US2979590A

US2979590A - Circuit interrupter

Info

Publication number: US2979590A
Application number: US731902A
Authority: US
Inventors: Sandin Jerome
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1958-04-30
Filing date: 1958-04-30
Publication date: 1961-04-11
Anticipated expiration: 1978-04-11

Description

April 11, 1961 J; SANDlN 2,

CIRCUIT INTERRUPTER Filed April so, 1958 3 SheetsSheet 1 WITNESSESI I gw ggfidm @DwmQR BY vim WMMWW mind/HM ATTORNEY April 11, 1961 J. SANDIN 2,979,590

CIRCUIT INTERRUPTER Filed April 30, 1958 3 Sheets-Sheet 2 sci 8" Be 8c I I! I I 0.! uu 86-- 80 Si) O B A r l )4 i 49 l'.'..'r. .1' f "L: I 1 I h I l I "q j\ -k -1: Z 48 it- 5 April 11, 1961 J; SANDIN CIRCUIT INTERRUPTER 3 Sheets-Sheet 3 Filed April 30, 1958 United States Patent CIRCUIT INTERRUPTER Filed Apr. 30, 1958, Ser. No. 731,902

11 Claims. (Cl. 200-143) This invention relates to circuit interntpters in general and, more particularly, to arc-extinguishing structures therefor.

A general object of the invention is to provide an improved circuit interrupter having an improved structure to render the same adaptable for the interruption of relatively high currents at relatively high voltages. Although the particular structure described is adaptable for the voltage range from 5,000 volts to 15,000 volts, it will be obvious to those skilled in the art that the described structure may, by suitable dimensioning of the parts, be employed at other voltage ranges and for higher or lower current rating.

A more specific object of the present invention is to provide an improved circuit interrupter involving one or more pole units of the swinging movable contact blade type, in which the structure is so adaptable as to be enclosed in a generally cylindrical housing.

Another object is to provide an improved circuit in. terrupter of the fluid-blast type in which one or more poles are enclosed in a generally cylindrical housing having a suitable arc-extinguishing fluid contained therein. Preferably, a piston structure is associated with each of the poles and is operable to force a blast of fluid toward the established arc to effect the latters extinction.

Yet a further object of the present invention is to provide an improved, compact and economical circuit interrupting device utilizing a suitable arc-extinguishing gas contained within a grounded, generally cylindrical container. Preferably, a piston structure is associated with each of one or more pole units extending laterally through the side Wall of the generally cylindrical container, each pole unit having a movable swinging contact blade bridging the interior contact members of each pole unit.

Another object of the invention is to provide a cornpact and economical circuit interrupter particularly adapted to contain a relatively expensive arc-extinguish ing gas, such as sulfur hexafluoride or selenium hexafiuoride either used alone or mixed together or admixed with one or more of the following gases: air, argon, helium, carbon dioxide and nitrogen. Preferably, a grounded cylindrical tank structure is employed enclosing one or more pole units, each pole unit having associated therewith a piston structure involving a piston member attached to and movable with the extremity of the movable contact blade of the pole unit.

In U.S. patent application Serial No. 477,466, filed December 24, 1954, now United States Patent 2,924,690, issued February 9, 1960, to Thomas E. Browne, Jr. and Albert P. Strom, and assigned to the assignee of the instant application, there is described and claimed a grounded tank structure enclosing one of the aforesaid relatively expensive gases, in which a piston structure is employed to effect extinction of an established arc. It is a further object of the present invention to improve upon the gas-type circuit interrupter of the aforesaid application rendering the same more suitable for use with a plurality of pole units and disposed within a spacesaving, grounded, generally cylindrical gas-confining chamber.

Still a further object of the present invention is to provide an improved interrupting structure for a circuit interrupter.

Further objects and advantages will readily become apparent upon reading the following specification, taken in conjunction with the drawings, in which:

Figure 1 is a sectional view, partially in end elevation, of a circuit interrupter embodying the principles of the invention, the contact structure being illustrated in the closed-circuit position;

Fig. 2 is a somewhat diagrammatic rear elevational view of the circuit interrupter of Fig. 1, more clearly illustrating the three-pole construction and a portion of the operating mechanism;

Fig. 3 is a perspective view of one of the insulating plates constituting the interrupting structure;

Fig. 4 is a sectional view taken along the line IV-IV of Fig. l; and

Fig. 5 is a sectional view taken along the line VV of Fig. 1.

