US3560685A - Arc chute for an electric cuircuit breaker - Google Patents

Abstract

Discloses an arc chute having spaced sidewalls of a first insulating material and arc runners having most of their active surfaces of a refractory metal. Between one of the runners and the sidewalls are two face plates of a second insulating material, such as glass-bonded mica, that is characterized by low gas evolution and greater surface resistivity than said first material under high humidity conditions. The face-plate surfaces adjacent an arc are shielded from the arc by a thermally-sprayed coating of refractory ceramic insulating material on said surfaces.

Description

United States Patent Inventors Cecil Bailey Woodlyn; Oscar C. Frederick, Springfield; Joseph L. Talento, Media, Pa. Appl. No. 827,583 Filed May 26, 1969 Patented Feb. 2, 1971 Assignee General Electric Company a corporation of New York ARC CHUTE FOR AN ELECTRIC CIRCUIT BREAKER 7 Claims, 5 Drawing Figs.

U.S. Cl...l 200/144, 200/ l 47, 200/149 Int. Cl H0lh 9/30, H01h 33/00 Field of Search 200/ 144,

[56] References Cited UNITED STATES PATENTS 1,915,969 6/1933 Barringer 200/144( .3) 2,366,485 l/1945 Brink et al. 200/144UX 2,645,693 7/1953 Cole et al 200/144( .3) 2,761,934 9/1956 Wood et al. 200/147 2,911,505 11/1959 Legg et al. ZOO/144(3) 3,009,041 1 1/1961 Zlupko ZOO/144(3) Primary ExaminerRobert S. Macon Attorneys-J. Wesley Haubner, William Freedman, Frank L.

Neuhauser and Oscar B. Waddell ARC CHUTE FOR AN ELECTRIC CIRCUIT BREAKER This invention relates to an arc chute for an electric circuit breaker and, more particularly. to an arc chute comprising metallic arc runners along which the terminals of the usual arc travel as the arc is driven into the chute.

In U.S. Pat. Nos. 2.366.485Brink et al. and 2.70438]- -Nelson. both assigned to the assignee of the present invention, there is disclosed an arc chute material made by reacting concentrated orthophosphoric acid and chrysotile asbestos. While this material has many properties which make it an excellent arc chute material, it has been found that its surface resistivity under high humidity conditions is not as high as might be desired. To avoid a dielectric breakdown along the arc chute surface under these high humidity conditions, it has been customary to provide, adjacent one of the arc runners and dielectrically in series with the phosphoric acid-asbestos material, face plates made of an insulating material having a high surface resistivity that is relatively unaffected by high humidity. The material customarily used for these face plates is a glass-bonded mica material, such as that sold under the trademarks Mycalex or l-Iavalex.

In copending application S.N. 756,863-Bailey et al., assigned to the assignee of the present invention, there is shown and claimed an arc chute of the above type which can interrupt exceptionally high values of current. A plasma-arc sprayed refractory metal coating on the runners of this are chute makes it possible for this are chute to interrupt higher values of current than were attainable without such refractory metal coating. Our studies of such chutes indicate, rather unexpectedly, that at these higher values of current, the glassbonded mica face plates are imposing an upper limit on the amount of current that can be successfully interrupted.

Although glass-bonded mica has customarily been considered to be relatively nongas-evolving (see, for example, U.S. Pat. 2,761,934-Wood, lines l8-28, column 12) it appears that at these extreme high current levels, the arc will evolve sufficient gases from the glass-bonded mica to detrimentally affect the interrupting capacity. Of previously unappreciated significance with respect to this point is the fact that the gases evolved from the glass-bonded mica contain low ionization potential components such as sodium and potassium. Where there is no refractory metal coating on the are runners, currents up to the maximum interrupting capacity of the circuit breaker either are not high enough to result in significant gas evolution from the glass-mica material or the effects of any such gas evolution from the glass-mica are dominated by the much more copious evolution of metal vapors from the runners. But at higher currents, with arc runners having a major portion of their surface of refractory metal, the gases evolved from the glass-mica do appear to be significant.

