US3031552A

US3031552A - Electric circuit interrupter

Info

Publication number: US3031552A
Application number: US816629A
Authority: US
Inventors: Vincent N Stewart
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1959-05-28
Filing date: 1959-05-28
Publication date: 1962-04-24
Anticipated expiration: 1979-04-24

Description

April 24, 1962 v. N. STEWART 3,031,552

ELECTRIC CIRCUIT INTERRUPTER Filed May 28, 1959 IIIIIIIIII IIIIII ml III I t A A a/ nven or:

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United States Patent O 3,031,552 ELECTREC CIRCUT INTERRUPTER Vincent N. Stewart, Springfield, Pa., assignor to General Electric Company, a corporation of New York Filed May 23, 1959, Ser. No. 816,629 8 Claims. (Cl. 200-144) This invention relates to electric circuit interrupters, and more particularly it relates to an electric arc extinguishing device of the type employing spaced metal plates.

Electric circuit interrupters are used for the purpose of interrupting the flow of current in electric power circuits. The current interruption process is begun by separating cooperating contact members of the interrupter, whereby a gap of air or gaseous matter is opened in the circuit. The gases in the gap between the separated contact members, although normally having relatively great dielectric strength or insulating ability, may temporarily be rendered electrically conductive due the phenomenum of ionization. If there is simultaneously a sufficient potential difference between the separated contact members and a sufcient degree of ionization of the gases in the gap,

the ionized gases will form an electric arc which must be permanently extinguished in order to interrupt the circuit current.

When interrupting an alternating current electric power circuit, there are periodic current zeros, and therefore the electric arc is discontinued naturally at the end of each half cycle. By sufficiently deionizing the gases in the gap at a current zero, reestablishment or reignition of the arc during the succeeding half cycle can be prevented. Accordingly, it is a conventional object in designing arc extinguishing devices for alternating current circuit interrupters to provide suitable means for obtaining deionization of the arc gases and otherwise impairing the conductivity of the current path so that the potential difierence between the separated contact members required to reignite the arc after a current zero, known as the reigni- `tion voltage, exceeds permanently the circuit recovery voltage impressed upon these members tending to reestablish the flow of current.

It is a well known practice in the art of electric circuit interruption to provide an arc extinguishing device or arc chute having a plurality of spaced-apart metal barriers or plates disposed across the path of the arc. These plates chop the arc into a family of serially related arclets which are subsequently deionized and extinguished as they move within the spaces between adjacent plates. Such arcchopping metal plates contribute to the arc quenching process in several different ways. Their relatively cool surfaces reduce the temperature of the arc thereby enhancing deionization and increasing arc resistance. The plates cause a turbulent mixing of the hot arc gases and the relatively cool air in the spaces through which the arclets move, thereby further enhancing deionization. Each arclet has its own anode and cathode voltage drop region where the voltage gradient is relatively high. In other words, a thin cathode or anode sheath of relatively high dielectric strength is formed adjacent the opposing surfaces of each pair of metal plates, and at least a certain minimum potential difference between adjacent plates is required in order to reestablish the associated arclet after a current zero. Accordingly, the cumulative effect of a plurality of spaced metal plates is to raise the reignition voltage of the circuit interrupter to a point where it exceeds permanenly the circuit recovery voltage.

When conventional are chutes of this type are properly designed and applied, the arc gases are sufliciently deionized by the action of the metal plates to extinguish the arc. However, the deionization may not be sulcient to the upper edge of this short plate.

3,931,552 Patented Apr. 24, 1962 C ICG prevent reestablishment or restriking of the arc across the edges of the plates as these gases exhaust from the spaces between plates. In order to meet this problem it has been proposed heretofore to provide insulating members closely fitted to the upper edges of the metal plates, thereby obstructing the continuous path which would otherwise exist for the formation of an arc at this point. This solution to the problem has not proved entirely satisfactory, and accordingly it is a general object of my invention to provide an improved arc extinguisher of the spaced metal plate type wherein restriking of the arc after it has been extinguished by the metal plates is effectively prevented.

