US3777089A

US3777089A - Vacuum interrupter

Info

Publication number: US3777089A
Application number: US00282130A
Authority: US
Inventors: A Nitz
Original assignee: Allis Chalmers Corp
Current assignee: Allis Chalmers Corp
Priority date: 1972-08-21
Filing date: 1972-08-21
Publication date: 1973-12-04
Anticipated expiration: 1990-12-04
Also published as: CA985352A; DE2342257B2; GB1437256A; DE2342257A1

Abstract

A vacuum type circuit interrupter is provided with an internal two-part shielding structure that operates as a unitary shield member for protecting the insulation of the interrupter from being impaired by arc generated metallic vapors condensating thereon. The shield structure provides a greater clearance between the shield surface and the contacts and the arc gap in a given diameter envelope than has heretofore been possible. The two-part shield structure is supported from adjacent end caps which eliminates the need for supporting the shield structure from the insulator housing.

Description

Primary Examiner-Robert S. Macon Att0rneyRobert C. Jones et al.

ABSTRACT A vacuum type circuit interrupter is provided with an internal two-part shielding structure that operates as a wmB shield surface and the contacts and the arc gap in a given diameter envelope than has heretofore been possible. The two-part shield structure is supported VACUUM INTERRUPTER Inventor: Allen R. Nitz, Milwaukee, Wis.

Allis-Chalmers Corporation, Milwaukee, Wis.

Aug. 21, 1972 [58] Field of References Cited UNITED STATES PATENTS United States Patent Nitz [73] Assignee:

[22] Filed:

21 Appl. No.: 282,130

rr m mm es n.m me t S a m tm u 30 g & m .m g dm h mm m h D w 2 m a d was .m mm m 6 C t... 2 nt 1 m m "m l amm m m mw fSh BBX B 44 4 44B 4 W mm m w m tam m m m 73 m M J: n "L N m M m m u n m W x m.mR m S I 3 m0 //////,C/, N mwfi T //0 u/ e t 7 /w. JWA U 1 M 502 o 677 7 999 N 9 6 0 7 11 m E 42 5 984 O0 F 0 0 0 940 6 2 333 PMENTED DEC 4 I975 SHEET 10F 2 SHEET 2 OF 2 PATENTEDDEB 4 ms VAOUUM INTERRUPTER BACKGROUND OF THE INVENTION erated metallic vapor from condensing on the insulating part of the interrupter.

In vacuum interrupters, the various shielding arrangements heretofore proposed for protecting the insulating surfaces of the interrupter from metallic vapor particles have not been entirely satisfactory. For example, some prior arrangements have been subject to the disadvantage that the shields are so arranged that manufacturing and assembling of the shield within the envelope is both difficult and relatively costly.

Another disadvantage of the prior art is that an effective mounting support for the shield operates to reduce the effective clearance between the surface of the shield, the contacts and the arc gap.

Accordingly, the general object of the invention is to provide an interrupter having shield means which effectively prevents metallic vapor particles from depositing on the insulation of the interrupter.

Another object of the invention is to provide a shield structure which provides more clearance between the surface of the shield structure and the contacts for a given diameter envelope.

Yet another object of the invention is to provide a shield structure for an interrupter which facilitates manufacturing and assembling of the units.

Still another object of the invention is to provide a shield structure for an interrupter which is formed in two pieces, yet which operates as a single unit when the interrupter is assembled.

A still further object of-the invention is to provide a shield structure for an interrupter which permits both radial and axial adjustments in assembling to compensate for manufacturing tolerances without stressing or damaging the'shield or supports and also provides for expansion and contraction of the shield structure should the interrupter expand or contract.

