US1991878A - Circuit interrupter - Google Patents

Description

Feb. 19,1935. B. P. BAKER Em 1,99 ,818

CIRCUIT INTERRUPTER Filed Jan. 24, 1951 2 Sheets-Sheet 1 34 INVENTOR 5:

Berybm/h PBaA er' andMr'vfiirop M Leeds.

ATT'ORNEY Patented Feb. 19, 1935 PATENT OFFICE CIRCUIT INTERRUPTER Benjamin P. Baker, Turtle Creek, and Winthrop M. Leeds, Wilkinsburg, Pa., assignors to Westinghouse Electric and Manufacturing Company, a corporation of Pennsylvania Application January 24, 1931, Serial No. 510.990

30 Claims.

Our invention relates to circuit interrupters and particularly to circuit interrupters of the liquid-immersed type.

One object of our invention is to provide a circuit interrupter of the above-mentioned type with a magnetic chamber which confines the arc and influences its movement within the chamber.

Another object of our invention is to provide a magnetic pot-type structure for a circuit interrupter of the above-mentioned type that shall have a plurality of slotted insulating members mounted within it in such manner that the slots of the members are aligned with the arc path.

A further object of our invention is to provide a chamber of magnetic material with a slot in its side wall which is aligned with slots of insulating plates mounted within the chamber for the purpose of effecting a predetermined .arc movement within slots f the insulated plates.

A still further object of our invention is to provide recesses along the sides of the slots of the insulating members of the above-described structure that shall retain a portion of the fluid in which the structure is immersed, adjacent to the arc, as the arc is moved in the slots.

A still further object of our invention is to provide an enclosing chamber for a plurality of slotted plates of the above-mentioned type that shall be provided with a plurality of vents in the side wall thereof that conform with the slots in the plates.

A still further object of our invention is to provide a chamber of the above-mentioned type, having a plurality of slotted plates mounted therein, with vents at the top side portion thereof conforming with. the slots in the plates and with a substantially closed bottom'portion to effect upward movement of the gases evolved by the arc.

Our invention will best be understood by referring to the following specification, taken in conjunction with the accompanying drawings, wherein:

Figure l is a sectional view, in elevation, of a circuit interrupter embodying my invention.

Fig. 2 is an enlarged sectional view. in elevation, of a portion of the arc-extinguishing structure shown in Fig.1 and taken along the line II-II of Fig. 3, thereof, and illustrates one embodiment of my arc-extinguishing structure.

Fig. 3 is a sectional view of the arc-extinguishing structure shown in Fig. 2, taken along the line III-III thereof.

Figs. 4 and 5 are plan views of unit members employed in the structure shown in Figs. 2 and 3.

Fig. 6 is a sectional view, in elevation, of a modified form of the arc-extinguishingstructure illustrated in Figs. 1 to 5, inclusive.

Fig. 7 is a sectional view of the structure shown in Fig. 6, taken along the line VII-VII thereof.

Fig. 8 is a side-view, in elevation, of the structure shown in Fig. 6.

Fig. 9 is a plan view of a unit member employed, along with the unit members shown in Figs. 4 and 5, to constitute the plate structure shown in Figs. 6 and 7. v

Fig. 10 is a sectional view. in elevation, of a modified form of the arc-extinguishing structure shown in Figs. 2 and 6.

Fig. 11 is a side view of the structure shown in Fig. 10.

Fig. 12 is a sectional view, taken along the line 1HI-XII of Fig. 14 of a further modified form of our arc-extinguishing structure shown in Figs. 2, Band 11. I

Fig. 13 is a side view, in elevation, of the structure shown in Fig. 10.

Fig. 14 is a sectional view of the structure shown in Figs. 12 and 13, taken along the line XIVX'[V of Fig. 12.

Fig. 15 is a plan view of a'unit member employed in the structure shown in Figs. 12, 13 and 14.