Accordingly, an object of my invention is to increase the current interrupting capacity of an arc chute that comprises (l) are runners having a major portion of their surfaces of refractory metal and (2) face plates of glass-bonded mica or a similar material containing low ionization potential components.

Another object is to appreciably reduce the quantity of gases that will be evolved from such insulating face plates under extreme high current conditions, yet without impairing the ability of such face plates to maintain a high dielectric strength under conditions of high humidity and without significantly impairing the mechanical strength properties of the face plates.

In carrying out our invention in one form, we provide an arc chute comprising arc runners each having a major portion of its arc-running surface of a refractory metal. A pair of plates of low-gas-evolving insulating material are positioned on opposite sides of one of the runners between the runners and the adjacent insulating sidewalls of the arc chute. These plates are of glass-bonded mica or a similar insulating material that is characterized by (l) a high surface resistivity under conditions of high humidity as compared to the material of the arc chutes sidewalls and (2) the inclusion of ingredients which decompose upon exposure to extreme high current arcs into low-ionization-potential metal vapors. The arc-exposed regions of these plates are coated with a thermally-sprayed coating of a refractory ceramic insulating material such as alumina. This coating acts as a shield between the arc and the base material of the plate which significantly reduces the amount of low-ionization-potential gases evolved from the base material.

For a better understanding of the invention. reference may be had to the following description taken in conjunction with the accompanying drawings, wherein:

FIG. I is a side elevational view, partly in section, showing an electric circuit breaker embodying one form of our invention.

FIG. 2 is a cross-sectional view taken along the line 2-2 of FIG. 1.

FIG. 3 is a sectional view taken along the line 3-3 of FIG. 1.

FIG. 4 is an enlarged view of a portion of FIG. 1.

FIG. 5 is a sectional view along the line 55 of FIG. 1.

The invention is illustrated in connection with a circuit breaker of the type shown and claimed in U.S. Pat. Nos. 2,90l,579-Simpon and 3,050,062-Korte et al., assigned to the assignee of the present invention. Referring now to FIG. I, the circuit breaker shown therein comprises a pair of terminal bushings l and 2, both of which are fixed in position relative to the supporting frame of the circuit breaker. The bushing 2 comprises a downwardly extending conductive stud 3 at the lower end of which a movable conductive switch blade 4 is mounted by means of a fixed pivot 5. At its outer end, the blade 4 carries suitable circuit-controlling contacts such as a current-carrying contact 6 and an arcing contact 7.

Bushing 1 comprises a conductive stud la to which a downwardly extending conductive member 8 is electrically connected. Attached to this conductive member 8 is a curved contact-retaining member 9 which coacts with the member 8 to form a holding pocket for receiving the anchored ends of main current-carrying contact fingers 10. These fingers 10 are pivotally mounted on a curved portion 12 of the conducting member 8 and are biased for limited rotative wiping movement in a closing direction by means of suitable compression springs 9a These compression springs 9a provide for highpressure circuit-closing engagement between the stationary current-carrying contact 10 and the movable current-carrying contact 6.

The movable arcing contact 7 cooperates with a stationary arcing contact 13, which is mechanically and electrically connected to the conducting member 8 by suitable clamping means 14. The material of the arcing contacts 7 and 13 is capable of withstanding arcing and is also of a relatively high resistivity in comparison to the material of the current-carrying contacts 10 and 6. Accordingly, when the switch blade 4 is in the closed position shown, most of the circuit current flows through the current-carrying contacts. It is only when the switch blade 4 is driven counterclockwise to open the breaker that the arcing contacts carry appreciable current. During each opening action, the current-carrying contacts first part, thereby diverting current through the arcing contacts which are still in engagement due to their extensive wipe. Thereafter, the arcing contacts part and draw a circuit interrupting are which is driven into an arc chute 20 and there lengthened, cooled, and extinguished in a manner soon to be described.

