US3210505A

US3210505A - Electrode structure for an electric circuit interrupter

Info

Publication number: US3210505A
Application number: US184704A
Authority: US
Inventors: Joseph W Porter
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1962-04-03
Filing date: 1962-04-03
Publication date: 1965-10-05
Anticipated expiration: 1982-10-05
Also published as: SE305020B; FR1353284A; GB964405A; CH406358A; JPS4121660B1; DE1226693B

Description

Oct. 5, 1965 J. w. PORTER 3,210,505

ELECTRODE STRUCTURE FOR AN ELECTRIC CIRCUIT INTERRUPTER Filed April 5. 1962 ATTORNEY.

United States Patent O 3,210,505v ELECTRODE STRUCTURE FOR AN ELECTRIC CIRCUIT INTERRUPTER Joseph W. Porter, Media, Pa., assignor to `General Electric Company, a corporation of New York Filed Apr. 3, 1962, Ser. No. 184,704 11 Claims. (Cl. 20o-144) This invention relates to electrode structure for an electric circuit interrupter and, more particularly, to electrode structure that is especially, though not exclusively, suited for use `in vacuum-type circuit interrupters.

. In the electrode structure of the present invention,y there are two electrodes between which arcing takes place during circuit interruption. One of these electrodes includes a contact portion that is movable into and out of engagement with the other electrode and is therefore referred to as the movable electrode. This movable electrode also includes a stationary portion that serves as an arc runner along which arcs are driven after being transferred thereto from the movable contact porti-on.

By dividing the movable electrode into two relatively movable parts, instead of forming it as a single unitary part, substantial reductions can be made in the mass that must be moved during opening and closing of the circuit interrupter. This is an important advantage for a number of reasons that will soon be explained, but there are some rather formidable problems that are usually present with such a construction.

One of these problems, particularly in a vacuum type circuit interrupter, is that the clearance space between the movable contact Iand its adjacent arc runner tends to become clogged with arcing products that can interfere with free motion of the movable contact. This problem can be overcome by making the clearance space larger, but the larger this space, the more diicult it becomes to effect a rapid transfer of the arc terminal across the clearance space from the movable contact to the arc runner. The longer the arc terminal is delayed in transferring acr-oss this clearance space, the greater will be the arc erosion of the contact and the less likely it will be that the interrupter will clear at the first current zero when interrupting high currents.

An `object of the present invention is to effect high speed transfer of the arc terminal across this clearance space, even though the clearance space is so large that clogging is not a problem.

Another object is to effect such transfer of the arc terminal across the clearance space by the time the moving contact has moved only a short distance through its opening stroke, yconsiderably less than the minimum distance between the arc runner and the other electrode.

Another object is to provide a contact structure in which the arc-initiating regions of the two electrodes are electrostatically shielded when the contacts are fully open so as to lessen the chances for a dielectric breakdown between these regions. y

In carrying out our invention in one form, wel provide an electric circuit interrupter that comprises a first contact and a second contact movable into and out of engagement with the iirst contact. Surrounding the first contact and electricallyconnected thereto is a first arc runner of annular form. Surrounding the second contact and physically spaced therefrom by a clearance space about the periphery of the second contact is a second annular arc runner. This second arc runner is mounted in generally aligned relationship with the first arc runner with an arcing gap between the two arc runners. The second contact is telescopically movably relative to its arc runner along a path extending across the arcing 3,210,505I Patented Oct. 5, 1965 gap. The second contact, which is of a cup-shaped configuration, comprises a base that is engageable with the lirst contact and a tubular wall that extends from the base in a direction away from the location of the first contact. Arc-transfer means is provided for forcing one terminal of arcs initiated `on said base to move along the outer surface of said tubular wall across said clearance space on to said second arc runner. This arc-transfer means comprises means for forcing substantially all current flowing through said cup-shaped contact to an arc terminal on said tubular wall to follow a path that extends through said base. Means is also provided for carrying current to and from an arc terminal on said second arc runner via a path that bypasses said second contact.

