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In this paper, the synergistic effect of CF3I mixed gas is theoretically analyzed using the Boltzmann method and experimentally studied under different applied voltage, pressure and electric field inhomogeneity. The experimental results show the inversion of synergetic effect, which reflects the influence of external conditions on synergetic effect. The results show that CF3I/N 2 and CF3I/CO2 mixtures under slightly uneven electric field at normal pressure have synergistic effect. CF3I/CO2 mixtures under power frequency voltage and lightning impulse have better synergistic effect than CF3I/N2. The effect of macro parameters on synergetic effect is different for different buffer gases. For CF3I/N2 mixture, the synergistic effect of the mixture can be improved by increasing the pressure and increasing the electrode gap distance. For CF3I/CO2, due to the abnormal breakdown of the mixture, negative synergistic will occur at some pressure and gap distance. [ABSTRACT FROM AUTHOR]

SF6 gas is widely used in power systems, however, it has a strong greenhouse effect. The search for a new environmentally friendly alternative gas has become an urgent task for the power industry. In this paper, CF3I/CO2 gas mixtures in the ratio of 3:7 was tested based on a lightning impulse experimental platform. The 50% impulse breakdown voltage of CF3I/CO2 gas mixtures was determined under various pressures (0.1~0.3MPa) and gaps (5~30mm) and compared to pure SF6 gas. The results indicate that CF3I/CO2 gas mixtures has good insulation properties, reaching 0.84 times that of SF6 gas under slightly non-uniform electric field and 0.65 times that of SF6 gas in extremely inhomogeneous electric field. The polar effect of CF3I/CO2 gas mixtures was also analyzed and the coefficient K is proposed to describe and compare the differences of 50% breakdown voltages under different electric field. The results show that the polar effect of CF3I/CO2 gas mixtures under extremely inhomogeneous electric field is more obvious than that under slightly non-uniform electric field, and the polar reversal phenomenon occurs only under extremely inhomogeneous electric field. Considering various factors, CF3I/CO2 mixtures has the capability of replacing SF6 gas in power equipment such as GIL. [ABSTRACT FROM AUTHOR]

In this paper, power frequency breakdown tests as well as positive and negative lightning impulse breakdown tests have been performed. The breakdown voltages of CF3I/CO2/N2, c-C4F8/CO2/N2, CF3I/c-C4F8/CO2 gas mixtures have been measured in different gas pressures, mixing ratios and electrodes distances in slightly non-uniform electric fields. In addition, the breakdown voltages of CF3I/c-C4F8/CO2 gas mixtures have been comparatively analyzed with SF6/CO2, CF3I/CO2, c-C4F8/CO2 gas mixtures. The results show that CO2 is excellent buffer gas to CF3I and c-C4F8 as it has synergistic effect. The power frequency breakdown voltages of CF3I/c-C4F8/CO2 gas mixtures are basically the same as that of c-C4F8/CO2 gas mixtures, which are higher than that of CF3I/CO2 gas mixtures. Besides, the 50% breakdown voltage of c- C4F8/CF3I/CO2 gas mixtures under lightning impulse are higher than that of CF3I/CO2. Compared with SF6/CO2 gas mixtures, CF3I/c-C4F8/CO2 gas mixtures have the same insulating performance in short electrode distance, and show more excellent insulating ability at an electrode distance more than 20mm. [ABSTRACT FROM AUTHOR]

SF6 is a kind of strong greenhouse gas, it is urgent for researchers to seek new alternative insulating gas. This paper studies the discharge characteristics of CF3I/N2 gas mixture with needle-plane and sphere-plane electrode under standard lightning impulse, which is important for CF3I and its mixtures applied in electrical equipment. The experimental results show that the breakdown strength of CF3I/N2 increases with increasing gas pressure and gap distance. The discharge characteristics of CF3I/N2 gas mixtures present significantly polarity effect both in highly non-uniform electric field and slightly non-uniform electric field. In the highly non-uniform electric field, the 50% breakdown voltage in negative lightning impulse is greater than that under positive polarity. Under slightly non-uniform field, breakdown voltage in negative lightning impulse is lower than that in the positive polarity. When the electrode gap is 5mm, the polarity reversal phenomenon appeared with the increase of gas pressure. The analysis shows that CF3I/N2 gas mixture appears polarity effect and polarity reversal phenomenon in the short gap is due to the migration and interaction of space charge between the electrodes gap. [ABSTRACT FROM AUTHOR]

As the greenhouse effect of SF6 gas, the research on seeking alternative insulating gas to SF6 has become an imperative case. CF3I and its mixtures have been considered as the most promising insulating gas to replace SF6 gas. In this paper, the discharge characteristics of gas gap and insulator in CF3I/N2 gas mixtures under lightning impulse and alternating voltage were investigated. The effect of voltage, pressure as well as decomposition product after flashover were studied. Experimental results showed that in inhomogeneous electric field the breakdown voltages of CF3I/N2 with 30% CF3I gas is lower than SF6/N2 mixtures with 20% SF6. However, the flashover voltage of insulator in CF3I/N2 is higher than that in SF6/N2 mixtures. When compared to CF3I/N2 itself, the 50% breakdown voltage under positive lightning impulse were lower than that under negative lightning impulse. The CF3I/N2 gas mixtures with insulator also had polarity effect and appear polar reversal phenomenon. Under lightning impulse, there is no decomposition product on the surface of insulator after flashover but under alternating voltage, obvious iodine was produced on the surface of insulator. [ABSTRACT FROM PUBLISHER]

The breakdown voltages in a needle-plate geometry have been measured by 50 Hz power frequency tests for the CF3I-N2 gas mixtures (5?30% CF3I) over the gas pressure from 0.1 to 0.3 MPa. The influence of different conditions on the breakdown performance is investigated. The synergistic effect of CF3I-N2 gas mixtures is verified from the respect of breakdown voltage. Moreover, the behavior of the gas mixtures in highly divergent fields is characterized by a pressure range of corona stabilization, which can explain the relation of the breakdown strength to gas pressure and mixing ratio. A comparison to the theoretical breakdown voltages in uniform electric field shows that the breakdown strength reduces with the rising non-uniform coefficient of electric field at relatively short gap distance. Furthermore, the sensitivity of the insulating ability to divergent field is weakened by the increasing CF3I ratio. [ABSTRACT FROM PUBLISHER]

This paper studied the insulation characteristics of C3F8 gas mixtures with N2 and CO2 from the point view of electron swarm parameters. The density-normalized effective ionization coefficient (α-η)/N and electron drift velocity Ve in binary C3F8-N2 and C3F8- CO2 gas mixtures are calculated by solving the Boltzmann equation in the condition of steady-state Townsend discharge experiment. Values of the limiting electric field strength for which the electron ionization exactly balances the attachment are derived from the effective ionization coefficient data. It is found that the limiting field strength of C3F8-N2 gas mixture is greater than that of C3F8-CO2 for C3F8 gas content k varied from 0% to 100%, and the C3F8-N2 gas mixture containing 20% proportion C3F8 can achieve 60% dielectric strength of pure C3F8. Additionally, the synergistic effects of the insulation strength for C3F8 gas mixtures are also evaluated and compared with that of SF6-N2 mixture. The calculation results, together with the discussions on liquefaction temperature and global warming potential indicate that gas mixtures containing C3F8 are feasible for applying in electric power apparatus as insulation medium. [ABSTRACT FROM AUTHOR]