US3626127A

US3626127A - Arc-breaking and quenching unit for electric circuit breakers

Info

Publication number: US3626127A
Application number: US17621A
Authority: US
Inventors: Enrico Baldini
Original assignee: Magrini Fabbriche Riunite Magrini Scarpa e Magnano MSM SpA
Current assignee: Magrini Fabbriche Riunite Magrini Scarpa e Magnano MSM SpA
Priority date: 1969-03-10
Filing date: 1970-03-09
Publication date: 1971-12-07
Anticipated expiration: 1988-12-07
Also published as: BE747144A; FR2037813A5; CH522946A; DE7007773U; GB1307895A; DE2009986A1

Abstract

An arc-quenching system of the magnetic blast type for electric circuit breakers wherein a pair of cooperating circuit breaker contacts are disposed in an arc-quenching chamber and are juxtaposed with respective arc-splitting primary electrodes located on opposite sides of the chamber and a pair of arc displacement secondary electrodes spaced apart above the primary electrodes such that, upon opening of the circuit breaker contacts, the circuit breaking arc is generated initially between the open contacts and thereafter jumps between the contacts and the primary electrodes and a proximal secondary electrode as well as between the secondary electrodes to form an arc path consisting of a substantially regular hexagon at approximately 0.01 second subsequent to contact opening. The secondary electrodes are in series with a blast coil having magnetic poles flanking the secondary electrodes and inducing the arc to move upwardly through a quenching column formed with packs or stacks of ceramic plates adapted to increase the arc length. The cooperating juxtaposed contact surfaces of the circuit breaker contacts being substantially parallel immediately upon opening and lying in planes generally perpendicular to the arc path therebetween.

Description

United States Patent [72] Inventor Enrico Baldlnl Primary Examiner- Robert S. Macon Berglmo, Italy Artorney-Karl F. Ross [21] Appl. No. 17,621 [22] Filed Mar. 9, 1970 [45] Patented De 7, 1971 ABSTRACT: An arc-quenching system of the magnetic blast [73] Assignee MagrinLFabbriche Rlunlte Mlgrlnl Scarpn type for electric circuit breakers wherein a pair of cooperating e Magnm -M,S M,.S ,A, circuit breaker contacts are disposed in an arc-quenching Milan, lul chamber and are juxtaposed with respective arc-splitting pri- [32] Priority Mar. 10, I969 mary electrodes located onopposite sides of the chamber and [33] [m a pair of arc displacement secondary electrodes spaced apart [31] 13872 A/69 above the primary electrodes such that, upon opening of the circuit breaker contacts, the circuit breaking arc is generated initially between the open contacts and thereafter jumps [54] ARC-BREAKING AND QUENCI-IING UNIT FOR between the contacts and the primary electrodes and a prox- ELECTRIC CIRCUIT BREAKERS imal secondary electrode as well as between the secondary 6Clalrns,5 Drawing Figs. electrodes to form an arc path consisting of a substantially [52] US. Cl 200/147 R regular hexagon at approximately second subsequent to [51 1 Int Cl "01h 33/18 contact opening. The secondary electrodes are in series with a [50] Field 0 sarch h 200/147 blast coil having magnetic poles flanking the secondary electrodes and inducing the arc to move upwardly through a [56] Ru (m d quenching column formed with packs or stacks of ceramic UNITED STATES PATENTS plates adapted to increase the arc length. The cooperating juxtaposed contact surfaces of the circuit breaker contacts being 322:2: substantially parallel immediately upon opening and lying in 3,307,004 2/1967 Bottonari 200/147 x Pm-ss-gfigmuy pmendcular the arc path therebetween r9 0.,- 1m- 1 t g l I i fo 44-15 Hit {m 6 HI ,lilb I m 5 l "H I I t y 41 slim 1 48 40 i iiiq 7c Sci iwl i m 41 :-2 2*" z j ui--- I r 3* a e A 'x e I 8 7: 2

i\:;-\: "Y 2'6- 25 18 {\I 3a \i Mr; -14

\s 1c j u 3g, 3)! 7s- 70. 4

PATENTED nu: Hen W 1 OF 4 3.626.127

F l G. 4

Enrico Baldini INVIJN'I'OR.

