US3467799A - Elimination of arcing effects in circuit breakers - Google Patents

Description

Sept. 16, 1969 A. R. NORDEN E 3,467,799

ELIMINATION OF ARCING EFFECTS IN CIRCUIT BREAKERS Filed Dec.

5 m z w 1 lllrl i Z fl l lU lH my rifllfl x -||L. w r a a w "fa x 6 M 2 7 w w// z a w m Q INVENTORS A4 "AA Me A. ,vupnv United States Patent 3,467,799 ELIMINATION OF ARCING EFFECTS IN CIRCUIT BREAKERS Alexander R. Norden, New York, and George W. Knecht, Brooklyn, N.Y., assignors to Murray Manufacturing Corporation, Brooklyn, N.Y., a corporation of New York Filed Dec. 8, 1965, Ser. No. 512,438 Int. Cl. H01h 9/44, 33/18 US. Cl. 200-147 6 Claims ABSTRACT OF THE DISCLOSURE In order to eliminate the deteriorating effects of arcover in electromagnetic circuit breakers, a runner of magnetic material, electrically coupled to one of the contacts and magnetically coupled to the magnetic circuit is disposed proximate one contact to take over the arc,upon contact separation.

This invention relates to circuit breakers in general and in particular to an improvement in circuit breakers of'the electromagnetic type for eliminating the effects of arcing.

It is often desirable, if not necessary, to protect electrical circuits against shorts and overload conditions as well as to provide means for controlling the operational status of the associated equipment via a manually operable switch. Because a circuit breaker is capable of serving both these functions, it has enjoyed widespread commercial and household application.

The protection provided by a circuit breaker is automatic; the breaker responding to a predetermined current condition to open the contacts maintaining the lineto-load continuity. As a rule, the breaker is set by manually closing the electrical contacts through a trippa-ble linkage, the linkage being actuated by a current-responsive device to trip upon overload, either immediately or after a predetermined overload time, thereby opening the contacts. In magnetic breakers the tripping force is provided by the magnetic flux induced by a coil through which the load current passes; the fiux acting upon a magnetic element which directly or indirectly unlatches the linkage. Reset, which is to be distinguished from the reclosing of the contacts, is either automatic or manual, and in the latter case, is effected by urging the breaker handle to the full OFF position. Subsequently, by placing the handle in the ON position, the circuit continuity is reestablished by the resultant closing of the contacts.

Because breakers must respond to and interrupt a short circuit condition by automatically breaking the lineto-load continuity, arc-over is a serious problem. This problem also exists in breakers of large capacity where a line-to-load continuity is manually broken during heavy inductive load conditions. No solution to this problem has proved completely satisfactory, and recent advances in breaker technology which allows breaker miniaturization tend to accentuate the problem rather than relieve it.

In an attempt -to obviate the tendency of the arc to transfer to the neck of the moving contact (burning away a portion, and eventually all of the contact arm), a variety of arm configurations have been proposed. All, however, met with only moderate success. A more satisfactory solution is predicated on the use of an arc runner. This is a piece of magnetic material electrically connected to the stationary contact and so arranged that the arc transfers to it as soon as contact continuity is broken. The are then travels along the runner, length- 3,467,799 Patented Sept. 16, 1969 ening and finally extinguishing. This arrangement substantially ameliorates the deteriorating effect of the are on breaker components. However, it gives rise to a Very disadvantageous side effect. When the arc is transferred, it melts some of the runner metal and expels it in the form of red hot globules through the adjacent gas vent, thus creating a serious fire risk. While this problem may be alleviated by including a de-ion arcchute totrap the globules, the trap location and size raise considerations diametrically opposed to miniaturizing the breaker.

Accordingly it is the object of this invention to provide an arrangement within the circuit breaker which obviates the deleterious effect of arc-over and does so in a simple inexpensive manner without necessitating additional room within the breaker.

The above mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will best be understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings wherein the single figure illustrates the circuit breaker according to the invention with casing portions cut away to reveal those internal portions necessary for an understanding of the invention.

The circuit breaker shown in the figure is, except for the inventive modification, identical to that depicted and described in copending application Ser. No. 388,259, filed Aug. 7, 1964 to the same assignee. While the description which follows is intended to be complete insofar as necessary for an understanding of the invention, reference may be had to above alluded to application for an illustration of a complete circuit breaker in which the invention may be used.

The circuit breaker casing 10 is preferably molded of insular material, such as Bakelite, and consists of two complementary interlocking sections (each having its main plane parallel the plane of the paper) held together by rivets 12. The lower forward portion of the casing is omitted on both sides of the'breaker at 10' to expose contact 13 adapted to engage in sidewiping fashion a panelboard bus bar stab, carrying line voltage.

