Effects of Oxygen on the Insulation Characteristics of Eco‐Friendly Insulating Gas HFO‐1336mzz(E)/CO2

D.c. breakdown voltage characteristics in supercritical helium: breakdown in nonuniform fields

The application of eco‐friendly C 4 F 7 N/CO 2 gas mixture has become a hot topic in the power industry. To obtain the influence law of micro‐water on the AC insulation characteristics of C 4 F 7 N/CO 2 gas mixture, breakdown tests were carried out under different non‐uniform electric fields and micro‐water volume fractions. With the gap distance of 1 mm and the electric field non‐uniform coefficient less than 4.42, the breakdown voltage is positively correlated with gas pressure. With the gap distance of 6 mm and the electric field non‐uniform coefficient of 9.28, the breakdown voltage shows a typical N‐type change trend with the increase of gas pressure. With the gap distance of 9 mm and the electric field non‐uniform coefficient up to 16.45, the breakdown voltage shows a typical N‐type change trend with the increase of gas pressure. Micro‐water has a negative effect on breakdown voltage under different electric fields, meanwhile the breakdown voltage of slightly non‐uniform electric field is greatly affected by micro‐water, and the influence of micro‐water on breakdown voltage is different under different gas pressures. Therefore, the influence of operating gas pressure and slightly non‐uniform electric field should be considered when the micro‐water control index of C 4 F 7 N/CO 2 gas mixture insulated equipment is formulated.

SF6 gas is considered as one of the most noxious kinds of atmospheric greenhouse gases with global warming potential (GWP) 23,500[10] times higher than that of CO2 and shelf life of 3200 years in the atmosphere. With threat of global climate change, policy makers all over the world have made regulations which promote renewable energy technologies. Developing countries including India are increasingly emphasising the need to rapidly restructuring of their energy system. A replacement for SF6 has been in testing and development for over a decade and have come up with different combination of gas and gas mixtures like N2, CO2, CF3I (Trifluoroiodo-methane), C4-fluoronitrile and C5-Fluoroketones along with different combination of the later with SF6. In recent years many gases are being investigated for breakdown voltage and partial discharge characteristics, such as C5F10O (C5 per uorinatedketone), C5F10O/N2 mixture, SF6 and CO2 gas mixture, Pd3-TiO2(101) (Titanium dioxide), C4F7N/CO2 mixed gases (Fluro nitrile and carbon dioxide), HFO-butene/ CO2 gas mixture (Hydrofluroolefin).

Sulfur hexafluoride (SF6) is widely used in the power industry because of its excellent insulation and arc extinguishing performance; however, as the global environment is deteriorating, the need to replace SF6 is becoming significantly critical. In recent years, C5F10O has received extensive attention as a potential alternative to SF6. In this study, a part of N2 in C5F10O/N2 was replaced by O2, and the breakdown voltages of C5F10O/N2/O2 at different oxygen concentrations under a slightly uneven electric field were tested. The dispersion of breakdown voltage and the discharge decomposition components of C5F10O/N2/O2 with different oxygen concentrations were analysed. It was found that as the oxygen concentration increased, the breakdown voltage of C5F10O/N2/O2 with 15 kPa C5F10O at 0.2 MPa increased, and the dispersion of the breakdown voltage became worse. When 0.5% O2 or more O2 was added to the C5F10O/N2 gas mixture, the carbon precipitates on the electrode surface disappeared. As the oxygen concentration continued to increase, another characteristic component, CF2O, could be detected, whereas C2F4 and C3F6 disappeared. It is believed that O2 can inhibit the formation of C2F6, C3F8, C4F10, and C3F7H. Therefore, it is recommended to use oxygen as the second buffer gas for the engineering applications of C5F10O. Moreover, the ratio of C5F10O to O2 is recommended to be 1 : 1.

