Abstract: A high voltage cable connector has a flanged insulating sleeve terminating the cable. The sleeve inserts in an insulating receptacle with some clearance space around it for being occupied by a fluid dielectric medium. The receptacle has a flange which is axially spaced from the flange on the sleeve when the sleeve is fully inserted and secured in the receptacle. A ring element is sealed between the flanges. It defines an annular chamber which communicates with the dielectric medium filled clearance space. A compressible element such as a bellows or diaphragm is disposed in the chamber for accommodating thermal expansion and contraction of the medium or the connector assembly to allow sealing of the system to prevent loss of dielectric and thereby prevent formation of cavities in the medium which could cause electrical breakdown.