Disconnect switch for metal-encapsulated high-voltage switching installations

Claim 1

In a disconnect switch for use in a metal-encapsulated high-voltage switching installation at voltages of 245 kV and above which includes a tubular grounded encapsulation containing a gaseous insulating medium, said switch including a movable switching pin and a mating contact axially associated therewith, said movable switching pin being adapted for axial movement toward and engagement with said mating contact when said switch is moved from an "off" to an "on" position, the improvement comprising a cylindrical member arranged in spaced surrounding relationship to said mating contact and formed so as to extend beyond that end face of said mating contact which is in facing relationship with said switching pin, said cylindrical member projecting beyond the end face of said mating contact and terminating in the gap between said mating contact and said switching pin when said switch is in said "off" position, said cylindrical member also projecting beyond the end face of said switching pin and surrounding said switching pin when said switch is in said "on" position, said cylindrical member being radially spaced apart from the surface of said switching pin by a distance which is greater than a preliminary breakdown axial distance between said mating contact and said switching pin at which breakdown between said mating contact and switching pin occurs as said switching pin moves towards said mating contact as said switch is moved to said "on" position, so that when said switch is moved to said "on" position, a preliminary breakdown takes place during movement of said movable switching pin to said "on" position of said switch only between said switching pin and said mating contact and not between said switching pin and said cylindrical member.