SUMMARY OF THE INVENTION In the exercise of the invention in one form, I encompass the arcing gap between the contacts of a vacuum circuit interrupter with a generally tubular metallic shield which is isolated from the contacts and ground. The shield is constructed in the form of two cup shaped members which have an interfitting relationship. Neither of the cup shaped shield members overlaps the arcing gap, but in cooperation with each other, encompass the arcing gap. The cup shaped shield members are maintained in cooperating operative positions within the envelope by electrical insulators which extend between an adjacent end cap and a cup shaped member. With this construction, the length of the insulators can be changed to meet electrical requirements. Also with the cup shaped shield members maintained in operative position from the end of the interrupter, the distance between the surface of the shield and the arcing gap and between the contacts is greater for any given diameter envelope than has heretofore been possible.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a view partly in vertical section and partly in elevation through an interrupter in which the invention is advantageously employed; and

FIG. 2 is a view partly in vertical section and partly in elevation through an interrupter incorporating a modification of the invention disclosed in FIG. 1.

DESCRIPTION OF THE INVENTION Referring now to FIG. 1, there is shown a vacuum type circuit interrupter 10 comprising an evacuated envelope 11. The envelope includes a tubular insulator housing 12 and a pair of end caps 14 and 16 joined to the tubular housing 12 at its opposite ends by suitable vacuum type seals 17 and 18. The present invention is applicable to an interrupter having various types of contacts and I have depicted the invention in connection with an interrupter having one type of contact. Thus, disposed within the envelope 11 is a pair of relatively

movable contacts

21 and 22, which are depicted in contactopen or disengaged position. The upper contact 21 is a stationary contact suitably secured to a conductive rod 23. The conductive rod 23 at its upper end is secured in vacuum tight sealed relationship to the upper end cap 14. The lower contact 22 is a movable contact supported on the inner end of axially movable conductive operating rod 24. Upward movement of the contact 22 from its open position into engagement with the upper contact 21 closes the interrupter; whereas, downward movement of the contact 22 to the position it occupies as depicted in FIG. 1 opens the interrupter.

The axially movable contact rod extends through an opening 26 in the lower end cap 16. A flexible metallic bellows 28 provides a vacuum tight seal about the contact rod 24 to-permit the rod to move axially without impairing the vacuum within the envelope 11. As shown, the bellows 28 is secured in vacuum tight sealed relationship at its respective ends to the rod 24 and to the lower end cap l6.

Each of the illustrated

contacts

21 and 22 is of a disc shape and has one major surface facing the other contact. Each

contact

21 and 22 is formed with a centrally located

recess

32 and 33, respectively, so that electrical engagement between the contacts occurs on an annular contact making surface 34 and 36. The annular surfaces 34 and 36 are of a diameter such that current flowing through the closed contacts follows a radially outwardly bowing loop shaped path, as indicated by the dot-dash line L. As is well known, the magnetic effect of current flowing through the loop shaped path L tends to lengthen the loop. As a result, when the contacts are separated, an are forms between the annular shoulders of 34 and 36 and the magnetic effect of the current through the loop will impel the arc radially outwardly. As the arc moves radially outwardly, it is subjected to a circumferentially acting magnetic force that rotates the are about the central axis of the contacts.

For condensing the metallic vapors that are generated by the arc, there is provided a vapor condensing metallic shield 37. The shield 37 is of cup shaped form and is provided about the bellows 28 to protect the bellows from the arc generated products. A shield struc ture 40 is a main or principle shield comprising a pair of cup shaped members 41 and 42 which are joined and surround the arc gap 43 and which are disposed between the housing- 12'and the arc gap. The shield structure is at a floating potential relative to the

contacts

21 and 22.

As shown, the upper cup shaped shield member 41 is formed with a relatively wide annular bottom straight lip circumference 44. The diameter of the bottom annular portion 44 is substantially equal to the internal diameter of the housing 12. At its upper end, the shield member 11 is reduced to form an annular shoulder portion 46 which terminates in a reduced tubular portion 47 having an incurved terminal end which forms a corona type shield 48.

