US3641293A

US3641293A - Arc chute plates for air curcuit breaker

Info

Publication number: US3641293A
Application number: US1443*[A
Authority: US
Inventors: Charles H Armitage; Henry L Peek; Herbert M Pflanz
Original assignee: Allis Chalmers Corp
Current assignee: Allis Chalmers Corp
Priority date: 1970-01-08
Filing date: 1970-01-08
Publication date: 1972-02-08
Anticipated expiration: 1989-02-08
Also published as: CA920186A

Abstract

The arc chute of a low-voltage air magnetic-type electric circuit breaker comprising a stack of spaced-apart porous metal plates made of fiber metal. All of the plates are impregnated or coated with ceramic insulating material at least on their lower regions.

Description

United States Patent Armitage et al.

[ Feb. 8, 1972 [54] ARC CHUTE PLATES FOR AIR CURCUIT BREAKER [72] Inventors: Charles H. Armitage, Wauwatosa, Wis; Henry L. Peek, Wellesley; Herbert M. Pflanz, Westwood, both of Mass.

[73] Assignee: Allis-Chalmers Manufacturing Company,

Milwaukee, Wis.

[22] Filed: Dec. 8, 1970 [21] App1.No.: 1,443

[52] U5. Cl. ..200/l44 R, 200/147 [51 Int. Cl. .Q H0lh 33/08 [58] Field ofSearch ..200/144, 147,147 B [56] References Cited UNITED STATES PATENTS 2,911,505 11/1959 Legg et a1 ..200/144 C I FOREIGN PATENTS OR APPLICATIONS 1,334,841 7/1963 France ..200/I47 B Priniary ExaminerRobert S. Macon Attorney-Thomas F. Kirby, Lee H. Kaiser and Robert B. Benson ABSIRAC'I The are chute of a low-voltage air magnetic-type electric circuit breaker comprising a stack of spaced-apart porous metal plates made of fiber metaL All of the plates are impregnated or coated with ceramic insulating material at least on their lower regions.

2 Claims, 4 Drawing Figures ARC CIIUTE PLATES FOR AIR CURCUIT BREAKER BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to are chutes for electric circuit breakers which employ a plurality of spaced-apart plates to divide up an are into smaller segments during extinguishment and, particularly, to metal plates which are coated with are resistant insulating material.

2. Description of the Prior Art Some circuit breakers for interrupting alternating current use an arc chute having a stack of spaced-apart plates of magnetizable metal located between a pair of arc runners and adjacent the circuit breaker contacts. Such plates divide the long are between the arc runners into a multiplicity of series connected smaller arcs and cause them to move through the arc chute; the object being to raise the reigrrition voltage. Extinguishment is aided by the cooling of the small arcs in contact with the metal plates and by the turbulence present as the arcs move through the space between the plates.

Plates made of solid insulating material have been interspersed between the metal plates to aid arc extinguishment by providing a more tortuous path for the are. US. Pat. No. 2,91 1,505 issued Nov. 3, 1959 to D. Legg et al. teaches an arrangement wherein all plates in the arc chute are made of solid sheets of magnetizable metal and completely coated with two different types of insulating material. While the latter arrangement achieves the desired electrical result, it involves costly and complicated arc chutes and requires plates of greater thickness than may be desirable for certain applications. It is desirable, therefore, to provide new and improved arc chute plates wherein the plates are constructed of fiber metals which are partially or completely coated or impregnated with refractory insulating material so as to improve the extinguishing ability of the arc chute and provide improved plates therefor.

SUMMARY OF THE INVENTION The present invention contemplates an arc chute wherein a stack of plurality of spaced-apart plates are disposed between a pair of arc runners. In accordance with the present invention it is proposed to provide plates made of fiber metal, preferably magnetizable, and to coat all or part of the metal plates with a single coat or layer of arc resistance refractory insulating material, such as ceramic.

OBJECT S OF THE INVENTION It is an object of the present invention to provide an improved arc chute which employs plates made of fiber metal and fully or partially coated with refractory insulating materia] Another object is to provide an arc chute which employs such plates which are of uniform size and configuration so as to provide an arc chute which has advantages of metal and insulating plates in combination.

Another object is to provide an arc chute plate of the aforesaid character which are electrically effective, mechanically strong and resistant to damage caused by thermal expansron.

Another object is to provide an arc chute which avoids close tolerance fitting between dissimilar constitutent elements to effect efficient arc extinguishment.