Pressurized oxy-fuel combustion characteristics of single coal particle in a visualized fluidized bed combustor

This paper investigates C4H2F6, a promising environmentally friendly insulating gas that possesses high dielectric strength and a low global warming potential. The study focuses on examining the insulation properties of C4H2F6 when combined with CO2/N2, aiming to assess its suitability as a substitute for SF6 in gas-insulated applications. Finite element analyses are performed to evaluate the field utilization factor and electric field distribution in the proposed mixture. The properties of liquefaction temperature were examined in this study to determine the optimal mixing ratio for applications that require a minimum working temperature. Extensive experimental investigations were carried out to assess the dielectric strength characteristics of the gas mixture in both uniform and quasi-uniform electric fields. It was found that pure HFO-1336mzz (E) exhibits a dielectric strength approximately 1.2–1.6 times higher than SF6. Experimental results have revealed that the insulation performance of a 30% HFO-1336mzz (E)/CO2 mixture closely resembles that of SF6, with a matching efficiency of up to 90% in a weakly uniform electric field. This remarkable performance can be attributed to a positive synergistic effect between HFO-1336mzz (E) and CO2, combined with the gas mixture’s excellent self-recoverability property. These experimental findings are further supported by finite element analysis, which confirms the observed results. The 30% HFO-1336mzz (E)/CO2 gas mixture at 0.15–0.20 MPa pressure and constant 0.6 mm air gap reveal superior insulation tolerance and less sensitivity to the electric field, confirming its promising medium-voltage engineering applications. The associated results of this research provide a critical reference for the engineering application of the alternating (AC) and direct current (DC) insulation characteristics of the HFO-1336mzz (E)/CO2 gas mixture.

Upper drift region double step partial SOI LDMOSFET: A novel device for enhancing breakdown voltage and output characteristics

This paper describes partial discharge (PD) inception and breakdown voltage characteristics of a CO2/N2/SF6gas mixture in a nonuniform field. These voltage characteristics were investigated with ac high voltage by changing the mixture rate of each gas of CO2, N2, and SF6gas and the gas pressure from 0.1 MPa to 0.6 MPa. It was found that adding a small amount of CO2gas into a N2/SF6mixture causes a drastic increase in the breakdown voltage. For instance, when the mixture rate of SF6in N2/SF6gas mixture is 50%, with the addition of 1% CO2the maximum breakdown voltage becomes 1.31 and 1.15 times higher than that of a 50% N2/50% SF6gas mixture and pure SF6gas, respectively. Moreover, those voltage characteristics of a CO2/N2/SF6gas mixture were also investigated by changing the electric field utilization factor as well as by applying positive and negative standard lightning impulse voltages in order to discuss the corona stabilization effect, which seems to be one reason for the drastic increase in the breakdown voltage. These results and breakdown mechanism of the CO2/N2/SF6gas mixture are discussed on the basis of the corona stabilization effect and the dissociation energies of the component gases by observing PD light images, PD light intensities through a blue and red filter, and PD current waveforms. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(3): 34–43, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10019

Plasma breakdown of low-pressure gas discharges

Experimental investigation on the NO formation of pulverized coal combustion under high-temperature and low-oxygen environments simulating MILD oxy-fuel combustion conditions

This study investigates the breakdown voltage characteristics in SF6 circuit breakers, employing a novel approach that integrates both experimental investigations and finite element simulations. Utilizing a sphere-sphere electrode configuration, we meticulously measured the relationship between breakdown voltage and electrode gap distances ranging from 1 cm to 4.5 cm. Subsequent simulations, conducted using COMSOL Multiphysics, mirrored the experimental setup to validate the model's accuracy through a comparison of the breakdown voltage - electrode gap distance curves. The simulation results not only aligned closely with the experimental data but also allowed the extraction of detailed electric field strength, electric potential contours, and electric current flow curves at the breakdown voltage for gap distances extending from 1 to 4.5 cm. Extending the analysis, the study explored the electric field and potential distribution at a constant voltage of 72.5kV for gap distances between 1 to 10 cm, identifying the maximum electric field strength. A comprehensive comparison of five different electrode configurations (sphere-sphere, sphere-rod, sphere-plane, rod-plane, rod-rod) at 72.5kV and a gap distance of 1.84 cm underscored the significant influence of electrode geometry on the breakdown process. Moreover, the research contrasts the breakdown voltage in SF6 with that in air, emphasizing SF6's superior insulating properties. This investigation not only elucidates the intricate dynamics of electrical breakdown in SF6 circuit breakers but also contributes valuable insights into the optimal electrode configurations and the potential for alternative insulating gases, steering future advancements in high-voltage circuit breaker technology.