Our invention comprises, in general, a casing 1 having a cover 2 supported thereon by bolts 3. The cover 2 supports the insulated conductors 4 by means ofthe flanges 5 and bolts 6, in a well known manner. Arc-deionizing-and-extinguishing devices 7 are supported on the enclosed ends of the conductors 4 and are provided with stationary contact members 8 which are bridged by a conducting bar 9. The conducting bar 9 is supported and actuated by means of the lift rod 11 which extends through the cover 2. A suitablearc-quenching liquid 12 is contained within the casing 1 in which the contact-members 8, theconducting bar 9 and, the arc-extinguishing dequenching fluid is trapped ahead of the arc. As the arc is moved toward the rear of the slot, the oil, retained in the pockets, is decomposed by the arc, and the gas is forced'transversely throughv the arc stream to cause the arc stream to be deionized by the turbulent flow of the gas therethrough until, upon the occurrence of a current zero in the course of its alternating cycle, the arc is extinguished. After the arc is extinguished,

the presence of the un-ionized gas in the space between the terminals quickly disintegrates the ionized stream therebetween so that the impressed voltage across the terminals is incapable of risingto such value as to cause arc reinitiation between the terminals.

In the present invention, similar plates having slots and recesses for trapping the oil adjacent to thearc path are employed, and the plates are enclosed within a chamber which is constructed of magnetic material that is employed to control the movement of the arc and the arc gas within the chamber. In order to effect a turbulent flow or un-ionized gas within the arc stream, our present structure effects a horizontal and a vertical flow of the gas within the slotted structure.

The arc-extinguishing device 7, shown enlarged in Fig. 2, comprises a magnetic casing 13 forming an inner shell surrounded by an outer shell of insulating material 14 and having groups of plates 15 distributed horizontally within the casing.

Two groups of insulating plates are provided within the casing 13, a group 17 comprising three plates 18 of fiber having a central hole 19 and a communicating slot 20, as shown in Fig. 4. A second group of plates 21 comprises three plates 22, as shown in Fig. 5, that are made of insulating material, such, tor example, as fullerboard, which absorbs the arc-quenching liquid. A central hole 19 is provided in the plates, together with holes 23 which communicate with the central hole 19 by means of the slots 24. When the groups of plates 22 are assembled between groups of plates 18, the holes 23 constitute pockets or recesses in which the arc-quenching liquid is trapped and retained ahead of the arc, as the arc is moved in the slot.

The oil or like arc-quenching medium evolves an un-ionized gas in the presence of an arc, and, in case suflicient of the liquid is not trapped in the pockets 23, the portion absorbed by the fullerboard material of the plates 22 will be available for liberating the gas. The fibre material of the plates 18, in the presence of an arc, also liberates an un-ionized gas. It will, therefore, be seen that, even in the absence of the liquid, our present construction will be almost as eflective for liberating un-ionized gas as when a quantity of decomposable liquid is actually trapped in the recesses.

As mentioned hereinabove, the trapped liquid in the recess 23 is retained ahead of the arc, as it is moved into the slot. Since our construction effects a vertical flow of the evolved gas upwardly within the slot and recesses toward the vents at the top of the structure, a turbulent motion of the gas and the liquid ensues. The gas and the liquid are thus carried into the arc stream, as the arc is moved in the slots, where the un-ionized gas effects deionization of the arc path, and the particles of liquid are decomposed into a gas that further deionizes the arc stream.

In order to provide a force to effect arc movement in the slots, the magnetic casing 13 is split longitudinally on its side opposite to that toward which the arc is to be moved, as shown at 25.

meters Au insulating member 26 inserted in the open ing between the ends of the magnetic casing to'add. strengtl'i to the surrounding insulating structure 14. The open. magnetic casing which. comprises a magnet of U-shape efiects a distorted magnetic field about the arc, and its move ment away from the slotted side ensues.

A movable contact member 2'7 mountedon the conducting bar. 9, extends within an opening 28 in. the bottom of the chamber 13 having a tight sliding fit therewith in order to effect a seal to prevent any substantial flow of gas therefrom. A stationary contact member 29 is provided on the top of the chamber 13 which is the means by which the chamber is secured to the contact 8 and to the conducting bushing 4.

Openings 30 are provided about the contact member 29 through which the gases generated within the chamber are vented. In this construction, the arc stream is subjected to a transverse flow of gas as the arc is moved within the slot and also to a vertical flow of gas as the gas moves upwardly to be vented from the opening 30.

The lateral arc movement in the slots is caused by the distorted magnetic field above referred to, eflected by the split magnetic casing 13 which surrounds the arc stream. Such a construction eliminates the iron plates heretofore distributed between the insulating plates for effecting arc movement, as specified in the above-mentioned patent.