The lower cup shaped shield member 42 is formed with a relatively wide annular upper straight lip portion 51. The lower end of the shield portion of member 42 is formed as a truncated cone, as at 52, the base 53 of which is of reduced diameter relative to the adjacent upper portion of the shield member and serves as a baffle to intercept are generated particles moving along a line-of-sight path toward the insulating portions of the interrupter. In providing the lower shield member 42 with the truncated cone portion 52, a sloping annular shoulder 54 is formed which provides a smooth transitional gradient connection between the upper and lower portions of the shield member 42. As shown, the upper annular straight lip portion 51 of the shield member 42 is formed with a plurality of axially extending spaced apart slots 56 which operate to form resilient tabs or fingers 57 that extend around the entire circumference of the lip portion 51. As illustrated, the diameter of the lip portion 51 in which the slots 56 are formed in substantially equal to the diameter of the bottom lip portion 44 of the shield member 41. Thus, in assembling the two shield portions 41 and 42 into a unitary shield structure within the interrupter 10, the tabs 57 will deflect radially inwardly to permit the lower shield member 42 to seat within the upper shield member 41. The tabs 57 are sufficiently flexible to deflect radially inwardly to permit the shield members 41 and 42 to interrelate to facilitate assembling thereof, but they are sufficiently resilient so as to establish and maintain a strong electrical relationship with the inner surface of the shield member 41.

With the two shield members 41 and 42 assembled into an operative shield structure 40, neither of the shield members 41 and 42 extend any substantial distance longitudinally past the arc gap 43. However, in an assembled condition, the shield structure 40 does extend longitudinally of the housing 12 for some distance towards the end caps 14 and 16. In the assembled condition, the shield structure 40 provides a relatively large diameter central portion 61 around the

contacts

21 and 22 so as to give added clearance between the shield structure 40 and the

contacts

21 and 22. It will be apparent that substantially all straight line paths extending from the area of the arc gap 43 and from the

contacts

21 and 22 to the insulating housing 12 are intercepted by the shield structure 40. Thus, substantially all are generated metallic particles will be intercepted and condensed by the shield structure 40 and the end caps 14 and 16.

The assembled shield structure 40 is suitably supported within the interrupter from the end caps 14 and 16. In its supported position, the shield structure 40 is maintained at a voltage which is approxiamtely intermediate that of the

contacts

21 and 22 when the interrupter is opened. This intermediate potential is established by the substantially equal capacitance present between the shield structure and the opposite ends of the interrupter.

As previously mentioned, the shield members 41 and 42 are supported in assembled position from the end caps 14 and 16. To this end, the annular shoulder 54 of the shield member 42 is provided with projections 56 which are spot welded on suitable flats 57 formed in the annular shoulder portion 54. An equal number of projections 58 are spot welded on the inner surface of the end cap 16 and are spaced in a circular pattern which is substantially the same as the circular spacing of the projections 56. Thus, in assembling the lower shield member 42 within the interrupter, the shield is angularly oriented so that its projections 56 are axially aligned with the end cap projections 58. Insulating stand-off support rods or dowels 59 having aixial end openings are engaged on oppositely located projections 56-58 and serve to maintain the shield member 42 in operative position relative to the associated lower end cap 16.

In a similar manner, the annular shoulder 46 of the upper shield member 41 is formed with a plurality of equispaced circularly arranged flats 60. Projections 62 are spot welded on each of the flats 60 and cooperate with associated projections 63 spot welded on the inner surface of the top end cap 14. Insulator stand-off rods 64 having axial end openings are engaged on axially aligned projections 62-63.

Thus, with the upper shield member 41 assembled to the lower shield member 42, the insulating

rods

59 and 64 operate to space the shield structure equidistant from the end caps 14 and 16. The entire assembled interrupter is then placed in a jig so that the desired axial compression may be applied to the assemblage before joining the end plate 14 to the flange of seal 17. With the sleeve fit arrangement as provided by the shield members 41 and 42 all tolerance variations are absorbed by the deflection of the tabs 57 of the lower shield member 42.

As shown, the shield structure 40 is entirely supported in operation position from the end caps 14 and 16. It is also apparent that the arrangement of supporting the shield structure 40 from the end caps eliminates the need of providing any projecting elements from the wall of the housing 12. Thus, the external diameter of the shield structure 40 can be substantially equal to the internal diameter of the insulator housing 12. This arrangement then provides for a greater clearance spacing between the shield structure and the contacts than has heretofore been possible with the same diameter envelope housing.

