US2147419A

US2147419A - Circuit interrupter

Info

Publication number: US2147419A
Application number: US27353A
Authority: US
Inventors: Benjamin P Baker
Original assignee: Westinghouse Electric and Manufacturing Co
Current assignee: CBS Corp
Priority date: 1935-06-19
Filing date: 1935-06-19
Publication date: 1939-02-14
Anticipated expiration: 1956-02-14

Description

- Feb. 14, 1939.

B. P. BAKER CIRCUIT INTERRUPTER Filed June 19, 1935 3 Shoots-Sheet l ago WITNESSES:

KJQ l INVENTOR Wk/W/k/ fifaz" ATTORNEY Feb. 14,1939. 8. P. BAKER CIRCUIT INTERRUPTER Filed June 19, 1935 3 Sheets-Sheet 2 w x M M w M v 2 J %m w fix ATTORNEY Feb. 14, 1939. B. P. BAKER CIRCUIT'INTERRUPTER Filed June 19, 1935 3 Sheets-Sheet 3 jm/v. Jrzw 7/" E f [va/v INVENTOR Patented Feb. 14, 1939 UNITED STATES PATENT OFFICE CIRCUIT INTERRUPTER Pennsylvania Application June 19,

17 Claims.

My invention relates to circuit interrupters, and particularly to are extinguishing devices of the spaced-plate type for use therewith.

In their usual form, these devices include a plurality of spaced, superposed plates of magnetic material which are supported adjacent to the path along which the arc is established by the associated are drawing means. Each of the plates of magnetic material is provided with a notch or slot which extends inwardly from one edge thereof, and these slots or notches so alter the magnetic field adjacent the are that the arc is caused to move into the extinguishing device by the resultant magnetic reaction thereon.

' When the'arc contacts the inner end of these slots, it sub-divides into a plurality of serially connected short arcs, each of which exists in the spacebetween two adjacent plates. The magnetic reaction which caused the main arc to move into the arc extinguisher is still efiective at the time that this sub-division occurs, and each of the short arcs is caused to move laterally in the space wherein it is established.

By proper esign of the plates, it is possible to cause the short arcs to be moved at such speed that they may at times exist in the so-called cold cathode state, which is to say that the ends of each of the short arcs are allowed to contact the surfaces of the adjacent plates between which the arc exists for such a short period of time that no portion of the opposed plate surfaces is heated to a sufiiciently high temperature to cause the emission of free electrons at a rapid rate or to effect the liberation of substantial amounts of metallic vapor.

When an alternating current are is being extinguished in such a structure, the existence of are conditions which even approximate the cold cathode state will make it necessary for the arc to restrike after each zero point in the current wave across the space between the adjacent plates without material aid from the electron emission which would result if the opposed metallic surfaces between which the arc had previously existed were heated to an electron emitting temperature. In view of this, it is apparent that it is much more diflicult for the arc to restrike, and hence the operation of the are extinguisher is much more efficient, if the individual short arcs can be caused to move at a sufficiently rapid speed to minimize electron emission and to prevent substantial volatilization of the conductors between which the arc exists.

While, for the purpose of decreasing the probability that the short arcs shall restrike after the 1935, Serial No. 27,353

occurrence of a zero point in the current wave, it is desirable to move those short arcs as rapidly as possible, some difliculty has been experienced in the past, particularly with the higher voltage are extinguishing devices, as a result of the short arcs being moved entirely through the are extinguisher. This difficulty may in some instances be corrected through the utilization of larger plates of magnetic material, but larger plates require more space, and in many applications, larger plates are impracticable for the reason that the amount of available space within the circuit interrupter does not permit their use. Thus the primary object of the present invention is to provide means whereby the voltage rating of spaced plate type are extinguishing devices of given physical dimensions may be substantially increased without danger that the arc shall be moved entirely through the extinguisher and thereby produce undesirable flash-overs or the like duringthe normal operation of the device.

A second object of the invention is to provide means for directing and controlling the path of movement of the individual short arcs which are formed during the operation of spaced plate type are extinguishing devices while at the same time allowing free venting of the spaces wherein the short arcs are caused to move.