Referring to the drawings, and more particularly to Fig. 1 thereof, the reference numeral 1 generally designates a circuit interrupter including three pole units, designated by the reference numerals A, B and C and diagrammatically indicated in Fig. 2. Each pole unit includes a pair of horizontally extending

terminal studs

2, 3 extending through

insulating sleeves

4, 5, the latter being fixedly secured by any suitable means to a pair of cylindrical boss portions 6, 7 of a grounded metal tank 8.

Preferably, the tank 8 is generally cylindrical in configuration and extends substantially horizontally, as illustrated in Fig. 2. End plates 8a, 8b are provided and are removable, as shown, by unscrewing machine bolts 80. Gaskets 8d are provided for a gas-tight construction. A filling inlet pipe 8e permits filling the tank 8 with fluid.

As shown in Fig. 1, the horizontally positioned generally cylindrical tank 8 is supported by a pair of longitudinally extending

brackets

9, 10, the latter being secured to the upper side 11 of a mechanism housing or truck 12. For portable movement of the circuit interrupter 1, it is desirable to mount the mechanism housing 12 upon wheels 13, rotatable about axles 1 so that the entire circuit interrupter may be transported laterally into a cubical, or cell housing structure, not shown, but well known to those skilled in the art.

Considering an end pole unit C, fixedly secured to the interior end of the terminal stud 3 is a relatively stationary hinge contact member 15 having pivotally mounted thereon a movable contact blade 16, adapted for swinging opening and closing movement. As more clearly shown in Fig. 1, the pivotally mounted blade 16 is pivotally mounted around an axis 17 which, it will be noted, is off center, by the distance D, from the central axis 18 of the generally cylindrical tank 8.

Fixedly secured to the interior end of the upper terminal stud 2 is a curved stationary contact member 19, having a plurality of contact fingers 20 mounted thereon. Preferably, the outer contact finger 20a projects farther along the path of opening travel of the swingable blade 16 than the adjacently disposed contact fingers 20, so that, in parting last from said contact finger 20a, the blade 16 will establish an are from the lengthened arcing con tact fingers 2011 as indicated by the reference numeral 21. Thus, although Fig. 1 shows the movable blade 16 in its fully opened position, indicated by the dotted line 16a, nevertheless, for the purpose of illustration, the relative position of the are 21 has been indicated.

Fixedly secured to the stationary contact member 19 is a mounting plate 22, which supports a stationary operating cylinder 23, within which moves a piston 24, pivotally connected, as at 25, to a pair of insulating piston rods 26. The insulating piston rods 26 extend through a pair of slots 27 in the lower substantially closed end of the operating cylinder 23, and are pivotally connected, as at 28, to the outer extremity of the movable blade 16. Although the lower end of the operating cylinder 23 has hereinbefore been described as substantially closed, never-the less, as Fig. 1 clearly shows, there is provided a nozzle 29 for the flow of compressed gas out of the interior region 30 of the cylinder 23 to flow against the established arc 21.

Preferably, during the opening operation, the movable contact blade 16 swing about its pivot axis 17, separating from the

fingers

20, 20a of the stationary contact 19, and carrying with it, by means of the two insulating piston rods 26, the movablepiston 24 within the operating cylinder 23. The compression of gas within the region 3% interiorly of the operating cylinder 23 will cause the ejection of this compressed gas out of the region 30, within the operating cylinder 23, through the stationary nozzle 29 and toward the established are 21 to effect the latters extinction.

To facilitate the interruption of the arc 21, and to more effectively direct the compressed gas issuing out of the nozzle 29, a generally rectangular orifice structure 31 is provided. Generally, the orifice structure 31 includes a pair of mating insulating plates 32, more clearly shown in Fig. 3. As illustrated in Fig. 3, the insulating plates 32 have an outer flange portion 33, the flanges 33 of both plates 32 engaging each other to close off the outer side of the rectangular orifice 34-. In addition, each plate 32 has an upper flange portion 35 with a slot 35a to accon1- modate a piston rod 26 and a semicircular slot 35b to accommodate the nozzle 29. Also, the flanges 35 of both plates 32 accommodate the fingers 20, 26a with recesses 350, so that, in effect, the upper end of the rectangular orifice 34 is closed.

