US2976382A - Arc extinguishing structure for an electric circuit interrupter - Google Patents

Description

March 21, 1961 Filed June 29, 1959 T. H. LEE ARC EXTINGUISHING STRUCTURE FOR AN ELECTRIC CIRCUIT INTERRUPTER 2 Sheets-Sheet 1 Inventor: Thomas H. Lee,

b His Attorney.

March 21, 1961 T. H. LEE 2,976,382

ARC EXTINGUISHING STRUCTURE FOR AN ELECTRIC CIRCUIT INTERRUPTER 2 Sheets-Sheet 2 Filed June 29. 1959 Inventor: Thomas H. Lee

by His Attohneg United States Patent ARC EXTINGUISHING STRUCTURE FOR AN ELECTRIC CIRCUIT INTERRUPTER Thomas H. Lee, Media, Pa., assignor to General Electric Company, a corporation of New York Filed June 29, 1959, Ser. No. 823,731

18 Claims. (Cl. 200 144) This invention relates to arc-extinguishing structure for an electric circuit interrupter and, more particularly, to arc-extinguishing structure which is especially, though not exclusively, suited for use in circuit interrupters of the vacuum type.

The usual vacuum-type circuit interrupter comprises a vacuum chamber in which a circuit-interrupting arc is established across an arcing gap between two electrodes. Assuming that the circuit is an alternating current circuit, the arc maintains itself until about the time a natural current zero is reached, after which the arc is prevented from reigniting by the high dielectric strength of the vacuum.

One way of increasing the interrupting capacity of such an interrupter is by moving the terminals of the are at high speed along suitable arc-running surfaces provided within the interrupter. Such movement tends to minimize the amount of metallic vapors generated from the arc-running surfaces by the arc and tends also to increase the degree of diffusion of the vapors that are generated. These factors enable the vacuum to recover its dielectric strength at an increased rate after a current zero and thus render the vacuum more capable of preventing re-establishment of the arc during this critical interval.

In a vacuum circuit interrupter, it is highly desirable that arc motion be rotational rather than translational. This follows from the fact that vacuum arcs tend to move at very high speeds (considerably higher than the speeds occurring under corresponding conditions in more dense media, such as liquids and gases), and unless the path of arc motion is recurrent, as is the case with rotational movement, there will be insufiicient arc-ruin ning surface length available to accommodate continuous arc-motion. Since continuous arc-motion contributes to increased interrupting capacity, the desirability of rota tional arc-motion in obtaining increased interrupting capacity will be apparent.

Another way in which the interrupting capacity of a vacuum interrupter can be increased is by dividing the circuit-interrupting arc into a plurality of shorter arcs, or arclets, across a plurality of series-related gaps. After a current zero has been reached, the total dielectric strength which is developed across the series-related gaps exceeds that which would be developed across a single gap had the arc been allowed to persist across the single gap. The result is increased voltage-interrupting ability and increased current-interrupting ability as well.

An object or" my invention is to provide a simple arcextinguishing structure which employs both of these principles, i.e., rapid arc-motion in a recurrent path and division of an are into series-related smaller arcs, to aid in extinguishing the arc.

Another object of my invention is to effect the desired arc-rotation by magnetic means which is structurally simple and which requires no external coils or other similar and cumbersome magnetic devices for successful rotation of the short series-related arcs.

2,975,382 Patented Mar. 21, 196i Another object is to construct the arc-extinguishing structure in such a manner that operation of the magnetic arc-rotating means for any one of the arcing gaps does not interfere with operation of the arc-rotating means for the remaining arcing gap or gaps.

In my arc-extinguishing structure the short arcs or arclets that are formed across the secondary gaps are biased radially outwardly by a radially-outwardly-acting magnetic loop effect. Another object is to rotate the arclets about such a path that this radially-outwardlyacting magnetic loop efiect does not significantly retard or oppose the rotational motion of the arclets during any portion of their rotational travel.

In carrying out my invention in one form, I provide within a vacuum chamber a pair of electrodes defining therebetween a main arcing gap across which a circuitinterrupting arc is adapted to be established. Surrounding this main arcing gap, I provide a plurality of pairs of annular disc-shaped members radially spaced from the electrodes. The disc-shaped members of each pair are spaced apart to define between the two disc-shaped members a secondary arcing gap of annular shape surrounding the main gap. Means are provided for driving the circuit-interrupting are from the main arcing gap radially outwardly into contact with the disc-shaped members so as to divide the are into a plurality of seriesrelated arclets respectively bridging the secondary arcing gaps. Thereafter the arclets are driven onto the outer peripheral region of the disc-shaped members by means providing a magnetic force acting to hold said arclets on said outer peripheral region for substantially all angular positions of said arclets. These arclets are driven repetitively about the outer peripheral region of the disc-shaped members by magnetic forces derived as a result of slot means extending from the outer periphery of at least one disc-shaped member of each pair in such a manner that the current path extending through this one disc-shaped member to an arclet terminal located at substantially any angular point on the outer peripheral region has a net component extending generally tangentially with respect to the periphery in the vicinity of the arclet terminal.

