Study on oxygen/nitrogen gas mixtures for the surface insulation performance in gas insulated switchgear

Abstract

This paper presents a comparative study on SF 6 alternative candidate gases for the surface insulation performance of eco-friendly Gas Insulated Switchers (GIS) and Solid Insulated Switchers (SIS). The candidate gases including N 2 /O 2 mixture gas, dry air, and compressed air were proposed based on AC surface flashover experiment. These gases were compared and examined based on their surface insulation performance, pressure and gap dependence, surface insulation reliability in different temperatures, economic feasibility and easiness of manufacture. The comparison results verified that dry air had excellent properties on the comparison criteria and was the most suitable eco gas among the candidate gases for eco-friendly GIS and SIS. In addition to the comparative study on the candidate gases, their surface flashover characteristics were described in detail based on the effect of moisture contained in the candidate gases on flashover voltage and the correlation among electric field intensity, collision-ionization coefficient, electron attachment coefficient, and gap length.

Insulation Strength and Decomposition Characteristics of a C6F12O and N2 Gas Mixture

“…The results, before and after the breakdown, are shown in Figure 4. According to standard gas and the corresponding GC-MS spectra similarity detection report (see Figure 5), the main decomposition products of compounds can be produced by the fluorocarbon compounds such as CF 4 , C 2 F 6 , C 3 F 8 , C 3 F 6 , C 4 F 10 , and C 5 F 12 . The characteristic peaks of C 3 F 6 and C 4 F 10 overlap.…”

“…The molecular structure of C6F12O indicates that the formation of the products is mainly due to the formation of free radicals by the breaking of C-C bonds, and the free radicals are bonded to form the corresponding compounds. 4 Impurity Figure 4. Test results of C6F12O/N2 mixed gas decomposition components.…”

“…The experimental detection of the C 6 F 12 O reaction with N 2 shows that the main products are CF 4 , C 2 F 6 , C 3 F 8 , C 3 F 6 , C 4 F 10 , and C 5 F 12 , and these products also have certain insulation performance. The decomposition process is calculated using density functional theory (DFT), and the insulating property of several kinds of decomposition products is analyzed by calculating the ionization energy of the molecules, affinity energies, and molecular orbital gaps.…”

“…The free radicals, such as CF 3 •, C 2 F 5 • and C 3 F 7 •, can produce F atoms by bond breaking reaction and form relatively stable fluorocarbon compounds, such as CF 4 , C 2 F 6 , C 3 F 8 , C 3 F 6 , C 4 F 10 , and C 5 F 12 , between the radical combination process, as shown in Figure 7. CF 3 • can be derived from the C 1 -C 2 breaking and the C 4 -C 5 or the C 4 -C 6 breaking (shown in Figure 5).…”

“…To obtain the equivalent of SF 6 gas dielectric strength, the pressure of N 2 must be increased to 3-4 times of SF 6 given that the insulation strength of pure N 2 is low [3]. Korea Hyundai Heavy Industries [4], Toshiba, and other researchers have used air-solid composite insulation technology to enhance the role of its insulation [5]. The results show that the appropriate insulation materials on the high electric field electrode surface coating can effectively improve its electrical strength.…”