Insulation properties of a CO2/N2 50% SF6 gas mixture in a nonuniform field

Abstract

AbstractThis paper describes partial discharge (PD) inception and breakdown voltage characteristics of a CO2/N2/SF6 gas 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 SF6 gas and the gas pressure from 0.1 MPa to 0.6 MPa. It was found that adding a small amount of CO2 gas into a N2/SF6 mixture causes a drastic increase in the breakdown voltage. For instance, when the mixture rate of SF6 in N2/SF6 gas mixture is 50%, with the addition of 1% CO2 the maximum breakdown voltage becomes 1.31 and 1.15 times higher than that of a 50% N2/50% SF6 gas mixture and pure SF6 gas, respectively. Moreover, those voltage characteristics of a CO2/N2/SF6 gas 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/SF6 gas 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