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

Fig. 1 is a sectional view of a vacuum-type circuit in terrupter embodying one form of my invention.

Fig. 2 is a sectional view taken along the line 2-2 of Fig. 1.

Fig. 3 is a view similar to that of Fig. 2 but showing a modification of the structure shown in Fig. 1.

Fig. 4 is a sectional view taken along the line 4-4 of Fig. 1.

Referring now to the interrupter of Fig. 1, there is shown a highly evacuated envelope 10 comprising a cylindrical casing 11 and a pair of metallic end caps 12 and 13 closing off the ends of the casing. The casing 11 is of an imperforate vacuum-tight construction and is joined to the end caps by means of suitable seals 14 forming a vacuum-tight connection between the end caps and the casing 11.

The casing 11 is constructed from a series of collinearly arranged cylinders 16, 17, 18, 19, 20, and 21 of an insulating material such as glass and a series of annular metallic structures interconnecting the insulating cylinders. The annular metallic structure interconnecting the insulating cylinders 16 and 17 comprises a pair of rings 22 or L-shaped cross-section with an annular disc 24 welded between the radially extending flanges of the L-shaped rings 22 in such a manner as to provide a vacuum-tight seal between the rings 22. The opposite ends of the L-shaped rings 22 are embedded in the adjacent insulating cylinders to provide a known type of vacuum-tight seal between the rings 22 and the insulating cylinders.

The annular metallic structures interconnecting the other ably thicker than the annular disc 24. The reason for this will appear more clearly hereinafter.

Located within the envelope is a pair of separable cup-shaped contacts, or electrodes, and 31 shown in their engaged or closed-circuit positions. The upper contact 30 is a stationary contact suitably secured to a conductive rod 30a which at its upper end is united to the upper end cap 12, which serves as one electrical terminal of the interrupter. The lower contact 31 is a movable contact joined to a conductive operating rod 31a which is suitably mounted for vertical movement. The operating rod 31a projects through an opening in the lower end cap 13 and a flexible bellows 34 provides a seal about the rod 31a to allow for vertical movement of the rod 31a without impairing the vacuum inside the envelope 10. As shown in Fig. 1, the bellows 34 is secured in sealing relationship at its respective opposite ends to the operating rod 31a and the end cap 13. The lower end cap 13 serves as the other terminal of the interrupter and is electrically connected to the conductive operating rod 31a by suitable means, such as conductive braid 33, which relieves the bellows 34 of any current-carrying duty.

Coupled to the lower end of the operating rod 31a, suitable actuating means (not shown) is provided which is capable of driving the contact 31 out of engagement with the contact 30 and into the dotted line position of Fig. 1 so as to open the interrupter and which is also capable of returning the contact 31 to its illustrated solidline position so as to close the interrupter. A contactopening operation will soon be explained in greater detail.

Each contact is of a cup-shape form and has a central recess 35 surrounded by an annular contact making area 36. These annular contact-making areas 36 abut against each other when the contacts are in their closed position of Fig. l and are of such a diameter that the current flowing through the closed contacts follows a loop-shaped path L, as is indicated by the dot-dash lines of Fig. 1. This loop-shaped path has a magnetic effect which tends in a well-known manner to lengthen the loop. As a result, when the contacts are separated to form an are between the areas 36, the magnetic efiect of the loop will impel the arc radially outward.

For receiving the respective terminals of the are when it is impelled radially outward by the magnetic loop effeet, a pair of annular arc-runners 37 and 38 of a gen erally conical form are provided. The upper arc-runner 37 is mechanically and electrically joined to the upper contact 30, whereas the lower arc-runner 38 is mechanically separate from the movable contact 31 but electrically connected thereto by means of a tubular support 38a, slightly flared at its upper end, fastened to the lower end cap 13 and located at the inner periphery of the arcrunner 38. Any current flowing through either of these arc-runners to an arc terminal located thereon must flow from the inner periphery of that particular runner radially outward. Thus the path for such current will coact with the arc to form a radially-outwardly bowing loop circuit. Accordingly, when the arc terminals are located at any point on the runners 37 and 38, the radially-outwardly acting-loop circuit is still present to impel the arc radially outward. For example, note the radiallyoutwardly bowing loop circuit when the arc is passing through a typical position on the arc-runners such as shown at 39; The fact that the lower arc-runner 38 is separate from the movable contact 31 appreciably reduces the mass of the structure that the interrupter actuating means is required to accelerate during an interrupter op- 4 eration and therefore contributes to the desired high operating speeds.