With reference to Fig. 4, it will be observed that each insulating side plate 32 has a restricted portion 36. When the side plates 32 are assembled, as shown in Fig. 4, the restrictions 36 cooperate to provide the rectangular orifice 34. Closing the inner side of the rectangular orifice 34 is a movable baffle plate 37, secured by bolts 38 to an in termediate part of the contact blade 16. From the previously described construction, it will be apparent that during the opening motion, the bafiie plate 37 substantially closes the inner open side of the interrupting structure 31 so that compressed gas, ejected from the nozzle 29 of piston structure 39, will be compelled to flow through the rectangular orifice 34, and against the established are 21, bringing about the latters extinction.

It is desirable to effect opening, swinging motion on all three movable contact blades 16 of the three pole units A, B, C, simultaneously from a single mechanism source. To effect this, each movable contact blade 16 has pivotally connected thereto, as at 4%), an insulating operating link 41. Each operating link or rod 41 is pivotally connected, as at 4-2, to the outer extremity of a crank-arm 43. The three crank-arms 43, associated with the three pole units A, B, C (Fig. 2), are secured, as by welding, to a single rotatable drive shaft 44-, extending lengthwise along the generally cylindrical grounded tank 8 off center from the central axis 18 of the tank.

One end of the drive shaft 44 is journaled in a bearing bracket 47, as illustrated in Fig. 2. The other end of the drive shaft 44 extends through a gas-tight seal 48 and protrudes externally of the tank 8. Fixedly secured, as by welding, to this external end of the drive shaft 44 is a crank-arm 49, which is operated by a link 50, the latter being operated by suitable mechanism disposed internally Within the mechanism housing 12.

The particular mechanism disposed within the mechanism housing 12 may be of any suitable type, and constitutes no part of the present invention. For one particular type of mechanism, which is suitable, reference may be had to U.S. Patent 2,515,994, issued July 18, 1950, to Joseph D. Findley, In, Alvin W. Ogg and Fritz E. Florschutz, and assigned to the assignee of the instant application.

By way of recapitulation, during the opening operation, the mechanism disposed within the mechanism housing 12 is etfective through the link 5% to effect counterclockwise rotative motion of the crank arm 49, as viewed in Fig. 1. This will effect corresponding counterclockwise rotation of the drive shaft 44-, as viewed in Fig. 1, thereby causing corresponding counterclockwise rotative travel of the three crank-arms 43 disposed interiorly within the generally cylindrical tank 8.

The opening rotative motion of the three crank-arms 43 for the three pole units A, B, C will effect, through the three insulating operating rods 41, opening movement of the three movable contact blades 16 about their pivot axes 17. As stated hereinbefore, the opening rotative movement of each movable contact blade 16 will not only eifect arc drawal between the lengthened fingers 2% and the blade 16, but also will effect, through the insulating piston rod 26, downward movement of the piston 24- within the operating cylinder 23. Thus, upon establishment of the are 21, there will be forced out of the piston nozzle 29 compressed gas from the region 30 interiorly of the operating cylinder 23.

This compressed gas, ejected from the nozzle 29, will flow in close contact with the are 21 by being compelled to flow between the restrictions 36 of plates 32, namely through the rectangularly-shaped orifice 34. Since the insulating baffle plate 37, carried by the movable contact blade 16, closes the inner opening between the plates 32, in efiect, there is formed a substantially closed, generally rectangular, orifice structure 31, compelling the compressed gas to flow through the rectangular orifice 34 and in contact with the are 21, effecting the latters rapid extinction.

Following extinction of each are 21 within each pole unit A, B, and C, the continued opening rotative travel of the movable contact blade 16 within each pole unit forms an adequate isolating gap distance in the fully open circuit position of the interrupter, as indicated by the dotted lines 16a in Fig. 1.

During the closing operation, the mechanism, disposed Within the mechanism housing 12, is efiective to cause through the linkage 5b and crank arm 49, rotative movement of drive shaft 44, thereby causing clockwise rotative travel of each of the three movable contact blades 16. This closing movement will not only effect contacting engagement between each movable contact blade 16 and its cooperating

stationary contact fingers

20, 20a, but also the piston 24 for that particular pole unit Will be forced, by the linkage 26, upwardly within the operating cylinder 23, gas being dravm into the region 30 interiorly of the operating cylinder 23 through the piston nozzle 29.

