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C5-PFK (C5F10O), with high dielectric strength and low global warming potential, is the new environmental-friendly potential alternative gases to SF6. In order to reduce its excessively high liquefaction temperature while retaining its excellent properties, a certain amount of buffer gases, such as N2 can be added to it. Therefore, to understand the plasma behavior of under C5F10O-N2 mixtures, the composition, thermodynamic properties and transport properties of the C5F10O-N2 mixtures in a temperature range of 300K to 30000K and a pressure range of 0.1 MPa to 0.8 MPa is calculated under the assumption of local thermodynamic equilibrium. Then, the influence of mixing ratios and pressures are analyzed. The results can be used to determine the optimal proportion of C5F10O-N2 mixtures. Several peaks of the specific heat can be observed below 5000K, which could be a favorable factor for arc quenching. [ABSTRACT FROM AUTHOR]

CF3I-N2 mixtures have garnered much attention as potential SF6-substitutes due to their excellent dielectric strengths, and the dielectric strength of SF6-N2 mixtures has a good synergy effect. This paper attempts to propose an approach of adding a small amount of SF6 to improve the dielectric strength of the CF3I-N2 mixture, by making an all-around consideration of dielectric strength, impact on the environment and the limitations of engineering pressure and the lowest ambient temperature. The influences of adding different amounts of SF6 on the electron energy distribution function, the reduced ionization, attachment and effective ionization coefficients, the critical reduced electric field strength and critical electron temperature of ternary SF6-CF3I-N2 mixtures are investigated by Boltzmann analysis. Then the relations of the critical electric fiend strength, mixed ratio and saturated vapor pressure of the ternary SF6-CF3I-N2 mixture are built and analyzed. The results demonstrate that an effective improvement of its dielectric strength can be obtained by adding a small amount of SF6 into the CF3I-N2 mixture, and that a proper choice of the mixed ratio and the gas pressure of the ternary SF6-CF3I-N2 mixture can provide a comparable dielectric strength to pure SF6. [ABSTRACT FROM AUTHOR]

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]

Fluorides and their CO 2 mixtures are considered as promising choices of SF 6 -substitute gases due to their low global warming potentials and high dielectric strength. This paper investigates physical and chemical properties and breakdown characteristics of different common fluorides and their mixtures for application in the power system. For dielectric characteristics of fluorides and their mixtures, their power frequency breakdown voltages are determined experimentally, and the results are compared with SF 6 . For physical and chemical characteristics, the saturated vapor pressures, global warming potentials (GWPs), toxicities, prices of fluorides and their mixtures are calculated, and the corresponding characteristic curves are obtained. Based on characteristics mentioned above, a method for obtaining the optimal gas parameters of a specific fluoride mixture is proposed, which can be used as a feasible solution to find an SF 6 alternative gas that meets the application requirements. The results show that CO 2 mixtures with hexafluoropropene (HFP), 1,1,1,2-tetrafluoroethane (HFC-134a) and perfluoroisobutyronitrile (C4-PFN) are three types of good SF 6 -substitute gases. HFP/CO 2 mixtures with HFP component ratios 0.32 to 0.6 are suitable for applications at 0.1 to 0.3 MPa. HFC-134a/CO 2 mixtures (HFC-134a component ratios from 0.16 to 0.2) are suitable for applications at 0.3 to 0.5 MPa. C4-PFN/CO 2 mixtures (C4-PFN component ratios from 0.09 to 0.12) could be used for the applications at 0.1 to 0.5 MPa, regardless of the gas price. [ABSTRACT FROM AUTHOR]

The presence of metal particles in power equipment may cause gas discharges and threaten insulation reliability. The discharge phenomenon in the presence of particles involves complex physical processes. To describe these processes, a numerical method is proposed to analyze the relationship between the motion of the particle and the discharge at the same time. First, processes including the generation of the first electron, the formation of a streamer corona, the transition from the streamer to the leader, and the leader propagation are considered. Voltage–time characteristics are calculated with particles of different shapes. Then, the characteristics of the particle motion driven by the Coulomb force are analyzed. Finally, the threshold field for partial discharge and the breakdown in the presence of the particle are discussed taking into account the voltage–time characteristics and the analysis of the particle motion mentioned above. The results demonstrate that there is a threshold field when breakdown occurs in the presence of a long and narrow particle at the negative electrode before the particle leaves the electrode. [ABSTRACT FROM AUTHOR]

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]

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]

The perfluoronitriles and its mixtures have great dielectric strength and are environmentally friendly, which are considered as a typical class of alternative gases. This paper investigates the frequency breakdown characteristics of C4-PFN/CO2 mixtures in the nonuniform electric field. The influences of the electric field distribution, pressure and the C4-PFN component ratio on the dielectric strength of C4-PFN/CO2 mixtures are studied, which is compared with the cases for SF6 under the same conditions. It is shown that the sensitivity of C4-PFN/CO2 mixtures to the nonuniform electric field increases with the increase of the C4-PFN component ratio. For C4-PFN/CO2 mixtures containing more than 5% C4-PFN, the sensitivity is much greater than that of SF6. [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]

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 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]

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]

