US3441697A - Circuit interrupters with improved arc chutes - Google Patents

Description

April 29, 1969 H. s. WINGARD 3,441,697

CIRCUIT INTERRUPTERS WITH, IMPROVED ARC CHUTES Filed April 5, 1966 United States Patent U.S. Cl. 200144 9 Claims ABSTRACT OF THE DISCLOSURE A circuit interrupter in which a curved arc splitter plate is disposed in the space between a movable contact and an arc runner. The moving contact travels along a given line which diverges from the arc runner. The are splitter plate extends along a line which is between the arc runner and the path of the movable contact.

The present invention relates to circuit interrupters, particularly interrupters of the type having overload release mechanisms and known as circuit breakers. The invention is particularly concerned with the improved arc chutes for such apparatus.

A particularly severe condition that is encountered in the normal use of circuit breakers is to withstand short circuit operations, and to interrupt the current under short-circuit conditions. Circuit breakers have an arc chamber in which the arc is drawn by a moving contact, and it has for long been customary to place in the arc chamber an assembly of transverse mutually spaced arc splitter plates. This construction has found wide acceptance and has met with considerable success. Such are splitter plates are commonly held in assembly by a socalled wrapper of insulating material. Arc splitter-plate assemblies represent a substantial element of expense. In multipole circuit breakers the expense is multiplied by the number of poles, three being most common.

A feature of the present invention resides in the provision of a novel are chute having effective short circuit interruption characteristics yet being of remarkably simple construction and being inherently lower in cost than multiplate splitter-plate assemblies.

In achieving this feature of the invention a curved arc splitter late is disposed in the space between a movable contact and an arc runner. The moving contact travels along a given line which is divergent from the arc runner; and the :arc splitter plate extends along a line which is between the arc runner and the path of the movable contact, both the arc runner and the path of the movable contact diverging at opposite sides of the splitter plate. This arc chute construction is of elemental simplicity and is remarkably effective. Tests show that it is substantially the equivalent of the customary arc chute having many generally parallel spaced-apart arc splitter plates. The novel are splitter plate is evidently essential to the circuit breakers tested. This is demonstrated by short-circuit tests of alike circuit breaker omitting such are splitter plate, for in such tests the cases exploded during short-circuits. As will be seen in the detailed description of the preferred embodiment which follows below, the novel arc chute has further features of specific value.

The ability of a circuit breaker to interrupt shortcircuit currents depends in part on the capacity of the connected power line ot deliver any given level current under short-circuit conditions. It is obvious that the interruption process at any given voltage is more difficult with increasing levels of available short-circuit current. Conversely, if the current can be limited in some way, then the interruption process is made less severe and more easily accomplished. Various arrangements have been known in which impedance elements are injected in series with the circuit breaker during current-interrupting operation.

A further object of the present invention resides in providing a novel, effective and simplified arrangement for injecting impedance in series with the are formed during current interruption.

In achieving this object, the novel circuit breaker is equipped with an arc runner which is not normally in the circuit but which is injected into the circuit when the arc is struck. The are travels from a contact adjacent to the arc runner and along the arc runner to a remote point. Pursuant to this feature of the present invention the arc runner is made of metal having high resistivity (in contrast to metals such as copper known for good electrical conductivity). As a result, an increasing amount of resistance is injected into the circuit as the end of the arc travels along the are runner away from the contact associated with the arc runner. Further, by making the arc runner of progressively reduced cross section, the injected resistance is increased by an additional factor. This arrangement thus limits the rise of short circuit current well below that which would be attained with any given power line when short circuited and facilitates interruption of the arc by the circuit breaker.

The nature of the invention, and the foregoing and other objects and novel features of the invention, will be better appreciated from the following detailed description of an illustrative embodiment shown in the accompanying drawings.

In the drawings:

FIG. 1 is a lateral perspective view of a circuit breaker with a portion of one side wall of the enclosure broken away to reveal the arc chute thereof;

FIG. 2 is a vertical cross section through the circuit breaker along the line 2--2 in FIG. 1;

FIG. 3 is a plan view of certain of the components in FIGS. 1 and 2; and

FIG. 4 is a lateral view of certain components in the arc chute, showing a contact arm in various positions in solid and phantom lines and including various arc paths in phantom lines.

