High voltage liquid-free insulating bushing with improved voltage distribution

Claim 1

A HIGH VOLTAGE INSULATING BUSHING COMPRISING A TUBULAR SHELL OF INSULATING MATERIAL, A CENTRALLY LOCATED CONDUCTOR ADAPTED TO BE ENERGIZED AT A HIGH VOLTAGE EXTENDING AXIALLY OF SAID INSULATING SHELL, A TUBULAR SLEEVE OF INSULATING MATERIAL CLOSELY ENCOMPASSING SAID CONDUCTOR AND LOCATED WITHIN SAID TUBULAR SHELL IN RADIALLY SPACED RELATIONSHIP TO SAID SHELL SO AS TO LEAVE AN AIR GAP BETWEEN SAID SHELL AND SAID SLEEVE, METALLIC STRUCTURE ABOUT THE OUTER PERIPHERY OF SAID SHELL ADAPTED TO BE CONNECTED TO GROUND, SAID METALLIC STRUCTURE EXTENDING ALONG A SHORT PORTION OF THE TOTAL LENGTH OF SAID SHELL, A FIRST CONDUCTIVE SHIELD IN THE FORM OF A COATING ON THE INNER PERIPHERY OF SAID SHELL EXTENDING ALONG A PORTION OF THE LENGTH OF SAID SHELL LOCATED AXIALLY OF THE SHELL IN THE REGION OF SAID METALLIC STRUCTURE, SAID FIRST SHIELD BEING ELECTRICALLY ISOLATED FROM SAID METALLIC STRUCTURE ABOUT SAID OUTER PERIPHERY BY MEANS OF SAID INSULATING SHELL, A SECOND CONDUCTIVE SHIELD ON SAID SLEEVE NEAR THE OUTER SURFACE THEREOF EXTENDING AXIALLY OF THE SLEEVE IN GENERALLY LONGITUDINALLY ALIGNED RELATIONSHIP RELATIVE TO SAID FIRST CONDUCTIVE SHIELD, SAID SECOND SHIELD BEING ELECTRICALLY ISOLATED FROM SAID CONDUCTOR BY MEANS OF SAID SLEEVE OF INSULATING MATERIAL, SAID SECOND CONDUCTIVE SHIELD HAVING ITS AXIALLY OPPOSED ENDS COVERED BY INSULATING MATERIAL CONSTITUTING A PORTION OF SAID SLEEVE SO AS TO LOCATE THE HIGH DIELECTRIC STRESS REGION ADJACENT SAID ENDS IN THE SOLID INSULATION OF SAID SLEEVE, CONDUCTIVE BRIDGING MEANS EXTENDING ACROSS SAID AIR GAP AND ELECTRICALLY INTERCONNECTING SAID TWO CONDUCTIVE SHIELDS, THE SPACE BETWEEN SAID SLEEVE AND SAID SHELL BEING SUBSTANTIALLY FREE OF INSULATING LIQUID, THE VOLTAGE IN THE REGION OF SAID METALLIC STRUCTURE BEING DISTRIBUTED BETWEEN SAID INSULATING SHELL AND SAID INSULATING SLEEVE WHEN SAID CONDUCTOR IS ENERGIZED.