Study of partial discharges and gassing phenomena within gaseous cavities in insulating liquids

Gassing phenomena under an AC voltage in various dielectrics liquids subjected to partial discharges produced in different gases are discussed. The roles of the numerous experimental parameters which affect the results have been studied using a uniform field test cell. It is shown first that from the classical PD equivalent circuit, a more refined analysis permits a good description of the influence of parameters such as gas and solid thickness as well as the amplitude and frequency of the applied voltage on gas volume variations, and discharge characteristics. This allows one to get suitable measurement of the charge and energies involved in the gaseous discharges, from which one can deduce the energy required to absorb (or to create) a gas molecule. This gassing energy, which is independent of the experimental parameters, is characteristic of each gas/liquid pair and constitutes a valuable quantitative evaluation of the gassing properties