China
Africa
Explore chapters and articles related to this topic
Circuit Protection, Vacuum Circuit Breakers, and Reclosers
Published in Paul G. Slade, The Vacuum Interrupter, 2020
One disadvantage of SF6 is that it is a greenhouse gas [115] and its use is generally being discouraged. To overcome this disadvantage, manufacturers who use SF6 for insulation have developed hermetically sealed designs that prevent the gas from leaking into the environment. It is possible to reduce the amount of SF6 and maintain about 86% of its dielectric strength of ~9kV/mm (at 1 atmosphere) by adding up to 60% N2 [116], see Table 6.14. Nitrogen by itself is a reasonable dielectric gas with about 39% the dielectric strength of SF6. Its dielectric strength can be doubled by adding as little as 10% SF6. The effect of adding SF6 to a poor dielectric gas such as He can be quite dramatic as can also be seen in Table 6.14. There have been suggestions of using other gases and gas mixtures gases to replace SF6 One example presented by Widger et al. [117] for use in ring main units (see Section 6.8.4) is a mixture of trifluoroidomethane (C3F3I) and carbon dioxide (CO2). Investigations using C3F3I–CO2 ratios of 30% to 70% demonstrate promising insulation properties. The global warming potential of CF3I is less than 5 compared to that of SF6. which is 22,500. Zhou et al. [118] have analyzed the dielectric performance of C3F3I–N2 gas mixtures using a sphere-to-plane electrode system. Figure 6.58 shows a comparison of the dielectric performance for CF3I–N2(20/80) with SF6–N2 (20/80) and pure SF6. The lightning impulse withstand voltage (BIL) for CF3I–N2(20/80) is 90% of that for SF6–N2 (20/80) and 77% of that for pure SF6. One disadvantage is C3F3I’s high boiling point of–22C. Other gas mixtures discussed by Guo et al. [119] are the perfluoronitriles (PFN) (e.g., C4-PFN or (CF3)2CFCN) and perfluoroketons (PFK) (e.g., CF5-PFK or CF3COCF(CF3)2) mixed with air, CO2, and SF6. Again, these gases also have high boiling points. I expect that the search to find an effective insulating gas or gas mixture to replace SF6 will continue.
Assessing the performance of air, argon, and oxygen as dielectric mediums during dry-micro-EDM of Ti6Al4V alloy: A comparative study
Published in Materials and Manufacturing Processes, 2023
Ramver Singh, Tanmay Tiwari, Akshay Dvivedi, Pradeep Kumar
The current study was performed using a locally customized 3-axis computer numerical controlled (CNC) electrical discharge machine (Make: Excetek; Model 30C). The machine, which was outfitted with a transistor-type pulse generator, could produce a spark discharge with a minimum length of 1 µs and a minimum pulse current intensity of 1 A. As a result, the chosen machine was suited for performing micro-EDM operations. Modifications were necessary, however, to deliver a gaseous dielectric medium into the machining zone between the tool and work electrodes. The dielectric gas was supplied via the nozzles, as indicated in Fig. 1.
Determination of the relative humidity at the parts-per-million (ppm) level in gases by a nanoporous alumina thin-film on a surface acoustic wave (SAW) resonator
Published in Instrumentation Science & Technology, 2022
Shamim Alam, Shakeb A. Khan, Upendra Mittal, Tarikul Islam
Moisture measurement in ppm level in gases is essential for applications including semiconducting device fabrication, packaging for increasing food life, incandescent bulb production, avoiding explosions in chemical plants, soldering of electronic components, minimization of corrosion of stainless-steel (ss) during electroplating, to flash out oxygen during a fire in mining industry, and monitoring the electrical apparatus in smart grids.[1–3] Dried and pressurized nitrogen gas is used as a dielectric gas for high voltage equipment. Ammonium nitrate, gunpowder, and solid fuel are extremely moisture sensitive materials and are rendered ineffective if stored in uncontrolled atmospheric conditions. In all such cases, dry nitrogen gas is used.[4] Therefore, moisture in nitrogen gas even at ppm level has detrimental effects on various products and their performances. It is difficult to detect such a low concentration of water molecules by a relative humidity sensor. Numerous research articles are reported in various journals for the measurement of humidity from 10 to 98 percentage relative humidity (% RH). Large concentrations of water vapor in air are easily measured using a capacitive or a resistive sensor.[5] Various nanostructure porous hygroscopic materials have been investigated for the measurement of relative humidity but the literature for moisture measurement in ppm is limited.[5–6] Conventionally, the chilled mirror hygrometer, and the optical spectroscope are used for ppm moisture measurements but these techniques are costly, require skilled professionals, and are unsuitable for field use.[7–8] Efforts are also made to use the capacitive hyper thin-film sensor for ppm moisture measurement. However, the size of the sensor is large, and mostly uses costly gold electrodes for fabrication, although low cost fluorine doped tin oxide metal has also been reported.[3] Some commercial dew point meters which are based on porous aluminum oxide capacitive sensors are used for ppm moisture detection but have relatively long response times and are expensive.[9–11] The quartz crystal microbalance with polymer film is reported for low humidity measurement but has low sensitivity.[12]