefficients in C4F7N/CO2 Gas Mixture as Substitute Gas to SF6

Yunxiang Long,Wenjun Zhou,Zhenyu Shen,Cheng Chen,Fang Li,Liping Guo,Yiheng Chen

doi:10.1109/access.2020.2990301

Yunxiang Long, Wenjun Zhou + Show 5 more

Open Access

https://doi.org/10.1109/access.2020.2990301

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Abstract

As one of the alternative insulation gases, C4F7N/CO2 gas mixtures have attracted much attention recently. In this study, the normalized Townsend first ionization coefficient $\alpha /N$ and the normalized attachment coefficient $\eta /N$ were measured in C4F7N/CO2 gas mixtures by using the Steady-State Townsend (SST) method over a range of electric fields $E/N$ from 100 to 550 Td. The concentrations of C4F7N studied were 4.99, 7.00, 9.00, 13.13 and 20.02%, and the gas pressure were 500 Pa at $20^{\circ }\text{C}$ . The effective ionization coefficients and the critical electric field were obtained at 500, 1000 and 2000 Pa to investigate the effect of gas pressure on dielectric strength in 9.00%C4F7N/91.00%CO2 respectively. The results indicated that the $(E/N)_{\mathrm {lim}}$ have not significant change on the SST experimental conditions. Meanwhile, a comparison with SF6 gas indicates that 20.02% C4F7N/79.98% CO2 has a similar insulation performance with $(E/N)_{\mathrm {lim}}$ as 358.82 Td. However, when the liquefaction temperature is considered, the C4F7N/CO2 gas mixtures with 9.00% C4F7N could be considered as an appropriate substitute gas for SF6, because the critical electric field of this gas mixture is over 70% of SF6 gas and could be used under −15°C at 0.7 MPa.

Highlights

Due to the great insulation ability, toxic safety and the heat transfer properties, sulfur hexafluoride (SF6) is widely used in high voltage applications, such as gas insulted switchgear (GIS), gas insulted transmission line (GIL) and so on [1]–[3]
IONIZATION AND ATTACHMENT COEFFICIENTS The normalized ionization coefficient α/N and the attachment coefficient η/N of C4F7N/CO2 mixtures were measured for 100 Td < E/N < 550 Td, and the results with the comparison to SF6 gas [3] are shown in Figures 1 and 2
EFFECTIVE IONIZATION COEFFICIENT The results of the normalized effective ionization coefficient (α−η)/N in the C4F7N/CO2 mixtures were obtained and plotted in Figure 3, which were compared with the (α−η)/N coefficients for SF6 [3] and CO2 [16]

Summary

INTRODUCTION

Due to the great insulation ability, toxic safety and the heat transfer properties, sulfur hexafluoride (SF6) is widely used in high voltage applications, such as gas insulted switchgear (GIS), gas insulted transmission line (GIL) and so on [1]–[3]. There is few reports about the normalized ionization coefficient α/N and the normalized attachment coefficient η/N measured by using the SST method in C4F7N/CO2 with different ratio of C4F7N. Several C4F7N/CO2 mixtures were suggested as potential alternative gases when considering the critical electric fields and boiling points

EXPERIMENTAL

RESULTS AND DISCUSSION

CONCLUSION