Referring to Figs. 6 to 9, inclusive, a modified form of our arc-extinguishing structure is illustrated. In this construction, a grid structure is built up by employing a plurality of insulating plates 18 similar to those heretofore referred to and illustrated in Fig. 4. The plates are alternately spaced by iron plates 31, shown by the broken line in Fig. 7, and insulating plates 22' shown in Fig. 9 that are similar to plates 22 shown in Fig. 5, with the exception of the provision of a vent 32.

The plates are assembled within an insulating casing 33 which has a series of openings 34 to register with the vents 32 of the plates 22'. The upper portion of the chamber 33 is provided with a stationary contact member 35. A movable contact member 27 fits snugly in the opening 28 in the bottom of the chamber 33 through which it extends to engage the stationary contact member 35.

In this construction, when an .arc is established between the contact members 27 and 35, the presence of the magnetic plates 31 causes the arc to be moved laterally in the slots. The liquid 12, trapped within the pockets 23 of the plates 22 is decomposed, and the resulting gas passes transversely through the arc stream. The gas, upon passing through the arc, becomes heated and ionized and is thereafter cooled and deionized during its passage through the slots 32, while in intimate contact with the cool surfaces of the adjacent insulating plates 18.

Figs. 10 and 11 disclose an embodiment of our invention that is similar to the one described above, as shown in Figs. 6 and 8, with the exception that unvented plates 22 are used in the lower portion of the stack, and the slots 32 are provided in plates 22' only in the upper portion of the structure.

In this construction, the decomposed gases not only pass transversely through the arc stream but also pass vertically therethrough, as they move upwardly within the slots to pass from the this application.

vents 34. In each of the modifications, it is our desire to pass as much of the cool un-ionized gas through the arc stream as is possible, and the constructions heretofore described effect this large turbulent flow by having the gas pass both horizontally and vertically through the arc stream.

Referring to Figs. 12 and 15, inclusive, in which a modification of the structure shown in Figs. 2 and 3 is shown, the arc movement is effected by the employment of the enclosing casing 13 constructed of magnetic material that is provided with an opening at one of its sides. Inthis construction,'a contact-bar 37 extends within the slot 38 and, when moved to closed-circuit position, engages the stationary contact member 39.

Plates 22' similar to those disclosed in Fig. 9, are employed to provide pockets for the arcextinguishing liquid, while plates 41, located therebetween, are provided with a long narrow slot 42. When an arc is drawn, upon the movement of the conducting bar 37 downwardly away from the stationary contact member 39, the infiuence of the magnetic casing 13 causes the arc to be moved laterally within the slots 42 away from the opening 43 provided in the side of the chamber 36. During this movement, the gas passes turbulently through the arc stream and,

as explained hereinabove; upon extinguishment;

the arc will be prevented from reigniting.

It will thus be seen that we have provided a deionizing and arc-extinguishing device that utilizes means for moving the are into pockets of arc-quenching liquid and for causing the gases, evolved from the liquid in the presence of the arc, to pass turbulently through the arc stream. The movement of the arc is effected by the presence of magnetic material about the arc path which may be either plates interposed between insulating plates or may be the material employed in the enclosing casing that provides a distored magnetic field about the arc path because of a cutaway portion on one of its sides. The turbulent fiow of gas throughout the arc path is eifected by a construction which causes the gas to fiow transversely through the arc stream and by venting the slots at one of its ends to cause the gas to also fiow verticallytherethrough.

While we described several embodiments of our invention, it is to be understood by those skilled in the art that many modifications, additions, omissions, andsubstitutions may be made thereinwithout departing from the spirit and scope of our invetnion, as set forth in the accompanying claims.

Application, Serial No. 599,678 of W. M. Leeds, filed March 18, 1932, is a continuation in part of We claim as our invention:

1. A chamber associated withthe contact members of a circuit interrupter provided with venting means in the wall thereof, and a plurality of plates within the chamber some of which are provided with slots which are aligned with the venting means in said chamber.

2. A chamber associated with the contact members of acircuit interrupter provided with venting means in the wall thereof, and a plurality of plates within the chamber some of which are provided with slots which are aligned with the venting means in said chamber and recesses in the plates associated with the slots.

3. An arc extinguishing chamber for association with the contact members of a circuit-interrupter, said are extinguishing chamber having an outer shell provided with venting means the sidewall thereof, and a plurality of plates within the chamber some 01'- which are provided with slots which are aligned with the venting means in said shell and recesses in the plates associated with the slots and magnetic. means.

for eflecting arc movement toward said recesses.

