SF6 Alternative Gas Research Articles

Interruption characteristic of 3%C5F10O/97%CO2 gas mixture in a 40.5 kV circuit breaker

The C5F10O/CO2 gas mixture is one of the most promising SF6 alternative gases at the present stage, which was initially applied in high-voltage electrical equipment. This paper mainly studies the interruption performance of 3%C5F10O/97%CO2 gas mixture (k = 3%) with a charging pressure of 0.6 MPa in high-voltage circuit breakers. First, the thermodynamic parameters, transport coefficient, and net radiation coefficient were calculated for k = 3%. On this basis, a 40.5 kV circuit breaker was used as a prototype to establish the magnetohydrody-namic model for breaking 20 kA short-circuit current, and the arc temperature and pressure distribution in the arc extinguishing chamber of the circuit breaker were calculated. The LC oscillation circuit was used to build an arc-extinguishing characteristic test platform to verify the accuracy of the numerical calculation. Finally, based on the Mayr arc model and the critical electric field strength, the post-arc thermal breakdown and electrical breakdown characteristics of SF6, CO2, and k = 3% were quantitatively analyzed. The results show that under 0.6 MPa, the thermal breakdown performance of k = 3% is about 89.7% of SF6, which is nearly twice higher than that of CO2 and has better thermal breaking ability. The electrical breakdown performance of k = 3% is about 20.4% of SF6, and the probability of electrical breakdown in the front end of the fixed contact is high. This problem should be paid attention to in the design of high-voltage circuit breakers. This study can provide a reference for the development and optimization of environmentally friendly high-voltage circuit breakers.

Decomposition characteristics of C4F7N-based SF6-alternative gas mixtures

C4F7N [2,3,3,3-tetrafluoro-2-(trifluoromethyl)propanenitrile]/CO2 gas mixtures are being developed as an eco-friendly electrical insulator to replace SF6, the most potent greenhouse industrial gaseous dielectric. However, recent studies have reported complicated and often conflicting decomposition pathways for C4F7N/CO2 gas mixtures, which has raised concerns. In this work, the decomposition characteristics of C4F7N/CO2 gas mixtures were studied comprehensively by both designed computations and experiments. Computations were performed starting from fundamental propositions of C4F7N/CO2 decompositions, which were further experimentally verified by pyrolysis, long-term thermal aging with/without catalytic materials (industrial-grade molecular sieves 4A), and electrical decomposition by spark discharge. The results of both computations and experiments suggest that in an ideal thermal decomposition, C4F7N is likely to decompose into C2F6 and small fluoronitriles first at high temperatures. The generation of C3F6 and C2N2 from C4F7N thermal decomposition at lower temperatures appears because of the catalytic effect of incompatible materials, for example, the industrial-grade molecular sieves 4A that we tested. The electron impact dissociation of C4F7N plays an important role in C4F7N electrical decomposition, leading to additional formation of distinctive small molecules of CF4 and C2N2 of low concentrations. It was pointed out based on a real arcing test in a load disconnector that the decomposition of C4F7N gas mixtures in real applications will be at a much moderate and manageable rate than what was obtained from the highly accelerated laboratory tests presented in this work. The signatures of decomposition products extracted in this study provide invaluable guidance for developing decomposition-based diagnosis and fixation of decomposition byproducts toward SF6-free power grids.

Studies of C2H2F4 and SF6 alternative gas mixtures for HPL RPC detectors for High Energy Physics applications

This research investigates the viability of replacing greenhouse gases C2H2F4 and SF6 with eco-friendly gas mixtures in Resistive Plate Chamber (RPC) detectors used at CERN LHC experiments. The study focuses on the addition of CO2 as a substitute of C2H2F4 to minimize greenhouse gas emissions and reduce operational costs. Initial performance studies with cosmic muons evaluate key parameters such as efficiency, current, streamer probability, prompt charge, cluster size, and time resolution of the detectors. Subsequent assessments take place at the CERN Gamma Irradiation Facility, emulating the LHC experiment background radiation. Furthermore, the study explores alternatives to SF6, including 3M NOVECTM 4710 and AMOLEATM 1224yd, presenting perforances results about these gas alternatives in High Pressure Laminate RPCs.

Effect of Copper Vapor on Radiation Properties of C4F7N Gas Mixtures

C4F7N and its mixture with buffer gases are regarded as the most promising SF6-alternative gases in gas circuit breakers. The switching arc can severely ablate the electrodes, producing copper metal vapor that combine with the C4F7N gas mixture to chang radiation characteristics. This paper compares the net emission coefficient of C4F7N mixtures at various mixing ratios and assesses the effect of 20% copper vapor. It is found that adding copper vapor can greatly enhance radiation.