In FIG. 2, a modification of the invention of FIG. 1 is disclosed. As therein shown, a vacuum type circuit interrupter inlcudes an evacuated envelope 1.11. The envelope includes a tubular insulator housing 112 and a pair of end caps 114 and 116 joined to the housing 112 at its opposite ends by suitable vacuum type seals 117 and 118. Within the envelope-111 is a pair of contacts 121 and 122. The upper contact 121 is a stationary contact suitably secured on the end of the conductive rod 123 which, at its upper end, is secured in vacuum tight sealed relation to the upper end cap 114. The lower contact 122 is secured to the inner ends of an axial movable conductive rod 124. A metallic bellows 128 provides a vacuum tight seal between the rod and the end cap 116. The contacts 121 and 122 are similar to the

contacts

21 and 22.

For condensing the are generated metallic particles, the interrupter is provided with a shield structure 140 comprising an upper shield member 141 and a lower shield member 142. As shown, the shield members 141 and 142 are substantially identical, with the upper shield member 141 varying from the associated lower shield member 142 only in its diameter. The lower shield member 142 is cup shaped having an outwardly extending rolled upper circular edge 142A. The lower bottom portion of the shield member 142 is formed with a circular axially inwardly extending edge 1428 which forms a curved outer surface 142C to minimize arc sparking.

The upper shield member 141 has the same general configuration as the shield member 142 with the exception that as previously mentioned, its diameter is somewhat smaller than that of the shield member 142. Thus, the lower circular end of the shield member 141 is formed with a rolled outwardly extending circular edge 141A. The diameter of the circular edge is preferably such that with the shield member 141 assembled as depicted, the circular edge portion 141A makes electrical contact with the interior surface of the shield member 142. This physical relationship between the shields 141 and 142 which is the preferred arrangement capacitively connects the two members 141 and 142 together. However, if so desired the diameter of the edge 141A of the shield member 141 can be less than the diameter of the shield 142, so that the two members are resistively connected. The upper end of the shield members 141 is formed with a circular axially inwardly extending edge 14113 which forms a'curved outer surface 141C to minimize sparking.

Each of the shield members 141 and 142 are supported from an associated end cap. To this end, a plurality of stand-off insulators 159 are interposed between the lower end of the shield member 142. The

axial ends of the stand-off insulators 159 are metallized and the insulators are butt brazed to the shield member and the end cap 116. In a similar manner, a plurality of stand-off insulators 164 are interposed between the end cap 114 and the shield member 141. Both ends of each of the insulators 164 are metallized, and the insulators are butt brazed to the end cap 114 and to the shield member 141. Thus, both shield members 141 and 142 are supported from their associated end caps 114 and 116, respectively. Each of the contact rods 123 and 124 is provided with a flat disc shaped shield 171 and 172, respectively. The shields 171 and 172 are mounted on a reduced portion 123A and 124A of the respective contact rods, abutting shoulders 1238 and 1248, respectively, being brazed thereto. The diameter of each of the shields 171 and 172 is greater than the diameter of the opening in the end of an associated shield member that is adjacent the end caps -114 and 116, respectively, and through which the rods 123 and 124 extend. The shields 171 and 172 serve to interpose a barrier to a line-of-sight path which is tangential to the peripheries of the contacts 121 and- 122 and the in turned circular edge 1418 and 1428. Thus, the shields 171 and 172 cause a longer path for are generated particles trying to reach any insulator or the rods 123 and 124. A bellows shield 137 which is shown brazed to the under surface of the shield 172 surrounds the bellows 128 to protect it from arc generated vapor particles. It

is, of course, apparent that if the shield 172 was not utilized the bellows shield 137 would take the form of the shield 37 associated with the interrupter 10.