4. An arc extinguishing chamber for associa-- tion with the contact members of a circuit interrupter, said are extinguishing chamber having an outer shell provided with venting means along one side at the top portion thereof only and a plurality of slotted plates within said chamber with the ends of said slots leading to said venting means.

5. A chamber associated with the contact members of a circuit interrupter and provided with venting means in the top portion thereof, a plurality of plates positioned within said chamber and having elongated slots extending toward said venting means and a contact: member extending;

structure including means of insulating material having an opening therethrough having narrow portions, means for causing an arc in said opening in said are extinguishing structure, an enclosing casing surrounding said are extinguishing structure, said enclosing casing including a member of magnetic material which is generally cylindrical and of such configuration as to move the arc in said opening in the arc extinguishing structure due .to the reaction between the arccurrent and the magnetic material of the enclosing casing.

8. In a circuit interrupter, an arc extinguishing structure including a plurality of plates of insulating material having elongated slots therein, said slots being aligned forming a groove, means for causing an arc in said are extinguish ing structure, an enclosing casing surrounding said are extinguishing structure, said enclosing casing including a member of magnetic material which is generally cylindrical and of such configuration as to move the arc in said aligned slots in the insulating plates of the arc extinguishing structure due to the reaction between the arc current and the magnetic material of the enclosing casing.

9. In an arc extihguishing structure for a circuit interrupter, a cylindrically shaped enclosing casing of magnetic material having a slot in one side extending longitudinally thereof, said enclosing casing. of magnetic material distorting the magnetic field due to the arc current to move the arc, and forming a-pressure chamber about the arc.

10. In an arc extinguishing structure for a circuit interrupter, anenclosing casing forming a pressure chamber and including an outer shell of insulating material and an inner shell of magnetic material having a slot extending longitudinally along one side thereof, and insulating means in said casing defining a narrow groove extending substantially the length of said casing.

11. In a circuit interrupter, a body of liquid, an arc extinguishing structure including means oi insulating material having a passage therethrough, means for causing an arc in said passage, and said means of insulating material having portions extending into close proximity to the path where the arc is caused and having recesses opening into said path for retaining said liquid, a generally cylindrical casing enclosing said means of insulating material, and venting means extending through the side wall of said cylindrical casing on one side only from any portion along the length of said passage.

12. In a circuit interrupter, a movable contact member and an arc extinguishing structure including a stack of plates having openings therein through which said contact member is movable, said openings in some of said plates having portions of a width not materially greater than the width of said movable contact member, and said openings in some of said plates extending to one outer edge thereof, a cylindrical casing enclosing said stack of plates, and venting means in the side wall of said casing aligned with said openings which extend to the edge of some of said plates.

13. In a circuit interrupter, a body of liquid, a movable contact member, and an arc extinguishing structure including a stack of plates having openings therein through which said contact member is movable, said openings in some of said plates having a closed periphery and having portions of a width not materially greater than the width of. said movable contact member, and said openings in other of said plates forming pockets for retaining said liquid and extending to one outer edge of the plates, a cylindrical casing enclosing said stack of plates, and venting means in the side wall of said casing aligned with said openings which extend to the edge of some of said plates.

14. In a circuit interrupter, a relatively fixed contact member and a movable contact member, a body of liquid, and an arc extinguishing structure including a stack. of plates of insulating material having openings therein through which said movable contact member is actuated, said openings in some of said plates at intervals along the length of the stack having a closed periphery and having portions of a width not materially greater than the width oi. said movable contact member, said openings in some of said plates at intervals along the end of said stack adjacent said fixed contact forming pockets for retaining said liquid and extending to an outer edge of the plates, and said openings in some oi said plates at intervals along the other end of said stack forming pockets for retaining said liquid, and a cylindrical casing enclosing said stack of plates and having venting means in the side wall thereof opposite and aligned with said openings which extend to the edge of said plates at the end of said stack adjacent said fixed contact only.

15. In a circuit interrupter, an arc extinguishing structure including means of insulating material having a passage therethrough for the are, and an enclosing casing for said means or insulating material including a generally cylindrical member of magnetic material having a slot along one side thereof, and venting means in the wall of said enclosing casing, said venting means having an area which is. small compared to the longitudinal cross-sectional area of said enclosing casing whereby pressure is built up'in said enclosing casing and a blast of gas is caused to flow out said venting means.