Anofl'rer object is to provide plates which are strong, .damage resistant, and relatively thinner than other coated plates.

Another object is to provide an arc chute and plates of the aforesaid character which are economical to fabricate and re liable in use.

Other objects and advantages will hereinafter appear.

BRIEF DESCRIPTION OF THE DRAWING The accompanying drawing illustrates preferred embodiments of the invention but it is to be understood that the embodiments illustrated are susceptible of modifications with respect to details thereof without departing from the scope of the appended claims.

In the drawing:

FIG. 1 is a side elevational view, partly in section, of a portion of a circuit breaker arc chute incorporating the present invention;

FIG. 2 is a view taken along line II-II of FIG. 1;

FIG. 3 is a cross-sectional view taken along line IIIIII of FIG. 2; and

FIG. 4 is an elevational view of an arc plate in accordance with another embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 and 2 of the drawing, the numerals l0 and 12 designate stationary and movable contacts, respectively, of an electric circuit breaker which separate to establish an arc. An arc chute 14 is associated with contacts 10 and 12 and comprises a pair of spaced-apart sidewalls l6 and 18 which are made of electrical insulating material such as ceramic, insulating fiber, or the like. It is to be understood that the sidewalls 16 and 18 are mirror images of each other and are formed with suitable projections and recesses to support various components therein when the sidewalls are fastened together. The sidewalls l6 and 18 define an arcing chamber 20 in the lower portion of arc chute 14 wherein stationary contact 10 and movable contact 12 are disposed. Stationary contact 10 is rigidly mounted with respect to are chute l4 and is located at one end of chamber 20. Stationary contact 10 is electrically connected to a first stationary electrically conductive arc runner 22 which is also located at the aforesaid one end of chamber 20 of arc chute l4. Movable contact 12 is pivotally mounted for clockwise and counterclocklise movement (with respect to FIG. 1) within chamber 20 of arc chute 14 into and out of engagement, respectively, with stationary contact 10. When movable contact 12 is moved counterclockwise it comes into proximity with a second stationary electrically conductive arc runner 24 which is located at the other end of chamber 20 of arc chute 14 and spaced apart from arc runner 22. During circuit interruption, an are established between the contacts 10 and 12 is transferred therefrom so that it becomes established between the are

runners

22 and 24 and travels upward thereon, as hereinafter explained.

Arc chute 14 comprises a stack 26 of plates which span the sidewalls l6 and 18 above chamber 20 and are disposed in spaced-apart relationship between the

arc runners

22 and 24. One end of the stack of plates 26 is closer to the contacts than the other end. Arc chute 14 is provided with means for cooling the exhaust gases expelled from the top of the stack of plates 26. Such means take the form of hollow baffle members 42 which are supported by perforated insulating members 44.

All plates in stack 26 may be are of the same configuration and size. The plates in stack 26 are arranged with respect to each other so that the upper edges of all plates (the edges most remote from the contacts) terminate in a first common horizontal plane. The upper edges of the

arc runners

22 and 24 also terminate in or below the aforesaid first plane. The lower edges of all plates in stack 26 (the edges nearest the contacts) terminate in a second common horizontal plane. The plates in stack 26 are held in position by entrapment in grooves 30 provided in the sidewalls l6 and 18. Each plate in stack 26 is provided with a triangular slot 28 at its lower edge to guide the arc into the stack of plates during operation of the arc chute.

The spacing between each plate and an adjacent plate in the stack is regular and is the same as the spacing between the

arc runners

22 and 24 and the plates adjacent thereto.

In accordance with the invention each plate 32 in stack 26 comprises a sheet 34 of magnetizable metal such as steel which is in the form of fiber metal. In accordance with the embodiment of the invention shown in FIGS. 1 and 2, the metal in each plate is entirely coated with arc resistant insulating material 36, such as ceramic, which has been suitably fired to harden it and to cause it to bond securely to the metal. Bonding is improved by the fact that the surface of the fiber metal is irregular and provided with many interstices. The fiber metal portion 34 of plates 32 is somewhat more resilient or flexible than a solid metal plate would be.- Accordingly, when it is bonded to the ceramic material a greater mismatch in thermal expansion characteristics is permissible between the fiber metal and the ceramic than would be thecase with a solid sheet of the same metal. However, it is desirable to select magnetizable fiber metal which has a coefiicient of thermal expansion which is as close as practical to that of the ceramic material which is chosen to further reduce the possibility of cracking the ceramic when the plates are subjected to high temperatures during and after arcing. The ceramic may be applied in any conventional manner as by dipping, spraying or painting prior tofiring. Since only a single coating of ceramic is required and since such coating is relatively thin, i.e., on the order of a few thousands of an inch thick, the total thickness of each plate 32 and the overall dimensions of the arc chute 14 are not substantially greater than they would be if uncoated metal plates were used. 7