Influence of oxygen on solid carbon formation during arcing of eco-friendly SF6-alternative gases

During the arc breaking process of high-voltage circuit breakers, the eco-friendly SF6-alternative gases will inevitably decompose and generate various decomposition products. In some cases, this will contain solid by-products such as solid carbon, which will have a deterioration effect on the electrical insulation performance of the equipment. It has been found that adding a proper amount of O2 can effectively inhibit the formation of solid carbon. In this paper, based on the improved Gibbs free energy minimization method, a calculation model considering the solid decomposition products was established, and the arc plasma composition of CO2/O2 mixtures with the new eco-friendly gases, such as C4F7N, C5F10O, HFO-1234ze(E) and HFO-1336mzz(E), in local thermodynamic equilibrium state was calculated. The change of decomposition products with the initial O2 ratio is studied, and the criterion expression of inhibiting solid carbon formation is obtained. We also applied the method to the calculation of other SF6-alternative gases containing sulfur atoms such as NSF3 and CF3SO2F. Finally, we showed that solid carbon can be inhibited when a proper molecule formula is satisfied. This work may provide new ideas for further exploring the potential of SF6-alternative gases.

Theoretical process for the investigation of dielectric characteristics of F3NO as an alternative gas for SF6

To examine the possibility of using a gas molecule as an SF6 alternative gas, the insulation properties of the molecule must be estimated. In this work, we present a theoretical approach to calculate geometry parameters, electron scattering cross sections, and transport properties of nitrogen fluoride oxide (F3NO), which we have selected as an alternative to SF6. The molecular minimum structure of F3NO was optimized using the ɷB97X-D functional combined with the aug-cc-pVTZ basis set. Using this initial geometry obtained by the molecular structure calculation, the R-matrix calculation was done to obtain the elastic and momentum transfer cross section. The BE-f method was used for electronic excitation cross section. For the ionization cross section, the binary encounter Bethe method was used. From the calculated cross section data, the electron transport coefficients and reaction coefficients were calculated by solving the two-term approximated Boltzmann equation to investigate the discharge and insulation characteristics.

Numerical simulation of streamer discharge with different electrode shapes in C4F7N

In recent years, the environmentally friendly gas, C4F7N, has been recognized as a potential SF6 alternative gas due to its excellent insulation. To study the streamer discharge characteristics of different electrode shapes in C4F7N, a fluid model was established by COMSOL, and simulations were performed. Streamer discharge as a function of varying electrode shapes was analyzed, and the variation law of electric field intensity and photon flux was obtained, which serves as a theoretical basis for optical detection and reliable diagnosis of partial discharge. Simulation results demonstrate that under the same discharge conditions, the electric field inhomogeneity of the needle–plane model, rod–plane model, and ball–plane model decreased successively and the breakdown difficulty increased. With the increase in the applied voltage, the peak electric field intensity of the streamer head was found to increase, whereas an increase in the electrode spacing was found to decrease this property. The change in photon flux was found to be similar to the change in the electric field intensity.

Introduction to Domestic and International Sulfur Hexafluoride (SF6) Greenhouse Gas Emission Reduction Technologies for Power Grid Enterprises

Since its introduction in 1930, sulfur hexafluoride (SF6) has rapidly become the primary insulation material for high-voltage electrical equipment such as transmission lines, switches, transformers, circuit breakers, and reactors, owing to its exceptional electrical properties. However, the flip side of its excellent performance is its extremely high global warming potential (GWP), which is over 23,000 times that of carbon dioxide (CO2). Managing SF6 has thus become a key aspect of emission reduction efforts. The primary strategies for reducing SF6 emissions include minimizing gas leakage during the production, operation, and maintenance of electrical equipment, as well as purifying and recycling emitted SF6 gas. Various purification and monitoring methods have been developed for routine operations and have already been implemented by power grid companies globally. In addition to ongoing daily monitoring, research is also underway concerning the transformation, degradation, and substitution of SF6 gases. Degradation and transformation methods primarily focus on high-temperature degradation, photocatalysis, and arc degradation. In the context of substitution, the idea is to use conventional gases or various organic compounds to form SF6 mixtures or alternative gases, with the aim of reducing effect of leakage while maintaining performance. Finally, recommendations are made for power grid enterprises to reduce SF6 emissions, emphasizing the importance of source control and the exploration of alternatives. Effective equipment management to prevent gas leakage, comprehensive monitoring and assessment, as well as the proper handling of unusable SF6 devices, are also crucial steps in emission reduction efforts.

