On the calculation of the dielectric time constant of DC insulators containing cavities

This paper presents an analytical derivation of the dielectric time constant of DC insulators containing cavities. It is based on two different methods including Maxwell- Wagner-Sillars (MWS) equations and an equivalent charging circuit. It is shown how the time constant varies depending on the ratio between cavity height and the thickness of the dielectric in series with the cavity, and how a rough calculation on the time constant made referring only to the dielectric or medium filling the cavity can be valid when cavities with certain size are present.