From the foregoing description of the invention, it will be apparent that by the particular arrangement disclosed, considerable space is saved, particularly when it is desired to employ a particular confined gas for effective are extinction. It will be noticed that the pivot axis for the three movable contact blades 16 is off center from the central axis of the tank 3 by the distance D. Also, it will be observed that the drive shaft 44 is disposed adjacent the lower end of the tank 8, as viewed in Fig. 1 also off center from the tank axis 18. More importantly, considerable expense is saved by employing a generally cylindrical configuration of the tank 8, since, as well known generally, it is cheaper to manufacture a tank of cylindrical shape rather than any other configuration. Moreover, by having a generally cylindrical configuration for the tank 8, it is enabled to withstand considerably internal pressure before rupture occurs.

The structure illustrated represents an arrangement which results in a sturdy breaker, economical in both space and cost. Generally, in some types of gas-blast breakers, porcelain or other fragile enclosures are employed with insulating tie-rods to hold the parts together. Such an arrangement makes a rather fragile breaker and also requires more space. For applications involving considerable operational life, that is, for example, 50,000 to 100,000 operations, it is desirable to have a sturdy and space-saving structure employing finger-type contacts for good contacting engagement with long operational life.

By employing preferably a cylindrical, steel, grounded housing, not only is an interrupter provided completely safe for personnel, but also considerable rigidity is obtained. Where desired, the interrupter may be movable laterally into a cubical or cell housing, as well known to those skilled in the art. Since the contacts are of the standard blade and finger construction, which have been found in the past to be satisfactory for long life, a breaker results, which is suitable for long operational life and requires little maintenance.

Where sulfur hexafiuoride (SP or selenium hexafluoride (SeF are utilized as the enclosed gas, preferably the interrupter plates 32 and the rotatable bafi le plate 37 are formed of polytetrafiuoroethylene, which has the characteristic of resisting deleterious arcing effects. The use of the putter 39 not only assists considerably in arc extinction, but, in addition, it will be noted that the piston rod 26 is fastened to the outer extremity of the swinging contact blade 16, thereby making it possible to obtain a maximum piston movement, with corresponding greater flow of gas through the piston orifice 29.

Although the invention has been described employing a generally cylindrical tank structure enclosing a suitable arc-extinguishing gas, nevertheless it will be apparent to those skilled in the art that certain features of the inven tion may be used in other applications, where a confining structure is not employed. For example, certain features of the interrupting structure 31 and others pertaining to the location of the piston structure 39 and the point of attachment of the piston rod 26 has general utility apart nrent are set forth and claimed in US. patent application Serial No. 729,368, filed April 18, 1958, by Jack E. Schrameek and Richard E. Kane and assigned to the assignee of the present application.

Although there has been illustrated anddescribed a particularcircuit interrupting structure, it is to be understood that the same was merely for the purpose of illustration, and that changes and modifications may readily be made therein by those skilled in the art, without departing from the spirit and scope of the invention.

I claim as my invention:

1. A circuit interrupter including a pair of relatively stationary contacts, a movable contact blade having a movable contact portion intermediate the ends thereof pivotally mounted upon one relatively stationary contact and adapted for swinging movement of the movable contact portion into and out of contacting engagement with the other relatively stationary contact, a piston structure associated with said other relatively stationary contact and including an operating cylinder, a piston movable within said operating cylinder, an orifice disposed at one end of said operating cylinder for directing a blast of fluid substantially transversely of the contact blade, connecting means interconnecting said piston with said movable contact blade so that during the opening operation compressed fiuid may be ejected out of said operating cylinder through said orifice and substantially longitudinally of the are established between said movable contact portion and said other relatively stationary contact, and said 6 connecting means being connected to the outer free extremity of the movable contact blade for maximum movement of the piston.

2. A circuit interrupter including a generally cylindrical grounded metallic tank, one or more pairs of terminal bushings extending laterally through the side walls of said tank forming one or more pole units, relatively stationary contact structures disposed at the interior ends of said one or more pairs of terminal bushings, rotatable bridging contact means pivotally mounted at the inner end of one of eachpair of terminal bushings for electrically bridging the relatively stationary contact structures of each pair of terminal bushings, and the rotatable bridging contact means rotating in one or more planes generally normally of the longitudinal axis of the generally cylindrical tank.

3. A multi-pole circuit interrupter including a generally cylindrical elongated grounded metallic tank, a plurality of spaced pairs of terminal bushings extending through the side wall of said metallic tank, a relatively stationary contact structure mounted at the inner end of one of each pair of terminal bushings, a rotatable contact blade pivotally mounted at the inner end of the other terminal bushing ofeach pair of terminal bushings, the several rotatable contact blades making engagement and disengagement with the several relatively stationary contact structures for closing and opening the connected circuits, the rotatable contact blades rotating in generally parallel planes which are substantially normally of the longitudinal axis of the cylindrical tank, a common operating shaft extending lengthwise interiorly of the elongated cylindrical tank and carrying a plurality of crank arms thereon, and means interconnecting the crank arms With the rotatable contact blades for simultaneous contact operation.