When an arc is initiated by contact-separation, the upper arc terminal is first driven off the contact making area 36 of contact 30 onto the upper arc-runner 37, and shortly thereafter, as the lower contact 31 approaches its dotted line open position, the lower arc terminal is driven onto the lower arc-runner 38. Because the lower arc-runner 38 surrounds the movable contact, the lower arc terminal will be driven onto the lower arc-runner irrespective cf its particular circumferential location at this instant. The magnetic loop ettect drives the arc terminals radially outward at high speed along the arc runners until the arc encounters arc-splitting and rotating means 40 surrounding the annular arc-runners 37 and 38. The arc-splitting and rotating means 40 acts in a manner soon to be described to divide the arc into a plurality of series-related shorter arcs, or arclets, and thereafter to rotate these arclets about the longitudinal axis of the interrupter.

The arc-splitting and rotating means 40 comprises a plurality of discs 41, 42, 43, 44, 45, and 46 arranged in substantially parallel spaced-apart planes to define a series of secondary arcing gaps between certain of the discs, as will soon be pointed out more clearly. The upper disc 41 is supported on the upper end cap 12 by means of a conductive tube 48 integrally united at one end to the disc 41 at the inner periphery of the disc 41 and integrally united at its other end with the upper end cap 12. Lower disc 46 is similarly joined to the lower end cap 13 by means of a conductive tube 49 integrally joined at its opposite ends to the disc 46 and the end cap 13. The upper set of intermediate discs 42 and 43 are conductively interconnected by means of a conductive tube 50 integrally joined at its longitudinally-opposite ends to the discs 42 and 43 at the inner peripheries of the discs 42 and 43. Likewise, the lower set of intermediate discs 44 and 45 are conductively interconnected by means of a conductive tube 2 integrally joined at its opposite ends to the discs 44 and 45 at the inner peripheries of the discs. The location of the tubular conductors 49-52 at the inner periphery of the discs contributes in an important manner to the desired performance of my arc-extinguishing structure, as will soon become more apparent.

The upper intermediate structure 42, 43, St is supported from the casing 11 by means of the previously described annular support 26, which is welded or otherwise secured at its inner periphery to the tube 50. The lower intermediate structure 44, 45, 50 is likewise sup ported from the casing 11 by means of the supporting annulus 23 which is welded or otherwise secured at its inner periphery to the tube 52.

As will be apparent from Fig. 1, the insulating cylinders 16 and 17 electrically isolate the discs 41 and 42 from each other, and thus a first secondary arcing gap 53 is defined between these two discs 41 and 42. The insulating cylinders 18 and 19 isolate the discs 43 and 44 from each other and thus a second secondary arcing gap 54 is defined between these two discs 43 and 44. Similarly, the insulating cylinders 20 and 21 electrically isolate discs 45 and 46 from each other so that a third secondary arcing gap 55 is defined between the discs.45 and 46.

Each of the discs 41-46 is provided with slots 57, shown in Fig. 2, extending from the outer periphery of the disc inward. These slots collectively divide each of the discs into a series of discrete segments 58 angularly spaced about the inner periphery of each disc. In the preferred form of my invention illustrated in Fig. 2, these slots 57 are shown as being of a generally spiral configuration terminating in a mouth 59 at the disc periphery. Each slot extends from its mouth 59 in a generally tangential direction with respect to the periphery and terminates only after extending at least to a point near the angular position of the mouth of an adjacent slot. Preferably, the adjacent slots angularly overlap each other as is shown in Fig. 2. The importance of the above-described slot configuration will soon be pointed out in more detail.

Assume now that an arc established during a circuit interrupting operation is driven radially outward along the arc-runners 37 and 38. As soon as the arc encounters the arc-splitting means 40, it is divided into three shorter series-connected arcs across the respective arcing gaps 53, 54, and 55. Each of these shorter arcs, or arclets, continues to move radially-outward until its two terminals reach the outer peripheral region of the discs. A typical position for the upper terminal of the arc across the upper gap 53 is shown for example in Fig. 2 where the arc terminal is designated 60. Considering now that current is flowing to or from the upper arc terminal 60 solely through the tube 48 at the inner periphery of the disc 41, it will be apparent that because of the slots 57 substantially all of the current flowing between the conductive tube 48 and the arc terminal 60 is concentrated in that particular segment 58 which is then carrying the arc terminal. Because of the generally spiral configuration of the slots 57, this current is required to follow a path which is to an effective extent tangential with respect to the disc periphery in the region of the are, as is illustrated by the dotted line of Fig. 2. As a result of this tangential configuration of the current path, the magnetic loop has developed a net tangential force component. This not tangential force component drives the arc in an angular, or circumferential, direction about the disc periphery, causing it to move to the end of the segment 58 and to jump across the slot 57 to the next segment 58. The current flow to the arc is then concentrated in this next segment, and because of the configuration of this segment, there is a new tangentially-acting loop which continues motion of the arc around the contact periphery. For each of the segments 58, there is a net tangential force component on the are acting in the same angular direction, and, as a result, circumferential motion of the arc continues at high speed until the arc is finally extinguished. It will be apparent, of course, that if the arc is not extinguished before one revolution is completed, motion will continue repetitively about the disc periphery until the arc is finally extinguished.