A further object of the invention is to provide a simple and inexpensive means, readily adaptable to existing designs of spaced plate type are extinguishing devices, for increasing their voltage rating either by preventing the short arcs formed incident to their operation from being moved'entirely through the spaces between the adjacent superposed plates or by providing auxiliary arc extinguishing means of high are extinguishing capacity for backing up the spaced plate portion of the extinguisher.

In accomplishing the above objects of the invention, I provide plates or other means of insulating material scientifically positioned within the spaces intermediate the slotted plates of magnetic material for controlling the path of movement of the individual short arcs and for preventing those arcs from being moved entirely through the arc extinguishing device. In one embodiment of my invention, these insulating members takethe form of notched plates somewhat similar in outline to the plates of magnetic material, and in another embodiment which, incidentally, has been found particularly effective, the insulating means comprises perforated members disposed between the plates of magnetic me.-

terial in the rear of the arc extinguishing structure. In this latter structure, the perforated members comprise the high capacity are extinguishing means for backing up the spaced plate extinguisher.

Due to the limited space requirements for circuit breaker structures generally, the art is continuously confronted with the problem of increasing the voltage rating of such devices without increasing the space occupied by the interrupter itself. The amount of contact separation for a breaker of any given size is ordinarily rather definitely limited, because it is impossible to utilize an actuating mechanism of more than a predetermined size in any given space. Thus, any increase in the rating of a breaker must be accomplished principally through the improvement of the arc extinguishing means. In the foregoing, it has been shown how increased rating of the arc extinguishing means may be effected through control of the paths of movement of the short arcs. ,It is also possible to secure increased rating by the provision of additional plates in the arc extinguishing structure. To successfully utilize additional plates, however, some means must be provided for assuring sufficient lengthening of the arc incident to the opening of the breaker over and above that produced by the separation of the breaker contacts. The accomplishing of this arc lengthening comprises an additional object of the invention.

The features of the invention which I believe to be new are particularly pointed out in the appended claims, and for a full understanding of those principles and the preferred method of accomplishing them, reference may be had to the accompanying drawings and description, in which:

Figure 1 is a plan view, partially in section, of a three-pole circuit interrupter utilizing arc extinguishing devices constructed according to the present invention. A substantial portion of the cover of the circuit interrupter has been cut away in order to more clearly illustrate the structural features.

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

Fig. 3 is an enlarged plan view of one of the arc extinguishing devices forming a part of the interrupter illustrated in Figs. 1 and 2.

Figs. 4 through '7, inclusive, are plan views of the various plates which are used in the arc extinguishing structure illustrated inliig. 3.

Fig. 8 is a fragmentary view showing one of the arc extinguishing devices and the associated movable contact member of the interrupter shown in Figs. 1 and 2. The movable contact is in the open circuit position and a portion of one of the side walls of the arc extinguisher has been cut away in order to more clearly illustrate several elements thereof.

Fig. 9 is a view similar to Fig. 3 of a modified form of the spaced plate type arc extinguisher of my invention.

The three pole circuit interrupter shown in Figs. 1 and'2 comprises generally a base I of molded insulating material, a cover 3 also of molded insulating material and adapted to cooperate with the base I so as to substantially completely enclose the several elements of the interrupter, six terminal members 5, each of which is supported upon the base I for connecting each pole of the interrupter into an electrical circuit, three stationary contacts 1, three moving contacts 9 for cooperating therewith, an actuating mechanism I I for simultaneously moving the contacts from one position to the other, an arc extinguishing device I3 for each pair of cooperating contacts, and a trip device I5, which includes electro-responsive means operable upon the occurrence of predetermined conditions to cause the actuating means to automatically move the contacts to the open circuit position. Neither the actuating mechanism II nor the trip device I5 comprises an important part of the present invention, and any of the structures well known in the art may be used. The particular structures illustrated in the drawings are substantially similar to those shown in the copending applications of Jerome Sandin, Serial No. 640,214, filed October 29, 1932, and Ture Lindstrom, Serial No. 667,624, filed April 24, 1933, and which are assigned to the assignee of this application.