From the foregoing description, it is readily apparent that the shield members 41-42 and 141-442 can have other shapes of the same diameter, and that they may be longer or shorter as may be required. To this end, it would only require that the stand-off insulator rods 59-64 and 159-l64 be shortened or lengthened to accommodate the length of other forms of shield members. It is also apparent that with the shield structure disclosed in either FIG. 1 or FIG. 2, the individual shield members can be manufactured by the metal fabricating method of deep-drawing rather than by the more costly method of spin-casting or spin-forming. Because of the inherent rigidity of the shapes of the shield members 41-42 and 141-142, these members can be made of copper which is a material well adapted and facile to the manufacturing process of deepdrawing. It is also apparent that the shield structures herein disclosed provide a structural arrangement in which the electrical field is substantially symmetrical.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a vacuum circuit interrupter;

an evacuated envelope including a generally tubular housing of an insulating material;

end caps disposed at each end of said housing in vacuum tight relationship;

a pair of contacts disposed within said envelope and operable during a circuit interrupting operation to define a gap across which arcing occurs;

a metallic circular shield comprising a pair of cup shaped members assembled in overlapping physical engagement disposed between said tubular housing and said contacts in position to intercept and condense metallic vapors generated by said arcing; and,

means disassociated from said housing and operable to maintain said pair of cup shaped members in operative particle protecting position and a floating potential with respect to said contacts.

2. A vacuum circuit interrupter according to claim 1 wherein said means on one of the cup shaped members for making physical engagement with the interior of the other of said cup shaped members are a plurality of axially extending tabs formed on the circular edge of the cup shaped member which interengages with the other cup shaped member.

3. A vacuum circuit interrupter according to claim 1 wherein said means disassociated from said housing for maintaining said cup shaped shield members in operative position includes a plurality of insulator rods extending between the end of each of said cup shaped members and an associated adjacent end cap.

4. A vacuum interrupter according to claim 1 wherein said disassociated means comprises a plurality of stand-off insulator rods interposed between the ends of said cup shaped members and said end caps and operable to support and maintain said cup shaped members in predetermined axial position within said envelope.

5. A vacuum interrupter according to claim 4 wherein said stand-off insulator rods are mechanically interlocked between each end of said cup shaped members and an adjacent associated end cap.

6. A vacuum interrupter according to claim wherein said mechanical interlock is established by cooperating projections formed on said cup shaped members and on said end caps; and,

said stand-off insulator rods are provided with axial end openings which receive said projections to lock said stand-ofi insulator rods and thereby said cup shaped members in a predetermined operative position.

7. A vacuum interrupter according to claim 4 wherein the axial ends of said stand-off insulator rods are metallized and said rods are butt brazed to said cup shaped member and to said end caps.

8. A vacuum interrupter according to claim 2 wherein one of said cup shaped members has a diameter substantially equal to the internal diameter of said housing; and,

the other of said cup shaped members has a plurality of axial slots formed from the circular edge thereof to thereby form said plurality of tabs which are resiliently deflectable,

whereby upon interengagement of said cup shaped members said tabs deflect to absorb all tolerance variations which exist due to manufacturing and said tabs are sufficiently resilient to establish a good electrical relationship between said cup shaped members.

9. In a vacuum circuit interrupter;

an evacuated envelope comprising a generally tubular housing of insulating material having its ends sealed by metallic end caps;

a pair of contacts disposed within said housing in spaced apart relationship during a circuit interrupting operation to form an arcing gap;

a first cup shaped shield member disposed within said housing in a position so that it is interposed between at least, one half of said insulating surface of said housing and said arcing gap, said first cup shaped shield member having a diameter which is substantially equal to the internal diameter of said housing to thereby provide maximum clearance between the surface of said shield and said contacts and the arcing gap;

a second cup shaped shield member disposed within said housing in a position so that it is interposed between at least the other half of said insulating surface of said housing and said arcing gap, said second cup shaped shield member having a diameter substantially equal to the diameter of said first cup shaped shield member to provide maximum clearance between the surface of said second cup shaped shield and said contacts and the arcing gap, said second cup shaped shield member being constructed and arranged to complete said first cup shaped shield member in a manner that said first and second cup shaped shield members cooperate to protect substantially all of the insulating surface of said housing from are generated particles; and,

insulator support means extending from said end caps into supporting engagement with said first and second cup shaped shield members to maintain said cup shaped shield members in cooperating shielding position.

