US2352984A - Circuit breaker - Google Patents

Description

y 1944- L. s. WALLE 2,352,984

C IRGUIT BREAKER Filed June 25, 1942 Fig, l.

GAS EM/777N6 /NSUL A T/ON all Inventor: Ludwig S. Wal le,

:75 Attorney.

Patented July 4, 1944 CIRCUIT BREAKER- Ludwig S. Walle, Lansdowne, Pa., assignor to General Electric Company, a corporation of New York Application June zz, 1942, Serial No. 448,066

-8 Claims.

My invention relates to circuit breakers, and particularly to gas-blast circuit breakers of the enclosed or compression chamber type.

Manually operated current responsively tripped circuit breakers are widely used for the connection and protection of branch circuits, particularly where large numbers of such circuit breakers must be grouped within a confined space. These breakers are depended upon to provide the short-circuit protection of a fuse as well as the advantages of a manually-operated switch. It

' has been found that the interruption of currents of short-circuit magnitude, for example, in excess of 10,000 amperes for a breaker having a normal rating of 225 amperes at 600 volts, may be very efliciently carried out in an enclosed or substantially enclosed chamber within which a gaseous dielectric at considerable pressure may be confined during the interruption.

While compression chamber interrupting units heretofore built have been quite successful in quenching arcs of short-circuit magnitude, they have been subject to certain drawbacks in operation and maintenance. For example, single break compression breakers must be very well sealed in order to build up sufficient pressure to insure positive interruption upon low currents. Such efficient sealing retains the high pressure generated by high currents for a relatively long time, thereby preventing prompt reclosing of the breaker. To make the chambers as gas-tight as possible, they have been assembled as unitary structures without means for access to the contacts. Such an arrangement contributes to the d fficulty and expense of repair and replacement, since an inaccessible chamber must be removed and replaced as a unit, and the casing must be dismantled for repair. It is much more desirable from the viewpoint of manufacturing and maintenance facility to provide the chamber with a detachable cover or other such normally closed means for access to the contacts. From the operators position a breaker with a substantial exhaust port for escape of gases will permit more immediate reclosure. In order to permit the use of a separable casing with an appreciable exhaust port, it is necessary to provide an interrupting unit which will function efiiciently without the excessive gas pressures which have been used heretofore, and in which slight gas leakage from the casing during the interruption does not hamper the operation. I have found that in en-' closed compression chamber interruptcrs, an electric arc may be interrupted even more efficiently at relatively low pressure than has heretofore been effected at high pressure if means are provided for passing a blast of dielectric gas transversely of the arc, creating turbulence of the gas, and exhausting the gas through a constricted exhaust port at a point remote from the arc. The effect of the transverse gas blast and the turbulent flow is so enhanced by the presence of more than one break in a single chamber that a multi-break interrupter embodying my invention exhibits an interrupting capacity considerably larger than that ordinarily to be expected from the connection of an equal number of breaks in series circuit relation.

In order to assist in cooling the the arc, it is desirable to generate the extinguishing gas within the compression chamber itself by permitting the arc to react upon gas emitting material. I have also found that in such enclosed breakers where the gas pressure is generated by the arc itself, a greater eiiiciency may be attained if a gaseous dielectric under an initial pressure is present in the chamber prior to the drawing of the main arc. At the present time it appears that the presence of such an initial pressure enables the arc to increase the gas pressure to interrupting value in a considerably shorter time and with considerably less maximum pressure.

Accordingly, it is one object of my invention to provide a simple, reliable, and inexpensive circuit breaker of the compression chamber type.

It is another object of my invention to provide, in a circuit breaker of the above type, a compression chamber interrupting unit in which all parts are easily accessible for repair and replacement.

It is a further object of my invention to provide a circuit breaker of the compression chamber type having means for establishing an arcextinguishing gas blast transversely of the arc, creating turbulence in the gas flow, and cooling and exhaustingthe gas from the chamber at a point remote from the arc.

It is a still further object of'my invention to provide a plural break compression chamber interrupter in which a dielectric gas under pressure is generated within the chamber by the action of the arc itself and automatically directed to have an optimum effect in extinguishing the generating arc.

It is a still further object of my invention to provide gas-emitting means within a circuit interrupter of the compression chamber type arranged in intimate gas-generating relation with an electric arc to be interrupted and so constructed and arranged that gases emanating from the gas-emitting means are forced to pass through the arc in a direction substantially transverse thereto.