A plate constructed as above described, therefore, combines the magnetic characteristics of the conventional ferrous metal arc plate with the advantages of conventional arc chute plates made of solid insulating material. Furthermore, plate 32 is an improvement over are chute plates of solid metal coat with an insulating coating because of the thermal characteristics and behavior described above and because of the smaller dimensions resulting from the sue of a single thin insulating coating which is firmly bonded to the fiber metal. Furthermore, in a plate using a fiber metal it is possible through careful selection of the fiber material and orientation of the fiber to amplify and capitalize on the magnetic characteristics of the metal to achieve improved arc chute perforrnance.

Arc chute 14 operates as follows: Assume that the contacts 10 and 12 of the circuit breaker are closed and the current is flowing therethrough. As movable contact 12 is moved counterclockwise (with respect to FIG. 1) from closed toward open position, an arc appears between contacts 10 and 12. Because of the electromagnetic forces present, the terminal point of the are on contact 10 transfers to are runner 22 and the terminal point of the arc on contact 12 moves to the extreme tip of contact 12. The arc forms an inverted U-shape with its highest point entering within the slots 28 in the stack of plates 26 at the end of the stack nearest arc runner 22. As movable contact 12 moves closer to are runner 24, the arc terminal on the former transfers to the latter, and an elongated arc is established between the

arc runners

22 and 24. As the elongated arc moves up through and past the slots 28 in the stack 26, it is divided into a plurality of series related small arcs. The small arcs tend to move upward through the stack at a relatively uniform rate. In the embodiment shown, the arcing forces and are byproducts are most numerous at the end of the arc chute nearest stationary contact 10 (i.e., the point of arc initiation). Since the arcing forces and byproducts are less effective at the upper end of the stack the insulated plates thereat are sufficient to reduce the likelihood of flashover across the top of the plates. However, these factors are offset to some extent because during interruption of an arc, the hot gas from arcing is vented through the arc chute in an upward direction.

As a result of cool air or gas entering from the bottom a temperature gradient exists along the vertical path of the arc chute. The hot gas in the upper zone has a lower breakdown voltage than the cooler gas in the lower zone.

As previously mentioned, it is desirable to retain as many 7 metal plates as possible in the stack in order to increase the arc voltage. The use of coated metal plates permits this. Exhaust products from the arc are cooled and condensed by means of the baffles 42 before being expelled from the arc chute.

FIG. 4 shows another embodiment of arc chute plate 40 in accordance with the present invention. Arc chute plate 40 is understood to be similar to arc chute plate 32 hereinbefore described except that its uppermost portion 42 is not provided with a ceramic insulating material. By omitting the ceramic coating on the top or upper end of plate 40 an efficient cooling surface is obtained which permits more rapid cooling of arc chute 14. Of course, the overall dimensions of plate 40 and the arc chute must be such that the insulating coating is not eliminated in regions where arc reignition might occur.

Plate 40 is understood to be arranged and operates in substantially the same manner as the plates 32 hereinbefore described, except as regards its cooling characteristics.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An arc chute plate for use in an electric circuit breaker which employs at least one plate located between spaced apart arc runners,

said plate comprising a sheet of magnetizable fiber metal,

said sheet of fiber metal comprising fibers which are oriented to amplify the magnetic characteristics of said plate,

said sheet having front and rear surfaces and side, top and bottom edge surfaces,

and a single layer of ceramic material bonded by firing directly at least to the lower half of said front and rear surfaces, to the lower half of said side edge surfaces, and to said bottom edge surface.

2. A plate according to claim 1 wherein said insulating material covers all of said surfaces of said sheet.

Claims

1. An arc chute plate for use in an electric circuit breaker which employs at least one plate located between spaced apart arc runners, said plate comprising a sheet of magnetizable fiber metal, said sheet of fiber metal comprising fibers which are oriented to amplify the magnetic characteristics of said plate, said sheet having front and rear surfaces and side, top and bottom edge surfaces, and a single layer of ceramic material bonded by firing directly at least to the lower half of said front and rear surfaces, to the lower half of said side edge surfaces, and to said bottom edge surface.