US2908787A - Electric circuit interrupter - Google Patents

Description

1959 T. J. SCULLY 2,908,787

ELECTRIC CIRCUIT INTERRUPTER Filed Dec 18, 1957 aa. as .5: 39.; 20 as in Q7 12: i 42 P/lg-4- 0 United States Patent ELECTRIC CIRCUIT IN TERRUPTER Thomas J. Scully, Bridgeport, Pa., assignor to General Electric Company, a corporation of New York Application December 18, 1957, Serial No. 703,567

6 Claims. (Cl. 200144) This invention relates to electric circuit interrupters, and more particularly it relates to an arc extinguishing device for an electric circuit interrupter of the type having cooperating separable contact members.

Electric circuit interrupters are used for the purpose of interrupting the flow of current in electric power circuits. The current interruption process is begun by separating the cooperating contact members of an interrupter, whereby a gap of air or gaseous matter is opened in the circuit. The gases in the gap between the separated contact members, although normally having relatively great dielectric strength or insulating ability, may temporarily be rendered electrically conductive due to the phenomenon of ionization. If there is simultaneously a suflicient potential difference between the separated contact members and a sufficient degree of ionization of the gases in the gap, the ionized gases will form an electricarc which must be permanently extinguished in order to interrupt the circuit current.

When interrupting an alternating current electric power circuit, there are periodic current zeros, and therefore the electric arc is discontinued naturally at the end of each half cycle. By deionizing the gases in the gap at a current zero, reestablishment or reignition of the arc during the succeeding half cycle can be prevented. Accordingly, it is a conventional object in designing are extinguishing devices for alternating current circuit interrupters to provide suitable means for obtaining deionization of the arc gases and otherwise impairing the conductivity of the current path so that the potential difference between the separated contact members required to reignite the are after a current zero, known as the reignition voltage, exceeds permanently the circuit recovery voltage impressed upon these members tending to reestablish the flow of current.

In direct current electric power circuits, there are no periodic current zeros. In order to interrupt a direct current circuit, therefore, it is necessary to force the circuit current to zero by increasing the arc voltage until it is greater than the available circuit voltage. This is done by providing suitable means for rapidly increasing the resistance of the arc and otherwise impairing the conductivity of the current path so that the voltage drop between the separated contact members of the circuit interrupter equals or exceeds the circuit voltage impressed upon these members tending to maintain the flow of current.

I It is well known in the art of electric circuit interruption to provide arc extinguishing devices or are chutes having aplurality of metal barriers or plates stacked in spaced-apart planes disposed generally perpendicular to the'path of the are. A stack of such plates is located across the exhaust end of the arc chute and the arc is driven against the exposed transverse edges of these plates. The metal plates chop the arc into a family of serially related arclets which are subsequently deionized and extinguished as they move within the spaces between ad- 'jacentvplates. Such arc-chopping or arc-splitting metal -plates contribute to the arc extinction process in several ICC different ways. Their relatively cool surfaces reduce the temperature of the are thereby enhancing deionization and increasing arc resistance. The plates cause a turbulent mixing of the hot arc gases and the relatively cold air in the spaces through which the arclets move, thereby further enhancing deionization. Perhaps most significant of all, each arclet will have its own anode and cathode voltage drop region where the voltage gradient is relatively high. In other words, a thin cathode or anode sheath of relatively high dielectric strength is formed adjacent the opposing surfaces of each pair of metal plates, and at least a certain minimum potential difference between adjacent plates is required to sustain or establish the associated arclet. Accordingly, the cumulative effect of a plurality of spaced metal plates is to raise the are or reignition voltage of the circuit interrupter.