Each of the stationary contacts I includes a fiat strip ll of conducting material which is affixed to the base I by means of a pair of cap screws I9 and two contact members 2I and 23 supported on the strip 11. The lower contact member 23 of silver comprises the main current carrying contact and the upper contact 2I of silver tungsten alloy is the arcing contact. The movable contact member 9 includes a portion of silver for cooperating with the main stationary contact 23 and a portion 21 of silver tungsten alloy for cooperating with the arcing contact 2I. During the operation of the interrupter, the cooperating

main contacts

23 and 25 are separated first and the arcing contacts 2| and 21 are separated last. Thus the circuit through each of the poles is always finally interrupted by the arcing contacts, and the resultant arc is established adjacent the cooperating arc extinguisher I3.

Each of the arc extinguishing devices I3 comprises a plurality of spaced, superposed plates which are arranged in converging planes as is shown particularly in Figs. 2 and 8. These plates are supported by a pair of-flat side members 29 of insulating material such as hard fiber, and some four types of plates are utilized in the assembling of the structure. All of the plates are provided with projecting lugs or ears 3!] which engage suitable cooperating openings formed in the side members 29, and in the assembled device these ears are swedged'over to provide a. rigid interconnection between the several plates and. their supports. The uppermost plate 3I is of magnetic material, preferably iron, and is shown I trated in Fig. 5, another of the insulating plates 35, the second of the larger iron plates 31, the third of the smaller iron plates 39, the fourth insulating plate 35, the third of the larger iron plates 31, the fourth of the smaller iron plates 39, the fifth insulating plate 35, the fourth larger iron plate 31, the fifth smaller iron plate 39, the sixth and last insulating plate 35, and finally the third smaller iron plate 3|. All of the plates are arranged in planes which are substantially perpendicular to the path of movement of the movable contact member 9. These planes converge in the direction of the moving contact and as a result, the distance separating adjacent plates is much greater toward the upper end of each of the arc extinguishers l3 than at the lower end.

It will be noticed that a substantial number of the plates of each of the arc extinguishers are disposed in planes which lie without the space between the engaging flat contact surfaces of the cooperating arcing contacts 2| and 21 when those contacts are in the open circuit position. In order to assure efi'ective utilization of these plates an arcing horn of magnetic material, preferably iron, is disposed adjacent the upper plate 3| in each of the arc extinguishing devices. During the operation of the interrupter, these horns, by virtue of the fact that they are of magnetic material and electrically connected to the associated movable contact member, cause the upper end of the arc initially established by each pair of separating contacts to transfer from the movingarcing contact which draws that are to the adjacent arcing horn. This transfer brings about a substantial lengthening of each of the arcs over and above the maximum possible amount of contact separation and assures an effective utilization of all of the plates of each arc extinguishing device.

In the two outer poles of the breaker, each of these arcing horns comprises a bent strip 4| of iron which is mechanically supported, and at the same time electrically connected to the circuit through its cooperating pole, by a screw 43.

The arcing horn 45 for the central pole, as shownin Figs. 1 and 2, comprises a small, substantially V-shaped member which is ailixed to a suitable projection 46 by means of a screw 48. The projection 46 may be formed integral with the actuating mechanism II, which s electrically con nected to the circuit through the central pole. It should be noted that while each of the arcing horns is at the same potential as the moving contact associated therewith, thus assuring a rapid transfer of one end of the are from the moving contact to the arcing horn and effective utilization of the upper arc extinguishing plates, an air gap exists between each arcing horn and the adjacent arc extinguisher when the breaker is in the open circuit position. In other words, the arcing horns 4| and 45 are mechanically isolated from the outer plate 3| of their respective arc extinguishing structures |3. This gap minimizes the danger of insulation breakdown due to creepage over the insulating side plates 29 of the respective structures l3 and adds much to the reliability of the breaker.

As mentioned above, the actuating mechanism will eifect the simultaneous separation of all of the contacts, either in response to movement of the operating handle 47 or in response to actuation of the trip device [5. During each opening operation, the separation of the arcing contacts causes the arc incident to the opening of the circuit controlled by each of the poles to be established within the aligned V-shaped slots 33 formed in the iron plates 3|, 3'1, and 39 of the adjacent arc extinguishing device I 3. The resultant magnetic reaction produced by the proximity of these plates to the arcs causes each of the arcs to move laterally into the adjacent arc extinguisher.