Breakdown voltage versus gap length characteristics were obtained for dehydrated transformer oil and oil containing emulsion droplets of water with fibrous impurities. In general, the breakdown voltage increases with increasing oil gap spacing between electrodes. The breakdown voltage values are higher when aluminum electrodes rather than stainless steel electrodes are used. The breakdown voltage for oil containing emulsion droplets of water by (0.2% by mass) was decreased by about 50% as compared with dehydrated oil. The breakdown voltage decreases with increasing temperature. When an insulating oil was subjected to an impulse electric field between aluminum and stainless steel electrodes, the dielectric loss increased with increasing electric field. The measured increase in the dielectric loss coincides with the visually detected onset of liquid motion. >

In recent years, SF 6 /N 2 gas mixtures with low SF 6 mixing ratio was getting used as insulating medium in gas-insulated metal-enclosed transmission line in order to replace pure SF 6 . For the application of SF 6 /N 2 gas mixtures in power equipment, this paper studied on the breakdown characteristics of SF 6 /N 2 gas mixtures with low SF 6 mixing ratio in different electric field non-uniformity under power frequency voltage, and the characteristic of partial discharge initial voltage was studied in non-uniform electric field. In order to study the breakdown characteristic of SF 6 /N 2 gas mixtures under high voltage grade, a fully enclosed power frequency voltage test device was set up. The sphere-plane and rod-plane electrodes were used to simulate the slightly non-uniform field and local-field enhancement in GIS or GIL. The research indicates that the breakdown voltage of SF 6 /N 2 gas mixtures increases linearly with increase of gas pressure in slightly non-uniform electric field. With the increase of the electric field non-uniformity, the linearity of breakdown voltage weakens and the stable corona discharge appears. Because of the space charge effect, the N-curve characteristic of breakdown voltage appears in SF 6 and its mixtures. When electric field non-uniformity exceeds a certain value, the stable corona discharge appears before the electric breakdown of electrodes gap. But the breakdown occurs immediately with the appearance of corona when the gas pressure exceeds a certain value. Meanwhile, the synergistic effect was strengthened and then weakened. And the amplitude and range of N-curve extend when electric field non-uniformity increased.

Metallic particle contamination is one of the areas of insulation design that are considered critical. This paper demonstrates the control of metallic particles in gas insulated bus duct (GIBD) by using dielectric coating on the inside surface of the outer enclosure of a coaxial electrode system. Several models of GIBD with single and multi-contaminating particles will be studied. In this paper, the Finite Elements Method (FEM) is used to evaluate the electric field distribution on and around single and multi-contaminating wire particles which in contact with dielectric coating of earthed enclosure inside GIBD. The effect of changing the length and the radius of middle particle for multi-contaminating particles on the electric field values are studied. Breakdown Voltage calculations for gas mixtures with single and multi-contaminating wire particles are studied. The effects of gas pressure on the breakdown voltage for various fractional concentrations of SF 6 -gas mixtures with and without particle contamination and also with and without coating of earthed enclosure are studied. The optimum gas mixture which gives higher dielectric strength with lower cost is also determined. The effect of coating thickness of earthed enclosure on the breakdown voltage for various fractional concentrations of SF 6 -gas mixtures is also studied. Finally, the effect of length and hemi-spherical radius of multi-contaminating particles on the breakdown voltage with various SF 6 -gas mixtures and varying gas pressure one time and another time with fixed pressure are studied. DOI: http://dx.doi.org/10.11591/ijece.v4i4.5693

Ar:CO2 gas mixtures have recently received research interest due to the possibly beneficial effects of Ar addition to CO2 for CO2 conversion using electrical discharges. For any gas discharge, knowledge of fundamental parameters, such as the effective ionization coefficient, is necessary to optimize the efficiency of the discharge for a particular application. The reduced apparent effective ionization coefficient αea/N is a measure of total ionization. αea/N is influenced by electron impact ionization, electron attachment and also by charge transfer reaction, Penning ionization, and photoionization. This study determined the αea/N of Ar:CO2 gas mixtures in the pressure range of 10–800 Torr and reduced electric field strength E/N range of 40–1200 Td utilizing a steady-state non-self-sustaining Townsend discharge. Experimental results were compared with calculations of Boltzmann equation solver BOLSIG+. Differences between measurements and calculations increased with decreasing CO2 content in the mixture down to 20%, and the differences were highest at low E/N values (below 150 Td). As the simple modification of the model, contribution of ionization of CO2 by Penning transfer from Ar* 3p53d excited states (13.86 eV) was added to the BOLSIG+ calculations, which resulted in good fit of the experimental measurements. Comparison of CO2 addition to Ar with the addition of O2 or N2 revealed that ionization of CO2 or O2 from Ar* 3p53d excited states influences ionization in Ar:CO2 and Ar:O2 mixtures but not in Ar:N2 mixtures, due to the different ionization energies of CO2, O2, and N2.