-T he interrupting ability of a metal-plates type are chute will increase with the number of plates efiiciently utilized. The maximum number of plates that may be provided is determined by the necessity of maintaining a minimum spacing or clearance between adjacent plates and by the practical limitations of the overall size and configuration of the particular are chute. The minimum space maintained between adjacent plates should be sufficient to permit effective performance of the arc-chopping function, that is, to enable the are products to be rapidly vented and the arc itself to move freely into and through the space. In order to successfully interrupt relatively high currents in very short times, it is particularly important that all of the available pairs of adjacent plates be utilized quickly and substantially simultaneously, and conventional metal-plate arc chutes of which I am aware have not been entirely satisfactory in this regard.

In conventional arc chutes of economic construction the stacks of spaced apart metal plates are typically arranged so that each pair of adjacent plates are separated by the same distance, and a stack of such uniformly spaced plates is disposed in a straight line across the exhaust end of the chute so that some of the plates are located more remotely than others from the point of arc initiation. This arrangement does not adequately take into account the fact that the are products to be exhausted are not under uniform pressure in the arc chute, and as a result, some of the plates are unable efficiently to contribute to the arc extinction process. In the conventional arrangement of uniformly spaced metal plates, the arc will not reach the plates located adjacent high pressure regions of the chute, if at all, until after other portions of the are have been driven into contact with and chopped into arclets by the plates located closer to the lower pressure regions where the volume of are products exhausted is relatively small.

Accordingly, it is an object of this invention to provide an arc extinguisher of economical construction having a stack of spaced-apart metal plates so arranged that all pairs of adjacent plates are substantially equally and simultaneously effective in extinguishing the are.

A further object of the invention is to provide an arc chute having a stack of spaced-apart metal plates so arranged that the total voltage drop across this stack is distributed substantially equally among all of the pairs of the adjacent plates even though some of the plates are more remotely located from the point of arc initiation than others.

In carrying out my invention in one form, I provide an electric arc chute having spaced-apart sidewalls defining an arcing area and an outlet for the arc products. Separable contact members are provided for initiating an are at a predetermined point within the chute, and suitable means are provided for propelling the arc toward the outlet. I provide a plurality of metal plates stacked across the outlet in spaced-apart planes disposed generally perpendicular to the sidewalls and to the arc, and the spacings between adjacent planes are progressively varied so that there is less area available for venting the are products between the adjacent plates nearest to the arcing area where the least volume of arc products is generated than between adjacent plates located closer to arcing areas where larger volumes of are products are being generated.

My invention will be better understood and its various objects and advantages will be more fully appreciated from the following description taken in conjunction with the accompanying drawing in which:

Fig. 1 is a side elevation of an arc extinguisher or are chute constructed in accordance with a preferred form of my invention;

Fig. 2 is an enlarged section taken along lines 2-2 of Fig. 1;

Fig. 3 is an enlarged section taken along lines 33 of Fig. 1;

Fig. 4 is an enlarged section taken along lines 4-4 of Fig. 2; and i Fig. 5 is a side elevation diagrammatically illustrating an improved result obtained by the illustrated embodiment of my invention.

Referring now to Fig. 1, l have shown for the purposes of illustration an arc extinguisher or are chute 11 for a circuit interrupter of the type that may be used in direct current electric power circuits. It should be understood at the outset that my invention is not limited to direct current circuit interrupters, and it may be applied to alternating current interrupters as well. However, the specific circuit. interrupter that I have chosen to show and describe in order to best illustrate my invention is particularly well suited for use as an anode breaker in a power rectifier system. As such, the interrupter may be called upon to interrupt unidirectional arc-back current which rises at an extremely high rate, such as 8,000,000 amperes per second, to a very large peak magnitude. In this application it is important to interrupt the arc-back current at a relatively low magnitude (such as 50,000 amperes) before it reaches the available peak, and therefore the arc extinguishing process that takes place in the arc chute 11 must be completed in an extremely short time.