An even further object of my invention is to provide a circuit breaker of the compression chamber type with means for establishing an initial pressure within the chamber prior to the drawing of the main arc.

In carrying out my invention in one form, I provide a metallic pressure-confining casing comprising a base and a detachable cover and provided with a liner or gasket of suitable arc-resisting compound. Within the casing I arrange a pair of stationary contacts and a pivotally mounted I i-shaped bridging contact arranged to form an electrical connection between the stationary contacts. The E-shaped bridging contact is loosely connected, preferably pivotally and below its center of gravity, to a movable actuating arm and is provided at the extremities of its outer arms with suitable contact elements. The stationary contacts are partially enclosed within insulator means of gas-emitting material, the stationary contacts being positioned well within and closely adjacent the insulator. Preferably each stationary contact is located within a separate generally cup-shaped insulator. Where separate insulators are used each insulator may be apertured at one side to permit exhaust of the gases generated therein transversely across the generating arc. Preferably also such aperture of each other will create within the interrupting chamber 1 a great turbulence of gas flow which further enhances the interrupting capacity of the breaker. With such an arrangement it is also believed that, due to the fact that the E-shaped bridging contact is mounted in a position of unstable equilibrium, the stationary contacts are rarely disengaged simultaneously, so that one are is always formed before the other. In this way the first are formed acts as a pressure-generating are which establishes an initial gas pressure in the casing prior to the drawing of a main arc of the contact last to open. The metallic casing is apertured to provide a constricted exhaust port which is connected with the interior of th casing through the tortuous passageways of a gascooling device.

My invention itself will be better understood and its objects and advantages further appreciated by referring now to the following detailed specification taken in conjunction with the accompanying drawing in which Fig. 1 is a plan view of a circuit breaker embodying my invention, the outside casing being partially broken away and the cover of one of the interrupting units being removed in order more clearly to illustrate the details of construction; Fig. 2 is a Side view of the circuit breaker, one of the interrupting units being shown in section; and Fig. 3 is an exploded perspective view of the gas-cooling chamber shown at Fig. 2, certain parts being broken away in order more clearly to illustrate the parts below.

Referring now to the drawing, and particularly to Figs. 1 and 2, I have shown a circuit-breaker mounted upon an insulating base Ill and provided with an insulating cover Ii. Preferably the base l and cover II are formed of a molded insulating compound of which many types are well known to those skilled in the art. Mounted upon the base III at one end is a suitable snapacting operating mechanism (not shown) Such a mechanism may be of the type described and claimed in Patent 2,169,085, issued to W. A. Atwood on August 8, 1939. As shown in the patent referred to, the mechanism is preferably of the manually-operated current-responsively tripped type and is connected to operate a crank arm I! which is rigidly connected to an operating shaft I3. An operating handle ll projects through the cover I I for convenient control of the mechanism. Mounted upon the opposite end of the base Ill and within the cover i I, I provide a plurality of enclosed compression chambers, each comprising a steel base l5 and a steel cover it. While I have shown for purposes of illustration a three-phase breaker having a separate compression chamber for each phase of the circuit and a single interrupting device within each chamber, I wish to have it understood that any desired number of such individual enclosed interrupting units may be connected to a single operating mechanism or that, if desired, a plurality of interrupting devices may be arranged within a single compression chamber. In the breaker shown, all the chambers are of similar construction and, therefore, only one chamber will be described in detail.

The base of each chamber is lined at the bottom and sides with a liner H, the side walls of which extend upwardly to provide a liner for a portion of the cover i6. The liner i1 is provided with a peripheral flange ll, arranged as a gasket between the abutting edges of the base I! and cover I6, thereby to form a gas-tight seal between the parts of the steel chamber. The liner is made of arc-resisting insulating material, and preferably consists of a molded, synthetic, rubber-like, arc-resisting compound, such as aplasticized polyvinyl chloride. Small strips I! of the same material are provided in the upper part of the steel cover It to insulate the current-carrying movable contact from the casing. In order that the steel cover It be readily detachable, a pair of bearings 20 for the operating shaft I! are molded as integral parts of the liner H at opposite sides of one end thereof. While I prefer to mold the shaft bearings 20 in the liner IT for simplicit of manu. facture and assembly, I wish to have it understood that I do not desire to 'be limited to such an arrangement, but that the bearings may be provided in connection with other portions of the contact chamber. To facilitate easy removal of the compression chamber cover ii, the cover and base are held together by a singl centrally-located bolt 24 and a nut 2%. The nut 25 is permanently fixed in place upon the steel base I! so that removal and replacement of the cover may be effected simply by removal and replacement of the bolt 2. The bolt 24 is also internally threaded at its end for cooperation with a fixed stud 28 thereby to connect the compression chamber as a unit to the base Ill.