A g'quss Attorney Fiel E nrI'CO Ba/dim' INVEN'IUR.

Attorney PATENTED DEC 7 I97! SHEET [1F 4 FIG. 5

Pie. 4

Enrico Baldini INVISN'IY'UR.

ARC-BREAKING AND QUENCIIING UNIT FOR ELECTRIC CIRCUIT BREAKERS FIELD OF THE INVENTION My present invention relates to arc-quenching arrangements for electric circuit breakers and the like and, more particularly, to an arc-quenching system of the magnetic blast type in which are quenching is carried out by subdividing the circuit breaking arc into a plurality of secondary arcs and magnetically inducing arc movement through an arcquenching column.

BACKGROUND OF THE INVENTION Electric circuit breakers have been provided heretofore with arc'quenching arrangements operating under the principle that high-voltage circuit breaking electric arcs, struck between the relatively movable contacts of a circuit breaker upon opening can be quenched by splitting the primary are between the contacts into two or more secondary arcs with the aid of electrodes to which the arc is transferred, whereupon the secondary arcs are displaced through a quenching column, generally containing heat-resistant, nonconductive members adapted to increase the arc length, curl the arc sections and thereby extinguish the arc.

Several principles are involved in arc quenching of this nature. Firstly, the arc struck between the contacts of the circuit breaker is produced when the gas (generally air) or other dielectric in the gap between the contacts is ionized. In gasopening circuit breakers in which gas is ionized in the manner described, quenching is carried out at least in part by thermally induced movement of the ionized gases sustaining the arc-type discharge away from the contacts, thereby increasing the arc length until the discharge can no longer be sustained. In such blast-type arc-quenching arrangements for circuit breakers, the efficiency may be increased by promoting the movement of the gas through the quenching chamber.

In conjunction with arc-quenching systems of this character, it has been proposed to subdivide the circuit breaking are at least in part by transferring the primary arc to secondary or auxiliary electrodes spaced apart in the arc-quenching chamber. Two electrodes in spaced-apart relationship may thus be provided in the arc-quenching chamber independently of the contacts and in such orientation that the primary arc struck between the circuit-opening contacts will be transferred to these electrodes shortly after the contacts have opened to some extent. Secondary arcs are then formed between each contact and one of these electrodes as well as between the electrodes. By thereby increasing the arc length, the blast effect and quenching is promoted.

The arc itself is an electric current having the properties of electric current flow through a conductor and thus is associated with a magnetic field. Especially when the arc is formed into a loop or curl, as is invariably the case when the dielectric movement displaces the central portions of the arc upwardly, the magnetic field accompanying the current flow reacts to drive the arc further away from the contacts and thus additionally promotes arc quenching.

It has already been proposed, using the latter principles, to provide magnetic blast arc quenching by disposing an electromagnetic system in the arc-quenching chamber. The poles of the electromagnetic arrangement induce a magnetic field which cooperates with the magnetic field associated with the arc itself to augment the movement of the are through the quenching chamber and thereby further promote extinction. The electrodes may be separated by, and the chamber provided with, stacks of arc-breaking plates which remain undamaged by the are but have the task of increasing the arc path length between the electrodes or between each contact and the respective electrode such that, in cooperation with the tendency of the magnetic field and the gas movement to displace the arc, an early quenching is assured even with quenching chambers of relatively limited size.

The principles involved in the use of arc-lengthening plates have been described in commonly assigned copending applications, Ser. No. 630,592 filed Apr. 13, 1967 (now U.S Pat. 3,518,387) and Ser. No. 635,346 filed May, 2, 1967 (now abandoned).

The present invention is particularly applicable to arequenching systems of the magnetic blast type, i.e., to systems as described above in which magnetic poles are provided and are energized by blast coils which may be connected with the electrodes so as to generate the magnetic field upon transfer of the arc to these electrodes.

Prior art systems of this character are generally of complex construction, are provided with parts prone to failure and requiring replacement and are of relatively large size. They are, moreover, sensitive to the construction of the ceramic plates and the positioning thereof and, in addition to their large volume, are heavy and often prohibitively expensive to construct and maintain. They are also characterized by relatively low arc-quenching efficiency as measured, e.g., in terms of the time required for total arc extinction.