4. A multi-pole circuit interrupter including a generally cylindrical elongated grounded metallic tank, a plurality of spaced pairs of terminal bushings extending through the side wall of said metallic tank, a relatively stationary contact structure mounted at the inner end of one of each pair of terminal bushings, a rotatable contact blade pivotally mounted at the inner end of the other terminal bushing ofeach pair of terminal bushings, the several rotatable contact blades making engagement and disengagement with the several relatively stationary contact structures for closing and opening the connected circuits, the rotatable contact blades rotating in generally parallel planes which are substantially normally of the longitudinal axis of the cylindrical tank, a common operating shaft extending lengthwise interiorly of the elongated cylindrical tank and carrying a plurality of crank arms thereon, means interconnecting the crank arms with the rotatable contact blades for simultaneous contact operation, and the pivot axis of the several rotatable contact blades being off-center within the tank to conserve space.

5. A multi-pole circuit interrupter including a generally cylindrical elongated grounded metallic tank, a plurality of spaced pairs of terminal bushings extending through the side wall of said metallic tank, a relatively stationary contact structure mounted at the inner end of one of each pair of terminal bushings, a rotatable cont-act blade pivotally mounted at the inner end of the other terminal bushing of each pair of terminal bushings, the several rotatable contact blades making engagement and disengagement with the several relatively stationary contact structures for closing and opening the connected circuits, the rotatable contact blades rotating in generally parallel planes which are substantially normally of the longitudinal axis of the cylindrical tank, a common operating shaft extending lengthwise interiorly of the elongated cylindrical tank and carrying a plurality of crank arms thereon, means interconnecting the crank arms with the rotatable contact blades for simultaneous contact operation, and the axis of said common operating 7 shaft being closely positioned to the side wall of the tank. 6. A multi-pole circuit interrupter including a generally cylindrical elongated grounded metallic tank, a plurality of spaced pairs of terminal bushings extending through the side wall of said metallic tank, a relatively stationary contact structure mounted at the inner end of one of each pair of terminal bushings, a rotatable contact blade pivotally mounted at the inner end of the other terminal bushing of each pair of terminal bushings, the several rotatable contact blades making engagement and disengagement with the several relatively stationary contact structures for closing and opening the connected circuits, the rotatable contact blades rotating in generally parallel planes which are substantially normally of the longitudinal axis of the cylindrical tank, a common operating shaft extending lengthwise inten'orly of the elongated cylindrical tank and carrying a plurality of crank arms thereon, means interconnecting the crank arms with the rotatable contact blades for simultaneous contact operation, the pivot axis of the several rotatable contact blades being off-center within the tank to conserve space, and the axis of said common operating shaft being closely positioned to the side wall of the tank.

7. A truck-mounted, multi-pole circuit interrupter including an elongated generally cylindrical grounded metallic tank, means including a roller-mounted truck for supporting said tank in a generally horizontal position, a plurality of pairs of terminal bushings extending laterally through the side wall of the tank, planes extending through the individual pairs of terminal bushings being generally vertical and also generally normal to the longitudinal axis of said elongated cylindrical tank, separable contact structure movable in said planes associated with the inner ends of said each pair of terminal bushings, and the direction of rolling motion of said roller-mounted truck being substantially parallel to said planes.

8., A circuit interrupter including a movable contact and a relatively stationary contact cooperable to establish an arc, blade means pivotally mounting said movable contact for swinging opening and closing movement, insulating arc-chute means having spaced insulating side Walls for extinguishing said arc. and having said relatively stationary contact mounted adjacent one end thereof, said movable blade means moving along one open side of the arc-chute means, means closing the side of the arc-chute means opposite said open side thereof, said spaced insulating side walls defining an enlarged chamber adjacent said relatively stationary contact and having inwardly extending projections which cause the enlarged chamber to taper smoothly inwardly to form an extended substantially rectangular restricted orifice portion intermediate the ends of the arc-chute means, said extended restricted substantially rectangular orifice portion of the arc-chute means being positioned substantially parallel to said movable blade means and extending substantially the full width of the arcchute means, said substantially rectangular restricted orifice portion of the arc-chute means flaring smoothly outwardly toward another open end of the arc-chute means for the exhausting of fluid from the arc-chute means during circuit interruption.

