https://iopscience.iop.org/article/10.1088/1361-6463/aab314/pdf

SF6-alternative gases for application in gas-insulated switchgear

Assessment on the toxicity and application risk of C4F7N: A new SF6 alternative gas.

The electrical insulation properties of pure C4F7N and of C4F7N/N2 and C4F7N/CO2 mixtures are investigated in a pulsed Townsend setup. The electron rate and transport coefficients and the density-reduced critical electric field of these mixtures are obtained, and a synergy effect is observed in C4F7N/N2 and C4F7N/CO2 mixtures. The total electron attachment cross section of C4F7N is estimated based on the attachment rate to C4F7N in diluted C4F7N/N2, C4F7N/CO2 and C4F7N/O2/CO2 mixtures. Measurements in pure C4F7N at pressures of a few hundred pascal show that ion kinetics play a major role in C4F7N discharges and that further modelling is required to assess the electric strength of C4F7N at high pressures.

/pdf/electrical-insulation-properties-of-the-perfluoronitrile-2j1pcolt0e.pdf

Electrical insulation properties of the perfluoronitrile C4F7N

Recent studies suggest that fluoronitriles compound Novec 4710 possesses a dielectric strength two times higher than that of SF
 6
, while with a low global warming potential of only 2400. Mixed with CO
 2
 buffer gas, the Novec
 TM
 4710 mixtures offer excellent dielectric properties and the possibility to be used as an eco-friendly alternative to SF
 6
 for medium voltage switchgears. This paper focuses on the comparative study of the breakdown strength and partial discharge (PD) characteristics between the fluoronitrile/CO
 2
 mixtures and SF
 6
 under AC voltages. Breakdown tests are conducted under different electrode configurations, i.e., plane-plane, sphere-plane, rod-plane, and needle-plane, at different pressures and electrode gaps. In the uniform field, equivalent dielectric strength to SF
 6
 at 100 kPa can be reached by a mixture containing 15% fluoronitrile at identical total pressure; while in non-uniform and highly non-uniform fields, SF
 6
 exhibits higher dielectric strength than 20% mixture. The PD analysis suggests that SF
 6
 has much more PDs with lower magnitude and the 20% fluoronitrile/CO
 2
 mixture has less PDs but with higher magnitude. Due to the different PD characteristics, the corona stabilization effect may be responsible for the higher breakdown strength of SF
 6
 under highly non-uniform field.

Fluoronitrile/CO 2 mixture as an eco-friendly alternative to SF 6 for medium voltage switchgears

Environmental considerations are increasingly taking a front seat in all arenas of our daily lives. Among the major concerns are greenhouse gases and the resulting global warming problem. Although sulfur hexafluoride (SF6) is the most widely used insulation and arc-interruption medium in electrical power equipment, it is an extremely potent greenhouse gas with a very high global warming potential (GWP). Hence, the global power industry has been actively seeking SF6-alternative gases for decades. In recent years, much progress has been made in developing promising new gases that have dielectric properties similar to, or even better than, SF6 but with much lower GWPs. Many engineering-oriented tests have been performed on the technical performance of these gases and some manufacturers have announced their application in pilot projects. However, their large-scale application still seems premature, in particular because of the lack of some critical fundamental physicochemical information for these relatively novel compounds. To provide a better understanding of these SF6-alternative gases, this paper reviews the recent advances in obtaining their fundamental physicochemical properties, emphasizing basic data calculations and fundamental experiments. The most important properties are analyzed comprehensively. These include the basic physical properties of arc plasmas formed from the gases, decomposition characteristics, materials compatibilities, swarm parameters, cross-sections and some dielectric properties. Finally, perspectives on current research and future research directions are presented.

https://iopscience.iop.org/article/10.1088/1361-6463/ab6ea1/pdf

Fundamental physicochemical properties of SF6-alternative gases: a review of recent progress

The density normalized effective ionization coefficients and critical breakdown electric field of the Heptafluoro-iso-butyronitrile (Fluoronitriles), and Fluoronitriles-CO2 mixture are investigated using the steady state Townsend (SST) experimental setup, over a range of the density normalized critical electric field (E/N) from 200–1066 Td (E is the electric field and N the gas density). Breakdown voltage measurements are also performed to plot the Paschen curves for small product values (N×d) (d being the electrode gap), to identify the Paschen minimum, and to validate the density normalized critical electric field (E/N)0 when α=η (α and η are the ionization and attachment coefficients, respectively). The influence of electrode surface roughness is also analyzed.

H. E. Nechml

Papers

Effective ionization coefficients and limiting field strength of fluoronitriles-CO2 mixtures