It will thus be. seen that my arc-splitting and rotating structure 40 acts not only to divide the main are into a plurality of series-related shorter arcs but also to rotate the shorter arcs' about the longitudinal axis of the interrupter. Such are motion tends to minimize the amount of vapors generated from the are running surfaces by the arc and tends also to increase the degree of diffusion of the vapors that are generated. These factors enable the vacuum to recover its dielectric strength at an increased rateafterra current zero and, thus, render the vacuum more capable of p eventing reestablishment of the arc during this critical interval. Dividing the main arc into three series-related arcs also contributes to increased current and voltage interrupting capacity because the total dielectric strength developed across the series-related arcing gaps after a current zero exceeds that which would have been developed across a single gap had the arc been allowed to persist across the single gap.

' It is to be noted that when the arclets have been established across the secondary arcing gaps 53, 54, 55, the

current paths leading to the arclets no longer extend.

through the arc-runners 37 and 38 but rather extend through the conductive tubes 48 and 49. This follows from the fact that these tubes 48 and 49 are directly connected to the discs 41 and 46, respectively, rather than being electrically isolated therefirom, as is the case with arc-runners 37 and 38, which are separated from the discs 41 and 46 by means of vacuum gaps 70 surrounding the outer peripheries of the arc-runners. These gaps prevent current from flowing through the tubes 48 and 49 While the arc is still on the runners 37 and 38 and thus insure 6 that the magnetic loop circuit acts in a' radially-outward direction during such interval.

In the disclosed interrupter, the net tangential force component acting on each series-related arclet is more pronounced when the arclet is located near the outer periphery of the disc, as compared to when the arc is located near the inner periphery of the disc. It is therefore important that the arclets be consistently driven on to the outer peripheral region of the discs, rather than be allowed to hang on to the inner peripheries, where there is no appreciable arc-rotating force. To assure that the arclets are driven onto the outer periphery, I locate and construct the conductors leading to and from the discs- 41-46 in such a manner that the current path leading to and from the arc terminal on the disc always forms with the are a loop that has a magnetic .eflect acting radially outward. In this regard, it is to be noted that the tubular conductors 48-52 leading to and from the discs 41-46 are located at the inner peripheries of the discs. Hence, any current flowing through a disc to or from the terminal of an arclet must follow a path that extends radially outward from the inner periphery of the disc, thus providing a radially-outwardly acting loop circuit with the arc, as is desired. To provide for the transient situation that occurs when the terminal of an arclet is positioned at the inner periphery of the discs, each disc is provided with a bevel b at its inner periphery. Because of this bevel the radially innermost position on the disc at which an arclet is likely to be positioned is at the radially outer periphery of the bevel, as is illustrated for example by the position of arclet 62 is Fig. 1. Even at this position, the current path 63 extending through the tubes 48 and 50 through the terminals of the arclet forms a loop bowing radially outward and therefore providing a magnetic force acting radially outward on the arclet. As the arclet moves radially outward from this point, the loop and, hence, the radially-outwardly acting magnetic force becomes more pronounced, thus tending to bias the arclet toward the outer periphery of the disc where the arc-rotating force is greatest.

It will be apparent that the tubular conductor 50 between the adjacent discs 42 and 43 in forcing all the current flowing between these discs to follow a path through the inner periphery of the discs 42 and 43, assures that a radially-outwardly-acting loop circuit will be present on the arclet 62a at gap 54 no matter where the arclet at the upper gap 53 is located. Accordingly, the arclet at the gap 54 can be driven on to the outer periphery of discs 43 and 44 and rotated in the desired manner irrespective of the location of the arclet at gap 53. Similarly, the arclet at gap 53 can be driven onto the outer disc periphery and rotated in the desired manner irrespective of the location of the arclet at gap 54. A similar independence is present between the arclet 62b at the lower gap 55 and the other arclets due primarily to the inner peripheral location of the various tubular conductors 48-52. Thus, it will be apparent that the operation of the magnetic means at any one of the gaps does not interfere with the operation of the magnetic means at the other gaps.

