# Green Gas for Grid as an Eco-Friendly Alternative Insulation Gas to SF\({}_{6}\): A Review
## 3 Green Gas for Grid
Figure 1: AC breakdown voltage depending mixture ratio and gas pressure [66]. Figure 2: DC breakdown strength of the NovecTM 4710/carbon dioxide (CO\({}_{2}\)) mixture depending on gas ratio and pressure [57]. The switching bus-transfer current test was carried out on a 420 kV disconnector over a 100 close and open operation under 1600 A and 20 V. Comparison of the arcing time between \(\mathrm{Novec^{TM}}\) 4710/CO\({}_{2}\) gas mixture and SF\({}_{6}\) is shown in Figure 4. It indicates that the arcing time of g3 gas proved to be stable, and the average arcing time is about 12 ms, compared with a typical value of 15 ms for SF\({}_{6}\)[67]. The arc-quenching capability was verified according to IEC 62271-100, also indicating that g3 gas maintained the appropriate dielectric withstanding ability after repeated interruptions [68; 71; 72]. Temperature rise tests of g3 gas were performed on a fully equipped three-phase GIS bay, and the results are shown in Figure 5. There were temperature rise differences of 5 K to 6 K between the gas mixtures and SF\({}_{6}\)[26; 67]. The temperature rise can be compensated for by typical measures such as adding cooling fins to the enclosure or machining slots and holes to conductors to improve convection around live parts of the GIS. Figure 4: Arcing time of \(\mathrm{Novec^{TM}}\) 4710/CO\({}_{2}\) gas mixture and SF\({}_{6}\)[26]. Figure 3: Partial discharge inception voltages of SF\({}_{6}\) and g3 in the protrusion defects [70]. NovecTM 4710 has a liquefaction temperature of -4.7 \({}^{\circ}\)C at 0.1 MPa, which makes it impossible to be applied in gas-insulated power facilities alone. N\({}_{2}\) or CO\({}_{2}\) is used as a buffer gas to increase the liquefaction temperature. The liquefaction temperature of NovecTM 4710/N\({}_{2}\) and NovecTM 4710/CO\({}_{2}\) gas mixture at different gas ratios and pressures can be calculated according to Equation (1). The results are illustrated in Figure 6. To meet the minimum ambient operating temperature requirement of -30 \({}^{\circ}\)C, NOVECTM 4710 should be at least at 13% at 0.2 Mpa in the NovecTM 4710/N\({}_{2}\) and NovecTM 4710/CO\({}_{2}\) mixture. Materials of the gas-insulated structure have been found to be compatible with the NovecTM 4710. There is no research so far indicting the chemical reaction of NovecTM 4710 with other materials. According to Equation (3), the GWP of g3 gas mixed with CO\({}_{2}\) or N\({}_{2}\) can be calculated according to the Intergovernmental Panel on Climate Change and the Regulation No 842/2006 of the European Parliament and the Council of 17 May 2006 on Certain Fluorinated Greenhouse Gases [62, 63]. Figure 7 shows the GWP of the g3 gas mixture with NovecTM 4710 ratio up to 20%. The GWPs of 20% NovecTM  
Figure 5: Temperature rise results in switchgear (GIS) filled with the NovecTM 4710/CO\({}_{2}\) gas mixture and sulfur hexafluoride (SF\({}_{6}\)) [67]. Figure 6: Liquefaction temperature of the gas mixture at different gas ratios and pressures. (a) NovecTM/Nitrogen (N\({}_{2}\)) [27] and (b) NovecTM/CO\({}_{2}\)[58]. 4710/80% CO\({}_{2}\) and NovecTM 4710/80% N\({}_{2}\) are 1104 and 1334, which are only 4.7% and 5.7% that of SF\({}_{6}\), respectively. Therefore, the application of g3 gas results in a significant reduction in GWP. In addition, g3 gas has an ODP of zero, and its atmospheric lifetime is much shorter than that of SF\({}_{6}\). g3 is not a carcinogenic and mutagenic gas, and is classified as nontoxic, nonflammable, and nonexplosive [61; 70]. g3 gas has been verified as an effective and high-performance substitute of SF\({}_{6}\) for environmentally sustainable high-voltage applications. At present, g3 gas-insulated power facilities are commercially available for GIS up to 145 kV, GIL and GCB up to 420 kV, and GIT up to 245 kV, after stringent laboratory and equipment testing [30]. These facilities feature the same dimensional footprint as SF\({}_{6}\) equipment, while significantly reducing greenhouse gas emissions.