Microdischarges and Microdischarge Simulation in Uniform-Field High-Voltage Vacuum Gaps

It is shown that microdischarges can be caused to occur between vacuum insulated electrodes by exposing the electrode surfaces to oil contamination or to the condensation of electronegative gases (H2O, CO2). The presence of the condensed H2O layers at low electrode temperatures lowers the microdischarge onset by a factor of 3 and the implication of this for microdischarge theory and vacuum cable development are discussed. A theory is presented which enables the onset of breakdown in the gas released by the microdischarge to be calculated.