9. A circuit interrupter including a movable contact and a relatively stationary contact cooperable to establish an arc, blade means pivotally mounting said movable contact for swinging opening and closing movement, insulating arc-chute means having spaced insulating side walls for extenguishing said are and having said relatively stationary contact mounted adjacent one end thereof, said movable blade means moving along one open side of the arc-chute means, means closing the side of the arc-chute means opposite said open side thereof, said spaced insulating side walls defining an enlarged chamber adjacent said relatively stationary contact and having inwardly extending projections which cause the enlarged chamber to taper smoothly inwardly to form an extended substantially rectangular restricted orifice portion intermediate the ends of the arc-chute means, said extended restricted substantially rectangular orifice portion of the arcchute means being positioned substantially parallel to said movable blade means and extending substantially the full width of the arc-chute means, said substantially rectangular restricted orifice portion of the arc-chute means flaring smoothly outwardly toward another open end of the arc-chute means for the exhausting of fluid from the arc-chute means during circuit interruption, and a movable baflie plate carried by the movable blade means for preventing excessive exhausting of fluid out of the first mentioned open side of the arc-chute means.

10. A circuit interrupter including a movable contact and a relatively stationary contact cooperable to establish an arc, blade means pivotally mounting said movable contact for swinging opening and closing movement, insulating arc-chute means having spaced insulating side walls for extinguishing said are and having said relatively stationary contact mounted adjacent one end thereof, said movable blade means moving along one open side of the arc-chute means, means closing the side of the arc-chute means opposite said open side thereof, said spaced insulating side walls defining an enlarged chamber adjacent said relatively stationary contact and having inwardly extending projections which cause the enlarged chamber to taper smoothly inwardly to form an extended substantially rectangular restricted orifice portion intermediate the ends of the arcchute means, said extended restricted substantially rectangular orifice portion of the arc-chute means being positioned substantially parallel to said movable blade means and extending substantially the full Width of the arc-chute means, said substantially rectangular restricted orifice portion of the arc-chute means flaring smoothly outwardly toward another open end of the arcchute means for the exhausting of fluid from the arc-chute means during circuit interruption, fluid-blast means in cluding a piston chamber disposed adjacent the first-mentioned end of the arc-chute means, and a piston actuated by the movable blade means for forcing a fluid blast between the spaced side walls in the direction of arc elongation.

11. A circuit interrupter including a movable contact and a relatively stationary contact cooperable to establish an arc, blade means pivotally mounting said movable contact for swinging opening and closing movement, insulating arc-chute means having spaced insulating side Walls for extinguishing said are and having said relatively stationary contact mounted adjacent one end thereof, said movable blade means moving along one open side of the arc-chute means, means closing the side of the arc-chute means opposite said open side thereof, said spaced insulating side walls defining an enlarged chamber adjacent said relatively stationary contact and having inwardly extending projections which cause the enlarged chamber to taper smoothly inwardly to form an extended substantially rectangular restricted orifice portion intermediate the ends of the arc-chute means, said extended restricted substantially rectangular orifice portion of the arc-chute means being positioned substantially parallel to said movable blade means and extending substantially the full width of the arc-chute means, said substantially rectangular restricted orifice portion of the arc-chute means flaring smoothly outwardly toward another open end of the arcchute means for the exhausting of fluid from the arc-chute means during circuit interiuption, a movable baffie plate carried by the movable blade means for preventing excessive exhausting of fluid out of the first-mentioned open side of the arc-chute means, fluid-blast means including a piston chamber disposed adjacent the first-mentioned end of the arc-chute means, and a piston actuated by the movable blade means for forcing a fluid blast between the spaced side walls in the direction of arc elongation.

(References on following page) 9 References Cited in the file of this patent UNITED STATES PATENTS Corey Oct. 13, 1908 Allan Nov. 25, 1930 Houst July 11, 1933 Trencham et a1. July 3, 1934 Howe Oct. 12, 1937 10 Linde et a1 Oct. 22, 1940 Baskerville May 2, 1944 FOREIGN PATENTS Germany Aug. 24, 1928 France Feb. 9, 1923 Great Britain July 25, 1956 Great Britain Dec. 12, 1956 France Sept. 13, 1937 France June 7, 1948