For a better understanding of my invention, reference may be had to the following description taken in conjunction with the accompanying drawings, wherein:

FIG. l is a cross-sectional view through a vacuumtype circuit interrupter embodying one form ofmy invention. The contacts of the interrupter of FIG. 1 are shown in the closed position. y

FIG. 2 is a cross-sectional view showing the contacts of the interrupter of FIG. l in a partially open position.

FIG. 3 is a `view similar to that of FIG. 2 except that the contacts have advanced through slightly more of their opening stroke.

FIG. 4 shows the contacts in their fully open position.

FIG. 5 is a cross-sectional view along the line 5-5 of FIG. 1.

Referring now to FIG. l, therel is shown a vacuumtype circuit interrupter comprising a highly evacuated sealed envelope 10. This envelope 10 com-prises a cylindrical casing 11 of insulating material and a pair of metallic end caps 12 and 13 at opposite ends of the casing 11. Suitable seals 14 are provided between the end caps and the casing 11 to provide a vacuum-tight joint between these parts. The normal pressure within the envelope is lower than 10*4 mm. of mercury, so that a reasonable assurance is had that the mean free path for all electrons will be longer than the potential breakdown paths in the interrupter. n

The internal insulating surfaces of the casing 11 are' protected from the condensation of arc-generated metallic vapors thereon by means of a tubular metallic shield 15 suitably supported on the casing 11 and preferably isolated from both end caps 12 and 13. This shield acts in a known manner to intercept arc-generated metallic vapors before they can reach the casing 11.

Located within the envelope 10 is a pair of electrodes 17 and 18 shown in FIG. 1 in their engaged or closed circuit position. The upper electrode 17 is a stationary electrode suitably attached to a conductive rod 17a, which at its upper end is united to the upper end cap 12. The lower electrode 18 is referred to hereinafter as the movable electrode although only a portion of this lower electrode is movable. The movable portion of the lower electrode is a centrally-disposed part 20 referred to hereinafter as a movable contact. This contact 20 is suitably attached to a conductive operating rod 21, which isv suitably mounted for vertical movement along the axis of the rod 21. In FIG. l, the movable contactv 20 is shown in its uppermost postion engaging a stationary contact 24 constituting a part of the stationary electrode 17. When the

contacts

20 and 24 are in this engaged position, the interrupter is closed and current can iiow therethrough via the conductive rod 17a, stationary contact 24, movable contact 20, and conductive rod 21. Downward movement of the rod 21 separates the movable contact 20 from the stationary contact 24 and thereby opens the interrupter. The position of the parts when the interrupter is fully open is depicted in FIG. 4, where the movable contact 24 has been withdrawn from the stationary contact through its full downward opening stroke. To close the interrupter, the movable contact 20 is driven upwardly from its position of FIG. 4 to its position of FIG. 1 to reengage the

contacts

20 and 24 and thereby complete the circuit through the contacts. The operating rod 21 projects through an opening in lower end cap 13, and a flexible metallic bellows 29 provides a seal about the rod 21 to allow for vertical motion of the rod without impairing the vacuum inside the envelope 10. As shown in FIG. 1, the bellows 29 is secured in sealed relationship at its respective opposite ends to the operating rod 21 and the lower end cap 13.

The movable electrode 18 comprises a stationary arc runner 30 in the form of an annular ring surrounding the movable contact 20. This stationary arc runner 30 is mounted on the lower end cap 13 by means of a tubular conductor 32 that is secured at its opposite ends to the end cap 13 and the arc runner 30. The joint between the tubular contact 32 and annular arc runner 30 is preferably located at the inner periphery of the annular arc runner for reasons which will soon be explained in more detail. There is a relatively large clearance space 33 between the movable contact 20 and the annular arc runner 30 about the entire outer periphery of the movable contact 20 so as to permit free vertical movement of the movable contact within the annular arc runner 30, as will soon appear more clearly. The movable contact 20 and the annular arc runner 30 are electrically connected together by means of a flexible braid 34 located outside of the evacuated envelope 10.

The stationary electrode 17 also includes an annular arc runner surrounding its centrally-disposed contact portion 24. This annular arc runner, which is designated 36, is generally aligned with the other arc runner 32 and is spaced therefrom to provide a secondary arcing gap 37 of annular configuration between the opposed faces of the arc runners. Preferably, the annular arc runner 36 is supported on the conductive rod 17a by means of a radially-extending integrally-formed body portion 38 that is suitably brazed at its inner periphery to the rod 17a.