Referring now to the drawings, a so-called sandwich case including two parts 10, 10 of molded material contain a conventional circuit breaker operating mechanism including an overload release (not shown) of the type causing quick-make and quick-break of the contacts when operated by handle 12 and quick-break operation in case of overload release. The mechanism operates movable contact 14b on contact arm 14 from the open position illustrated in FIG. 1 to a closed position bearing against companion stationary contact 16. A copper strip 18 provides a current path from contact 16 to terminal 20 of the breaker for connection to a circuit wire.

The case 10 is hollowed to form an arc chamber 22 between one end of contact arm 14 and the end of the breaker where terminal 20 is mounted. Within this chamher there is provided a curved arc splitter plate 24 of cold rolled steel, for example, having a V-shaped notch which forms two legs whose extremities 24a are disposed slightly above and laterally outward of contact 16. When the breaker is closed, the end of contact arm 14 is disposed between tips 24a of the arc splitter plate.

An arc runner 26 is provided in either of two forms, being either cold rolled steel or a material such as Nichrome having a distinctively high resistivity (in contrast to the high conductivity of strip 18). Arc runner 26 is secured directly to copper strip 18 laterally adjacent to the stationary contact 16, is thus connected thereto electrically. The are runner is curved, including a portion extending along the bottom of the arcing chamber and aportion extending upward as shown, away from the shown portion of the contact arm 14 and the rest of the circuit breaker operating mechanism. As shown in each of the figures, arc runner 26 is widest adjacent to contact 16 and it is of progressively reduced cross section toward its remote extremity. Arc runner 26 is curved upward forming a progressively widening arcing space between the arc runner and the curved arc splitter plate, this space being a minimum at the stationary contact.

Spaced from the tip of arc runner 26 and disposed opposite the end of arc splitter plate 24 is a piece of wire mesh 28 whose lateral edges are retained in slots in the casing parts 10. Wire mesh 28 closes a vent from the arcing space 22 to the exterior of the enclosure.

A circuit breaker having an arc chute in accordance with the foregoing has been found to operate highly success-fully in the normal current-interrupting condition of the circuit breaker, and under overload conditions, and during short-circuit interruption. In an example an arc chute of this form has been demonstrated effective to interrupt short circuit current of ,000 amperes in a 277 volt AC line. In these tests it has ben found at least equal to arc chutes of more conventional construction in which multiple V-notched iron are splitter plates are disposed in successive parallel or divergent planes, separated transversely of the arc. In this example, plate 27 was formed of A thick cold rolled steel. Where plate 24 was omitted in a test, the case exploded in a short-circuit test.

It is believed that the arc is originally struck between the contacts as they part and that this are travels outward along arc runner 26; and this action is promoted by the attraction for the arc of the legs 24a which are of ferromagnetic material. The are races outward along arc runner 26 and it also races upward along an edge of the V-notch in plate 24. Arc damage after a test is readily visible along the surface of the arc runner and along one or both edges of the V-notch in plate 24. Moreover, following short-circuit the tip 14a of the contact arm reveals arc damage, while the contact face of contact 14b is remarkably clean. Some surface melting of the splitter plate occurs at the upper extremity of the V-notch, so that the arc definitely travels to that point. At the surface of plate 24 remote from contact arm 14 there is a blackened deposit following a test, but there is virtually no sign of melting.

At the top of plate 24 there is an edge 24b spaced from the upper wall of the arcing chamber, providing for crossventing of hot gas from the space adjacent contact arm 14 to the exterior of the circuit breaker through mesh 28.

At the surface of any metal part engaged by an arc, the arc theoretically extends perpendicular to that surface. The diverging extent of arc runner 26 and plate 24, away from the stationary contact 16 where the arc originates, is eifective in setting up the geometry of parts that promotes outward travel and elongation of the arc between the arc runner and splitter plate 24. By like token an expanding upward-travelling segment of the arc develops between plate 24 and contact arm 14 as that contact arm rises away from its position between tips 24a of the splitter plate, and as the contact arm swings upward. The space forms an upward progressively increased length of arc segment between the end of contact arm 14 and the splitter plate 24.