The stationary contact structure comprises a pair of fixed contacts 11 and 28 having V- shaped tip portions 29 and 30, respectively. While the body of the contacts 21 and 28 may be of copper or other material having a relatively high conductivity, the V-shaped tips 29 are preferably formed of a material which, while a good electrical conductor. also possesses a high degree of arc-resistivity. For example, one material which may be used for the contact tips 29 and 30 to obtain long life and minimum burning comprises an alloy of sintered tungsten impregnated with copper, silver or the like material. Such an alloy is described and claimed in Patent 1,552,184, issued to Nathan H. Adams on September 1, 1925.

Each stationary contact 21, 28 is mounted in the base of a substantially cylindrical insulator cup 3| in such manner that the contact tips 29 and 30 lie within the base of the cup, and the shank portion of the contact extends through the base of the cup where it terminates in a threaded portion 32, arranged for connection with a suitable electrical conductor. A rubber washer 32a is positioned between each contact tip and the base of the associatedinsulator cup 3|. As will be observed from Fig. 2, the upwardlyextending cylindrical portions of the insulator cups 3| define restricted spaces in which electric arcs between the stationary contacts and the bridging contact must be drawn and are positioned in close proximity to the arc paths. The cups 3| are also apertured at their adjacent sides, as at 3211, to accommodate the downwardlyextending outer legs of an E-shaped bridging contact 33. The stationary contacts may be located as closely together as mechanical and electrical limitations permit.

As is well known to those skilled in the art, gas under substantial pressure is possessed of considerable dielectric strength and facilitates the rapid quenching oi. an electric arc. Furthermore, a blast of gas through an arc, and especially substantially transversely therethrough, aids in cooling and quickly deionizing the arc thereby rapidly to extinguish it. With a view to combining these effects, I form the insulating cup 3| of a molded gas-emitting material in order to supply a gas under pressure from a source within the compression chamber and specifically from a source within the restricted space defined by the insulator cup. I also shape the cups in the manacrylate, a filler of quartz, magnesia, alumina, I

flint, wood flour, china clay, asbestos, spun glass in woven form, mica, or the like, in combination with a gas-emitting material, such as urea, ureaformaldehyde resins, urea phosphates, or other compounds of urea, ammonium carbonate or ammonium bicarbonate or other organic or inorganic substances which in the circuit-interrupting process emit gases (nitrogen, carbon dioxide,

water vapor, etc.) having arc-extinguishing properties.

It will be understood that the gas-emitting insulators 3| are positioned closely adjacent each of the contacts so that arcs formed at the contacts will be brought into intimate gas-generating relation with the insulators. The more completely the insulators enclose the contacts the greater will be the insulating effect because of the increased length of the creepage path between the contacts. On the other hand, the apertures 3217 at the sides of the insulators serveto provide an exhaust passage for gases formed within the cups so located that in exhausting from the cups the gas streams must pass substantially transversely across the generating arcs. This effect is enhanced by the fact that the moving contacts themselves substantially close the upper ends of the insulating cups. It is well known that a gas blast transverse to an electric arc is more effective in quenching the arc than a gas blast directed longitudinally of the arc. Furthermore, by aperturing' my cup-shaped gas-emitting insulators on the sides adjacent each other, I not only force the gases produced within each cup to cross the generating arc in a substantially transverse direction but also to emerge from the cup in a direction opposed to the blast from the other cup. In this manner the gas blasts encounter each other immediately after they emerge from the cups thereby to create a great turbulence of gas flow and to force both blasts upwardly into cooler air, and ultimately outside of the compression chamber through an exhaust port remotely located with respect to the arcs. The exhaust port will be more fully described hereinafter.