The upper end of each of the arcs transfers from the movable contact member- 9 drawing that are to the adjacent arcing horn 4| or 45, and at the time the arc contacts the inner edge of the slots 33 formed in the plates of magnetic material, it has been lengthened sufiiciently to encompass all of the plates of the device. After cont-acting the inner end of the slots 33, the arc sub-divides into a plurality of short arcs each of which exists in the space between an adjacent pair of the plates of magnetic material. Lateral movement of each of these short arcs is efiected by the same magnetic reaction which produced the sub-division, and at the first zero point in the current wave the arc is extinguished. The slotted plates of insulation prevent the short arcs from being moved entirely through the extinguisher, and it has been shown by actual tests that the addition of these plates to standard commercial forms of spaced-plate arc extinguishers will effect a substantial increase in the rating of those devices.

By staggering the apices of the slots in the plates of magnetic material the sub-division of the are initially drawn by the separable contacts is caused to take place in two steps. This arrangement increases the capacity of the are extinguisher and makes it much more reliable in operation.

The are extinguishing structure shown in Figs. 9 and 10 is generally similar to the device just described. A somewhat different arrangement of the plates is followed, however, and the structural details of those plates and the means for supporting them differ from the corresponding features of the previously described extinguisher.

The several plates are supported by a pair of spaced side members SI of insulating material, and the individual plates are heldin position through the engagement of cars 63 formed integral therewith with suitable slots formed in the side members 6 exactly as in the previously described embodiment. Excepting the top plate 65 all of the iron plates 61 in the device are substantially similar in outline and take the form shown in Fig. 12. The V-shaped notch 69 in the plates'65 and 67 terminates in a widened slot H of uniform width for accommodating two refractory members 13 (shown particularly in Fig. 17) which aid in guiding the are into the extinguisher.

As a further means for assuring proper movement of the arc into the device and for preventing short circuiting of the adjacent ends of the iron plates in the lower portion of the extinguisher, one of the members 15 of insulating material shown in Figs. 14, 15, and 16 is positioned at either side of the lower end of every other one of the iron plates, the opening 11 in the members 15 of insulating material being adapted to engage the adjacent outwardly projecting ear 63 of the plate, so that when the ear is swedged over during the assembly of the device the member I is Gil gig,

securely held in place. The insulating members '85 are ordinarily made oi fish paper or some similar insulating material, and to facilitate assembling of the device, they are pre-forrned to the shape shown in Figs. 15 and 16.

In the structure shown, two rectangular insulating plates it, each of which has a plurality oi circular holes 8! formed therein, are provided for preventing the are from being moved entirely through the arc extinguisher and thereby serve to minimize the danger of fiashover or insulating breakdown in the rear of that device. At least a portion of each of these plates iii is positioned within the space between one. of the pairs of adjacent plates ill in the upper end of the are extingiiisher. Laboratory tests have proven that the eifectiveness of these plates is greatly en hanced when the holes ti illustrated in: the drawings are provided.v

The upper iron plate 65 is substantially similar to the other iron plates bl except that it is provided with a pair of downwardly projecting lugs 85. These lugs serve to aidin positioning the members-l3 of refractory material which are disposed within the rectangular portion H of the slots in the iron plates during the assembling of the device.

This modified form of the invention is somewhat less expensive to manufacture than the one previously described for the reason that it utilizes only two forms of magnetic plates and one form of insulating plates. Moreover, this modified structure has proven somewhat more satisfactory in operation, perhaps in part due to the fact that the adjacent ends of each of the plates of magnetic material are positively insulated from each other by the formed members of flshpaper. Further, the individual arcs established between the adjacent plates 6i are capable of a somewhat greater freedom of movement than in the previously described form of the invention, which fact may also contribute to the greater efficiency of operation of the modified form.