Another object of this invention is the provision of a relatively simple and economical arc extinguisher having spaced metal plates wherein restriking of the arc after being extinguished by the plates is prevented by means which do not require ine manufacturing tolerances or tight fitting assembly.

Still another object is to provide a compact arc extinguisher of the spaced metal plate type wherein the path across the edges of the plates is so long and tortuous that restriking will not occur.

A further object of the invention is the provision of an arc extinguisher having an unusually large number of spaced metal plates tted into a relatively limited space.

In carrying out my invention in one form, an electric arc chute is provided with a pair of spaced sidewalls de- -ining an arcing chamber, a plurality of spaced-apart arcchopping metal plates spanning the sidewalls above the arcing chamber, and a plurality of spaced-apart baile members of insulating material spanning the sidewalls intermediate the plates and an outlet through which the arc products are exhausted. A perforated metallic muffler is disposed across the outlet of the chute for cooling the arc products exhausted and thereby preventing conduction to any grounded metal structure which may be located above the outlet. At least one of the metal plates of the arc chute is made shorter than the others with its upper edge being disposed at a level below the upper edge of the plates adjacent thereto, and an associated baffle member is disposed in edgewise engagement with Consequently, the bafile member overlaps the uppermost portions of the plates adjacent to the short plate and impedes the establishment of an arc across the tops of the plates.

In one aspect of my invention, a plurality of pairs of grooves are respeectively provided in the opposing surfaces of the sidewalls of the arc chute for receiving the ends of the metal plates, two plates being disposed in each pair of grooves. A substantial portion of the span of each plate is laterally offset with respect to the end portions thereof so that the spacing between the spans of the two plates associated in each pair of grooves is greater than the spacing between corresponding ends thereof. This aspect of the invention is particularly useful in arc chutes for circuit iuterrupters designed to interrupt direct current circuits, since the interrupting ability of such a chute is significantly affected by the number of plates utilized. In direct current circuits there are no periodic current zeros, and in order to extinguish the arc the circuit current must be forced to zero by increasing the arc voltage, as by inserting arc chopping plates, until the voltage required to sustain the arc is greater than the available circuit voltage.

My invention will be better understood and its various objects and advantages will be more fully appreciated from the following description taken in conjunction with the accompanying drawing in which:

FIG. 1 is a side elevation, partly in section, of a circuit interrupter embodying a preferred form of my invention; f

FIG. 2 is a sectional view of the arc chute of FIG. 1 taken along the line 2 2;

FIG. 3 is a sectional view of the FIG. 1 arc chute taken along the line 3-3; and

FIG. 4 is an enlarged plan sectional view similar to FIG. 3 but showing another aspect of the invention.

Referring now to FIG. 1, I have shown for the purposes of illustration an electric circuit interrupter comprising contact structure 11 separable to establish an arc and an arc chute 12 for enclosing and extinguishing the arc. Although the contact structure 11 may take any suitable form, as illustrated it comprises a relatively stationary contact member 13 mounted on a current-conducting stud 14 and a cooperating contact arm 1S supported for pivotal movement into and out of circuitmaking engagement with the stationary contact member 13. In FIG. 1 the movable contact arm 15 is shown in its open circuit position.

The current-conducting stud 14 on which the stationary contact member 13 is mounted is suitably supported by means including a generally L-shaped angle 16. The supporting angle 16 extends above the stud 14, as is shown in FIG. 1, and serves as an arc runner in cooperation with the stationary contact member 13. Means 17 is provided for securing the angle 16 to a base member, not shown. The actuating means for moving the contact arm during circuit makingl and interrupting operations is also omitted from the drawing for the salie of clarity. A more detailed disclosure of the schematically illustrated contact structure 11 is believed unnecessary for a full and complete understanding of my invention.