To complete the stationary contact structure, th lower end or shank portion of each contact 21, 23 is enclosed within a second cup-shaped insulator 34 apertured at its base to receive a clamping nut for threadingly engaging a portion 32 of each contact. The insulators 34 are located outside the pressure-confining chamber and, since they are not acted upon by the arc, need have no gas-emittin properties. Thus each stationary contact 21, 23 acts as a bolt which in cooperation with the nut 35 clamps the cupshaped insulators 3| and to opposite sides of the steel base l5 and serves electrically to connect the contact tips 2! and 30 to suitably apertured lead-in conductors and 4|, which are held in clamped engagement between the insulators 34 and the heads of the nuts 35. The compression chamber itself is attached to the base l0 by the I stud 26 which threadingly engages the inner surface of the bolt.

Electrical connection between the stationary contacts 29 and 30 is formed by the E-shaped bridging contact 33. The bridging contact comprises a pair of conducting plates 42 and 43 fixed in. parallel spaced relation by a pair of transverse pins 44 and 45 and carrying upon their downwardly extending outer arm suitable diverging and laterally resilient contact tips for engagement with the V-shaped stationary contact tips 29 and 30. The central portions of the E-shaped plates 42 and 43 are laterally offset as may be observed at Fig. 1 in order to widen the space therebetween for accommodation of the bolt 24.

The E- shaped bridging contact 33 is pivotally supported, preferably at a point directly below its center of gravity, upon a pair of L-shaped actuating arms 41. Each actuating arm 41 has one long and one short leg and is nonrotatably attached at the end of the long leg to the operating shaft |3 thereby rotatably to mount the bridging; contact 33 upon the shaft l3. The short leg of each actuating arm 41 lies alongside the center arm of one of the E -shaped contact plates 42, 43 in substantially parallel spaced relation therewith and is pivotally attached thereto at its outer end by means of a pivot pin 48. The actuating arms 41 are laterally resilient and are each biased inwardly to hold the E-shaped plates of the bridging contact 33 together and to provide an initial contact pressure. Thus the E- shaped bridgin contact 33 is mounted at a point lying substantially directly below its center of i gravity and on a straightline between the contact tips 48. In order to limit relative rotation of the bridging contact 33 with respect to the actuating arms 41, pin and slot connections 49,

II are provided between these membersat points spaced from the pins 48.

As may best be observed at Fig. 2, the slots II are of such length that in the circuit-opening position of the interrupting unit the bridging contact ll may be flat against the top of the pressure-confining chamber II, II in substantially parallel spaced relation thereto, so that the ultimate break distance of each pair of cooperating nxed and movable contacts is substantially the same. It will be understood, of course, that when the interrupter is in its circuitclosing position, th bridgin contact 33 is in its lowermost position and also lies with its back in substantially parallel spaced relation to the top surface of the pressure-confining chamber. The slots ll must be of only sumcient length to permit the bridging contact 33 to assume these two limiting positions with respect to the actuating arms 41. It will be observed that in any position intermediate its uppermost and lowermost positions the bridiing contact I! will be supported upon the pin 48 in a position of unstable equilibrium if its back lies in parallel spaced relation with th upper surface of the casing l0.

Harmless escape of hot gases is provided through a pair of centrally bored screws 5! in the top of each steel chamber cover it at a point remote from the contact tip. The central bore of the screws ll provides constricted exhaust ports, while the screws themselves serve to attach to the inside of each cover I. a gas-cooling bailie and mulling chamber ll shown in detail at Fig. 3. It will be understood that the exhaust ports are constricted in the sense that they are sufliciently small to permit build-up of appreciable gas pressure during the interrupting period, but they are also sumciently large to limit the pressure and to permit rapid exhaust after interruption. Each gas cooler 56 comprises a box-dike metallic container II having a turned-over flange I apertured at II to form gas entrance ports. The container 51 is divided into two connected compartments by a baiiie plate 60, the length of which is somewhat less than the length of the container l1. Within the upper compartment are arranged a pair of permanently attached or integrally formed nuts 5 for threadingly engaging the hollow screws 55, while the lower compartment contains a heat-absorbing and muiiiing means such as, for example, a tumbled heat 68 of short lengths of copper tubing. The structure of the gas cooler is completed by a box-like cover 61 which slips over the container 51 and is provided with entrance ports 68 registering with the entrance ports 89 and bolt holes OI registering with bolt holes in the container 51. It will now be observed that the exhaust gases entering the gas cooler at the ports 59 and BI must first pass along the full length of the lower compartment in contact with the heat-absorbing mass 68 and then along substantially the full length of the upper compartment before reaching the exhaust port of the hollow screws Ii.