OBJECTS OF THE INVENTION It is, therefore, the principal object of the present invention to provide an improved arc-quenching system of the magnetic blast type in which the speed of arc quenching and the arcquenching efficiency is increased.

it is another object of the invention to provide an improved circuit breaker and arc-quenching arrangement which is of relatively low cost and small size, but which affords more effective and rapid quenching than earlier systems of the same general type.

SUMMARY OF THE INVENTION These objects and others which will become apparent hereinafter are attained, in accordance with the present invention, in a circuit breaker arrangement in which two electrodes of upwardly divergent configuration are disposed in the arcquenching chamber in spaced relationship with the cooperating circuit breaker contacts, the primary electrodes or arc horns being proximal to the respective contacts at least upon opening of the contacts and being separated by a stack of refractory nonconductive plates defining generally a zigzag arc path between them.

Spaced above the circuit breaker contacts and the divergent portions of these primary electrodes or are horns, is at least one pair of spaced-apart arc displacement horns or secondary electrodes to which the arc is transferred from the primary electrodes as the arc is induced to rise upwardly in the quenching chamber, the secondary electrodes being spaced apart by a further stack of plates.

1 have found, most surprisingly, that the efficiency of an arcquenching system as described can be improved remarkably by constituting the arcing or circuit breaker contacts with mutually juxtaposed and cooperating stretches or surfaces which are substantially flat and parallel to one another at least upon incipient openings so as to establish two closely spaced current paths adapted to induce the magnetic field which tends to push the arc upwardly and toward the arcing horns or primary electrodes. To this end, the contacts are provided in their mutually juxtaposed regions as relatively flat members lying substantially in a common plane and as upstanding formations having at upper parts thereof the actual mutually engaging contacts while being connected at lower parts, i.e., below these flat portions, with the respective terminals of the circuit breaker.

It is, therefore, an essential feature of the present invention that the arcing contact surfaces below the faces between which the arc strikes are mutually juxtaposed and face one another in both the closed position of the contacts and on incipient opening; these surfaces are parallel upon such opening or on movement of the movable contact away from the stationary contact to produce parallel and reciprocally inductive current fluxes adapted to displace the arc between the arcing horns.

The arcing horns or primary electrodes, according to another feature of this invention, consist of metal bars of substantially rectangular cross section and having throughgoing slots and are mutually divergent in the upward direction as noted earlier; they also are preferably disposed on opposite sides of the arc-quenching chamber so that their divergent legs are inclined upwardly from a common horizontal plane proximal to the circuit breaker contacts. The inclined legs are disposed symmetrically with respect to a vertical plane through the chamber which, with reference to the arrangement of the refractory plates and electrodes, may be considered a plane of symmetry.

The chamber itself is provided above the divergent legs of the primary electrodes with stacks of refractory and nonconductive plates, preferably of a ceramic such as hard paste porcelain and may define an arcquenching column, the central portion of which is provided with a magnetic circuit adapted to promote the movement of the arc upwardly until the arc is intercepted by the plates which define a zigzag or labyrinth path for the arc spanning the electrodes, e.g., as described in the aforementioned copending applications.

The magnetic circuit, according to the present invention, comprises a pair of spaced-apart arc displacement horns or secondary electrodes which reach down to a horizontal plane just below or coincident with the horizontal plane of the upper terminus of the inclined legs and are spaced apart by a distance equal to the closest distance between each of these secondary electrodes and the closest distance to a proximal primary electrode. Flanking these secondary electrodes is a pair of pole pieces spanned by a magnetic core or are about which the coil means of the magnetic circuit may be wound. The secondary electrodes and the pole pieces are symmetrically disposed with reference to the aforementioned plane of symmetry and to a further vertical plane of symmetry transverse to this first-mentioned plane. Advantageously, the coil means consists of a pair of coils connected in series and electrically connected to the secondary electrodes so as to be energized when the arc jumps to the latter, thereby producing a magnetic field tending to displace the arc upwardly.