The arc chute or extinguisher 12 comprises a pair of

Vspaced sidewalls

18 and 19 of electric insulating material. Preferably the sidewalls are made of a ceramic material, such as porcelain, which is conveniently formed in the desired shape. Each

sidewall

18, 19 is substantially the mirror image of the other, and both are provided at their right and left-hand ends, as viewed in FIG. 1, with abutting transverse portions 2t] and 21 which determine the psacing therebetween. The two

sidewalls

18 and 19 are surrounded by a thin protective sheath 22 of ber material, and the whole assembly is held together by suitable means, such as bolts 23 extending transversely through the abutting portions and 21, respectively.

The arc chute 12 is conveniently supported in the position shown in FIG. 1 by means of a hook-like protrusion 24 of the angle 16 snugly received in a vertical notch or recess 25 provided in the abutting portions 20 of the

sidewalls

18 and 19. In addition, I provide suitable retaining means, not shown, for securely 4holding the arc chute in place. As can be seen in FIG. 1, the

sidewalls

18 and 19 of the chute nest in and extend above a wraparound barrier 26 of insulating material which isolates the illustrated contact structure 11 from other parts of the circuit interrupter located nearby. The inner surfaces of the

sidewalls

18 and 19 define a Yrelatively narrow arcing chamber adjacent the lower end of the arc chute, and a suitable fiber barrier 27Vis disposed at this end of the chute to define a relatively restricted opening 28 therein.

The restricted opening 28 in the chute 12 admits the free end of the movable contact arm 15 as well as the relatively stationary contact member 13. During a circuit interrupting operation, the contact arm 15 is moved to effect separation or disengagement of the cooperating contacts 13 and 1S, and an electric arc is initiated within the arcing chamber of the arc chute 12.

Spanning the

sidewalls

18 and 19 above the arcing chamber of the arc chute are a plurality of spaced-apart solid metal plates 29 which extend transversely across the path of the electric are drawn between the

cooperating contacts

13 and 15. In a conventional manner, the arc is driven against the exposed lower edges of the plates 29, and the plates chop the arc into a family of serially relatedV arclets which are Isubsequent/ly deionized and extinguished as they move within the spaces between adjacent plates. Preferably, the lower portion of each plate is centrally recessed or notched so that its lowerV edge defines an inverted V, as best seen in FIG. 2.

In accordance with my invention, predetermined plates 29s are made shorter than the other metal plates 29. The upper edge 30 of each short plate 29s is disposed at a level below the upper edges of the plates immediately adjacent thereto. In other words, the upper edges 30 of the short plates lie below a horizontal plane defined by the upper edges of the regular plates 20. The purpose of this particular construction 1will be explained shortly hereinafter.

The spaced-apart metal plates 29 are held in place by means of appropriate pairs of Vertical grooves 31 respectively provided in the opposing surfaces of the

ceramic sidewalls

18 and 19, each pair of grooves receiving the opposite ends of one plate. Reduced-depth portions 32 of some of the grooves extend below the metal plates 29, as can be seen in FIG. 1, in order to increase the length of the electrical creepage path over this part of the surface of the sidewalls. According to the teachings of L. L. Baird, as contained in his copending patent application S.N. 764,642 (filed on October 1, 1958, and assigned to Vthe assignee of the present application) wherein this feature of the illustrated arc chute is claimed, the inner portions of these groove extensions 32 are shielded from the intense heat of the electric arc in the arcing charnber and hence are cooler than the remainder of the 'surface of the sidewalls. The electrical resistance of insulating materials is known to decrease with increasing temperature, and accordingly the shielded portions of the surface of the sidewalls provided by the extensions 32 of the grooves 31 serve to improve the resistance of this surface.

The arc products generated in the arc chute 12 during a circuit interrupting operation are exhausted or vented through an outlet 33 provided by an opening between the sidewalls 1S and 19 at the upper end of the chute. The hot arc products pass upward from the area of the metal plates 29 through a muffler 34 disposed across the outlet 33. The mufer 34, which comprises a plurality of serpentine strips of perforated metal, rapidly cools the arc products as they impinge against it. This suppresses flame emission from the arc chute 12 during a circuit interrupting operation and prevents conduction or flash-over to any grounded metal parts which may be located closely above the chute.