An important advantage that isderived from rotating the arclets about the electrodes 30, 30a as an axis is that the radially-outwardly acting magnetic loop effect that is present does not oppose the rotary motion of the arclets at any point in their circumferential travel. The arclets, in moving about the electrodes as an axis, are not required to move toward the electrodes and, thus, the radially-outwardly acting loop eflect does not interfere with the desired rotary motion. If, on the other hand, the arclets were rotated about some axis remote from the electrodes, part of the rotary travel would be generally toward the electrodes, and the radially-outwardly acting magnetic loop circuit would tend to oppose arc-rotation during this particular portion of the rotary travel. Such opposition would tend to diminish the desired high speed of arc-motion.

The arclets formed. across the secondary arcing gaps 53, 54,, and SS-Will generate metallic vapors that will be ejected radially outward toward the insulating casing 11. For protecting the insulating casing 11 from being metallically coated by the condensate of these metallic vapors, I have provided a cylindrical vapor-condensing shield for each secondary arcing gap. These shields, which are respectively designated 73, 75,. and 77, are preferably of metal and are supported on the casing 11 by means of the previously-described plates 24 sandwiched between the L-shaped rings 22. The vapors generated by arcing condense on these shields 73, 75, and 77 before they can reach the insulating cylinders 16-21 and thus the cylinders are protected from the build-up of a metallic coating thereon. It is to be noted that each of these vapor-condensing shields 73, 75, and 77 is electrically isolated from the disc-shaped electrode members 4-1-46 oneach side of its corresponding secondary arcing gap. For example, the shield 73' is electrically isolated from the disc-shaped electrodes 41 and 42 by the insulating cylinders 16 and 17; the shield 75 is electrically isolated from the disc-shaped electrodes 43 and 44 by the insulating cylinders 18 and 19'; and the shield 77 is isolated from the disc-shaped electrodes 45 and 46 by means of the insulating cylinders 20 and 21.

Preferably, the length of the insulating cylinders and the gaps between the disc-shaped electrodes and the shields are so selected that the shield for each secondary arcing gap is at approximately a mid-potential relative to the disc-shaped electrodes (41-46) of the corresponding arcing gap when the contacts 3% and 31 are separated. This, in combination with the fact that the opposed electrodes are disc-shaped and of substantially the same configuration, enables the electric field in the region of each secondaly arcing gap to be generally symmetrical With respect to a plane bisecting the arcing gap and extending generally perpendicular to the longitudinal axis of the interrupter or the contact rods a, 31a. Since substantially all of the vapors liberated by arcing are condensed on the metallic shields before they can reach the insulating casing, it will be apparent that the midpotential relationship of the shield relative to the electrodes of its corresponding arcing gap is not substantially changed by the metallic particles. Thus, the generally symmetrical configuration of the electric field for each arcing gap is retained without substantial change despite the condensation of metallic vapors on the shield. The generally symmetrical field relationship is of considerable benefit in minimizing the polarity effect that has been noted in connection with arcing gaps generally. More specifically, it has been noted that arcing gaps generally have a lower breakdown strength when subjected to voltage of one polarity than when subjected to voltage of an opposite polarity. The more non-symmetrical is the electric field in the region of the gap the more pronounced in this polarity effect. By providing a symmetrical electric field, I am able to minimize this polarity.

effect. As a result, my interrupter is not subject to the unduly prolonged arcing that could result from low dielectric strength during alternate half cycles. Because the symmetrical electric field is retained despite vapor condensation on the shields, the beneficial effects of the symmetrical electric field are retained despite repeated switch operations.

To aid in more precisely obtaining the desired voltage distribution between the secondary arcing gaps and between the shields and their associated electrodes, it is sometimes desirable to connect external grading capacitors across, each of the insulators 16-41. Such capacitors can boot a conventional form and are not shown in the drawing.

Although I prefer to slot the contact disc in the. general manner illustrated, in. Fig 2, other slot. configurations.

8 are also suitable. however, the disc should be slotted from its outer. periphery inward, and the slot configuration should be such that the current path extending through the disc to an arc:

terminal located at substantially any angular point. on the outer peripheral region has a net component extending generally tangentially withrespect to the periphery in the vicinity of the are. In addition, the slot configuration should be such that this net tangential component extends from the arc in the same angular direction for substantially all angular positions of the are on the peripheral region of the disc, so that motion of the arc terminal is continued in a single angular direction. By the term angular direction, used hereinabove, is meant a clockwise of counterclockwise direction relative to the central region of the disc.

As an example of another slot configuration which meets these requirements, reference may be had to Fig. 3, which is a plan view of a modified form of the discshaped member. in this arrangement of Fig. 3, a single slot extends from the outer periphery of the disc 41a inwardly toward the center of the disc. This slot 80 has an angular extent of more than 360 degrees, which is much greater than that of slot 57 of Pig. 2. As a result, this slot 80 is alone sufficient to force all current flowing to an arc terminal located at substantially any angular point on the outer peripheral region to follow a path having a net component extending generally tangentially with respect to the periphery in the vicinity of the arc.