In FIG. 4 it is seen that contact arm 14 moves from its closed circuit position designated 14 to an intermediate position 14" and to its extreme open position represented by solid lines, and in so doing it moves through an arcuate path represented by the broken line 14c. After the contact arm has reached point 14" it is indicated both theoretically and on the basis of arc damage, that two curved arc segments 30 and 32 develop. Due to the divergence between elements 24 and 26 (measured at increasing distances from the closed position of the contacts) are 30 tends to curve upward and as this occurs the arc is Stretched, Similarly, after contagt arm 14 has reached posi- 4 tion 14" an arc segment 32 exists between the tip of the contact arm and are splitter 32. During the continued arcuate movement of the end of the contact arm, are segment 32 is electrodynamically driven outward. Outward travel of the arc segments 30 and 32 continues, assuming position 30' and 32 and expanding further upward until extinction occurs. The space between the upper tip of arc runner 26 and the directly opposite portion of arc splitter plate 24 is relatively small as compared with the much greater distance between the tip of the arc runner and the upper extremity of the V-notch in arc splitter plate 24.

Inasmuch as arc runner 26 acts to carry the arc progressively outward toward its tip, it is of advantage to make the arc runner of a high-resistance alloy such as Nichrome. When this is done, and when the arc travels from contact 16 toward the tip of the arc runner, more and more resistance is interposed in the circuit in series with the arc. This effect contributes to the reduction in the current to be interrupted, and facilitates interruption of the arc. This feature was not utilized in the 10,000 amp short-circuit test mentioned above.

The foregoing represents a preferred embodiment of the invention in its various aspects, but of course it is subject to varied application and modification by those skilled in the art. Therefore, the invention should be construed broadly in accordance with its full spirit and scope.

I claim:

1. A circuit interrupter including a contact arm having at the end thereof a first contact operable between open and closed positions, a companion contact engaged by the first contact when the circuit breaker is closed, an enclosure forming an arcing chamber, said first contact operating in the arcing chamber toward and away from the bottom thereof, a curved arc runner connected to said companion contact and disposed in said arcing chamber and having a first portion extending from a point adjacent to said companion contact and along the bottom of the arcing chamber and having another portion curved up and away from the bottom of the arcing chamber and extending to an extremity remote from said contact arm, and a ferromagnetic arc splitter plate erect in said arcing chamber and disposed between said arc runner and the first contact in the open position of the contacts and extending close to the bottom of said arcing chamber, said are splitter plate having a V-notch, the edges of which diverge toward the bottom of the arc chamber.

2. A circuit breaker in accordance with claim 1 wherein the extremity of the arc runner remote from said companion contact is spaced much farther from the end of the V-notch than the space between said extremity and the directly opposite part of the arc splitter plate.

3. A circuit breaker in accordance with claim 1, further including a venting space opposite the end of the V-notch and remote from said companion contact.

4. A circuit breaker in accordance with claim 1, wherein said arc runner is of a metal having relatively high-resistivity and is of progressively reduced cross-section from said companion contact to the extremity remote therefrom.

"5. A circuit interrupter in accordance with claim 1 wherein said arc splitter plate is curved and includes portions at the bottom thereof that are spaced from said companion contact and which are disposed at opposite sides of a portion of said contact arm in the closed position thereof.

6. A circuit interrupter in accordance with claim 5 wherein said are runner and said arc splitter plate when viewed laterally have similar curvatures and diverge progressively from the bottom of the arc chamber.

7. A circuit interrupter in accordance with claim 1 wherein said arc runner and said arc splitter plate diverge from each other from the bottom toward the top of the arc chamber and wherein most of the path of the movable contact diverges from at least a large part of the upstandi ng arc splitter plate.

8. A c r uit interrupter in acco dance wi h claim 1 wherein said are splitter plate is curved similar to said are runner when viewed laterally, said arc splitter plate including portions disposed at opposite sides of a portion of said contact arm in the closed position of the latter.

9. A circuit interrupter in accordance with claim 1 further including means remote from said companion contact forming a venting area to the exterior of the enclosure.

References Cited UNITED STATES PATENTS 1,963,643 6/1934 Brainard et a1 200-144 2,065,356 12/1936 Von Hoorn 200147 ROBERT S. MACON, Primary Examiner.

U.S. Cl. X.R. 200-147

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