Since the exhaust port has no critical effect upon the arc interruption, such as by direction of a gas blast across or along an arc, it ma be located anywhere within the casing which is relatively remote from the arcs themselves. Similarly, slight leakage of gas through imperfect joints in the pressure-confining chamber, as through the Joints between the casing space II and casing cover It, will have no appreciable eifect upon the arc-interrupting capacity of the breaker. It will therefore be understood that by the term constricted exhaust port," when used in the claims, I mean any exhaust opening, whether specifically provided or constituted of accidentally or intentionally loose joints or fittings, which is sufiiciently small to permit a temporary build-up of pressure within the casing while arc gas is being generated and which is sufliciently large to effect a reduction of the pressure and exhaust of the gases from the casing within a reasonable time after the arc interruption.

In operation, when the crank arm I! is rotated by the operating mechanism in a clockwise direction as viewed in Fig. 2, the contact-carrying end of the actuating arms 41 is raised to move the bridging contact 33 from its circuit-closing position to its circuit-opening position. During this movement, and before the movable contact tips 48 are withdrawn from the upper ends of the cupshaped gas-emitting insulators ii, an electric arc is drawn between each pair of fixed and movable contacts and within each cup-shaped insulator. Due to the fact that the bridging contact is formed in the shape of an E with its contact tips positioned at the depending ends of its outer arms, the two arcs will be positioned in parallel spaced relation with the arc current flowing in opposite directions. This results in a concentration of magnetic lines of force between the gasemitting insulator cup 3| thereby forcing the arcs to bow outwardly in a manner well known to those skilled in the art. Thus by magnetic repulsion each arc is forced against the outer side of its associated insulator cup and into intimate gas-emitting contact with the cup, thereby facilitating generation of gas within the pressureconflning chamber. Because of the fact that the arc interruption takes place over a very short time interval and also because of the fact that the exhaust ports 15 are quite constricted and positioned at a remote point with respect to the point of generation of the gas, a considerable pressure is quickly built up within the chamber ll, l6. Furthermore, since the gas is generated within each of the insulating cups 3|, the greatest pressure exists within the restricted space inside the cups in the immediate region of the arc, and there is therefore a definite tendency to force the gas out of the cups and into the interior of the compression chamber l5, it. Since this action takes place largely before the movable contact tips 46 emerge from the upper ends of the cups ii, the path of least resistance for the exhaust of gases from the cups is through the apertures 321) on the inner sides of the cups. As each gas stream passes outwardly through the aperture 32b into the space between the insulator cups ll, it is forced substantially transversely across the path of the generating arc. This transverse gasblast effect arises largely from the fact that the major portion of the gas is generated at the outer side of each insulator cup due to the magnetic bowing effect, while the lateral exhaust apertures in the cups are located on the inner or adjacent sides of the cups.

As explained in the preceding paragraph, the stream of dielectric gas emanating from each cup II is directed inwardly toward the central bolt 24 so that these gas streams emerge from the cups in opposing directions and encounter each other with some degree of violence. The violent impact oi the gas streams creates an appreciable turbulent flow of gas in the central and upper portion of the chamber It, It, and the turbulence thus created appears to have a beneficial eliect in interrupting the arcs. This effect may be due to the fact that each particle of gas, due to the turbulent flow, encounters .the are a number 01' times.

It has been previously noted that while in its circuit-closing position the bridging contact 33 is retained with its back in substantially parallel spaced relation with the upper surface 01' the cover is because of its engagement with the stationary contacts 29 and 30, and while in its circuit-opening position it is retained in a similar position by engagement with the top of the casing cover l6, this parallel position 01' the bridging contact 33 is one of unstable equilibrium at any intermediate position of the actuating arms 41. Thus as soon as the circuit-opening movement of the actuating arm I! begins, the bridging contact II is placed in a position of unstable equilibrium, due to the fact that it is loosely mounted at a point directly below its center of gravity. It will therefore be evident that it is extremely unlikely that breaks will be made exactly simultaneously between each pair 01' fixed and movable contacts, especially since there almost certainly will exist a slight difference in the amount of friction between each pair 01' contacts. Accordingly, the two series breaks will be formed sequentially rather than simultaneously, so that the first are to be drawn may be regarded as a pressure-generating arc. It is unlikely that this pressure-generating arc attains any substantial length before an arc is drawn at the other pair of contacts, but apparently it is sufilcient to build up within the chamber i5, IS a considerable initial pressure prior to the drawing or the second or main are between the other pair of contact tips. The existence of such a gaseous dielectric under an initial pressure prior to the drawing of the second arc facilitates a more rapid quenching of both arcs and permits the interruption of a current of any predetermined short-circuit mag nitude within a much more confined space than has heretofore been considered possible.