The particular circuit interrupter illustrated in Fig. 1 is a simplified showing of an interrupter described in detail and claimed in Patent No. 2,329,003, issued to J. W. Seaman on September 7, 1943. The interrupter includes an upper terminal stud assembly .12 on which is movably supported a plurality of relatively stationary main contacts 13, only one of which appears in Fig. 1, and a stationary arcing contact 14. Cooperating with the relatively stationary main contact 13 is a movable main contact 15, and cooperating with the stationary arcing contact 14 is a movable arcing contact 16. Both the movable main contact 15 and arcing contact 16 are electri cally connected to a lower terminal stud 17 of the circuit interrupter. The circuit interrupter is shown as supported on a base 18 of suitable insulating material. In order to interrupt the flow of current in an external electric power circuit (not shown) connected to the upper and lower terminal studs 12 and 17, the cooperating movable and stationary contact members are separated by means of a suitable operating mechanism (not shown) coupled to the movable contacts at 19.

As can be seen in Fig. l, the arc extinguishing device or are chute 11 is adapted to be mounted on the circuit interrupter adjacent to and principally above the arcing contacts 14 and 16. The arc chute comprises a pair of spaced- apart sidewalls 20 and 21 of suitable insulating material for enclosing the are drawn between the contact members 14 and 16 upon separation thereof. As shown, the outline of the sidewalls 20 and 21 is that of a rectangle having a portion of generally trapezoidal form adjoining its lower edge. The are chute thus has relatively small and large arc initiating and exhaust openings, re-

spectively, that is, a relatively small opening where the arc is initiated upon separation of the contacts 14 and 16 at the lower end of the chute and a relatively large opening or outlet where the arc products are discharged at the opposite end of the chute.

The spacing between the opposing sidewalls 20 and 21 is determined and the arcing area is defined by suitable transverse members mounted therebetween. For example, a pair of abutting members 22 and 23 of insulating material are mounted between the sidewalls along the lower inclined edges thereof. Adjacent each vertical edge of the sidewall 20 and extending transversely to the corresponding edge of sidewall 21 is another insulating member 24.

The sidewalls 20 and 21 and the transverse members 2224 are fastened together by suitable means such as bolts or screws, and the rigidity of the whole structure is maintained by horizontal braces 25 and an interlocking vertical brace 26 on the outside of each of the sidewalls 20 and 21. These braces are bolted together with the sidewalls 20 and'2l. and the transverse members 22-24 by suitable means such as bolts 27. Another pair of horizontal braces 28 are mounted adjacent both sides of the outlet of the arc chute 11 at its upper end, and as can be seen in Fig. 2, the bolts 27 securing these braces and the sidewalls 20 and 21 are provided with suitable insulating bushings 29 extending between the sidewalls.

As is shown in Fig. l, the abutting transverse members 22 and 23 are disposed to extend divergently outwardly from the arc initiating end of the chute toward the discharge or exhaust end thereof. These members are arranged to support on their inner sides a pair of divergent arc runners 30 and 31, respectively. The'lower end of the arc runner 31 is bent around the lower end of its supporting member 23 for engagement by the movable arcing contact 16 upon circuit opening operation of the interrupter. The arc runner 31 is electrically connected to the lower terminal stud 17 by a suitable flexible conductor, not shown. The stationary arcing contact 14 is mounted on the lower end of the arc runner 30, and this arc runner may be electrically connected to the upper terminal stud 12 by a suitable flexible conductor, not shown. For protecting the sidewalls 20 and 21 against the eroding action of the arc terminal as it travels along the are runners, a protective plate 32 of high arc-resistant insulating material is inserted between the sidewalls and the transverse abutting member 23. Suitable blowout coils (not shown) may be connected between the above-mentioned flexible conductors and the arc runners 30 and 31 respectively.

