Pulse Breakdown of Overvolted Gaps Filled with CO2

Strong demand for low environmental impact fluids in high voltage power and pulsed power systems drives research in the field of breakdown and recovery properties of common gases such as air, nitrogen, carbon dioxide and their mixtures. Although the dielectric characteristics of these gases have been studied for many decades, their impulsive breakdown properties in overvolted gaps and in strongly non-uniform fields are not fully understood. This work is aimed at the study of the breakdown properties of CO2 in divergent electric field under impulsive stress. Breakdown voltage, Vbr, and time to breakdown, tbr, have been measured in an overvolted gap stressed with sub-microsecond positive high voltage impulses with a nominal rate of voltage rise of (1.2-1.4) kV/ns. The gas pressure was in the range from atmospheric pressure up to 5-bar (gauge). The reduced breakdown field, E/N, where N is the gas number density, and E is the field at the tip of the needle electrode have been obtained using an electrostatic model. The scaling relationships i.e. the functional relationships between E/N and Ntbr and Nd, have been obtained and compared with data from the literature for lower values of E/N.