Both the stationary contact 24 and the movable contact 20 illustrated in FIG. 1 are of a generally cup-shaped` configuration. Each of these cup-shaped contacts may be thought of as comprising a base and a tubular wall that extends from the base in a direction away from the location of the other contact. For example, the movable contact 20 comprises a base 40 and a tubular wall 42 that extends from the base 40 in a direction away from the location of the stationary contact 24. The stationary contact comprises a similar base 44 and a tubular wall 46 projecting therefrom. It will be noted that even when the contacts are closed as shown in FIG. l, the tubular wall 42 of the movable contact 20 terminates only after extending well beyond the uppermost surface of the arc runner 30 so that the contact 20, in effect, spans the secondary arcing gap 37. In each contact the outer surface of the cup is rounded to provide a smooth configuration devoid of sharp corners and edges.

The two cup-shaped

contacts

20 and 24 engage each other at a centrally-disposed contact-making point 50 on their bases. It is at this point that arcs are initiated when the contact 24 is separated from the contact 20. vAs will soon be explained, the cup-shaped configuration of the contacts contributes in an important manner to the desired high speed transfer of arcs from the contacts to the

arc runners

30 and 36 when the contacts are separated.

Another feature contributing to this high speed arc transfer is the presence of inserts 60 of high resistivity force current flowing through the point 50 to follow the dotted line path L. It will be noted from FIG. l that this dotted line path L is of a loop-shaped configuration in the immediate vicinity of the point 50. This loop bows to the left and therefore has a magnetic effect on an arc established at 50 which acts in a direction to drive the arc to the left. The farther this arc moves to the left, the more pronounced becomes the loop and the greater becomes the magnetic force acting to drive the arc to the left. For example, note FIG. 2 where the arc is shown in two successive positions B and C through which it passes as it moves to the left. It will be observed that the current loop becomes more and more pronounced as the arc moves through position B into position C.

FIG. 3 illustrates the probable position of the arc after it has passed through the position C of FIG. 2 and its upper terminal has transferred to the upper arc runner 36. The lower terminal has now reached the tubular wall portion 42 of the movable contact 20, thus introducing a downward bow into the configuration of the loop circuit. This increasingly forces the lower arc terminal to move along the outer surface of tubular wall 42ftoward the lower arc runner 30. Since the tubular wall 42 is spaced from the rod 21 about the entire inner periphery of the tubular wall, as shown particularly in FIG. 5, substantially all current flowing through contact 20 to an arc on the tubular wall 42 is forced to follow a path, such as L in FIG. 3, extending through the base 40. This accentuates the above-described downward bow in the loop circuit, thus increasingly forcing the lower arc terminal downwardly along the tubular wall 42 toward the lower arc runner 30. When the arc impinges on the arc runner 30, it extends between the two

arc runners

30 and 36 across the

secondary arcing gap

36, 37.

Thereafter, the arc is rotated at high speed about the axis of the interrupter along the opposed arc-runing surfaces of the

arc runners

30 and 36. This arc motion reduces the amount of vapor that is generated by the arc and helps to accelerate the diffusion of the vapor that is generated, thus increasing the likelihood that circuit interruption will be completed at the next current zero. The magnetic force for producing this high speed arc motion is derived from a series of skewed slots 70 cut in the

arc runners

30 and 36.

As shown in FIG. 5, these slots 70 extend across the entire radial thickness of each of the

arc runners

30 and 36. Each of the slots 70 also extends from the arc-running surface of the arc runner via a path that is disposed at an acute angle to the arc-runing surface. These slots force any current flowing to an arc terminal located at any angular point on the arc running surface to have a net component extending circumferentially with respect to the arc-running surface in the region of the arc. This net circumferentially-extending component forms with the arc a loop circuit that has a magnetic effect that acts to drive the arc in a circumferential direction about the arcrunning surface. A slotted construction similar to this is shown and claimed in application Serial No. 10,160-Smith, now Patent No. 3,089,936, filed February 23, 1960, and assigned to the assignee of the present invention. The high speed arc motion that is produced by the slots 70 reduces the amount of vapors generated by the arc and accelerates diffusion of these vapors away from the arcing region. This contributes to higher interrupting capacity and more likelihood that the arc will not reignite after the first current zero.