While I have described but one embodiment of my invention by way of illustration, many modifications will occur to those skilled in the art and I therefore wish to have it understood that I intend by the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

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

l. A circuit breaker adapted to interrupt currents of short-circuit magnitude comprising a pressure-confining chamber provided with a constricted exhaust port, a plurality of pairs of separable switch contacts mounted within said casing remote from said exhaust port, said pairs of contacts being connected in series circuit relation, movable means for separating said pairs of contacts to establish electric arcs therebetween, means within said casing for partially enclosing each of said pairs of separable switch contacts thereby to define within said casing a restricted space for the separation of each of said pairs of contacts, means within each of said enclosing means operable in conjunction with the electric arc established between the associated pair of separable contacts for generating within said enclosing means a dielectric gas at substantial pressure, and means for exhausting said gaseous dielectric from each of said enclosing means into the interior of said casing in opposing directions, the stream of gas from each of said enclosing means passing substantially transversely across the generating arc and encountering the opposing stream of gas to create within said casing a turbulent flow or gas between said contacts and said exhaust port and said casing confining said gas to create within said casing a pressure sufficient to prevent short-circuiting of said pairs of contacts by said opposing gas streams.

2. A circuit breaker adapted to interrupt currents of short-circuit magnitude comprising a pressure-confining casing provided with a constricted exhaust port, a plurality of pairs of fixed and movable circuit-interrupting contacts mounted within said casing, said pairs of contacts being connected in series circuit relation, a generally cup-shaped insulator of gas-emitting material partially surrounding each of said fixed contacts, said insulators being apertured at adjacent sides thereof to permit the escape oi dielectric gases generated therein, operating means common to said movable contacts for actuating said contacts from a circuit-closing to a circuit-opening position thereby to establish an electric are between each of said pairs of contacts and at least partially within the enclosing gas-emitting insulator, and means for causing said arcs to impinge upon said insulators opposite said apertures so that dielectric gases generated thereby must pass toward said apertures in streams substantially transverse to the generating arcs, said gas streams encountering each other upon emergence from said insulators thereby to create within said pressure-confining casing a turbulent flow of gas under a pressure sufiicient to prevent shortcircuiting of said pairs of contacts by said encountering gas streams.

3. An air circuit breaker adapted to interrupt currents of short-circuit magnitude comprising a pressure-confining casing provided with a constricted exhaust port, a pair of stationary contacts mounted in side-by-side relation within said casing, a generally cup-shaped insulator of gasemitting material partially enclosing each 01' said fixed contacts, each of said insulators being apertured on the side adjacent the other of said insulators thereby to permit the escape of hot gases in opposing and encountering streams passing transversely with respect to generating electric arcs formed within said insulators, a movably mounted bridging contact within said casing having its ends arranged to project within said insulators thereby to engage said fixed contacts and to connect said contacts together in series circuit relation, and actuating means for moving said bridging contact from a circuit-closing to a circuit-opening position to establish an electric are within each of said insulators, whereby the transverse gas-blast eilect of each escaping stream of gas and the turbulent flow resulting from their interaction upon each other combine to assist in the quenching of said arcs while the pressure of said gas within said casing is sufiicient to prevent short-circuiting of said stationary contacts by said encountering gas streams.

4. An air circuit breaker adapted to interrupt currents of short-circuit magnitude comprising a pressure-confining casing provided with a con stricted exhaust port, a pair of stationary contacts mounted within said casing, a bridging contact movably mounted within said casing for actuation between circuit-closing and circuit-opening positions, said bridging contact when moved from said circuit-closing position establishing with said stationary contacts a pair of electric arcs in parallel spaced relation, and gas-emitting means partially enclosing each oi said stationary contacts in intimate gas-generating relation with said arcs, said gas-emitting means being so disposed that the mutual magnetic blowout efl'ect oi said arcs induces said arcs to impinge upon said gas-emitting means thereby to establish within said casing a gaseous dielectric under pressure and being apertured on adjacent sides to direct exhaust gases irom said gas-emitting means in opposing and encountering streams passing transversely oi the generating arc, the pressure 01' said dielectric within said casing being sumcient to prevent short-circuiting oi said staationary contacts by said encountering gas streams.

