Influence of O2 on the dielectric properties of CO2 at the elevated temperatures

Abstract

SF 6 gas is widely used in the high voltage circuit breakers but considering its high global warming potential other substitutes are being sought. Among them CO 2 was investigated and even has been used in some practical products. However, at room temperature, the dielectric properties of CO 2 are relatively lower than SF 6 and air. The goal of this work is to investigate a CO 2 -based gas to improve the performance of the pure CO 2 . In this paper, the dielectric properties of hot CO 2 /O 2 mixtures related to the dielectric recovery phase of the circuit breaker were investigated in the temperature range from 300 K to 4000 K and in the pressure range from 0.01 MPa to 1.0 MPa. The species compositions of hot CO 2 /O 2 were obtained based on Gibbs free energy minimization under the assumptions of local thermodynamic equilibrium and local chemical equilibrium. The reduced critical electric field strength of CO 2 /O 2 was determined by balancing electron generation and loss. These were calculated using the electron energy distribution function by solving the Boltzmann transport equation. The validity of the calculation method and the cross sections data was confirmed by comparing the measurements and calculations of the electron swarm data in previous work. The results indicate that in pure CO 2 the critical electric field strength is higher only in higher temperature range. By adding the O 2 into the CO 2 , the critical electric field strength at lower temperature is effectively enhanced. CO 2 /O 2 mixtures have a much better dielectric strength than both the pure CO 2 and air and thus have the potential to improve the CO 2 -based gas circuit breakers. Similar conclusions can also be found in others' work, which further confirm the validity of these results. V C 2014 AIP Publishing LLC. [http://dx.

Influence regularity of O 2 on dielectric and decomposition properties of C 4 F 7 N–CO 2 –O 2 gas mixture for medium‐voltage equipment

“…The influence of O 2 on the dielectric properties of CO 2 at the elevated temperatures in discharge explored by Rong et al [41] also indicates that CO 2 –O 2 mixtures have a much better dielectric strength than both the pure CO 2 and air. It was pointed out that the electron energy distribution function increase with O 2 content due to the vibrational cross‐sections of O 2 is smaller than that of CO 2 .…”

“…In addition, the increase of η/N is attributed to the strong electronegativity of O 2 . Furthermore, the attachment cross-section of O 2 is larger than CO 2 for electron energy around 5-10 eV, which could lead to a reduction of the electron kinetic energy [40] The influence of O 2 on the dielectric properties of CO 2 at the elevated temperatures in discharge explored by Rong et al [41] also indicates that CO 2 -O 2 mixtures have a much better dielectric strength than both the pure CO 2 and air. It was pointed out that the electron energy distribution function increase with O 2 content due to the vibrational cross-sections of O 2 is smaller than that of CO 2 .…”

Equivalence between C5F10O Addition and PTFE Vapor Contamination in the Particle Composition and Critical Electric Field Strength of High‐Temperature CO2/O2 Gas Mixture

“…Alternative arc-extinguishing gases for gas circuit breakers are roughly categorized into two types, natural gases such as CO 2 , N 2 , O 2 , and so on, and artificial gases such as C 5 F 10 O, CF 3 I, C 4 F 7 N, and so on. As specifically proposed examples, CO 2 and its combinations, such as CO 2 /O 2 , CO 2 /C 5 F 10 O, CO 2 /CF 3 I, CO 2 /O 2 /C 4 F 7 N, and CO 2 /O 2 /C 5 F 10 O, have been researched [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. Here, the artificial gases should be mixed with natural gases, and not be used alone, because of their high liquefying temperature.…”

Boltzmann equation studies on electron swarm parameters for oxygen plasma by using electron collision cross – sections

“…were calculated at condition that reduced ionization coefficient (α/N) and reduced attachment coefficient (η/N) are in equilibrium, therefore the effective ionization coefficient equal to zero ( = (α/N)-(η/N) =0), this method was used by (Láska et al, 1984;Brand and Kopainsky, 1979;Itoh et al, 1980; to calculate electrical breakdown voltage using two-term approximation solution of Boltzmann equation. Critical field strength have been studied by both theoretical calculations (Tanaka, 2004;Rong et al, 2014;Zhao and Lin, 2016; and experimentally to find new gases with high dielectric field strength which used in electrical insulator, for example, experimentally (Xiao et al, 2018) reported that small addition of oxygen O 2 reduced breakdown voltage of the c-C 4 F 8 /N 2 mixed gas. (Beaty, et al 1979 andDutton, 1975) published a large data on the electron swarm parameters in number gases over a wide range of electric field strength E/N.…”