Identification of the discharge kinetics in the perfluoro-nitrile C₄F₇N with swarm and breakdown experiments

Abstract

We follow up on our previous publication on C 4 F 7 N and investigate the ion kinetics influencing C 4 F 7 N discharges with a pulsed Townsend experiment. The measured current signals at pressures between 6 and 69 kPa, in the range of density-reduced electric fields E/N from 500 to 1050 Td, show evidence of three anions: one long-lived anion with a detachment rate coefficient in the order of 10 −20 m 3 s −1 , a presumably non-detaching anion, and a short-lived anion with a detachment rate coefficient in the order of 10 −17 m 3 s −1. We obtain the corresponding rate coefficients for ionization, attachment and detachment in C 4 F 7 N. Using these results, we calculate a corrected value of the effective ionization rate coefficient (ν eff /N) * , taking into account detachment from negative ions. It results in a corrected value of the density-reduced critical electric field strength (E/N) * crit = 785 ± 15 Td, much lower than the previously obtained value of (E/N) crit = 975 ± 15 Td, which is valid only when electron detachment is negligible, i.e. for low pressure and small geometric distance. To find which value is most relevant for electrical insulation, we perform breakdown voltage measurements in homogeneous electric fields in C 4 F 7 N at 5 to 65 kPa. We compare the measured density-reduced breakdown field strength (E/N) bd to that calculated using the streamer criterion with the presently obtained rate coefficients, including electron detachment. We find excellent agreement between the measured and calculated (E/N) bd .

Measurement and modeling of electron and anion kinetics in N2O discharges

“…We observed similar signals in other gases with slowly detaching anions, as for instance in oxygen [6] or C 4 F 7 N [52]. Although it may look like it, but the current shape can not be reproduced by assuming lower ion mobilities (which would also be in conflict with measurements at lower pressures, where the mobilities fit well).…”

Breakdown Characteristics of C4F7N/CO2 Mixtures Under Steep-Wavefront Impulse Voltages

“…The biexponential wavefront time used in the test is shown in Figure 2. According to IEC 60060-1, the wavefront time T f can be calculated by the equation (1). T is the time between the amplitude of the impulse voltage waveform of 0.3∼0.9 (standard value) [14].…”

“…The environmentally friendly insulating gas C 4 F 7 N has the characteristics of high dielectric strength (at least 2.5 times SF 6 insulation performance), non-flammable, non-corrosive and low global warming potential (GWP near 2400) [1], [5]. The liquefaction temperature is lower than C 5 F 10 O and C 6 F 12 O, which has become a popular alternative to SF 6 .…”

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

“…Recently, as a newly potential candidate gas, Fluoronitrile (C 4 F 7 N), whose value of GWP is about 2100, is attracting much attention. [2], [6]- [11]. However, pure C 4 F 7 N have to be diluted with the buffer gas such as N 2 , CO 2 or dry air for electrical applications due to its high boiling point as −4.7 • C [6].…”

“…Chachereau et al [10], [11] used Puled Townsend (PT) method to obtained the electron rate and transport coefficients such as effective ionization rate coefficient and electron drift velocity in C 4 F 7 N/CO 2 mixtures with the concentration of C 4 F 7 N varying from 1% to 40 %. Nevertheless, 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 C 4 F 7 N/CO 2 with different ratio of C 4 F 7 N.…”