By dividing the movable electrode 18 into two relatively

movable parts

20 and 30, instead of forming it as a Single unitary part, substantial reductions can be madegin the mass that must be moved during opening and closing of the circuit interrupter. This is an important advantage because it enables a smaller operating mechanism to be used for actuating the movable contact and also because higher contact opening speeds can be obtained with a mechanism of a given size. Another advantage of the two part construction is that the resultant reduction in size of the moving part reduces the mechanical stresses resulting from interrupter operation.

One problem that has heretofore been encountered, however, when the movable electrode is made in two relatively movable parts is that the necessary clearance space between the two parts tends to become clogged with arcing products, and this can eventually interfere with free relative movement of the parts. This problem is particularly acute in a vacuum-type circuit interrupter since very little sliding friction can ordinarily be tolerated in a vacuum. This problem has been overcome in the illustrated contact structure, in part, by making the clearance space between the contact and the arc runner 30 so large that any loose particles produced by arcing either pass entirely through the clearance space or, if collected in this region, cannot bridge the clearance space because of its relatively great length.

Increasing the size of the clearance space, however,

tends to impede the transfer of the lower terminal of the arc across the clearance space from the contact 20 to the arc runner 30. This is disadvantageous because the longer the arc is delayed in transferring across the clearance space, the greater will be the erosion of the contact 20 and the less likely it will be that the interrupter will clear at the first current zero when interrupting high current. With regard to the reduced likelihood of clearing at the first current zero, it will be apparent that the longer the delay in transferring, the greater the share of the interrupting duty imposed on the

contacts

20 and 24 and the smaller the share of the interrupting duty borne by the

arc runners

30 and 36 which are far more suited for such interrupting duty due to the slots 70 and the large relatively cool surface area provided by the arc runners. Thus, the greater the delay, the less effective the interrupter is in handling the interrupting operation.

With the illustrated contact arrangement, I have been able to transfer the lower terminal of the arc across the clearance space by the time the movable contact 20 has moved through only a small fraction of its total opening stroke, even despite the fact that the clearance space has been enlarged to prevent clogging of the space and eventual jamming of the movable contact. This extremely rapid arc transfer I attribute to (1) the high magnetic forces which are present for driving the arc to the left in FIG. l from the instant the arc is initiated, as was explained hereinabove and (2) the fact that the tubular wall 42 of the movable contact 24 provides an immediately available conductive path along which the lower terminal of the arc can run into proximity with the arc runner 30 as soon as the arc is initiated without waiting for any further separation of the contacts. Another factor that may contribute to the high speed of arc transfer is that once the arc attaches to the lower arc runner 30 and moves slightly radially outward, there is a radiallyoutwardly acting magnetic force on it tending to drive it away from the clearance space and toward the outer periphery of the arc runner. This results from the fact that the conductor 32 for carrying current to and from an arc terminal located on the arc runner 30 is at the inner periphery of the arc runner 30. Thus, current flowing from this junction point to an arc terminal on the runner 30 ows radially outward forming an outwardly bowing loop with the arc.

In an extensive series of tests made with an interrupter constructed generally as shown in FIG. l, it was found that the arc transferred to the

runners

36 and 30 when the instantaneous gap between the contacts was only about 0.27 inch as compared to a spacing between the

arc runners

36 and 30 of about 0.625 inch. This was for an average instantaneous current of 8400 amperes at the instant of arc-transfer. For higher currents, the gap between the contacts was even shorter at the time arc-transfer to runner 30 occurred. For lower currents slightly 6 longer gaps were present when the transfer occurred, but since the lower currents can easily be interrupted anyway, these slightly longer gaps were not objectionable.

When the movable contact is in its fully open position, it is withdrawn behind the arc-running surface of the arc runner 30. This provides a desirable shielding effect since the end of the movable contact is then in a region of reduced electrical stress as compared to that present above the arc-running surface. This shielding effect reduces the likelihood of a breakdown occurring from the contact 20. The stationary contact 24 is likewise positioned behind the arc-running surface of its electrode 17 so that the same shielding effect is present at the stationary electrode to reduce the likelihood of a dielectric breakdown involving stationary contact 24.