Aflixed to the contact 13, for example by welding to its upper portion (concealed) is one end of the electromagnetic coil 14, the other end of which is led to the stationary contact member 15 carrying contact 15'. A complementary movable contact 16 is borne by the contact arm 16 pivoted between its extremities at 17. A flexible line 19 electrically connects this arm to the circuit breaker load terminal.

When the circuit breaker handle 20 is rotated clockwise a trippable linkage (not shown) bears upon the left end of contact arm 16, rotating it clockwise and closing the contacts.

Coil 14 is in series with the load and therefore carries the load current; generating a magnetornotive force (MMF) directly dependent upon the value of this current.

Preferably the electromagnet is of the type described in US. Patent No. 2,890,306 issued June 9, 1959 to the same assignee. That is, the electromagnet includes a core piece 40, freely disposed in a fluid medium within tubular member 21. As described in the patent when the current and therefore the MMF reaches a predetermined magnitude the core moves up decreasing the reluctance of the magnetic loop including the core, the side armature 23, bottom armature 26, and movable armature 24. The force upon the movable armature at the air gap 22 is dependent upon the flux density which in turn is inversely dependent upon the reluctance and consequently,

after a predetermined time (during which the core is moving up), the force of attraction surmounts the spring bias force 27 and the movable armature 24 rotates clockwise to eliminate the air gap. The resultant effect of the foregoing is the lifting of the retaining latch 24 which in turn triggers the contact opening linkage (a portion 30' of which is shown), thereby driving contacts 15 and 16' apart.

According to the invention, a second magnetic field or flux loop is provided which includes the bottom armature 26, the core 40, an air gap 30, and an extension 23' on the side armature, so formed and positioned that it acts as an arc runner. That is, this extension which is electrically connected for example at 26' to the stationary contact member 15 is sufliciently proximate contact 15' that it takes over the are leading it away from both contact members and towards vent 32.

Ordinarily, one would expect the arc to cause hot globules to emanate from the arc runner and spew out the vent. However, quite the opposite occurs, and instead of being expelled, the globules are attracted and held at the end of the arc runner, the runner showing little erosion after repeated tests. This phenomenon may be accounted for as follows:

When a short occurs (a condition which would cause severe arcing) an extremely large magnetic field is produced whose flux density is sufiicient to trip the linkage without the movement of core 40. Hence a sufiicient por- 4 nate the lower armature 26, utilizing the arc runner alone to complete the flux path through themain air gap 22.

This arrangement will slightly reduce the efficiency of the main function of the electromagnet i.e. tripping the linkage, however, it willmake more flux available to the arc runner.

We claim:

1. In a circuit breaker of the type having at least one pair of contacts, the separation of which is dependent upon a load-current dependent coil energizing a magnetic circuit through an armature member positioned adjacent said coil, the improvement for eliminating the deteriorat- 1ng etfects of arc-overcomprising, a runner of magnetic material electrically coupled to one of said pair of contacts, magnetically and physically connected to the armature of said magnetic circuit, and disposed proximate said one contact to take over the arc therefrom on contact separation.

coil.

tion of this core is available in the described second flux loop to sustain a second magnetic field of high flux density. Thus the iron globules which form are attracted and held to the runner.

Similarly, when the breaker is under a large load and is manually tripped, the second loop whose flux magnitude is commensurate in size with the load current, will function to effectuate the same result. The arrangement according to the invention is self-controlling; that is, the greater the current, the greater the arc, and hence the greater the magnetic field necessary to hold the globules. Since the arc represents coil, as well as load current, the greater the arc, the greater the coil current available to hold the globules and hence the desired objective is automatically obtained.

Needless to say, while the depicted magnetic circuit includes dual flux paths the existence of the two paths depends a great deal upon the core configuration. With some cores (e.g. stationary ones) it may be expedient to elimi- 2. The improvement claimed in claim 1 which said are runner is positioned adjacent one end of said coil.

3. The improvement claimed in claim 2 in which said armature is a side armature substantially parallel said 4. The improvement claimed in claim 3 in which said runner is angled with respect to said side armature and extends toward said coil end.

5. The improvement claimed in claim 1 in which the magnetic circuit includes a core slid able into said coil upon the energization thereof, a first flux loop including said coil and a portion of said core, and a second flux loop including a portion of said core and the arc runner.

6. The improvement claimed in claim 5 in which said first and second flux loops include an E shaped armature the middle branch of the B being common to the two loops and the lower branch being the arc runner.

References Cited UNITED STATES PATENTS 2,575,730 11/1951 Sandin et al.

1,391,966 9/1921 Moller 335201 XR 2,192,059 2/1940 Willmann 335-201XR 3,189,716 6/1965 Hugus 200-147 ROBERT S. MACON, Primary Examiner U.S. Cl. X.R. 335-201

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