5. An air circuit breaker adapted to interrupt currents oi short-circuit magnitude comprising a pressure-confining casing provided with a constricted exhaust port, a pair oi stationary contacts mounted within said casing, a bridging contact loosely mounted within said casing ior movement between circuit-closing and circuit-opening positions, said bridging contact when moved irorn said circuit-closing position establishing a pair of electric arcs in substantially parallel spaced relation. and gas-emitting insulator means partially enclosing each of said stationary contacts to present gas-emitting suriaces in intimate gasgenerating relation with respect to said arcs, said insulator means being iormed to provide exhaust passages for the gases generated therein from. said insulator means to the interior oi said casing, said exhaust passages directing said gases in separate streams transversely across the generating arcs and into engagement with each other to create within said casing a turbulent flow oi gas under pressure, said pressure resulting irom the constriction of said exhaust port and being sumcient to prevent short-circuiting oi said stationary contacts by said encountering gas streams.

6. An air circuit breaker adapted to interrupt currents oi short-circuit magnitude comprising a pressure-confining casing provided with a constricted exhaust port, a pair oi stationary contacts mounted within said casing in side-by-side relation and remote irom said exhaust port, a bridging contact loosely mounted within said casing ior movement-be tween circuit-closing and circuit-opening positions, said bridging contact when moved from said circuit-closing position establishing a pair oi electric arcs positioned substantially in parallel spaced relation and electrically connected in series circuit relation, and gas-emitting insulator means positioned closely adjacent said stationary contacts and arranged partially to enclose said electric arcs, the mutual magnetic blowout eiiect oi said electric arcs causing said arc-s to impinge upon said insulator means thereby to generate in the region oi said arcs a volume oi dielectric gas under pressure, said insulator means being iormed to provide exhaust passages irorn the interior thereof to the interior oi said casing, said exhaust passages being positioned to direct said gas into said casing in opposing and encountering streams each passing substantially transversely across the generating arc, whereby said opposing streams create within said casing a turbulent flow oi gas to assist in the quenching oi said arcs and under a pressure sumcient to prevent short-circuiting oi said stationary contacts by said encountering gas streams.

7. An air circuit breaker adapted to interrupt currents oi short-circuit magnitude comprising a pressure-confining casing provided with a constricted exhaust port, a plurality oi pairs oi separable switch contacts within said casing, said pairs oi contacts be ng connected in series circuit relation and arranged when separated to establish a pair oi electric arcs positioned in substantially parallel spaced relation, gas-emitting insulator means positioned closely adjacent each oi said pairs of contacts and arranged partially to enclose said electric arcs, the mutual magnetic blowout eiiect oi said electric arcs causing said arcs to impinge upon said insulator means thereby to generate in the region of said arcs a quantity oi dielectric gas under pressure, said insulator means being formed to provide exhaust passages irom the space enclosed thereby to the interior oi said casing, said exhaust passages being positioned to direct said gas into said casing in opposing and encountering streams each passing substantially transversely across the generating arc, and common actuating means ior separating both said pairs oi contacts, whereby said opposing streams oi gas create a transverse gas-blast eiiect upon each oi said arcs and interact to create within said casing a turbulent new of gas between said contacts and said exhaust port thereby to assist in the quenching oi said arcs, the pressure oi said gas within said casing being suilicicnt to prevent short-circuiting oi said pairs oi contacts by said encountering gas streams.

8. An arc extinguishing circuit interrupter oi the air break type comprising a pressure-confining casing, a plurality oi pairs oi separable switch contacts, a substantially cylindrical cup-like insulator oi gas-evolving material at least partially enclosing each oi said pairs oi contacts, said insulators being disposedin substantially parallel spaced relation and being apertured on adjacent sides to provide gas exhaust passages in opposing relation, operating means ior separating said pairs oi contacts substantially simultaneously to establish electric arcs within said insulators and in intimate gas-generating relation with the sides oi said insulators opposite said apertures, whereby the dielectric gases evolved within said insulators pass substantially transversely oi the generating arcs and through said apertures in opposing and encountering streams to create between said insulators a turbulent flow oi gas to aid the quenching oi said arc, said gases creating within said casing a pressure suiiicient to prevent short-circuiting oi said pairs oi contacts by said encountering gas streams.

-LUDWIG S. WALLE.

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