16. In a circuit interrupter, an are extinguishing structure including means 01 insulating material having a passage therethrough for the arc, and an enclosing casing for said means of insulating material including a generally cylindrical member of magnetic material having a slot along one side thereof, and venting means in the side wall of said enclosing casing through said slot, the width of said venting means being greatly less than the internal width of said enclosing casing.

17. In a circuit interrupter, a body of liquid, an arc extinguishing structure including a stack of plates having openings therethrough, means for causing an arc in said openings, some of said plates having portions extending into close proximity to said are, and some of said plates providing pockets for retaining said liquid adjacent to the arc, a casing enclosing said stack of plates and including a generally cylindrical member of magnetic material having a longitudinal slot therein, and venting means from said chamber having an area which is small compared with the longitudinal cross-sectional area of said enclosing casing for restricting the flow of gas therefrom. i

18. In a circuit interrupter, a movable contact member and an arc extinguishing structure including a stack of plates having openings therein through which said contact member is movable, saidopenings in some of said plates having portions of a width not materially greater than the width of said movable contact member, and said openings in some of said plates extending to one outer edge thereof, a casing enclosing said stack of plates and including a generally cylindrical member of magnetic material having a longitudinal slot along one side thereof, and portions of said slot being open adjacent the openings in some of said plates in which the openings extend to one outer edge thereof.

19. In a circuit interrupter, a movable contact member, and an arc extinguishing structure including a stack of plates of insulating material having openings therein through which said contact member is movable, some of said plates of insulating material having portions extending into close proximity to the path of said movable contact member, and some 01 said plates of insulating material having said openings extending to one outer edge of the plates, a plurality of plates of magnetic material positioned at intervals between said plates of insulating material, said plates of magnetic material having slots therein extending to one outer edge thereof, and a generally cylindrical casing enclosing said plates of insulating and magnetic materials, and said casing having openings in the side wall thereof aligned with some of said openings in said plates of insulating material in which the openings extend to one outer edge of the plates.

20. An electric circuit breaker comprising in combination, a'container for oil, a switch structure supported within said container and at least partly immersed in and filled with said oil and including a cylindrical casing having an internal switch chamber, relatively movable electrodes mounted in said switch chamber and also immersed in said oil and a plurality, of transverse bailie platessecured in said cylindrical casing and dividing said switch chamber into a plurality of shallow chambers, the walls of said cylindrical casing being formed with one or more unsymmetrically placed outlet passages in communication with said shallow chambers and leading from the vicinity of the point at which arcing commences so as to provide vents through which products formed by the arc escape from the switch chamber due to the pressure generated therein by the arc, said one or more outlet passages at any one portion along the length of the cylindrical casing all being in the same side of the casing, said bafiie plates being formed with apertures through which one of said electrodes moves, and some of said apertures being extended from said electrode, but not extending entirely through said outlet passages to the outside of said cylindrical casing.

21. In a circuit interrupter, a tank, a body of arc extinguishing liquid therein, means for establishing an arc in said liquid including a movable contact member, an arc extinguisher immersed in said liquid, said are extinguisher including a cylindrical casing having an opening in one end through which said contact member is moved to establish the arc, said casing having an opening through one side wall thereof and the other side walls and the other end thereof being closed to cause pressure to be built up in the casing due to the gas formed by the action of the are on said liquid, and means of insulating material positioned within said casing and having a passage for directing a portion of the fluid in said casing to flow laterally through the arc and out said opening through the side wall of the casing and into the main body of liquid in said tank.

22. In a circuit interrupter, a tank, a body of arc extinguishing liquid therein, means for establishing an arc in said liquid including a movable contact member, an arc extinguisher immersed in said liquid, said are extinguisher in eluding a cylindrical casing having an opening in one end through which said contact member is moved to establish the arc, said casing having an opening through one side wall thereof and the other side walls and the other end thereof being closed to cause pressure to be built up in the casing due to the gas formed by the action of the arc on said liquid, and means of insulating material positioned within said casing and having a passage for directing a portion of the fluid in said casing to flow laterally through the arc and out said opening through the side wall of the casing and into the main body of liquid in said tank, and said passage in the means of insulating material and said opening through the side wall of the casing permitting said flow of fluid to start before the moving contact has cleared the end of the opening through which it I is moved.