An important feature of this invention resides in the dimensioning of the arc-quenching chamber and the positioning of both sets of electrodes such that an equilateral or regular hexagon is defined between the contacts and the electrodes and establishes the arc path at a period of the order of hundredths of a second (e.g., about 0.01 sec.) after opening of the movable circuit breaker member.

DESCRIPTION OF THE DRAWING The above and other objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is a vertical cross-sectional view through an arcbreaking and quenching arrangement according to the present invention;

FIG. 2 is a detail view illustrating the arrangement of the contacts of the system of FIG. 1 and the arc path;

FIG. 3 is a cross section taken generally along the line III III of FIG. 1;

FIG. 4 is an enlarged view of the circuit breaking chamber, as illustrated in FIG. I, but with the contacts in the position which they assume upon incipient opening; and

FIG. 5 is a detail view, in plan, of a portion of an electrode in accordance with this invention.

SPECIFIC DESCRIPTION The circuit breaker 1 shown in the drawing comprises the usual mechanism for opening the movable contact of the breaker arrangement as contained in a housing 1a and not otherwise illustrated except for an actuating member 1b in the form of a rod extending from this chamber and pivotally connected at 1c to the movable contact 3.

The circuit breaker also comprises a terminal plate or panel 1d carrying the insulating posts 1e and 1f forming terminals lg and 1/1 for the high-voltage electric current circuit in which the breaker is connected. The panel 1d forms a support for the stationary contact 2 which, as illustrated in FIG. I, is mounted by a bolt 2a upon a conductive pedestal 2b carried by a plate 2c affixed to a copper rod 2d electrical connection with the terminal 13.

The movable electrode 3 is carried by a lever arm 3a pivotally mounted at 3b upon a support plate 3c affixed to the panel 1d and connected by the copper rod 3d with a terminal 1h. Upon movement of the rod lb upwardly, the arm 3a is swung in the clockwise sense to bring the contact face 3e, which is of trapezoidal configuration and composed of a lowwear material, such as silver, gold or other noble metal alloy and is substantially free from pitting, into abutting engagement with the contact face 2e of the stationary contact 2. Displacement of the rod lb downwardly swings the lever arm 3a in a counterclockwise sense, e.g., into the dot-dash position shown in FIG. 1.

Above the circuit breaker assembly 1, whose arc contacts have already been represented at 2 and 3, I provide an arcquenching chamber 4 whose lower portion 4a is a gas-filled space (in which the gas is air) enclosed between a pair of lateral walls 4b and a pair of transverse walls 40, the walls being assembled by means of bolts 4d as best represented in FIG. 3.

Above the chamber 4a, there are provided two

equal quenching columns

5 and 6 which will be described in greater detail hereinafter. The primary electrodes of the arcquenching system of this invention are constituted by the arcing

horns

7 and 8 mounted by

screws

7a and 8a along the interior of walls 4b and, consequently, at opposite sides of the arc-quenching chamber. The lower ends of the

arcing horns

7 and 8 are inclined downwardly and inwardly to constitute legs 7b and 8b which reach to a horizontal plane H lying just above the arcing

contacts

2 and 3. The

shanks

7c and 8c of the

arcing horns

7 and 8 extend vertically upwardly along the walls 4b and are separated from one another by ceramic plates disposed within the sections or

columns

5 and 6.

The lower edges of the plates 19 reach to a horizontal plane H disposed above the plane H and coinciding with the junctions of the legs 7b and 8b with the

shanks

7c and 8c. The arcquenching chamber 4 and the parts thereof, including the

electrodes

7 and 8 are located symmetrically with respect to the vertical plane Y-Y of FIG. 3 and FIG. 1.

The primary electrode or arc horn 7 has a tab 7d formed with a flange 7e which is held in electrical contact with the contact 2 by the screw 2a. Hence the electrode 7 is at the same potential as the contact 2. Similarly the conductive bar 8d is fixed at 8e to an outwardly turned arm 8fof electrode 8 and is also tied at 83 to the support 30 of arm 30 whereby the electrode 8 is at the potential of the contact 3. The spacing d between the proximal ends of the

electrodes

7 and 8 is such that the potential at the terminals 1g and 1h is insufiicient to break down the gap, absent a transfer of the electric arc thereto from the breaker contacts.