Long-Term Partial Discharge Behavior of Protrusion Defect in HVDC GIS

This article investigates the partial discharge (PD) behavior of protrusion defects in real-size high-voltage direct current gas insulated switchgear (HVDC GIS) for SF6 and SF6 alternative gases including fluoronitrile–CO2 mixture (10%) and fluoroketone–dry air mixture (6.6%). The evolution of PD apparent charge and PD repetition rate for all investigated gases is presented and discussed. The measurement results indicate that PD behavior changes as a function of time. The PD apparent charge increases and the PD repetition rate decreases with the increase of voltage application time. This evolution can be related to the change in protrusion tip radius due to electrochemical etching: radius of the protrusion’s tip being enlarged. In addition, the pulse sequence analysis (PSA) plots of the PDs caused by this defect are presented. It is observed that the PSA plots change over time. Therefore, for the development of a robust PD monitoring and defect-recognition tool, as well as for the assessment of risks in the operation of HVDC GIS, it is crucial to take these changes into account.

Voltage–Current Characteristic of Free Burning Arcs in SF₆ Alternative Gas Mixtures

Voltage–current characteristics of free burning arcs in SF6 and air have been known for decades. As the demand for an SF6-free solution is increasing, there is an accompanying need to determine arc parameters in the alternative gases. An unblown arc experiment has been established to determine the voltage–current characteristics of SF6 alternative gases, which have not yet been thoroughly studied. In this experiment, free burning arc measurements were performed in a number of gases under consideration of SF6 alternatives, including CO2 and mixtures of CO2/O2 with and without C4F7N or C5F10O additives at the concentrations of up to 10 %. Measurements were also performed in air and SF6 for comparison. Arc voltage was measured in each gas at pressures ranging from 1- to 5-bar absolute, and electrode separations ranging from 20 to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$95 \mathrm {~mm}$ </tex-math></inline-formula> . Voltage–current characteristic measurements for air and SF6 show good agreement with previously published results. A linear relationship of the arc voltage to the arc length is shown as well as the fourth root dependence of the arc voltage on the gas pressure. It was shown that neither the O2 nor the fluorinated additives to CO2 have any significant influence on the voltage–current characteristic. The minimum arc voltage in all measured gases was slightly higher than in SF6, but the arc in SF6 was the least stable and had the highest elongations resulting in high-voltage peaks. The arc voltage in air had a similar minimum value to the CO2-based gases, but the arc was much more stable, resulting in lower effective voltage, especially at low currents.

Surface discharge pattern of C4F7N/CO2 mixture under negative impulse voltages

Due to the excellent properties, C4F7N/CO2 mixture is the most concerned eco-friendly SF6 alternative gas. For a better understanding of the surface discharge characteristics, the surface discharge pattern of C4F7N/CO2 mixture under negative impulse voltages is investigated in this work. The morphology of the surface discharge is obtained by an optical method and a dust figure method. The structure of the surface discharge is established, which from the outside to the inside consists of electron cloud, streamer, streamer stem, and leader. The propagation pattern of the surface discharge in C4F7N/CO2 mixture under negative impulse follows the stepwise expansion pattern. The structure of the surface discharge in C4F7N/CO2 mixtures with different ratios and SF6 has no obvious difference, and the propagation pattern is also the same. The results of this work can help to better understand the surface discharge phenomenon and the insulation characteristics of C4F7N/CO2 mixture.

Influence of the mixed proportion on partial discharge decomposition properties of C 5 F 10 O/N 2 gas mixture

In recent years, C5F10O, as a potential SF6 alternative gas, has attracted extensive attention of researchers. C5F10O has high molecular freedom and strong energy absorption capacity. Due to the high fluorine content in C5F10O gas, it has excellent insulation characteristics, which is more than twice that of SF6 under the same conditions. It is considered to be the most potential SF6 alternative gas. As a new type of environmental protection insulating gas, there is little research on the decomposition characteristics of C5F10O mixed ratio mixed insulating gas at home and abroad. In this paper, the decomposition characteristics are analyzed by studying the content changes of CF4, C2F6, C3F8 and C3F6 in the decomposition products of C5F10O / N2 mixed gas. It is found that with the increase of the proportion of C5F10O, the decomposition products will decrease slightly.

