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The gas mixture CO2–O2 has been considered as an insulation and arc-quenching medium in gas-insulated switchgears. In this paper, the dielectric breakdown properties of CO2–O2 mixtures at different O2 concentrations and gas pressures were studied theoretically by considering ion kinetics in a spatial–temporal growth avalanche model. A kinetic scheme that includes all the main reactions likely to occur in CO2–O2 mixtures is presented. An improved method to calculate the dielectric strength of the gas mixture is developed, based on an avalanche model that considers both spatial growth and temporal processes. Next, the reaction rates of ionization, attachment, detachment and ion conversion, the effective ionization Townsend coefficient αeff/N, and reduced critical electric field strength (E/N)cr in CO2–O2 mixtures at different mixing ratios and gas pressures are analyzed in detail. Finally, a pulsed Townsend experiment is performed to verify the validity and accuracy of the calculation method. Based on this, one detachment reaction rate is modified to yield more accurate results. Better consistency between the results and the experimental values supports the validity of the kinetic system, reaction rates, and the improved calculation method. [ABSTRACT FROM AUTHOR]

Recently, C4F7N mixtures have attracted attention as a promising SF6 alternative due to their low global warming potential and excellent electrical performance. In this study, we introduce a newly built experimental setup for pulsed Townsend measurements as well as the physical model for the acquisition of electron swarm parameters. The effective ionization rate coefficients, electron drift velocity, and density-normalized longitudinal diffusion coefficients in C4F7N and its mixtures with CO2 and N2 were obtained. The reduced critical electric field for pure C4F7N at 100 Pa is determined to be 1002 Td, while it decreases with increasing pressure because of the effect of ion kinetics during the discharge process. C4F7N shows good synergism with CO2 and N2. To have a dielectric strength equivalent to that of SF6, the mixing ratio of C4F7N in its mixtures with CO2 and N2 should be 18% and 12%, respectively. The results provide fundamental data for modeling discharges in C4F7N and its mixtures. [ABSTRACT FROM AUTHOR]

The perfluoronitrile C4F7N is considered a promising SF6-alternative in high-voltage gas-insulated apparatus, thanks to its high dielectric strength and low global warming potential. However, a complete and consistent set of electron-neutral collision cross-sections of C4F7N is still lacking, which hinders relevant plasma modeling. In this contribution, the available electron-neutral collision cross-sections of C4F7N are first compiled and assessed. The initial cross-sections are adjusted iteratively by the electron swarm method to determine a complete and self-consistent cross-section set of C4F7N for the first time. The set is validated by a systematic comparison of electron swarm parameters between Boltzmann equation analysis and experimental measurements in pure C4F7N as well as C4F7N/N2 and C4F7N/Ar mixtures. The proposed cross-section set of C4F7N will be made available to the community in the LXCat database. It will be of particular importance for applications with an emphasis on the discharge mechanisms of this novel gas. [ABSTRACT FROM AUTHOR]

In this paper, a calculation method is proposed to predict the dielectric strength (DS) of gases and the DS of some promising SF 6 alternative gases and their mixtures is further evaluated by DC breakdown tests. The calculation method is based on the density functional theory (DFT), so that the DS of the gases can be obtained by only calculating their molecular parameters, including the average static electronic polarizability and adiabatic ionization energy. The paper also presents the DC breakdown strength of the C 4 F 7 N, C 5 F 10 O, and HFO-type gases, and it is found that the experimental DS values are in good agreement with the calculated values. In addition, DC breakdown tests for gas mixtures are also conducted and their synergistic effect is discussed in detail. The results show that the DS of C 4 F 7 N mixed gases is equivalent to that of pure SF 6 gas even under high pressures, indicating their potential applications in HV electrical equipment. The DS of C 5 F 10 O mixed gas is slightly lower than that of C 4 F 7 N mixed gas. Compared with CO 2 , mixing with air brings stronger synergistic effect in C 5 F 10 O and C 4 F 7 N in our experiment. The DS of HFO mixture is substantially less than that of SF 6 because of the weak synergistic effect when mixed with CO 2 or N 2. This paper presents an effective method to evaluate DS of SF 6 alternative gases and the results are useful for their future engineering applications. [ABSTRACT FROM AUTHOR]