23. In a circuit interrupter, a tank, a body of arc extinguishing liquid therein, means for establishing an arc in said liquid including a movable contact member, an arc extinguisher immersed in said liquid, said arc extinguisher including a cylindrical casing having an opening in one end through which said contact member is moved to establish the arc, said casing having an opening through one side wall thereof, and the other side walls and the other end thereof being closed to cause pressure to be built up in the casing due to the gas formed by the action of the are on said liquid, and means of insulating material positioned within said casing, said means of insulating material being provided of the casing to establish the arc, and said passage having a portion extending laterally within the casing from said opening through the side wall thereof across the path of movement of said movable contact member to permit fluid to flow laterally in the casing through the arc and out said opening through the side wall due to the pressure built up in the casing.

24. In a circuit interrupter, a container having a body of liquid therein, means for establishing an arc in said liquid including a movable contact member, an extinguisher for the arc ineluding a metal casing in which the arc is established by said movable contact member, said metal casing having its exterior side walls covered with insulating material, and said metal casing having an opening through the side wall thereof and said covering of insulating material,

means of insulating material positioned inside of said metal casing, said means of insulating material having a passage extending laterally across the arc path within the metal casing and directing the fluid in the metal casing to flow laterally through the arc and directly out said opening through the side wall of the metal casing due to the gas pressure built up in the metal casing due to the action of the are on said liquid in the metal casing.

25. In a circuit interrupter, a container having a body of liquid therein, means for establishing an arc insaid liquid including a movable contact member, ,an extinguisher for the arc including a metal casing in which the arc is established by said movable contact member, said metal casing having an opening therein through which said movable contact is actuated to establish the are, means of insulating material having a passage through which fluid flows through the arc and out said opening in the metal casing, said means of insulating material being formed of a stack of plates of insulating material, and

said passage being defined on two opposite sides casing being substantially closed except for an opening through which the movable contact member is actuated whereby pressure is built up in said casing due to the gas formed from said liquid by the arc, and said casing having a stack of contiguous plates of fibrous insulating material, said stack of plates having a passage through which the movable contact is actuated in drawing the arc and through which the fluid in the casing flows to escape out said opening in the casing due to the pressure therein.

27. In a circuit interrupter, a tank having a body of liquid therein, means for establishing an arc in said liquid including a movable contact member, means for extinguishing the arc including a metal casing immersed in said liquid, said casing being substantially closed except for an opening through which the movable contact member is actuated whereby pressure is built up in said casing due to the gas formed from said liquid by the arc, and said casing having a stack of contiguous plates of fibrous insulating material, said stack of plates having a passage through which the movable contact is actuated in drawing the arc and through which the fluid in the easing flows to escape out said opening in the casing due to the pressure therein, and said passage be ing defined on two opposite sides by edges of said plates, and said edges having portions extending substantially to the path of movement or said contact member.

28. In a circuit interrupter, a tank having a body of liquid therein, means for establishing an arc in said liquid including amovable contact member, means for extinguishing the arc including a metal casing immersed in said liquid, said. casing being substantially closed except for an opening through which the movable contact member is actuated whereby pressure is buiit up in said casing clue to the gas formed from said liquid by the arc, and said casing having a stack of contiguous plates of fibrous insulating material, said stack of plates having a passage through which the movable contact is actuated in drawing the arc and through which the fluid in, the casing flows to escape out said opening in the casing due to the pressure therein, and said passage being defined on two opposite sides by edges of said plates, and said edges having p01? tions extending substantially to the path of move .nent oi said contact member, and the pamage defined by said edges of the plates having a piurality oi recesses therealong at spaced intervals.

29. In a circuit interrupter, a body 0! liquid, an arc extinguishing structure immersed in said body of liquid, means for causing an arc in said are extinguishing structure whereby pressure is built up in said are extinguishing structure due to the gas formed by the action of the are on said liquid, an enclosing casing surrounding said are extinguishing structure, said enclosing casing including a member of magnetic material which is generally cylindrical and of such configuration as to move the arc in the arc extinguishing structure due to the reaction between the arc current and the magnetic material of the enclosing casing, and said member of magnetic material strengthening said enclosing casing to resist the pressure caused therein by the are.

30. In a circuit interrupter, a body of liquid, an arc extinguishing structure immersed in said liquid and including a cylindricaliy shaped enclosing casing of magnetic material having a slot in one side extending longitudinally thereof, said enciosing casing of magnetic material distorting the magnetic field due to the arc current to move the are, and forming a pressure chamber about the are.

BENJAMIN P. BAKER. WINTHROP M. LEEDS.

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