Although I prefer that both of the discs of each gap be slotted, it is to be understood that only a single disc of each gap may be slotted if lower speeds of arc-rotation can be tolerated.

It is to be understood that, in constructing the disclosed vacuum interrupter, the various parts inside the vacuum. envelope should be freed of the sorbed gases and other contaminants sufiiciently to avoid harmful impairment of the vacuum during operation. Conventional vacuum processing techniques can be used for attaining this desired end.

While I have shown and described particular embodiments 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 an desire to secure by Letters Patent of the United States is:

1. A vacuum-type circuit interrupter comprising an evacuated envelope defining a vacuum chamber, a pair of electrodes disposed within said vacuum chamber and defining therebetween a main arcing gap across which a circuit-interrupting arc is adapted to be established, a plurality of pairs of annular disc-shaped members surrounding said arcing gap and radially spaced from said electrodes, the disc-shaped members of each pair being spaced apart to define between the two disc-shaped members a secondary arcing gap of annular shape surrounding said main gap, means for driving said circuit-interrupting are from said main arcing gap radially outward into contact with said disc-shaped members and for thereafter dividing said circuit-interrupting are into a plurality of series-related arclets respectively bridging said secondary arcing gaps, means for thereafter driving each of said arclets onto the outer peripheral region of said discshaped members and for providing a magnetic force acting to hold said arclets on said outer peripheral region for substantially all angular positions of said arclets, means for producing motion of said arclets repetitively about the outer peripheral region of said disc-shaped members comprising slot means extending from. the1outer.

periphery of at least. one. disc-shapedmember: of: each In any of these slot configurations,

therebetween a main arcing gap across which a pair in such a manner that the current path extending through said one disc-shaped member to an arclet terminal located at substantially any angular point on said outer peripheral region has a net component extending generally tangentially with respect to said periphery in the vicinity of said arclet terminal.

2. In the vacuum-type circuit interrupter of claim 1, an annular arc-runner surrounding each of said electrodes and extending between its associated electrode and one of said disc-shaped members to provide means for transferring-said main arc'from said main arcing gap to said secondary arcing gaps.

3. In the vacuum-type circuit interrupter of claim 1, an annular arc-runner surrounding each of said electrodes and extending between its associated electrode and one of said disc-shaped members to provide means for transferring said main are from said main arcing gap to said secondary arcing gaps, means for conducting current to and from said disc-shaped members by a path independent of said arc-runners when said arclets are positioned across said secondary arcing gaps, means including insulation located between said disc-shaped members and the outer periphery of said annular arc-runners for forcing any current flowing through said runners to an are located on said runners to follow a path extending from the inner peripheral region of said annular arcrunners radially outwardly.

4. The vacuum-type circuit interrupter of claim 1 in combination with conductive structure electrically interconnecting the adjacent disc-shaped members of adjacent arcing gaps and conductive structure electrically interconnecting the outermost disc-shaped members with the electrodes of said interrupter, said conductive structure being joined to said disc-shaped members adjacent their innermost peripheries so that for each arcing gap the radially-acting loop circuit defined by the arclet and the current path leading through the disc-shaped member in the immediate region of the arclet acts in a direction radially outward.

5. An electric circuit comprising a housing,

a pair of electrodes disposed within said housing and defining circuitinterrupting arc is adapted to be established, a plurality of pairs of disc-shaped members surrounding said arcing gap and radially spaced from said electrodes, the discshaped members of each pair being spaced apart to define between the two disc-shaped members a secondary arcing gap of annular shape surrounding said main gap, means for driving said circuit-interrupting are from said main arcing gap radially outward into contact with said disc-shaped members and for thereafter dividing said circuit-interrupting are into a plurality of series-related arclets respectively bridging said secondary arcing gaps, means for thereafter driving each of said arclets onto the outer peripheral region of said disc-shaped members and for providing a magnetic force acting to hold said arclets on said outer peripheral region for substantially all angular positions of said arclets, means for producing motion of said arclets repetitively about the outer peripheral region of said disc-shaped members comprising slot means extending from the outer'periphery of at least one disc-shaped member of each pair in such a manner that the current path extending through said one discshaped member to an arclet terminal located at substantially any angular point on said outer peripheral region has a net component extending generally tangentially with respect to said periphery in the vicinity of said arclet terminal.