AIMD calculation on electron ionization induced fragmentations of C 5 F 10 O and its discharge decomposition products

Recently, perfluoroketone C5F10O has been regarded as a promising alternative gas for SF6, of which the global warming potential (GWP) is extremely high. C5F10O has a good insulation property and the GWP value is only 1, thus can be used as insulation medium in gas-insulated switchgears. In this study, the decomposition products of C5F10O under partial discharges are detected and qualitatively analysed by gas chromatography-mass spectrometry (GC-MS). The stable products like C2F6, C3F6, C3F8, C4F10 and CF2O are formed. Meanwhile, to theoretically obtain the gas phase fragmentation pathways of C5F10O and its decomposition products upon 70eV electron ionization, a method of combined stochastic and ab initio molecular dynamics simulations are carried out. The calculation could be performed without preconceived fragmentation channels, which simulate standard electron ionization mass spectrometry (EI-MS) conditions. The significant peaks in the experimental mass spectrum of the molecules could be reproduced well, indicating that the simulation accurately predicts the decomposition channel after electron-impact ionization. Moreover, the fragmentation channels for C5F10O by 20 eV electron ionization, which is not standard in EI-MS but near the ionization threshold, are also calculated. We suggest that the quantum chemistry calculation method could provide an insight into fragmentation processes for different gases during discharges, which is still quite unclear for the novel SF6-alternative gases.

Adsorption behaviour of CF4 and COF2 gas on the GaN monolayer doped with Pt catalytic: A first-principles study

GaN is an n-type semiconductor with a wide band gap and has broad application prospects in the field of gas detection. This paper uses the first-principles to study the adsorptions of five typical decomposition gases (CF4, COF2, CO2, O2 and N2) of SF6 alternative gas C4F7N by Pt doped GaN (Pt-GaN) monolayer and explores the feasibility of its application in the detection of decomposition components of C4F7N. The results show that the adsorption capacity of Pt-GaN to O2 (-0.263 eV) is greater than the other four gases (<-0.800 eV), and the adsorption mechanism of Pt-GaN as a resistive sensor is analysed in combination with its charge density difference and density of states represented by CF4 and COF2. On the other hand, the theoretical response values of these gases are obvious, amongst them, the theoretical recovery time of CF4 is almost 0, and the theoretical recovery time of COF2, CO2 and O2 at 498 K is only 2.2 s, 0 s and 0.149 s, respectively, indicating that Pt-GaN has industrial advantages in gas detection. After the five gases are adsorbed, the trend of work function change is different, which provides the possibility for Pt-GaN to be used as a field-effect transistor sensor to selectively detect gases All the content in this article provides theoretical guidance for Pt-GaN as a gas-sensitive material to realize the detection of C4F7N decomposition components.

Conceptual Design and Feasibility Study of Flexible Gas-Insulated Transmission Line Using CF3I Gas Mixture

SF6 is widely used in high voltage equipment because of its outstanding characteristics as insulation medium. However, SF6 is a potent greenhouse gas, so its use and emission are regulated. CF3I has been investigated as a candidate for SF6 alternative gas, whose environmental impact is much less than that of SF6 and other fluorocarbon-based gases. In addition, a flexible gas-insulated transmission line (FGIL) is expected to be used for power transmission from offshore wind farms due to its high flexibility and low capacitance. In this paper, the feasibility of 22 kV class FGIL utilizing atmospheric pressure CF3I gas is evaluated from the viewpoint of withstand voltage with actual lightning impulse tests. The cross-sectional size of FGIL is determined by considering insulation condition, heat transfer condition, sheath electric field condition and spacer stress condition. The impulse tests for FGIL are conducted in straight and bent states, and it is revealed that the 50% breakdown voltage V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</sub> of straight state exceeded lightning impulse withstand voltage (LIWV) for 22 kV class, and that V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50</sub> of bent state falls below LIWV.

Study of partial discharge characteristics in HFO-1234ze(E)/N2 mixtures

HFO-1234ze(E)(trans-1,3,3,3-tetrafluoropropene, chemical formula: C3H2F4) is an extremely environmentally friendly SF6 alternative gas with high electrical strength. In this paper, the partial discharge (PD) characteristics of HFO-1234ze(E)/N2 mixtures were studied using the gas insulation test platform. The PD inception voltage of insulating gas under positive and negative half cycles of power frequency was tested. Using SF6/N2 mixtures as a control group, the effects of electrode spacing, mixing ratio and pressure on the insulation performance of HFO-1234ze(E)/N2 mixtures were explored. The test results show that the PD inception voltage of the negative half-cycle of pure HFO-1234ze(E) under short electrode spacing can reach 0.96–1.04 times of pure SF6 under different pressures; the PD inception voltage of 40%HFO-1234ze(E)/60%N2 mixtures at 0.3 MPa is 0.67–0.89 times that of SF6/N2 mixtures under the same conditions, which has great application prospect.