For driving the switch blade 4 counterclockwise to effect circuit interruption, a reciprocable operating rod 24 pivotally joined to the switch blade at 26 is provided. When this operating rod is driven upwardly, it acts to move the switch blade counterclockwise to effect a circuit interrupting operation. The circuit can be reestablished simply by driving the operating rod downwardly to return the switch blade 4 in a clockwise direction to the closed position shown. The operating rod 24, which is of insulating material, is actuated by means of a suitable conventional operating mechanism (not shown).

Referring now to FIGS. 1 and 2, the arc chute assembly 20 comprises a pair of sidewalls 21 and 22 constructed of appropriate arc-resistance insulating material. These sidewalls are clamped together in spaced-apart relationship by suitable means, not shown. Each sidewall preferably comprises ribs 23 projecting toward the other sidewall and arranged to mutually interleave with the corresponding projecting ribs on the other sidewall, thereby forming a sinuous or zigzag passage as viewed from the entrance end of the chute. As shown in FIG. 2, these ribs taper toward the entrance of the chute and thereby provide a throat portion through which the arc first passes before entering the zigzag passage between the ribs 23. Generally speaking, this construction is of the type disclosed in US. Pat. No. 2,293,5 l 3Linde, assigned to the assignee of the present invention. A position of the are as it moves into the chute is illustrated by the dotted line 29.

For facilitating movement of the arc into the arc chute, a pair of conductive arc runners 30 and 31 are provided along the upper and lower edges of the chute. As shown in FIG. 1, these runners 30 and 31 extend transversely to the path of the arc and in generally divergent relationship with respect to each other from the region in which the arc is initiated.

The upper arc runner 30 is made up of a plurality of segments 32, 33 and 34 disposed in end-to-end relationship, with the adjacent ends thereof separated by insulating spacers 36. Electrically bridging the spacer 36 nearest the arc-initiation region is a magnetic blowout coil 37 having one terminal connected to runner segment 32 adjacent the spacer 36 and its other terminal connected to runner segment 33 immediately adjacent this same spacer 36. The other spacers 36 is bridged by blow-out coil 38 connected between adjacent runner segments in a corresponding manner/The runner segment 32 located nearest the arc-initiation region is preferably of a generally U-shaped configuration and is electrically connected to the terminal stud la. This electrical connection is through a conductive adapter 41 and an additional blow out coil 40, which has one terminal connected to the adapter 41 and its other terminal connected to the inner most end of runner segment 32. Considering an electrical circuit which extends between the outermost runner segment 34 and the terminal conductor la, it will be noted that the blowout coils 38, 37, 40 are connected in series-circuit relationship with each other as well as with the runner segments 32, 33, 34.

The lower arc runner 31 is constructed in substantially the same manner as the upper are runner 30. In this respect, the lower arc runner comprises a plurality of elongated segments 49, 50 and 51 disposed in end-to-end relationship and separated by insulating spacers52. Spacers 52 are respectively electrically bridged by blow-out coils 46 and 47 connected between the adjacent runner segments. The runner segment 49 nearest the arc-initiation region is of a U-shaped configuration and is electrically connected to the terminal conductor 3 of the circuit breaker through blow out coil 45. In this regard, a conductive strap 56 is electrically connected between the terminal conductor 3 and one terminal of blowout coil 45, whereas the other terminal of the blowout coil 45 is connected to the innermost end of the runner segment'49. An insulating spacer 57 is provided at the lower end of runner segment 49 to prevent the coil 45 from being short-circuited by the runner structure located across its tenninals.