The

sections

5 and 6 are composed of stacks of refractory and nonconductive plates 19 which define zigzag paths represented at Z in FIG. 1 between the

primary electrodes

7 and 8 and a pair of secondary or

arc displacement electrodes

10 and 11. These plates have, to this end, openings or windows, e.g., as represented in the aforementioned copending applications.

The secondary or are

displacement electrodes

10 and 11 are sheet metal plates as illustrated in FIGS. 1 and 3 and lie along the opposite inner flange of the

stacks

5 and 6 whose openings 5 and 6' vent the gases from the chamber and define the zigzag arc paths mentioned earlier. These secondary electrodes, also referred to as arc displacement horns l0 and 11, have their

shanks

10a and 11a lying symmetrically on opposite sides of the vertical plane of symmetry Y-Y and flanking a magnetic circuit which is described in greater detail hereinafter.

A gap b, 11b is maintained between each of these are

displacement homs

10 and 11 and

chambers

12 and 13 which serve the function of displacement arc quenching, the

chambers

12 and 13 being provided'with stacks of plates 12a and 13a respectively.

The magnetic circuit comprises a plurality of vertical plates 17 on each side of the chamber 4 (FIG. 3), connected to a yoke or core 18 of generally rectangular vertical section (FIG. 1) about which coils 14 and are wound in opposite senses but are connected in series (see FIG. 3 wherein the series connection of the coils is represented at 15a); the coils are additionally connected each to a respective

arc displacement horns

10, 11 so as to be energized by the magnetic circuit when the arc reaches these secondary electrodes.

As illustrated in FIG. 4, an essential feature of this invention is the configuration of the stationary and

movable contacts

2 and 3 in the closed condition of the breaker and upon incipient opening. To this end, the contact 2 is formed with an upwardly and outwardly turned horn 2f just above the contact face 2e and reaching toward the lower end of the leg 7b of the primary electrode 7, the surface 2f thereof being rounded so as to facilitate transfer of the are from the contact 2 to the leg 7b. Similarly, a horn 3f is provided above the contact face 3e to guide the arc onto the leg 8b of electrode 8 as the breaker contacts are opened.

More significantly, however, the

contacts

2 and 3 are provided below the contact faces 2e and 3e with confronting generally flat surfaces 21 and respectively, which lie parallel to one another as shown in FIG. 4 upon incipient opening of the contact 3. As the contact 3 is moved away from the contact 2, therefore, the normal current path represented in dotdash lines at 22, 23 and 24 develops the incipient breaking are at 22 At this instant, the legs or

branches

23 and 24 of the current flux induces reciprocal magnetic fields which, in accordance with the principles of interaction of electric current conductors and magnetic fields, drives the are 22 upwardly as represented by the arrow A.

The large section of the two arcing contacts at 20 and 21, permits large current flow through these portions and, consequently, a strong magnetic field to commence the magnetic blast. Consequently, it is important that the cross section at C and C of the

electrodes

3 and 2, respectively, be considerable and larger than the contact zones at 2e and 3e. It is also critical to the invention that the distance between the surfaces 20 and 21 be as small as possible consistent with the use of contact faces at 2e and 3e so that the current arms or

branches

23 and 24 will be as close as possible to one another.

The neck of each of the arcing

contacts

2 and 3, below the arc-striking

faces

2e and 3e should have a rectilinear outline of as large an extent as possible to provide the closed paths for the electric

current branches

23 and 24 mentioned earlier and provide the strong component of electromotive force (arrow A) driving the are 22 upwardly.

Furthermore, the shape and arrangement of the arcing horns or

primary electrodes

7 and 8 influence the speed and efiectiveness of displacement of the arc and the quenching process. It is, therefore, essential that the

primary electrodes

7 and 8 be constituted of metal bars having substantially rectangular uniform cross section as well as elongated or oblong slots 9. The slots 9, best shown in FIG. 5, extend through the thickness r of the bars and may have a width at of approximately one-third the total width b thereof. The length I of the slots 9 should be at least twice the distance D between the slots and may be up to 10 times this distance. Furthermore, the slots 9 should lie centrally of the

bars

7 and 8. Apparently, the slots 9 facilitate cooling of the bars and promote upward gas flow in the region of the legs 7b and 8b and possible spreading of the arc to augment the quenching effect. The current flow may also be branched along the webs between the slots and flanking the same, thereby contributing to the magnetic effect.

