Vacuum-type circuit interrupter with improved protection for bellows

A vacuum-type circuit interrupter comprising:

• a. a highly-evacuated envelope comprising a tubular casing of insulating material and a metal end cap that contains an aperture and is joined in sealed relationship to said casing at one end of said casing,
• b. separable contacts primarily of beryllium located within said envelope,
• c. a movable conductive contact rod extending freely through said aperture in said end cap and carrying one of said contacts at one end thereof,
• d. a plate located at the outer side of said end cap and joined to said end cap in sealed relationship thereto, said plate being spaced from said end cap and containing an opening through which said movable contact rod freely extends,
• e. a flexible metal bellows of generally tubular form surrounding said contact rod and having its axially-inner end joined to said contact rod and its axially-outer end joined to said plate, said bellows extending freely through said aperture in said end cap,
• f. a cup-shaped metal shield for said bellows comprising:
• f.sub.1. an end wall joined to said contact rod near said inner end of the bellows, and
• f.sub.2. a tubular body portion projecting from said end wall and surrounding said bellows along a portion of the bellows length, the free-end region of said tubular body portion being located substantially within said aperture during at least the final portion of an opening stroke of the movable contact rod, with only a small clearance between said aperture and said free-end region,
• g. a metal main shield within said casing, surrounding said contacts, and normally electrically isolated from said contacts for condensing beryllium vapors generated by arcing between said contacts, said main shield having an end portion surrounding said cup-shaped bellows shield,
• h. a metal end shield mounted on said end cap and electrically connected thereto, said end shield having a tubular portion surrounding the tubular portion of said cup-shaped shield and disposed between said tubular portion of the cup-shaped shield and the end portion of said main shield in radially-spaced relation to said end portion, the region between the tubular portions of said cup-shaped shield and said end shield being a region of very low electric stress.