The mode of operation of the structure shown in Figs. 9 and 10 is substantially the same as that of the embodiment previously described. The are is established within the space defined by the slots in the superposed iron plates. It is moved into the arc extinguisher by virtue of the resultant magnetic reaction, this movement being guided by the refractory guide members 73 and by the insulating members l5. When the are contacts the inner edge of the V-shaped slots 69 in the plates 65 and t'l of magnetic material, it sub-divides into a plurality of short, serially connected arcs, each of which exists in the space between two adjacent plates. These short arcs are moved laterally in the spaces wherein they are formed at high speed, and at the first zero point in the current wave are extinguished. The insulating plates 78 prevent the short arcs from be-= ing moved entirely through the extinguisher and minimize the danger of failure or the satin guisher.

The magnitudeiof the reaction iorce which moves the short arcs laterally within the spaces between the slotted iron plates is, generally, a function of the arc current, up to the point of saturation of the iron. As a result, when'extremely high current arcs are being extinguished by a structure such as that shown in Figs. 9 and 10 it sometimes happens that some of the short arcs may be moved through the extinguisher despite the presence of the insulating members are-acre l9, and the prevention of any undesirable conseouences as a result of this movement is the tunetion of the holes ill in the members Any of the short arcs may, under the above described abnormal conditions, be moved through the extinguisher restrilre along a path which includes one of the holes both because the path around the insulating members it] is longer than the paths through the holes at formed therein, and because the path around the insulating members it, being disposed at a greater distance from the normal arcing sunfaces, has a greater resistance to breakdown than the paths through the holes. The insu= lating members it) are preferably formed. at fiber or some other insulating material which is capable of evolving an arc extinguishing gas when placed in proximity to an electric arc, iiillE when an arc is established in any of the holes til that are is subjected to a longitudinally fiowing blast of arc extinguishing gas which quickly eilects its extinguishment. The arcs which have been driven with sufiflcient velocity to carry them beyond the ends of the plates iii are also restrained against further movement by virtue of the magnetic reaction set up in the iron plates 61. This reaction causes the are or arcs to be attracted toward the plates which either prevents further movement of the arcs beyond the plates or retards movement to such an extent that the arcs will readily strike through the holes 8! in the insulating plates Eli andbeestinguished. The magnetic reaction tending to prevent movement of the are beyond the ends of the plates bl may be augmented by indenting or notching the rear ends of the plates as shown more clearly in Figs. 9, 11 and 12. Through this arrangement an arc extinguisher which is capable of emciently extinguishing arcs, the current magnitude of which may vary over an extremely wide range, is provided, and absolute reliability of operation of the device is assured at all times.

(Joe of the features of the present invention which has not been particularly emphasized in the foregoing description of the structure and mode of operation of one embodiment thereof is the arrangement of the arcing horns. While each of these members is electrically connected to the associated moving contact at all times, it is mechanically isolated from the adjacent are extinguishing device. Through this arrangement, an air gap is caused to crust in the electrical circuit through each pole of the breaker when that device is in the open circuit position, and the danger of insulation breakdown due to creepage over the arc extinguisher when the breaker is used under adverse conditions is materially lessened. In effect, this arcing horn comprises the upper plate of the are extinguishing device and, as mentioned above, while it is maintained at the same potential as the are drawing contact, thereby facilitating the movement or one end of the are from that contact onto the arcing horn and assuring efiective utilization of all or the plates oi the are extinguish} ing structuregthe arcing horn does not actually contact any part of the extinguisher. The ad= vantages of this arrangement increasing the resistance of the breaker to insulation failure have been conclusively proven by tests, and the design utilizing an air gap has been approved for service on shipboard, devices lacking means for isolating the arcing horn have been refused 8.13- proval.

From the foregoing, it will be seen that have discovered a new and improved form or spaced-plate type arc extinguisher which has numerous advantages over the structures previously known to the art. By the provision of suitable means of insulating material interposed between the plates of magnetic material, under all ordinary conditions the arc is prevented from moving entirely through the arc extinguishing device, with a resultant minimizing of the dangerv of fiashovers or insulation breakdown. And in the structure shown in Figs. 9 and 10, means have been provided for efficiently extinguishing any arcs which may be moved through the extinguisher as a result of extremely severe overloads or other fault conditions. This increased margin of safety allows the voltage rating of arc extinguishing devices to be increased without any substantial change in the design except addition of the insulating means.