6. A vacuum-type circuit interrupter comprising an evacuated envelope defining a vacuum chamber, a pair of electrodes disposed within said vacuum chamber and defining therebetween a main arcing gap across which a circuit interrupting are is adapted to be established, a plurality of pairs of annular disc-shaped members disposed about said arcing gap and radially spaced from said electrodes, the disc-shaped members of each pair being spaced apart to define between the two disc-shaped members a secondary arcing gap of annular shape surrounding said main gap, means for driving said circuitinterrupting are from said main arcing gap radially outward into contact with said disc-shaped members and for thereafter dividing said circuit-interrupting are into a plurality of series-related arclets respectively bridging said secondary arcing gaps, means for thereafter driving each of said arclets onto the outer peripheral region of said disc-shaped members and for providing a magnetic force acting to hold said arclets on said outer peripheral region for substantially all angular positions of said arclets, means for producing motion of said arclets repetitively about the outer peripheral region of said disc-shaped members comprising slot means extending from the outer periphery of at least one disc member of each pair in such a manner that the current path extending through said one disc member to an arclet terminal located at substantially any angular point on said outer peripheral region forms with said arclet a loop circuit having a magnetic efr'ect exerting a net' component of force on the arclet generally tangential with respect to said periphery, said net tangential force component acting in the same angular direction for substantially all angular positions of said arclet on said periphery and thereby causing said arclet to travel rapidly in one angular direction along the outer peripheral region of said disc member.

7. A vacuum-type circuit interrupter comprising an evacuated envelope defining a vacuum chamber, a pair of electrodes disposed within said vacuum chamber and defining therebetween a main arcing gap across which a ci cuit-interrupting arc is adapted to be established, a plurality of pairs of annular disc-shaped members disposed about said arcing gap and radially spaced from said electrodes, the disc-shaped members of each pair being spaced apart to define between the two disc-shaped members of each pair a secondary arcing gap of annular shape surrounding said main gap, means for driving said circuit-interrupting are from said main arcing gapradially outward into contact with said disc-shaped members and for thereafter dividing said circuit interrupting are into a plurality of series-related arclets respective-1y bridging said secondary arcing gaps, means for thereafter driving each of said arclets onto the outer peripheral region of said disc-shaped members and for providing a magnetic force acting to hold said arclets on said outer peripheral region for substantially all angular positions of said arelets, means for producing motion of said arclets repetitively about the outer peripheral region of said discshaped members comprising a plurality of slots formed in at least one of said disc-shaped members, each slot having a mouth located at the outer periphery of said one discshaped member and each extending from said outer periphery inward, said slots having portions which extend in a generally tangential direction with respect to the adjacent periphery of said one disc-shaped member, the angular direction followed by the generally tangential portion of each of said slots in departing from the slot mouth being the same for each of said slots.

8. A vacuum-type circuit interrupter comprising an evacuated envelope defining a vacuum chamber, a pair of electrodes disposed within said vacuum chamber and defining therebetween a main arcing gap across which a circuit-interrupting arc is adapted to be established, a plurality of pairs of annular disc-shaped members surrounding said arcing gap and radially spaced from said electrodes, the disc-shaped members of each pair being spaced apart to define between the two disc-shaped members a secondary arcing gap of annular shape surrounding said main gap, means for driving said circuit-interrupting are from said main arcing gap radially outward into contact with said disc-shaped members and for thereafter dividing said circuit-interrupting are into a plurality of series-related arclets respectively bridging said second ary arcing gaps, means for thereafter driving each of said arclets onto the outer peripheral region of said disc-shaped members and for providing a magnetic force acting to hold said arclets on said outer peripheral region for substantially all angular positions of said arclets, and arc-rotating means for producing motion of said arclets repetitively about the outer peripheral region of said disc-shaped members, said arc-rotating means comprising means for generating a magnetic field which acts on said arclets in a generally tangential direction relative to said disc members.

9. The interrupter of claim 8 in which said envelope is constructed partially of insulating material and in which there is provided a plurality of metallic vaporcondensing shields respectively surrounding said secondary arcing gaps and disposed between said secondary arcing gaps and insulating portions of said envelope to protect said insulating port-ions from the condensation of arcliberated vapors thereon, and means comprising said protected insulating portions for electrically isolating the shield of each secondary arcing gap from the disc members of said secondary arcing gap and for electrically isolating said shields from each other.

10. The interrupter of claim 9 in which each of said shields is at substantially a mid-potential with respect to its associated disc members while said interrupter is in an open position. 11. The interrupter of claim 9 in which each of said shields has a potential relative to one of its associatetd disc members in open-circuit position of the interrupter which is a predetermined percentage of the potential between its associated disc members in open-circuit position of the interrupter, said predetermined percentage being retained without being substantially changed by the condensation of said metallic vapors on said metallic shield even from a time prior to the condensation of said metallic vapors thereon.

12. The interrupter of claim 9 in which each of said arcing gaps has an electric field which is generally symmetrical with respect to a central plane extending between the disc members of said arcing gap normal to said electrodes and which retains its general symmetry despite the condensation of said metallic vapors on the shield of said arcing gap.