YDisposed intermediate the exhaust outlet 33 and the spaced metal plates 29 of the arc chute is a baffle 35 comprising a plurality of pairs of rib-like protrusions 36 of the ceramic sidewalls V18 and 19. These paired protrusions or baffle members 36 are oriented generally parallel to the metal plates, one baffle member being disposed in coplanar relationship with every other plate. See FIGS. 1 and 3.

One of the important purposes of the bathe 35 is to prevent the reestablishment or restriking of an electric arc across the tops of the metal plates. In order successfully to fulfill this purpose in prior art arc chutes of which I am aware, it has been necessary to have the barrier members tightly fitted to the metal plates thereby complete shutting of a continuous path across the upper edges of the plates. This has not -been altogether satisf factory in that its effectiveness depends on using vvery.

small tolerances and a high degree of precision in manufacturing and assembling` the arc chute components.

In accordance with my invention, instead of ensuring that there is no continuous path across the tops of the metal plates for restriking, I have chosen to provide a relatively low cost and easily manufactured arrangement wherein the length of the path across the tops of the metal plates is lengthening to a degree which Yeffectively inhibits the formation of an arc across the plates. As is best seen in FIGS. l and 2, this desired result is accomplished by inserting among the baille members 36 a plurality of relatively long, imperforate barriers 36b of insulating material which are respectively disposed in abutting association with the short metal plates 29s. Each barrier or baille member 36h spans the

sidewalls

18 and 19 and, being of the saine thickness as the met-al plates, is received in the same pair of grooves 31 that receives the associated short plate 29s. In this manner the members 36h are securely locked between the sidewalls 18 and 19.

As is clearly seen in FIG. l, each baille member 36h reaches lower than the rib-like baille members 36 to make edgewise engagement with the associated short plate 29s. Thus, the baille members 36h are disposed in overlapping relationship with the uppermost portions of the regular metal plates 29 adjacent to each of the short plates 29s, and the establishment of an arc along the plane defined by the upper edges of the regular plates 29 is blocked. In this manner reestablishment of an arc across the edges of the metal plates in the area between the metal plates and the baille 35 is effectively impeded although there is appreciable space between the baille members 36 and the tops of the plates 29 and even though the bottom edges of the barriers 36b are not closely fitted to the upper edges of their associated short plates 29s.

The provision of short metal plates 29s in combination with long insulating barriers 36b lengthens the path which an arc would have to take in order to restrike across the tops of the metal plates. Although not completely deionized, the gases being vented from the arcchopping plates are nevertheless insufiiciently ionized to form an arc of this length. Thus, my invention is effective to impede reestablishment of an arc across the metal plates 29 without requiring relatively costly and troublesome tight fitting between baille and plates.

It is apparent in FIG. l that the insulating barriers or baflle members 36b are also extended upwardly above the rib-like barrier members 36 and through the muiller y34 intermediate adjacent sections thereof. The purpose of this arrangement is to prevent the perforated metal strips which form the muiller from providing a continuous conductive path `from the front to the rear of the arc chute. The baille members 36b are preferably made of fiber material and are quite easily inserted in the arc chute during assembly thereof.

In accordance with the aspect of my invention illus- .t-rated in FIG. 4, an unusually large number of arccnopping metal plates can be compactly in an arc chute of a given size. Since the direct current interrupting ability of a metal-plate type arc chute increases directly with the number of plates effectively utilized, this aspect of my invention permits increased interrupting ability to be obtained without increasing the physical size of the arc chute. As clearly shown in FIG. 4 the number of pairs of grooves 31a provided in the respective sidewalls 1'8 and 19 of the arc chute is smaller than the number of spaced metal plates 29a, received therein. More specifically, the corresponding ends of two plates 29a are received in each groove 31a.