Study on the insulation characteristics of environmentally friendly CF3I/N2/CO2 mixed gas

AbstractSF6 gas is a kind of gas medium widely used in the insulation of power equipment. However, due to the greenhouse effect of SF6, new environmentally friendly gas that can instead of SF6 has been the goal for researchers. CF3I gas is one of the most promising alternative gases for SF6. In this paper, two-term Boltzmann equations of CF3I/N2/CO2 ternary gas mixture at 0.1 MPa and 300 K are calculated to obtain an electron energy distribution function (EEDF), an electron drift velocity Ve, a critical fold breakdown field strength (E/N)cr of the ternary mixed gas, and the synergy effect coefficient is used to analyze the synergy effect between the mixed gases. The calculation results show that the CF3I/N2/CO2 ternary mixture has a synergistic effect, and the 50% CF3I/40% N2/10% CO2 ratio scheme makes the mixed gas most likely to replace SF6 from the physicochemical properties. Comparing the calculated data of this paper with the data of other works of literature, the validity of the calculation method and calculation data in this paper is verified, which provides theoretical support for the research of SF6 alternative gas.

Theoretical and experimental investigation on decomposition mechanism of eco-friendly insulation gas HFO1234zeE

Decomposition experiments under corona discharge and theoretical calculations using the density functional theory (DFT) method were accomplished to clarify the dissociation behavior and decomposition mechanism of HFO1234zeE (trans-1,3,3,3-tetrafluoropropene), an eco-efficient SF6 alternative gas. The discharge decomposition products of HFO are mainly fluorocarbon, unsaturated hydrocarbon and saturated hydrocarbons, which are containing no more than three carbons. Free radicals, CF3·, F· and H·, generated via bond-cleavage reaction are important structures to promote the decomposition, and HFO is more likely to dissociate with them by abstraction reaction to form CF4 and CF3H. Long-chain radicals, such as CF3CHCF·, CF3CHCH· and CF3CCHF·, will be decomposed into CF3CCH and CF3CCF, and small intermediates would be easier to combine to form HF, C2F6, C2F4, C2HF5, CF3HCF3H and C3F8. It is also likely to be converted to Z-isomer. Due to the high discharge intensity and ion bombardment, solid by-products appeared on the electrode surface may contain carbon dust and metal compounds. The solid attached to the surface has little effect on the electric field distribution, and most gas decomposition products still maintain the insulation strength, so the air-gap breakdown voltage only dropped by about 6.2% after long-term corona discharge. The obtained results not only reveal the decomposition mechanism in a comprehensive way, but also present useful reference for exploring the application potentials of HFO1234zeE.

Research status of replacement gases for SF6 in power industry

SF6 is widely used in the industrial field due to its stable structure and excellent properties. It is mainly used in electrical insulation equipment. Due to the boiling point of SF6, its use in extremely cold regions has been limited. It is harmful to the health of practitioners due to the toxicity of decomposition products. The gas has limited its wider use because of its strong greenhouse effect. As a result, researchers and electrical equipment manufacturing companies around the world are gradually searching for new environmentally friendly gases and have conducted research and exploration on theory and experiment. In this paper, the current status and existing problems of SF6 are summarized. The research contents and research methods of SF6 alternative gas direction are reviewed from the aspects of insulation performance, interrupter performance, and decomposition performance. The existing research results of the natural gas, SF6 mixed gas, perfluorocarbons, and CnFmX gas are summarized, and the future development trend of alternative gas for SF6 in the electrical industry is proposed.

Production of Graphite During the Extinguishing Arc with New SF6 Alternative Gases

Most high voltage circuit breakers in operation use SF6 as the arc interruption medium because of its high dielectric strength and good arc interruption properties. However SF6 also displays a high global warming potential which motivates the investigation of possible alternatives such as CO2–Novec™4710 and N2–Novec™5110 mixtures proposed by different HVCB manufacturers. CB power test comparison between pure CO2 and CO2–Novec™4710 mixture shows that the latter created a large amount of graphite and reduced CB performances after several current breaking shots. Using Gibbs free energy method, a theoretical study has been conducted on SF6 replacement candidates listed above. Aiming to understand graphite formation, several parameters impact were discussed: carrier gas such as CO2 and N2, pressure and O2 initial mixture proportions. The study focuses on graphite condensation temperature and graphite production amount evolutions in respect to the study parameters as well as in respect to CB inter-contacts space condition in terms of pressure and temperature at current-zero. It has been shown that a high percentage of CO2 in the mixture reduces graphite condensation temperature by 2600 K while adding N2 do not make such an impact. Pressure increases graphite condensation temperature and O2 reduces it. The amount of graphite produced is pressure independent but decreases with the increase of O2 proportion in the initial mixture. It has been shown that adding a sufficient O2 amount can prevent graphite production at all.