13. In the vacuum-type circuit interrupter of claim 8, an annular arc-runner surrounding each of said electrodes and extending between its associated electrode and one of said disc-shaped members to provide means for transferring said main are from said main arcing gap to said secondary arcing gaps.

14. In the vacuum-type circuit interrupter of claim 8, an annular arc-runner surrounding each of said electrodes and extending between its associated electrode and one of said disc-shaped members to provide means for transferring said main are from said main arcing gap to said secondary arcing gaps, means for conducting current to and from said disc-shaped members by a path independent of said arc-runners when said arclets are positioned across said secondary arcing gaps, means including insulation located between said disc-shaped members and the outer periphery of said annular arc-runners for forcing any current flowing to an are located on said runners to follow a path extending from the inner peripheral region of said annular arc-runners radially outwardly.

15. An electric circuit interrupter comprising a housing, a pair of electrodes disposed within said housing and defining therebetween a main arcing gap across which a circuit-interrupting are is adapted to be established, a plurality of pairs of annular disc-shaped members surrounding said arcing gap and radially spaced from said electrodes, the disc-shaped members of each pair being spaced apart to define between the two disc shaped members a secondary arcing gap of annular shape surrounding said main gap, means for driving said circuit-interrupting are from said main arcing gap radially outward into contact with said disc-shaped members and for thereafter dividing said circuit-interrupting are into a plurality of series-related arclets respectively bridging said secondary arcing gaps, means for thereafter driving each of said arclets onto the outer peripheral region of said disc-shaped members and for providing a magnetic force acting to hold said arclets on said outer peripheral region for substantially all angular positions of said arclets, and arc-rotating means for producing motion of said arclets repetitively about the outer peripheral region of said disc-shaped members, said arc-rotating means comprising means for generating a magnetic field which acts on said arclets in a generally tangential direction relative to said disc members.

16. An electric circuit interrupter comprising a housing, a pair of electric terminals located at opposite ends of said housing, a plurality of pairs of annular disc-shaped electrodes located within said housing in generally parallel planes, the disc-shaped annular electrodes of each pair being spaced apart to define an arcing gap between the electrodes of said pair, means for forcing substantially all current flowing between the adjacent annular electrodes of adjacent arcing gaps to follow a current path adjacent the inner peripheries of said annular electrodes comprising conductive structure electrically interconnecting said adjacent electrodes and located adjacent the inner peripheries of said adjacent annular electrodes, means for conducting current between the outermost annular electrodes and said terminals and forcing substantially all of said current to follow a path adjacent the inner pe' riphery of said outermost annular electrodes comprising conductive structure interconnecting said terminals and said outermost annular electrodes and located at the inner peripheries of said outermost electrodes, means for establishing an arc radially inwardly of said annular electrodes, means for forcing said arc radially outwardly into contact with said annular electrodes and for thereafter dividing said are into a series of arclets respectively bridging said arcing gaps, and means for rotating said arclets about the outer peripheral region of said disc-shaped members.

17. A circuit interrupter comprising an evacuated envelope defining a vacuum chamber, a pair of contacts disposed within said vacuum chamber, one of said contacts being movable with respect to the other of said contacts to establish a circuit-interrupting arc therebetween, an annular arc-runner fixed with respect to said envelope and closely surrounding the movable contact about substantially the entire outer periphery of said movable contact, means for driving one of the terminals of said circuit-interrupting arc radially outward from said movable contact to said annular arc-runner, means for carrying current to and from any arc terminal located on said annular arc-runner comprising conducting means located at the inner periphery of said annular arc-runner, and insulating means for forcing substantially all current flowing through said arc-runner to any arc terminal thereon to follow a path that extends through said conducting means at the inner periphery of said annular arc-runner and that forms with an are at any point on said annular arcrunner a radially-outwardly-acting magnetic loop circuit.

18. In an electric circuit interrupter comprising a housing, a pair of contacts disposed within said housing, one of said contacts being movable relative to the other of said contacts to establish a circuit-interrupting are therebetween, an annular arc-runner fixed with respect to said housing and closely surrounding the movable contact about substantially the entire outer periphery of said movable contact, means for driving one of the terminals of said circuit-interrupting arc radially outward from said annular arc-runner a radially-outwardly-acting magnetic movable contact to said annular arc-runner, means for loop circuit. carrying current to and from any are terminal located on said annular arc-runner comprising conducting means 10- Refel'finces Cited in the file of this Patent cated at the inner periphery of said annular arc-runner, 5 UNITED STATES PATENTS and insulating means for forcing substantially all current 2 027 836 Rankin et a1 Jan 14 1936 flowing through said arc-runner to any are terminal 2:051:378 Hampton et 1936 thereon to follow a path that extends through said conducting means at the inner periphery of said annular arc- FOREIGN PATENTS runner and that forms with an are at any point on said 10 389,463 Great Britain Mar. 6, 1933

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