Each of the metal plates 29a is less than half as thick as each of the metal plates 29 provided in the arc chute of FIGS. 1-3. A substantial portion of the span of each relatively thin plate 29a is laterally offset with respect to its end portions, and the offset portions of the two plates associated in common grooves are oppositely disposed in order to provide appreciable venting area therebetween. The plates 29a are constructed and arranged as shown so that the spacings between spans of adjacent plates are uniform, that is, the distance along the length of the arc chute is substantially equally divided by the respective plates 29a. With this arrangement, the number of arc-chopping plates accommodated by an arc chute of the size shown in FIG. l can be doubled.

In order to electrically insulate the paired plates 29a,

I provided thin strips 37 of insulating material disposed between the corresponding end portions of the plates. As can be seen in FIG. 4, each strip 37 has an L-shaped cross section with one leg extending across the end of one of the plates 29a. In this manner the strip 37 is conveniently retained in its proper disposition. The other leg of the strip protrudes into the space between the associated plates 29a thereby increasing the electrical creeplage path between paired plates in the arc extinguishing area. This ensures that each plate 29a is electrically isolated from the plates adjacent thereto, and each plate can successfully perform its independent arc-chopping function.

While I have shown and described preferred forms of my invention by way of illustration, many modifications will occur to those skilled in the art. Therefore, I contemplate by the concluding claims to cover all such modiiications as fall within the true spirit and scope of my invention.

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

l. In an electric circuit interrupter including contact structure separable to establish an arc, an arc extinguisher comprising: a pair of spaced sidewalls `for enclosing the arc, a plurality of spaced-apart metal plates `spanning the sidewalls above the contact structure, said plates being disposed across the path of the arc for chopping the arc into a family of serially related arclets, an opening in the arc extinguisher for exhausting the arc products, and a plurality of baffle members of insulating material disposed in between the opening and the plates in generally coplanar relationship, respectively, with predetermined plates, at least one of said predetermined plates being shorter than other plates and having in edgewise association therewith a coplanar baflle member which overlaps the uppermost portions of the plates adjacent to said shorter plate for impeding the reestablishment of an arc across the tops of the metal plates.

2. An electric arc chute comprising: a pair of spaced ceramic sidewalls defining an arcing chamber adjacent the lower end of the chute, a plurality of spaced-apart arcchopping metal plates extending between the sidewalls above the arcing chamber, at least two of the plates being shorter than the others, an exhaust outlet at the upper end of the chute, and a baille located in between the outlet and the plates including a plurality of rib-like protrusions of the ceramic sidewalls oriented generally parallel to the plates and at least two barriers of insulating material inserted among the protrusions and respectively disposed in coplanar relationship with said shorter plates, said barriers reaching lower than the rib-like protrusions and making abutting engagement, respectively, with the upper edges of said shorter plates, thereby impeding the establish-4 ment of an arc in the area between the plates and the baille.

3. An electric arc chute comprising: a pair of spaced sidewalls defining an arcing chamber adja-cent the lower end of the chute, a plurality of spaced-apart arc-shopping metal plates extending between the side-walls above the arcing chamber, the upper edge of at least one plate lying below a plane defined by the upper edges of the other plates, an exhaust outlet in the chute above the plates, and a plurality of spaced-apart imperforate baille members of insulating material disposed in between the outlet and the plates in generally parallel relationship to the plates, the bottom edges of some but less than all of the baille members lying above said plane and at least one other baille member extending below said plane in associationl with said one plate for blocking the establishment of an arc along said plane.

4. An electric arc chute comprising: a pair of spaced sidewalls defining an arcing chamber adjacent the lower end of the chute, a plurality of spaced-apart arc-chopping metal plates spanning the sidewalls above the arcing chamber, a plurality of pairs of grooves respectively provided in the opposing surfaces of the sidewalls for receiving the plates, an exhaust outlet in the chute, and a plurality of spaced-apart baille members of insulating material spanning the sidewalls in between the outlet and the plates, at least one of the metal plates being shorter than others with its upper edge being disposed at a level below the upper edges of the plates adjacent thereto, the upper edge of said shorter plate being engaged by one of the baille members, said one baille member having substantially the same thickness as said shorter plate and being received in the same pair of grooves that receives said shorter plate.