The purpose of the abovedescribed blowout coils is to accelerate the movement of the are along the runners into the interior of the chute. In this regard, each blow-out coil is provided with a centrally located core insulated from the coil and attached to pole pieces mounted on the outer surfaces of the sidewalls of the chute. For example, the coil 40 has a core 59 attached to pole pieces such as 61 shown by dotted lines in FIG. 1. The coil 37 has a core 62 attached to similar pole pieces 63. In a like manner, all of the other blowout coils have similar cores and pole pieces, only some of which are shown. When a particular coil is energized, its pole pieces provide a magnetic field transverse to the are path, and this magnetic field reacts with the magnetic field surrounding the arc to produce a resultant force which drives the are at high speed along the runners into the interior of the chute. The general manner in which these magnetic fields react to produce the arcmotivating force is well known and therefore will not be described in further detail.

When the switch blade 4 is driven counterclockwise to open the breaker, an interrupting arc is established between the arcing contacts 13 and 7 as soon as those contacts part. The upper terminal of this are quickly transfers to the runner segment 32, thereby connecting the blowout coil 40 in series with the arc. The energized coil immediately creates a magnetic effect which begins to drive the upper are terminal along the upper runner 30 toward the interior of the chute. As the upper arc terminal moves along the runner 30 past the insulating spacers 36, it acts to successively insert the connected blowout coils in series with the are, thereby progressively in creasing the magnetic forces tending to drive the are into the chute.

In the meantime, the movable switch blade 4 has swung rapidly away from the stationary contact 13. When the switch blade 4 moves downward into proximity with the runner segment 49 of the lower arc runner, the lower terminal of the arc transfers to the runner segment 49, thus inserting the lower blowout coil 45 in series with the arc. The energized coil 45 immediately creates a magnetic blowout effect which drives the lower terminal of the are along the lower runner 31 toward the interior of the chute. When the lower terminal of the arc passes the first insulating spacer 52, it acts to insert the next blowout coil 46 in series with the arc and the first blowout coil 45 thereby providing increased magnetic force for driving the are into the chute. As the are moves into the chute, it becomes elongated and cooled by the projecting ribs 23, and thus acts to quickly deionize and thereby extinguish the are so as to interrupt the circuit. Typically, the arc terminals move to the end of the runners before interruption is completed.

To facilitate transfer of the upper arc terminal from the arcing contact 13 to the first runner segment 32, a pair of projecting electrodes 60 are provided at opposite sides of the movable arcing contact 7. Each of these electrodes 60 is made of an arc-resistant material such as tungsten impregnated with copper or silver. The are that is drawn between contacts 7 and 13 upon arc separation strikes one of the electrodes, causing its upper terminal to attach thereto; and immediately thereafter the upper terminal moves toward the base of the electrode onto the runner segment 32.

On opposite sides of the lower are runner 31 are a pair of face plates and 81 of a glass-bonded mica material, such as that sold under the trademark Mycalex. This material has an exceptionally high surface resistivity, which it is able to maintain despite conditions of high humidity in the surrounding air. As shown in FIG. 3, the face plates 80 and 81 are sandwiched between the lateral edges of the arc runner 31 and the sidewalls 21 and 22, respectively. These face plates extend along the runner 31 over substantially the entire length of the runner that is exposed to the are.

The material of the sidewalls 21 and 22 and ribs 23 is preferably a reaction product of asbestos and orthophosphoric acid (such as disclosed in US. Pat. 2,366,845-Brink and Arone, assigned to the assignee of the present invention) and containing a suitable inert filler such as zircon. This material, while excellent for arc-extinguishing purposes, has a lower surface resistivity than the Mycalex material, particularly under conditions of high humidity; and the are chute must rely upon the Mycalex face plates to assure against a dielectric breakdown along its walls in the region between the are runners 30 and 31 under high humidity conditions.

Each of the metal runner segments 32, 33, 34 and 49, 50, and 51 is preferably of brass but has its surface that is exposed to the are completely coated with a layer of refractory metal, e.g., tungsten, applied by plasma-arc spraying. This latter fea ture is disclosed and claimed in the aforesaid Bailey et al. application, S.N. 756,863. FIG. 4 shows the layer of refractory metal in more detail at 65. This layer is preferably of greater thickness in regions such as 69 and 70 where there is greater exposure to the arc. The presence of this thennally-sprayed layer of refractory metal on the runners raises the current interrupting capacity of the circuit breaker to a level appreciably higher than is attainable without the refractory metal layer or with small refractory metal pads brazed to the runners at a few points thereon.