• The interaction of C 4 F 7 N with α-Al 2 O 3 (0001) surface belongs to chemisorption. • The dissociation of C 4 F 7 N on α-Al 2 O 3 surface is difficult to occur. • C 4 F 7 N and α-Al 2 O 3 shows good thermal compatibility below 170 ℃. • The α-Al 2 O 3 -based materials can be used as insulators in C 4 F 7 N-filled electrical equipment. In this paper, the compatibility between C 4 F 7 N and α-Al 2 O 3 (0001) surface has been evaluated based on the density functional theory (DFT). The adsorption energy, total charge transfer, states analysis, and electron density difference were obtained to analyze the interaction behavior of C 4 F 7 N on α-Al 2 O 3 (0001) surface. The results demonstrated a chemisorption between C 4 F 7 N and α-Al 2 O 3 (0001) surface. Moreover, the pathway of C 4 F 7 N dissociated on α-Al 2 O 3 (0001) surface after the adsorption was determined. However, the activation energy required for the dissociation is too large to achieve, which means that the dissociation of C 4 F 7 N on α-Al 2 O 3 surface is difficult to occur. Additionally, the thermal compatibility between α-Al 2 O 3 and C 4 F 7 N were verified by experiments, which shows a certain compatibility between C 4 F 7 N and α-Al 2 O 3 (0001) under up to 170 ℃. The results demonstrate that α-Al 2 O 3 -based materials can be used as insulators in C 4 F 7 N-filled electrical equipment. [ABSTRACT FROM AUTHOR]

• C 5 F 10 O starts to decompose at 500 ℃ and CO 2 , C 3 F 6 , and C 4 F 10 are dominant by-products. • A unique by-products C 2 F 6 O 3 is produced under partial discharge in C 5 F 10 O-air mixture. • Decomposition products CF 4 , C 3 F 6 , CF 2 O, CHF 3 , and C 3 HF 7 have good compatibility with Al (1 1 1) and Cu (1 1 1) surfaces. • The O atoms in C 2 F 6 O 3 show strong reaction activity with Al (1 1 1) and Cu (1 1 1) surfaces. Perfluoroketone C 5 F 10 O has drawn much attention in recent years as a promising environmental-friendly gas to substitute SF 6 in power equipment. In this paper, the decomposition characteristics of C 5 F 10 O and C 5 F 10 O/air mixture under pyrolysis and partial discharge conditions were explored by experiments using a gas chromatography/mass spectrometer. Besides, the compatibility of decomposition products with the copper and aluminum was evaluated based on the density functional theory calculation. We found that C 5 F 10 O has good thermal stability at 300 ℃. At 500 ℃, C 5 F 10 O starts to decompose and it produces CO, CO 2 , C 2 F 6 , C 2 F 4 , C 3 F 8 , C 3 F 6 , C 4 F 10 , C 4 F 8 and CHF 3 , among which CO 2 , C 3 F 6 , and C 4 F 10 are dominant. For C 5 F 10 O/air mixtures, the pyrolysis products are mainly saturated fluorocarbons and more CO 2 is produced. Partial discharges in C 5 F 10 O/air mixture mainly produce CO 2 , saturated fluorocarbons and a unique compound C 3 F 6 O 3. It is found that CF 4 , C 3 F 6 , CF 2 O, CHF 3 , and C 3 HF 7 have good compatibility with Al (1 1 1) and Cu (1 1 1) surfaces, while the interactions between C 2 F 6 O 3 and Al (1 1 1), Cu (1 1 1) surfaces are relatively strong, which are chemisorption. The identified by-products of C 5 F 10 O and C 5 F 10 O/air mixture under different conditions as well as their compatibility with metal materials is essential for online fault-diagnostic and long-term maintenance in engineering applications. [ABSTRACT FROM AUTHOR]

• Interaction between C4F7N and ZnO surface is stronger that on Zn surface. • The CN group shows a strong activity on the ZnO surface. • Activation energy of C 4 F 7 N dissociation on ZnO surface is higher than on Cu and Al. • Zinc shows potentials to be anti-corrosion material when using C 4 F 7 N. Recently, C 4 F 7 N has been considered as one of the most promising candidates to replace SF 6 due to its excellent insulation performance and environmental-friendly property. Metal zinc is widely used as a coating material in gas-insulated electrical equipment. However, its compatibility with C 4 F 7 N has never been explored before. In this paper, the adsorption properties of C 4 F 7 N on Zn(0 0 0 1) and ZnO(1 0 1 ¯ 0) surfaces were theoretically studied by a first-principles calculation. Adsorption energy, total charge transfer, density of states, and electron density difference were calculated to evaluate the compatibility of C 4 F 7 N with Zn and ZnO. The results demonstrated that the interaction between C 4 F 7 N and ZnO(1 0 1 ¯ 0) is stronger than that of Zn(0 0 0 1). The dissociation pathway of C 4 F 7 N after adsorption on the ZnO(1 0 1 ¯ 0) surface was also determined, which shows that ZnO(1 0 1 ¯ 0) has a catalytic effect on the decomposition process of C 4 F 7 N. Compared with Al(1 1 1) and Cu(1 1 1), the dissociation of C 4 F 7 N on ZnO(1 0 1 ¯ 0) has a higher energy barrier, indicating that the reaction is more difficult to occur. As a result, Zn and ZnO have certain compatibility with C 4 F 7 N, which was also verified by experiments. Therefore, we infer that Zn shows potentials to be used as anti-corrosion coating in C 4 F 7 N gas-insulated electrical equipment. [ABSTRACT FROM AUTHOR]