5. In an electric circuit interrupter including contact structure separable to establish an arc, an arc extinguisher comprising: a pair of spaced sidewalls for enclosing the arc, a plurality of spaced-apart metal plates spanning the sidewalls above the contact structure, said plates being disposed across the path of the arc for chopping the arc into a family of serially related arclets, `an opening in the `arc extinguisher for exhausting the arc products, a plurality of baille members of insulating material spanning the side-walls in between the opening and the plates edgewise in abutting association, respectively, with predetermined plates, at least one of said predetermined plates being shorter than other plates and the baille member associated therewith being disposed in overlapping relationship with Y the uppermost portions of the plates vadjacent said shorter plate for impeding the reestablishment of an arc across the tops of the plates, Iand a perforated metallic muiller disposed -across the opening for cooling the products exhausted.

6. An electric arc chute comprising: a pair of spaced ceramic sidewalls dening an arcing chamber adjacent the lower end of the chute, a plurality of spaced-apart arcchopping metal plates extending between the sidewalls above the arcing chamber, at least two of the plates being shorter than the others, an exhaust outlet at the upper end of the chute, a baille located in between the outlet and the plates including a plurality of rib-like protrusions of the ceramic sidewalls oriented generally parallel to the plates with at least two barriers of insulating material inserted among the rib-like protrusions in coplanar relationship with said shorter plates, said barriers reaching lower than the rib-like protrusions and making abutting engagement, respectively, with the upper edges of said shorter plates, thereby impeding the establishment of an arc across the tops of the plates, anda mufller comprising a plurality of perforated ymetallic sections disposed in the outlet of the chute, said barriers being extended above the rib-like protrusions of the baille and through the mufller in between adjacent sections thereof.

7. In an electric circuit interrupter including contact structure separable to establish an arc, an arc extinguisher comprising: a pair of spaced ceramic sidewalls for` enclosing the arc, a irst predetermined number of spaced apart solid `metal plates spanning the sidewalls above the Contact structure, said plates being disposed across the path of the arc for chopping the arc into a family of serially related arclets, a smaller predetermined number of pairs of grooves respectively provided in the opposing surfaces of the ceramic sidewalls for receiving opposite ends of the plates, the ends of more than one plate being received in each pair of said grooves and all of the plates being constructed and arranged so that the spacings between spans of adjacent plates are uniform, insulating means disposed between corresponding end portions of the plates received in each pair of said grooves in order electrically to isolate one plate from the other, and an opening in the arc extinguisher for exhausting the arc products.

8. In an electric circuit interrupter including contact structure to establish an are, an arc extinguisher comprising: a pair `of space sidewalls for enclosing the arc, a plurality of spaced-apart metal Vplates spanning the sidewalls above the contact structure, said plates being disposed across the path of the arc for chopping the arc into a family of serially related arclets, an` opening in the arc extinguisher for exhausting the arc products, and a plurality of baille members of insulating material disposed in between the opening and the plates in generally coplanar relationship, respectively, with predetermined plates, the upper edge of at least one of said predetermined plates lying entirely under a plane defined by the upper edges of the two plates adjacent to said one plate and one of said baille members `having its lower edge disposed in generally edgewise association with said one plate, said one baille member extending below said plane for blocking the establishment of an arc along said plane.

References Cited in the ille of this patent UNITED STATES PATENTS 2,147,419 Baker Feb. 14, 1939 2,215,797 Sauer Sept. 24, 1940 2,575,730 Sandin et al Nov. 20, 1951 2,606,982 Nye Aug. 12, 1952 2,908,787 Scully Oct. 13, 1959 2,934,629' Bonnefois et al Apr. 26, 1960 FOREIGN PATENTS 560,257 Great Britain Mar. 28, 1944 763,510 Great Britain Dec. 12, 1956 1,157,951 France Ian. 6, 1958