The C 4 F 7 N/CO 2 gas mixture has attracted much attention due to its excellent insulation property and eco-friendly character. In order to evaluate the feasibility of its application in DC GIL, this paper focuses on the surface charging characteristics of spacers under DC stress in the C 4 F 7 N/CO 2 mixture. First, the DC insulation strength was tested under uniform field. The results show that the critical dielectric strength of pure C 4 F 7 N is more than twice that of SF 6 and the dielectric strength of 15%∼20% C 4 F 7 N/CO 2 mixture is equivalent to that of SF 6. Next, the surface charge measurement of spacers was performed in C 4 F 7 N/CO 2 mixtures, which reveals that the surface charge density decreases slightly with the increase of C 4 F 7 N content. However, the surface charging level in 25% C 4 F 7 N/CO 2 mixture is still much higher than that in SF 6. It is found that most of the surface charge stems from partial discharges (PDs) near the flange. The PD measurement shows that in SF 6 , there are more PDs with low magnitude, but much less PDs with high magnitude compared to that in the 15%∼25% C 4 F 7 N/CO 2 mixtures. It is the different PD behaviors between C 4 F 7 N/CO 2 mixtures and SF 6 that lead to their different surface charging characteristics. [ABSTRACT FROM AUTHOR]

Recently, the C4F7N/CO2 mixture has been highly considered as a promising SF6 alternative due to its low greenhouse effect and excellent electrical performance. Apart from its dielectric strength and arc-quenching capability, the decomposition characteristics of C4F7N/CO2 also play an important role in its future applications in gas-insulated electrical equipment. Therefore, decomposition experiments of the C4F7N/CO2 mixture were carried out under multiple AC discharge breakdowns by using a needle-to-plate electrode configuration. The compositions of the gas mixture before and after breakdowns were detected by using a gas chromatography-mass spectrometer. The results show that a trace amount of C3HF7 exists in the C4F7N product; the decomposition of the C4F7N/CO2 mixture mainly produces CO, CF4, CO2, C2F4, C2F6, C3F8, CF3CN, C3F6, C4F6, C4F10, C2F5CN, C2N2, HCN, C2F3CN, and HF. As the number of breakdowns increases, the content of most decomposition products increases significantly, while the content of C3HF7 decreases. The possible formation pathways of the decomposition products were determined, and the corresponding reaction enthalpies were calculated by quantum chemistry calculation. Relevant results not only reveal the decomposition characteristics of C4F7N/CO2 under AC breakdowns but also help us to better understand the corresponding physicochemical mechanisms, which will provide a good reference for stable operation and safe maintenance in applications. [ABSTRACT FROM AUTHOR]

C5-PFK has attracted much attention as one of the most promising SF 6 substitutes for medium voltage (MV) power equipment because of its high insulation strength and low global warming potential (GWP). In this paper, the dielectric properties of C5-PFK-Air and C5-PFK-CO 2 mixtures are experimentally investigated, to explore the most effective solution for C5-PFK mixtures for application in MV power equipment. The basic physical properties of C5-PFK and its mixtures are calculated and compared with those of C4-PFN based gases and SF 6 -N 2 mixtures. The GWP and saturated vapor pressure for gas mixtures are calculated, and a relative value R-GWP is defined to evaluate the greenhouse effect at specific pressure. The 50% breakdown voltages of C5-PFK-Air and C5-PFK-CO 2 mixtures under lightning impulse voltage are determined experimentally. The mixture ratio and filling pressure are determined taking into account of the ambient temperature and pressure for MV apparatus. The possibility of practical applications for these mixtures are analyzed by combining the saturated vapor pressure characteristics and the breakdown electric field strength. The synergy effects of the C5-PFK-CO 2 and SF 6 -N 2 mixtures are greater than those of the C5-PFK-Air and C4-PFN-CO 2 mixtures. The C5-PFK-Air and C5-PFK-CO 2 mixtures have higher dielectric strength than SF 6 at 0.1 MPa when the C5-PFK is about 28% under the temperature limitation of −5°C. The pressure increments of 0.014 and 0.066 MPa are required for C5-PFK-CO 2 and C5-PFK-Air mixtures, respectively to reach the dielectric strength of pure SF 6 at 0.1 MPa under the temperature limitation of − 25°C. [ABSTRACT FROM AUTHOR]