Vapor-mist dielectrics

Abstract

Although it is well known that particles reduce the strength of many dielectrics, it was recently discovered that a dense mist of micron-size liquid droplets in an insulating gas actually can considerably increase its electrical breakdown strength. As an example, the strength of SF6 at one atmosphere (0.1 MPa) pressure doubled when mixed with a dense mist of C2Cl4; and at ∼0.01 MPa pressure, the mist increased the dielectric strength by an order of magnitude. It is believed that the mechanism which these mixtures achieve a high dielectric strength involves supersaturated vapor from the small droplets, the strength of the gas-vapor mixture which forms; and the capture of electrons by the droplets. As the micron-size liquid droplets will not freeze, then vapor-mist dielectrics can be used at low temperature where many vapors have poor dielectric strength. Consequently, vapor-mist dielectrics are now being investigated* as possible cooling and insulating media for vapor-cooled pOvler trans formers.