In a preferred embodiment of my invention, the contacts and the arc runners are made of different materials. The arc runners are preferably made of copper and the contacts of an alloy that has a high resistance to contact welding, e.g., copper-bismuth, copper-lead or one of the other materials disclosed and claimed in application S.N. 151,552, Lafferty et al., filed November 10, 1961, and assigned to the assignee of the present invention. The contact rods are preferably of copper. The inserts 60 are of a material such as stainless steel that has an electrical resistivity that is high in comparison to that of the material of the contacts and the rods.

It will be noted that the inserts 60 force the current flowing through the contacts to follow the desired loopshaped path L even though the contacts engage at a point 50 on the longitudinal axis of the two conductive rods 17 and 17a. This location for the contact make point is a desirable one inasmuch as it results in the impact forces produced by closing being almost entirely compressive insofar as the

rod

17a and 21 are concerned, with little or no cantilever component. The inserts 60 preferably fit tightly within their surrounding recess and are brazed to the juxtaposed walls of the recess, thus imparting mechanical strength to the contact structure to compensate for the weakening effect of the recesses. The brazed joint extends over both the top and bottom surfaces of each recess so as to enable tensile force to be transmitted through the insert, as during an opening operation. FIG. 5, which is a cross sectional view along the line 5 5 of FIG. l, provides a more detailed illustration of the shape of the insert 60. It will be noted that the insert 60 extends from one side of the rod 17a past the contact make point 50, thus forcing the current to follow a path at one side of the rod 17a before reaching the contact make point at the center of the contact. The insert 60 in the other contact is preferably identical to the insert 6) of FIG. l and is aligned therewith.

The cup-shaped configuration of each

contact

20 or 24 serves another highly advantageous function in addition to those already described. More specifically, this configuration results in the tubular wall 20 completely surrounding the insert 60 and, thus, hiding it very effectively from any arc initiated on the outer surface of the cup-shaped contact 20. Stainless steel is not a good material for high current interruptions, and if anarc did reach the insert 60, the interrupting ability of the interrupter would be impaired. The cup-shaped conguration shown effectively prevents such impairment.

For projecting the bellows 29 from being damaged by particles ejected through the clearance space 33, two metallic shields 75 and '76 are provided between the clearance space 33 and the bellows 29. The shield 75 preferably comprises an annular plate secured at its outer periphery to the tubular conductor 32 at a location between the bellows and the clearance space 33. At its inner periphery the shielding plate 75 is spaced from the rod 21 to permit free movement of the rod without interference from the plate 75. The other shield 76 is an annular plate secured to the rod 21 at its inner periphery and spaced from the tubular conductor 32 at its outer periphery. These

shields

75 and 76 intercept and condense particles from the arcing gap before they can reach the bellows 29. The lfact that the

plates

75 and 76 overlap in a radial direction decreases the likelihood that any such particles will be able to reach the bellows inasmuch as the path for such particles is labyrinth-like.

As a further aid in preventing any binding from occurring between the contact 20 and its surrounding arc runner 30, a suitable slide bearing 65 is provided for the operating rod 21 outside the envelope 10. This slide bearing 65 which is xed relative to end plate 13, provides precise guidance for the operating rod 21 so as to preclude appreciable radial movement of the contact 2t) and possible friction between contact 20 and runner 30.

It is to be understood that all of the internal parts of the interrupter are substantially free of surface contaminants. These clean surfaces are obtained by suitably processing the interrupter, as by baking it at a suitably high temperature during its evacuation. In addition, the arcing regions of the electrodes 17 and 18 are effectively freed of gases absorbed internally thereof so as to preclude evolution of these gases during high current arcing.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects and I, therefore, intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric circuit interrupter comprising:

(a) a first contact and a second contact movable into and out of engagement with said first contact,

` (b) a first annular arc runner surrounding said first contact and electrically connected thereto,

(c) said second contact being of a cup-shaped configuration and comprising a base that is engageable with said first contact and a tubular wall that extends from said base in a direction away from the location of said first contact, movement of said second contact out of engagement with said first contact initiating an arc between said contacts having one terminal on said base of said second contact,