We have found that we can raise the current interrupting capacity of this are chute even further by coating the glassbonded mica face plates 80 and 81 with a coating of a ceramic material such as alumina. This coating is indicated at 83 in H65. 1, 3, and 5. In a preferred form of the invention, we apply this coating by the plasma-arc spraying process described in copending application S.N. 731,466, Bailey et al. filed May 23, 1968. The alumina coating is not applied to the ribs 23 or sidewall 21, 22. However, all portions of the glassbonded mica face plates 80 and 81 that are exposed to the are are so coated.

A cross-sectional photomicrograph of the coating 83 shows that the coating is laminar in structure and is constituted by flattened interlocking particles of alumina.

Studies have been made to determine the reasons why the alumina coating increases the current interrupting capacity of the arc chute. It appears from these studies that, although the bare Mycalex material will evolve relatively little gas when exposed to a high current are, if the arc is of extreme high current, some of the Mycalex will decompose into vapors containing sodium and potassium. These vapors have a relatively low ionization potential, and any which are not condensed at current zero can be ionized by the high voltages then appearing to initiate a dielectric breakdown. By applying a relatively thick alumina coating to the surface of the face plates, we can greatly reduce the extent to which the Mycalex material is heated and vaporized by the extreme high current are, thus substantially eliminating the sodiumand potassium-containing vapors. In a preferred form of the invention the alumina coating is to 25 mils in thickness.

The refractory metal coating on the arc runners and 31 plays an important role in enabling the alumina on the face plates 80 and 81 to make its contribution to increased interrupting capacity. At currents up to the highest values that can i be interrupted by the illustrated are chute without the refrac' tory metal coating on its runners, the glass-bonded mica, even if uncoated and exposed to the arc, will evolve so little glass that its presence does not appear to detract from the current interrupting capacity of the chute. The refractory metal coating on the arc runners enables higher currents to be interrupted by the arc chute, i.e., currents above 25,000 amperes, r.m.s.; and it is only when such higher currents are being interrupted that the glass-bonded mica, if uncoated and exposed to the arc, would evolve a quantity of vapors sufficient to detract from interrupting ability. It is under these particular high-current conditions that the alumina coating acts to effectively prevent vaporization of the glass-bonded mica into low ionization potential vapors.

Although we have described our invention particularly in connection with a base material containing sodium and potassium compounds, it is to be understood that, in its broader aspects, the invention is intended to apply to base materials containing only one of these compounds or some other lowionization-potential ingredient. By low-ionization potential, we mean a first ionization potential under 5.5 electron volts.

An additional advantage of using glass-bonded mica material for the face plates 80 and 81 is that this material has exceptional mechanical properties that facilitate fabrication of the face plates and their assembly into the chute. More specifically, this material has greater mechanical strength, toughness, and flexibility, and is more readily machined than most ceramics. The plasma-arc sprayed alumina coating 83 that we apply to the glass bonded mica does not significantly detract from these very desirable properties of the glassbonded mica but does significantly improve the performance of the glass-bonded mica under extreme high-current arcing conditions as was explained hcreinabove. The plasma-arc sprayed alumina coating has a surface resistivit much higher t an the material of the arc-chute sidewalls, an this high surface resistivity is maintained under high humidity conditions,

thus enabling the coated face plates to function in the same way as the bare face plates in preventing dielectric breakdowns. Because the glass-bonded micaevolves relatively little gas under high-current conditions, particularly when it is shielded by the alumina coating, the alumina coating is able to remain tightly bonded thereto despite exposure to high-current arcing. This would not be the case with a base material such as the phosphoasbestos material of the arc-chute sidewalls, which evolves much greater quantities of gas when exposed to the temperatures produced by a high-current arc.