It should be noted that the insulating means for guiding the arc and for preventing flashover does not prevent free venting of the extinguisher. This feature is important in preventing the building up of undesirable pressures within the extinguishers during their operation.

Further, I have disclosed a new and improved form of arcing horn which is particularly suitable for use with are extinguishing devices of the spaced plate type. My improved arcing horn allows the utilization of larger numbers of plates than has been heretofore believed possible and thus brings about an increase in the operative range of the arc extinguisher.

Ail of these improvements, while of great valhe in increasing the efficiency of arc extinguishers and circuit interrupters wherein they are used, are relatively simple in form and may be embodied into existing structures at a very low cost.

accordance with the patent statutes, 1 have,

"oing, disclosed the details of certain sediments of my invention. it is to however, that these details are merely illustrative, and that the principles disclosed are capable of wide application to the generally. In View of this, it is my intention that the language of the accompanying claims shall be accorded the broadest reasonable construction and shall be limited only by what is expressly stated therein and by the prior art.

I claim the following as my invention:

1. In a circuit interrupter, means for establishing an arc, and extinguishing means for said arc including a plurality of superposed, slotted plates of magnetic material between which said are is adapted to play, means for supporting said plates in spaced relation with respect to each other, said plates being positioned with respect to said means for establishing an are that said arc is caused to move toward the closed end of the slot in each of said plates solely by the magnetic reaction resulting from the proximity of said slotted plates to said arc, and means of insulating material having a thickness less than the spacing between adjacent plates of magnetic material disposed within a plurality of the spaces between adjacent pairs of said plates for preventing the movement of said arc beyond the ends of the plates of magnetic material.

2. In a circuit interrupter, means for establishing an arc, and extinguishing means for said are including a plurality of superposed plates of magnetic material, each of which has a converging slot formed therein, said plates being spaced apart so as to have open spaces therebetween, a

plurality of plates of insulating material, each of which likewise has a converging slot formed therein and each of which is disposed in one of said open spaces between adjacent pairs of said plates of magnetic material, each of said plates of insulating material having at least one major surface thereof spaced from the adjacent surface of one of the pairs of plates of magnetic material between which it is positioned, and a common support means for said plates of insulating material and said plates of magnetic material, said slotted plates of magnetic material being disposed adjacent said means for establishing an arc in order that said are may be moved toward the apex of said converging slots formed therein by the resultant magnetic reaction, and said plates of insulating material determining how far said arc may be moved by said magnetic reaction.

3. In a circuit interrupter, means for establishing an arc, and extinguishing means for said are including a plurality of superposed plates of magnetic material between which said are is adapted to play, each of said plates having a slot formed therein, said plates being spaced apart so as to provide open spaces therebetween, means for so supporting said plates with respect to said means for establishing an are that said are is caused to move toward the closed end of the slots formed therein, and to sub-divide into a plurality of short arcs upon contacting the inner edge of said slots, at least in part by the magnetic reaction resulting from the proximity of said plates to said are, each of said short arcs existing in the open space between an adjacent pair of said plates of magnetic material and being moved laterally in that space by said magnetic reaction, and a plurality of plates of insulating material, each of which has a plurality of openings formed thereinthrough which the short arcs may play, each of said plates of insulating material being disposed within the space between an adjacent pair of said plates or" magnetic material for preventing the short arcs established therein from being moved entirely through said are extinguishing means during the arc extinguishing operation.

4. in an arc extinguishing means, a pair of spaced substantially parallel supported plates of insulating material, a plurality of metallic plates supported in spaced relation between said support plates, each of said metallic plates having a slot therein for receiving the arc'to be extining material spaced some distance from each other, a plurality of superposed plates of magnetic material supported by said support plates in such manner that there are open spaces therebetween, each of said plates of magnetic material having a converging slot formed therein for so altering the magnetic characteristic of those plates that an are drawn in proximity to said slots will be moved into said are extinguishing structure by the resultant magnetic reaction thereon, and a plurality of plates of insulating material of thickness less than the minimum distance between adjacent plates of magnetic material, each of said plates of insulating material being provided with a slot and disposed within one of said open spaces existing between adjacent pairs of said magnetic plates with its slot in alignment with the slots in the magnetic plates for preventing said are from being moved entirely through said structure during the operation thereof.