Moreover, it has been found that the angle included between the legs 7b, 8b and the horizontal will depend upon the voltage which must be sustained by the arcing horns or electrodes, for example, it has been found that must range between 40 and 50 inclusive for 6 to 12 kv. service and between 30 and 40 inclusive, for 15 to 24 kv. service.

According to an important feature of this invention, the distances x and x of closest approach of the

primary electrodes

7 and 8 to the

secondary electrodes

11 and 10, respectively, and the distance x between the

secondary electrodes

10 and 11 are substantially equal. Furthermore, at about 0.01 second subsequent to opening of the

contacts

2, 3, it is desirable to insure a spacing x between the

faces

2e and 3e and the distances x and x between the

faces

2e and 3e and the lags 7b and 8b which are equal to the distances x, x and x so that the

arc paths

22, 25, 26, etc., define an equilateral hexagon. Consequently,

arc portions

25 and 26 between the arcing horn 8 and are displacement horn 10 and between arcing horn 7 and are displacement horn 11 are equal, and since

sections

5 and 6 of the quenching chamber are of equal dimensions, the quenching plates 19 are equally stressed and more effectively exploite'd. Plates 19 are preferably composed of hard past porcelain although any refractory material known for this purpose may be used.

The plates forming the

auxiliary chambers

12 and 13, however, are composed of magnetic metal, according to the present invention and not only function to break the displacement are but are magnetically effective to elongate and split the are by increasing the length thereof. The hexagonal arrangement mentioned earlier and best illustrated in FIG. 2, wherein m and n represent the vertices of the hexagon at the lower ends of the

arc displacement horns

10 and 11, 0 and r represent the vertices of the hexagon at the ends of the legs 7b and 8b of the

primary electrode

7 and 8, and p and q represent the contact faces of the fixed contact and the movable contact, respectively, when achieved at about l/lOO of a second after opening of the contact, produces maximum upward force to promote the magnetic blast.

Of course, the principles involved here, while described with reference to a magnetic blast circuit breaker of the airbreak type may be used for gas breakers having dielectrics other than air or for liquid content breakers and various mechanisms may be employed for actuating the contacts. These and other modifications, which will be readily apparent to one of ordinary skill in the art and representing substitution of the equivalents or the like, are intended to be included within the spirit and scope of the appended claims.

I claim:

1. in a circuit breaker, in combination:

a. a pair of breaker contacts connectable in an electric circuit and relatively displaceable together to close said circuit and apart to open said circuit, said contacts having mutually engaging contact faces separable upon movement of said contacts apart, terminals for connecting said contacts in said circuit, and generally flat closely spaced but mutually juxtaposed parallel portions adjacent said faces and between said faces and said terminals for defining parallel electric current branches immediately upon opening of said contacts to induce displacement of a break arc bridging said faces away from said faces;

b. means defining an arc-quenching chamber above said contacts;