(d) a second annular arc runner surrounding said second contact, electrically connected thereto, and physically spaced therefrom by a clearance space surrounding the outer periphery of said tubular wall,

(e) means for mounting said annular arc runners in generally aligned relationship, with an arcing gap therebetween,

(f) said second contact being telescopically movable relative to said second arc runner along a path extending across said arcing gap,

(g) and arc-transfer means for forcing said one terminal of arcs initiated on said base to move along the outer surface of said tubular wall across said clearance space on to said second arc runner,

(h) said arc-transfer means comprising means for forcing substantially all current flowing through said cup-shaped contact to an arc terminal on said tubular wall to follow a path that extends through said base,

(i) and means for carrying current to and from an arc terminal on said second arc runner via a path that bypasses said second contact.

` 2. The circuit interrupter of claim 1 in which said interrupter is a vacuum type circuit interrupter comprising a highly evacuated envelope in which said contacts and arc runners are located, and in which said clearance space is large enough to prevent binding of said second contact within its arc runner as a result of any accumulation in the clearance space of arcing products from short circuit interruptions.

3. The circuit interrupter of claim 1 in which said annular arc runners include arc-running surfaces facing each other and in which said tubularwall of the second contact projects lfrom said base into a terminal position located behind the arc-running surface of said second arc runner when said second contact engages said rst contact.

4. The circuit interrupter of claim 1 in which:

(a) a support is provided for each of said contacts, and the contacts and the adjacent portion of said v supports constitute contact structure,

(b) said arc-transfer means comprises transverselyextending recesses in the contact structure located behind the point at which said contacts engage, said recesses being shaped to force current flowing through the point of contact engagement to follow a loopshaped path in the immediate vicinity of the contact engagement point, and

(c) there are provided inserts disposed within said recesses of a material having a high resistivity compared to that of the adjacent contact structure,

5. The circuit interrupter of claim 1 in which said contacts are mounted on generally-aligned rods extending longitudinally of said interrupter and in which said con-A tacts normally engage at a point generally aligned with the longitudinal axes of said rods, said arc-transfer means comprising recesses in the contact structure comprising said contacts and said rods extending transversely of said rods and located behind the point at which said contacts engage, said recesses being shaped to force current flowing through the point of contact engagement to follow a loop-shaped path in the immediate vicinity of the contact engagement point, and inserts disposed within said recesses of a material having a high resistivity compared to that of the adjacent contact structure.

6. The circuit interrupter of claim 1 in combination with means for producing a magnetic force on any arc between said arc runners that acts in a direction to drive the arc in a generally circular path about said contacts along said annular arc runners.

7.*An electric circuit interrupter comprising:

(b) a first, annular arc runner surrounding said first Contact and electrically connected thereto,

(c) said second contact comprising a base that is engageable with said first contact to provide an arcinitiating region and a projecting wall extending from said base in a direction away from the location of said first contact, movement of said second contact out of engagement with said first contact initiating an arc between said contacts having one terminal on said base of said second contact,

(d) a second annular arc runner having an inner periphery, said second annular arc runner surrounding said second Contact, electrically connected thereto, and physically spaced therefrom by a clearance space extending about the inner periphery of said second arc runner,

(f) said second Contact being telescopically movable relative -to said second arc runner along a path extending across said arcing gap,

(g) and arc-transfer means for forcing said one ter- Y 8. The circuit interrupter of claim 7 in which said interrupter is a vacuum type circuit interrupter comprising a highly evacuated envelope in which said contacts and arc runners are located, and in which said clearance space is large enough to prevent binding of said second contact within its arc runner as a result of any accumulation in the clearance space of arcing products from short circuit interruptions.

9. The interrupter of claim 7 in which said annular arc runners have arc ruiming surfaces facing each other and in which said projecting wall of said second Contact terminates in a position located behind the arc-running surface of said second arc runner when said second con- `tact engages said first contact.