6. In an arc extinguishing device, a pair of opposed support plates of insulating material .disposed in parallel planes which are spaced some distance from each other, a plurality of substantially rectangular plates of magnetic material, two edges of which are adapted to be engaged by said support plates, each of said plates of magnetic material having a converging slot formed therein in order that an arc drawn in proximity to said are extinguisher will be moved therein by the resultant magnetic reaction and said plates being spaced apart so as to haveopen spaces therebetween, and a plurality of fiat plates of insulating material, each of which is disposed within one of said open spaces between adjacent pairs of said plates of magnetic material at the end of said space opposite the end in which said converging slot is positioned, said plates of insulating material having a thickness less than the separation of said plates of magnetic material at said end occupied by said plates of insulating material, and each of said plates of insulating material being provided with a plurality of openings formed therein, for preventing said are from being moved entirely through said arc extinguisher during the operation thereof.

7. In a circuit interrupter, means for establishing an arc, means for extinguishing said are comprising a plurality of superimposed slotted plates of magne ic material, said plates being disposed in spaced relation with respect to each other with the slots thereof in alignment to form a groove in which the arc may play, said arc being adapted to be moved to the inner edge of said slots and to form a series of short arcs playing between said plates as a result of the magnetic reaction produced in said plates by the arc, and means including at least one member of insulating material of thickness less than the spacing between two adjacent plates of magnetic material disposed adjacent the ends of said plates towards which said are is moved, said member of insulating material being provided with a plu rality of holes through which at least some of said short arcs may play.

8. In a circuit interrupter; means for establishing an are; means for extinguishing said arc including a plurality of superposed plates of magnetic material, each of'which has'a substantially V-shapecl slot formed therein and between which said arc plays during the operation of said extinguishing means, said plates being spaced apart from each other a sufficient distance to provide open spaces therebetweenj means for so supporting said plates with respect to said means for establishing an arc that said are is caused to move toward the closed end of the slots formed therein, and to subdivide into a plurality of short arcs upon contacting the inner edge of said slots, at least in part by the magnetic reaction resulting from the proximity of said plates to said arc; each of said short arcs existing in the space between a pair of adjacent plates and being moved laterally in that space during the are extinguishing operation by said magnetic reaction;

and means including at least one member of an insulating material which is capable of evolving an arc extinguishing gas when placed in proximity to an electric are disposed adjacent the ends of said plates toward which said short arcs are moved by said magnetic reaction, said member of insulating material being provided with a plurality of holes formed therein for defining a plurality of separate arc passages for at least some of said short arcs.

9. In a circuit interrupter, a pair of separable contacts for establishing an arc, means for extinguishing the are including a plurality of plates of conducting material, insulating means holding said plates in spaced relation, an arc terminal member separate from said contacts and to which one end of the arc is transferred from one of said contacts, said are terminal member being electrically connected to said contact from which said end of the arc is transferred and being supported at a point remote from said plates and said insulating means in a fixed position with respect to said plates and with an air gap between it and said plates and said insulating means of dimensions to withstand line voltage to prevent electrical creepage across said plates and insulating means to the other said contact.

10. In a circuit interrupter; means including a pair of separable contacts for opening-and for closing the electrical circuit therethrough; means for extinguishing the arc formed incident to the opening of said interrupter; said extinguishing means including insulating means having a pair of substantially parallel side portions spaced some distance from each other, and a plurality of slotted metallic plates, between which the arc plays during the operation of said extinguishing means, supported upon said insulating means in such manner that open spaces are provided there- 'between; and an arcing horn disposed in fixed spaced relation with respect to said are extinguishing means; said arcing horn being supported at a point remote from said plates and said insulating means and electrically connected to one of said separable contacts and being separated from said metallic plates and said insulating means by an air gap of dimensions capable of withstanding line voltage when said interrupter is in the open circuit position.