10. In a vacuum interrupter;

a pair of contacts disposed within said housing in spaced apart relationship during a circuit interrupting operation to define an arcing gap;

a generally tubular metallic shield surrounding said are gap and extending longitudinally in each direction to points short of said end caps, the distances between each end of said shield and said end caps being substantially equal, said shield having an external diameter substantially equal to the internal diameter of said housing thereby providing maximum spacing between the surface of said shield and said contacts; and

a plurality of insulator stand-off rods extending between the ends of said shield and said end caps and operable to maintain said cup shaped shield within said housing substantially equidistant from said end caps, said insulator stand-off rods constituting the sole mechanical connection between said shield and said envelope.

11. In a vacuum circuit interrupter;

a first cup shaped metallic shield member disposed within said housing and supported therein by insulators extending from one of said end caps, said first cup shaped shield member having a diameter substantially equal to the internal diameter of said housing to thereby provide maximum clearance between the surface of said shield member and said contact and the arcing gap;

a second cup shaped metallic shield member disposed within said housing and supported therein by insulators extending from the other of said end caps, said second cup shaped metallic shield having an external diameter to permit it to enter into and engage the interior circular surface of said first cup shaped metallic shield member,

whereby said first and second cup shaped metallic shield member protects substantially all of the insulating surface of said housing from arc generated metallic particles.

12. In a vacuum circuit interrupter;

a first cup shaped shield member disposed within said hosuing in position that it is interposed between at least, one half of said insulating surface of said housing and said arcing gap, said first cup shaped shield member having a diameter which is substantially equal to the internal diameter of said housing to thereby provide maximum clearance between the surface of said shield and said contacts and the arcing gap;

a second cup shaped shield member disposed within said housing in interengaged relationship with said first cup shaped shield member and interposed between the other half of said insulating surface of said housing and said arcing gap;

axially extending resiliently deflectable means on said second cup shaped shield member to engage with the internal surface of said first cup shaped shield member to establish an electrical interrela- 9 10 tionship between said first and second cup shaped insulator support means extending from each of said Shleld memb'elts, axlally extending deflectable end caps into supporting engagement with said first means permmmg Sald first and second cup shaped and second cup shaped shield members to maintain shield member to adjust axially relative to each other to compensate for a variation in manufactur- 5 ing tolerances and for contraction and expansion of shleldmg P the interrupter; and,

said cup shaped shield members in cooperating

Claims

1. In a vacuum circuit interrupter; an evacuated envelope including a generally tubular housing of an insulating material; end caps disposed at each end of said housing in vacuum tight relationship; a pair of contacts disposed within said envelope and operable during a circuit interrupting operation to define a gap across which arcing occurs; a metallic circular shield comprising a pair of cup shaped members assembled in overlapping physical engagement disposed between said tubular housing and said contacts in position to intercept and condense metallic vapors generated by said arcing; and, means disassociated from said housing and operable to maintain said pair of cup shaped members in operative particle protecting position and a floating poteNtial with respect to said contacts.

6. A vacuum interrupter according to claim 5 wherein said mechanical interlock is established by cooperating projections formed on said cup shaped members and on said end caps; and, said stand-off insulator rods are provided with axial end openings which receive said projections to lock said stand-off insulator rods and thereby said cup shaped members in a predetermined operative position.

8. A vacuum interrupter according to claim 2 wherein one of said cup shaped members has a diameter substantially equal to the internal diameter of said housing; and, the other of said cup shaped members has a plurality of axial slots formed from the circular edge thereof to thereby form said plurality of tabs which are resiliently deflectable, whereby upon interengagement of said cup shaped members said tabs deflect to absorb all tolerance variations which exist due to manufacturing and said tabs are sufficiently resilient to establish a good electrical relationship between said cup shaped members.