10. The circuit interrupter of claim 7 in which said interrupter is a vacuum type circuit interrupter comprislng:

(a) a highly evacuated envelope in which said contacts and arc runners are located,

(b) a tubular conductor within said envelope and having an inner end on which said second arc runner is supported,

(c) a conductive rod extending through said tubular conductor and having an inner end on which said second contact is supported,

(d) a flexible bellows secured between said rod and said envelope for permitting movement of said rod without impairing the vacuum inside said envelope,

(e) metal shielding means disposed internally of said tubular conductor between said clearance space and said bellows for protecting said bellows from arcing products ejected through said clearance space.

11. In an electric circuit interrupter,

(a) a pair of separable contacts,

(b) one of said contacts being of a cup-shaped configuration and comprising a base that is engageable with the other Contact at a predetermined contact making region and a tubular wall that extends from said base in a direction away from said other contact,

(c) a conductive rod for carrying current to and from said one contact and joined to said one contact at said base,

(d) said tubular Wall surrounding said rod and being radially spaced therefrom,

(e) a transversely-extending recess in the Contact structure comprising said one contact and rod located behind said contact-making region,

(f) said recess being shaped to force current flowing through said contact making region to follow a 1oopshaped path in the immediate vicinity of said contact-making region,

(g) and an insert disposed within said recess of a material having a high resistivity compared to that of the adjacent contact structure,

(h) said recess being located within the space bounded said cup-shaped contact so as to hide said insert from arcs drawn between said contacts.

References Cited by the Examiner UNITED STATES PATENTS FOREIGN PATENTS 787,846 12/57 Great Britain.

BERNARD A. GILHEANY, Primary Examiner,

Claims

1. AN ELECTRIC CIRCUIT INTERRUPTER COMPRISING: (A) A FIRST CONTACT AND A SECOND CONTACT MOVABLE INTO AND OUT OF ENGAGEMENT WITH SAID FIRST CONTACT, (B) A FIRST ANNULAR ARC RUNNER SURROUNDING SAID FIRST CONTACT AND ELECTRICALLY CONNECTED THERETO, (C) SAID SECOND CONTACT BEING OF A CUP-SHAPED CONFIGURATION AND COMPRISING A BASE THAT IS ENGAGEABLE WITH SAID FIRST CONTACT AND A TUBULAR WALL THAT EXTENDS FROM SAID BASE IN A DIRECTION AWAY FROM THE LOCATION OF SAID FIRST CONTACT, MOVEMENT OF SAID SECOND CONTACT OUT OF ENGAGEMENT WITH SAID FIRST CONTACT INITIATING AN ARC BETWEEN SAID CONTACTS HAVING ONE TERMINAL ON SAID BASE OF SAID SECOND CONTACT, (D) A SECOND ANNULAR ARC RUNNER SURROUNDING SAID SECOND CONTACT, ELECTRICALLY CONNECTED THERETO, AND PHYSICALLY SPACED THEREFROM BY A CLEARANCE SPACE SURROUNDING THE OUTER PERIPHERY OF SAID TUBULAR WALL, (E) MEANS FOR MOUNTING SAID ANNULAR ARC RUNNERS IN GENERALLY ALIGNED RELATIONSHIP, WITH AN ARCING GAP THEREBETWEEN, (F) SAID SECOND CONTACT BEING TELESCOPICALLY MOVABLE RELATIVE TO SAID SECOND ARC RUNNER ALONG A PATH EXTENDING ACROSS SAID ARCING GAP, (G) AND ARC-TRANSFER MEANS FOR FORCING SAID ONE TERMINAL OF ARCS INITIATED ON SAID BASE TO MOVE ALONG THE OUTER SURFACE OF SAID TUBULAR WALL ACROSS SAID CLEARANCE SPACE ON TO SAID SECOND ARC RUNNER, (H) SAID ARC-TRANSFER MEANS COMPRISING MEANS FOR FORCING SUBSTANTIALLY ALL CURRENT FLOWING THROUGH SAID CUP-SHAPED CONTACT TO ARC TERMINAL ON SAID TUBULAR WALL TO FOLLOW A PATH THAT EXTENDS THROUGH SAID BASE, (I) AND MEANS FOR CARRYING CURRENT TO AND FROM AN ARC TERMINAL ON SAID SECOND ARC RUNNER VIA A PATH THAT BYPASSES SAID SECOND CONTACT.