Under high-current arcing conditions, an alumina coating on such a base material would be forced off by the pressures developed underneath it by gas evolution from the base material.

While we have shown and described a particular embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the invention in its broader aspects; and we, therefore, intend herein to cover all such changes and modifications as fall within the true spirit and scope of our invention.

We claim:

1. An electric circuit breaker comprising an arc chute into which an arc is adapted to be driven for the purpose of extinguishing the are, said are chute comprising:

a. a pair of spaced-apart sidewalls of a first insulating material extending along the length of said are;

a pair of conductive arc runners spaced apart within said chute for defining paths along which the terminals of said are travel as the arc is driven into said chute;

c. said runners having refractory metal surfaces along a major portion of the paths traveled by said are tenninals during circuit interruption;

. a pair of face plates of low-gas-evolving insulating material positioned on opposite sides of one of said runners between said runners and said insulating sidewalls, said plates being of a second insulating material that has a much greater surface resistivity under humid conditions than the material of said insulating sidewalls;

e. said second insulating material containing one or more low ionization potential metallic components that will vaporize at temperatures produced at the surface of said plates by arcs on said one runner carrying high currents within the current interrupting rating of said circuit breaker, assuming said plate surface was bare; and

f. and means for shielding the surfaces of said plates adjacent said one runner from said arcs comprising a thermally sprayed coating of refractory ceramic insulating material on said plate surfaces.

2. The circuit breaker of claim 1 in which said refractory metal surface is constituted by thermally sprayed refractory metal.

3. The circuit breaker of claim 1 in which said second insulating material is a glass-bonded mica material.

4. The circuit breaker of claim 1 in which said second insulating material is a glassbonded mica material and said refractory ceramic insulating material comprises alumina.

5. The circuit breaker of claim 1 in which said first insulating material is a phosphoric acid-asbestos material, said second insulating material is a glass-bonded mica material, and said refractory ceramic insulating material comprises alumina.

6. The circuit breaker of claim I in which the interrupting rating of said are chute is higher than 25,000 amperes r.m.s.

7. The circuit breaker of claim 4 in which said coating of alumina has a thickness of at least 20 mils.

Claims (7)

1. An electric circuit breaker comprising an arc chute into which an arc is adapted to be driven for the purpose of extinguishing the arc, said arc chute comprising: a. a pair of spaced-apart sidewalls of a first insulating material extending along the length of said arc; b. a pair of conductive arc runners spaced apart within said chute for defining paths along which the terminals of said arc travel as the arc is driven into said chute; c. said runners having refractory metal surfaces along a major portion of the paths traveled by said arc terminals during circuit interruption; d. a pair of face plates of low-gas-evolving insulating material positioned on opposite sides of one of said runners between said runners and said insulating sidewalls, said plates being of a second insulating material that has a much greater surface resistivity under humid conditions than the material of said insulating sidewalls; e. said second insulating material containing one or more low ionization potential metallic components that will vaporize at temperatures produced at the surface of said plates by arcs on said one runner carrying high currents within the current interrupting rating of said circuit breaker, assuming said plate surface was bare; and f. and means for shielding the surfaces of said plates adjacent said one runner from said arcs comprising a thermally sprayed coating of refractory ceramic insulating material on said plate surfaces.

2. The circuit breaker of claim 1 in which said refractory metal surface is constituted by thermally sprayed refractory metal.

3. The circuit breaker of claim 1 in which said second insulating material is a glass-bonded mica material.

4. The circuit breaker of claim 1 in which said second insulating material is a glass-bonded mica material and said refractory ceramic insulating material comprises alumina.

5. The circuit breaker of claim 1 in which said first insulating material is a phosphoric acid-asbestos material, said second insulating material is a glass-bonded mica material, and said refractory ceramic insulating material comprises alumina.

6. The circuit breaker of claim 1 in which the interrupting rating of said arc chute is higher than 25,000 amperes r.m.s.

7. The circuit breaker of claim 4 in which said coating of alumina has a thickness of at least 20 mils.

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