9. In a vacuum circuit interrupter; an evacuated envelope comprising a generally tubular housing of insulating material having its ends sealed by metallic end caps; a pair of contacts disposed within said housing in spaced apart relationship during a circuit interrupting operation to form an arcing gap; a first cup shaped shield member disposed within said housing in a position so that it is interposed between at least, one half of said insulating surface of said housing and said arcing gap, said first cup shaped shield member having a diameter which is substantially equal to the internal diameter of said housing to thereby provide maximum clearance between the surface of said shield and said contacts and the arcing gap; a second cup shaped shield member disposed within said housing in a position so that it is interposed between at least the other half of said insulating surface of said housing and said arcing gap, said second cup shaped shield member having a diameter substantially equal to the diameter of said first cup shaped shield member to provide maximum clearance between the surface of said second cup shaped shield and said contacts and the arcing gap, said second cup shaped shield member being constructed and arranged to complete said first cup shaped shield member in a manner that said first and second cup shaped shield members cooperate to protect substantially all of the insulating surface of said housing from arc generated particles; and, insulator support means extending from said end caps into supporting engagement with said first and second cup shAped shield members to maintain said cup shaped shield members in cooperating shielding position.

10. In a vacuum interrupter; an evacuated envelope comprising a generally tubular housing of insulating material having its ends sealed by metallic end caps; a pair of contacts disposed within said housing in spaced apart relationship during a circuit interrupting operation to define an arcing gap; a generally tubular metallic shield surrounding said arc gap and extending longitudinally in each direction to points short of said end caps, the distances between each end of said shield and said end caps being substantially equal, said shield having an external diameter substantially equal to the internal diameter of said housing thereby providing maximum spacing between the surface of said shield and said contacts; and a plurality of insulator stand-off rods extending between the ends of said shield and said end caps and operable to maintain said cup shaped shield within said housing substantially equidistant from said end caps, said insulator stand-off rods constituting the sole mechanical connection between said shield and said envelope.

11. In a vacuum circuit interrupter; an evacuated envelope comprising a generally tubular housing of insulating material having its ends sealed by metallic end caps; a pair of contacts disposed within said housing in spaced apart relationship during a circuit interrupting operation to define an arcing gap; a first cup shaped metallic shield member disposed within said housing and supported therein by insulators extending from one of said end caps, said first cup shaped shield member having a diameter substantially equal to the internal diameter of said housing to thereby provide maximum clearance between the surface of said shield member and said contact and the arcing gap; a second cup shaped metallic shield member disposed within said housing and supported therein by insulators extending from the other of said end caps, said second cup shaped metallic shield having an external diameter to permit it to enter into and engage the interior circular surface of said first cup shaped metallic shield member, whereby said first and second cup shaped metallic shield member protects substantially all of the insulating surface of said housing from arc generated metallic particles.

12. In a vacuum circuit interrupter; an evacuated envelope comprising a generally tubular housing of insulating material having its ends sealed by metallic end caps; a first cup shaped shield member disposed within said hosuing in position that it is interposed between at least, one half of said insulating surface of said housing and said arcing gap, said first cup shaped shield member having a diameter which is substantially equal to the internal diameter of said housing to thereby provide maximum clearance between the surface of said shield and said contacts and the arcing gap; a second cup shaped shield member disposed within said housing in interengaged relationship with said first cup shaped shield member and interposed between the other half of said insulating surface of said housing and said arcing gap; axially extending resiliently deflectable means on said second cup shaped shield member to engage with the internal surface of said first cup shaped shield member to establish an electrical interrelationship between said first and second cup shaped shield members, said axially extending deflectable means permitting said first and second cup shaped shield member to adjust axially relative to each other to compensate for a variation in manufacturing tolerances and for contraction and expansion of the interrupter; and, insulator support means extending from each of said end caps into supporting engagement with said first and second cup shaped shield members to maintain said cup shaped shield members in cooperating shielding position.