11. In a circuit interrupter, a pair 'of separable contacts for establishing an are, means for extinguishing said are comprising a plurality of plates of conducting material, insulating means for holding said plates in spaced relation, each of said plates having a slot therein, means for moving said arc into said slots and into the spaces between said plates, and a plurality of plates of insulating material also held in spaced relation by said insulating means, each of said last named plates being of thickness less than the separation of said plates of conducting material and having at least a portion thereof disposed -within the space between two adjacent conducting plates for lengthening the arc to thereby prevent the movement thereof beyond said conducting plates.

12. In a circuit interrupter, a pair of separable contacts for establishing an arc, means for extinguishing said are comprising a plurality of plates of conducting material, insulating means for holding said plates in spaced relation, eachengagement with respective adjacent plates throughout the greater portion of their length, and a plurality of plates of insulating material also held in spaced relation by said insulating means, each of said last named plates having a portion thereof lying adjacent a relatively short portion of one face of a conducting plate and its remaining portion extending beyond said conducting plates for lengthening the arc to thereby prevent the movement of the arc beyond said conducting plates.

13. In a circuit interrupter, a pair of separable contacts for establishing an arc, means for extinguishing said are comprising a plurality of plates of conducting material, insulating means for holding said plates in spaced relation, each of said plates having a slot therein, means for moving said are into said slots to establish a short arc in each space between said plates and for moving said short arcs with their ends in engagement with respective adjacent plates over a considerable portion of the length of said plates, and means partially obstructing some of the spaces between the ends of said plates against which some of said arcs are adapted to play for producing a blast of an arc extinguishing gas to thereby prevent the movement of said arcs beyond said plates,

14. In a circuit interrupter, a pair of separable contacts for establishing an arc, means for extinguishing said are comprising a plurality of plates of conducting material, insulating means for holding said plates in spaced relation, each of said plates having a slot therein, means for moving said arc into said slots and into the space between said plates, and a plurality of plates of insulating material also held in spaced relation by said insulating means, each of said-last named plates having at least a portion thereof disposed within the space between two adjacent conducting plates, the portions of said last named plates extending beyond said conducting plates having openings therein through which said arc may play, the walls of said openings being capable of producing a blast of gas for extinguishing the arc therethrough,

15. In a circuit interrupter, a stack of plates of conducting material having an aligned slot extending inwardly from one end thereof, means of insulating material for supporting said plates in spaced relation with respect to each other, an arc terminal member disposed adjacent one end plate of said stack, means supporting said are terminal member independently of said plates and said means of insulating material at a point remote from said plates and means of insulating material to provide a fixed air gap of dimensions sufiicient to withstand line voltage between said terminal member and said plates and means of insulating material, and a pair of contacts at least one of which is movable for establishing an arc in said slots between the other of said contacts and said are terminal member, the gap distance betwen said contacts when in the opened position being less than the distance between the end plates of said stack.

16. In a circuit interrupter, a stack of plates of conducting material having an aligned slot extending inwardly from one end thereof, means of insulating material for supporting said plates in spaced relation with respect to each other, an arc terminal member disposed adjacent one end plate of said stack, means supporting said are terminal member independently of said plates and said means of insulating material at a point remote from said plates and means of insulating material to provide a substantial fixed air gap capable of withstanding line voltage between said terminal member and said plates and means of insulating material, a pair of contacts at least one of which is movable for establishing an arc in said slots between the other of said contacts and said are terminal member, the gap distance between said contacts when in the opened position being less than the distance between the end plates of said stack, and insulating members disposed on opposite sides of the entrance portion of said slot for causing said are to contact said terminal member before engaging said plates.

17. An arc extinguisher for circuit breakers comprising a plurality of superimposed spaced plates of magnetic material, said plates having aligned slots extending inwardly from the front edges thereof and in which an arc is adapted to be drawn, said are being moved in a direction toward the closed ends of said slots at least in part by the magnetic reaction set up in said plates for causing it to be split up into a plurality of short arcs, and means for preventing movement of the short arcs beyond the ends of said plates comprising at least one plate of insulating material of a thickness less than the distance between adjacent plates of magnetic material and disposed at least in part between an adjacent pair of plates of magnetic material, said plates of magnetic material being notched inwardly from their rear edges to augment the magnetic reaction tending to retard the outward movement of said-arcs for maintaining the arc in intimate engagement with said plate oi insulating material.

BENJAMIN P. BAKER.