c. arc-splitting electrode means in said chamber in the direction of displacement of said are for subdividing and elongating same, said electrode means including a pair of primary electrodes each electrically connected with one of said contacts and disposed opposite one another across said chamber, said primary electrodes being formed with metal bars of rectangular cross section and each provided with a multiplicity of spaced oblong throughgoing slots inclined to the horizontal downwardly and inwardly into the region of said contacts; and a pair of secondary are displacement electrodes disposed above said legs and 7. 8 spaced from each other and from said legs, said primary and between 40 and 50 for a 6 to 12 kv. service circuit. and secondary electrodes being symmetrical with respect 3. The combination defined in claim 2 wherein said slots exto a vertical plane through said chamber, said primary tend through the thickness of said bars and have a width apele ll ng paced r m the r p c v secondary proximately one-third the total width of the bar and a length electrodes and Said Secondary electrodes being spaced between two and ten times the distance between the slots of apart by substantially identical distances to define with h b said contacts substantially 0.01 second subsequent to the 4 Th bi i d fined in claim 1 wherein said P f B of 531d the Vemces of Substamlany chamber is provided with a stack of refractory nonconductive equilateral hexagon; plates between each primary electrode and the associate d. a magnetic circuit in said chamber connected with said secondary electrode Said refractory plmes defining zigzag Secondary elecuodes mdusmg paths for the arcs bridging said primary and said secondary ment of said are away from said contacts, said magnetic electrodes circui including a core between Said F 5. The combination defined in claim 1 wherein said magelectrodes andacoilelectrtcally connected to said seconneflc circuit comprises a pair of pole plates flanking Said deaf-odes for magneuzmg Said core} and chamber and said primary and secondary electrodes. an are a respecnve plate composed of magnenc meta between 5 annin said ole lates between said stacks of refractory each of said secondary electrodes and said core while exp g p p tending into Said hexagon to break the displacement are plates, said coil comprises respective series-connected coil and to elongate and split the latter are by increasing the pomons i upon Sald core and havmg terminals con ength thereof. nected with said secondary electrodes.

2 The combination defined in claim 1 wherein said bars 6. The combination defined in claim 5 wherein said refracclude with the horizontal angles ranging between 30 and 40 wry pates we composed of porcelam' for use of the circuit breaker in a 15 to 24 kv. service circuit

Claims

1. In a circuit breaker, in combination: a. a pair of breaker contacts connectable in an electric circuit and relatively displaceable together to close said circuit and apart to open said circuit, said contacts having mutually engaging contact faces separable upon movement of said contacts apart, terminals for connecting said contacts in said circuit, and generally flat closely spaced but mutually juxtaposed parallel portions adjacent said faces and between said faces and said terminals for defining parallel electric current branches immediately upon opening of said contacts to induce displacement of a break arc bridging said faces away from said faces; b. means defining an arc-quenching chamber above said contacts; c. arc-splitting electrode means in said chamber in the direction of displacement of said arc for subdividing and elongating same, said electrode means including a pair of primary electrodes each electrically connected with one of said contacts and disposed opposite one another across said chamber, said primary electrodes being formed with metal bars of rectangular cross section and each provided with a multiplicity of spaced oblong throughgoing slots inclined to the horizontal downwardly and inwardly into the region of said contacts; and a pair of secondary arc displacement electrodes disposed above said legs and spaced from each other and from said legs, said primary and secondary electrodes being symmetrical with respect to a vertical plane through said chamber, said primary electrodes being spaced from the respective secondary electrodes and said secondary electrodes being spaced apart by substantially identical distances to define with said contacts substantially 0.01 second subsequent to the spreading of said contacts, the vertices of a substantially equilateral hexagon; d. a magnetic circuit in said chamber connected with said secondary electrodes for magnetically inducing movement of said arc away from said contacts, said magnetic circuit including a magnetic core between said secondary electrodes and a coil electrically connected to said secondary electrodes for magnetizing said core; and e. a respective plate composed of magnetic metal between each of said secondary electrodes and said core while extending into said hexagon to break the displacement arc and to elongate and split the latter arc by increasing the length thereof.

2. The combination defined in claim 1 whErein said bars include with the horizontal angles ranging between 30* and 40* for use of the circuit breaker in a 15 to 24 kv. service circuit and between 40* and 50* for a 6 to 12 kv. service circuit.

3. The combination defined in claim 2 wherein said slots extend through the thickness of said bars and have a width approximately one-third the total width of the bar and a length between two and ten times the distance between the slots of each bar.

4. The combination defined in claim 1 wherein said chamber is provided with a stack of refractory nonconductive plates between each primary electrode and the associate secondary electrode, said refractory plates defining zigzag paths for the arcs bridging said primary and said secondary electrodes.

5. The combination defined in claim 1 wherein said magnetic circuit comprises a pair of pole plates flanking said chamber and said primary and secondary electrodes, an arc spanning said pole plates between said stacks of refractory plates, said coil comprises respective series-connected coil portions wound upon said core and having terminals connected with said secondary electrodes.

6. The combination defined in claim 5 wherein said refractory plates are composed of porcelain.