When the cooperating movable and stationary contact members are separated or opened while the circuit interrupter is carrying current of substantial magnitude, the gases in the resulting gap become ionized and an electric arc is drawn or initiated. Due to the combined influence of several different factors, the stream of ionized gases comprising the arc is driven or propelled away from the point of arc initiation toward the outlet or discharge end of the arc chute 11. For example, there is a thermal effect whereby the heat and resultant buoyancy of the generally horizontal arc cause the arc to rise vertically and to form an upward loop. There is also a magnetic action which propels the arc toward the outlet of the chute. The central portion of the arc moves more rapidly than the terminals or roots of the are which tend to stick to the relatively hot metal are runners 30 and 31. As a result of all of these factors, a looping arc of gradually extending length is directed toward the exhaust end of the arc chute. Various are products evolved in the chute during the current interruption process are propelled or pushed toward the outlet ahead of the arc.

As the ends of the hot arc move up the arc runners 30 and 31, a certain amount of vaporization takes place along the surface of the runners. In order toavoid c011 centrated heating of individual spots and the consequent deterioration of the arc runners at their upper, divergent ends (not shown), the improved arc runner configuration fully disclosed and claimed in Patent No. 2,460,727 issued to W. A. Atwood and E. W. Boehne on February 1, 1949, may be used. In accordance with this patent, recidivous arcing pockets are provided so that the running ends of the arc will oscillate rather than remain relatively fixed at the outward ends of the arc runners.

In order to aid the cooling of the arc and the arc products, a plurality of spaced-apart insulating barriers 33 may be provided in the arc chute 11. The barriers are disposed in parallel relationship with respect to the sidewalls and 21. The original arc is divided or split into a plurality of relatively thin parallel arcs in the narrow slots or. chambers defined by adjacent barriers 33, and these parallel arcs are cooled more readily than the whole are could be cooled.

In accordance with my invention, a plurality of generally rectangular plates are stacked across the outlet of the arc chute 11 in spaced-apart planes disposed generally perpendicular to the sidewalls 20 and 21 and to the arc. The lower portion 34 of each of these transversely extending rectangular plates is made of metal, as is best seen in Fig. 4, and spans the sidewalls 20, 21 intermediate the exhaust opening or outlet of the chute and the arc drawing means 14, 16. The upper portion 35 of each plate is made of insulating material. The electric arc in the arc chute 11 is driven against the lower-exposed edges of the metal plates 34, and the arc is chopped into a family of serially related arclets.

When the arclets move through the interplate spaces,

' they rapidly transfer their heat to the relatively cool surfaces of the adjacent metal plates 34. This action, combined with the turbulent gas-mixing action which occurs inthe interplate spaces, rapidly reduces the degree of ionization of the arcing gases, thereby increasing the arc resistance. The total are voltage across the stack of metal plates 34 is determined by the aggregate of the arclet voltages, the voltage of each arclet including anode and cathode voltage drops as explained in greater detail hereinbefore. As a result of all of these effects, the electric arc is rapidly extinguished. The insulating plates 35 are provided, among other reasons, to cool the streams of arcing gases and to maintain these streams segregated until safely cooled, thereby minimizing the possibility of an are being established exterior to the arc chute 11.

The manner in which the stack of arc-chopping plates is constructed may now be considered in detail. As indicated in Fig. 1, the plates are divided into six serially related groups 36a, 36b, 37a, 37b, 38a and 38b. The use of six separate groups rather than one continuous stack of plates is a matter solely of manufacturing and assembling convenience. The various groups of plates may have approximately the same overall dimensions but do not necessarily include the same number of plates.

Each group of plates comprises a plurality of the metal and insulating plates 34, 35, a plurality of spacer strips 39, and four insulated rods or bolts 40. The relatively narrow spacer strips 39 are interposed between plates at transversely opposite ends thereof, as can be seen in Figs. 2 and 3. The plates and the spacer strips are clamped together in a horizontal direction by means of the bolts 40, one bolt being located at each end of the metal plates 34 and one bolt at each end of the insulating plates 35. In accordance with the illustrated embodiment of my invention, the centrally located groups of plates The six groups of plates assembled in the manner described above are disposed in series relationship across the outlet of the arc chute 11. These groups are clamped in a vertical direction against a horizontal ledge 41 formed on the inside surface of each sidewall 20 and 21 by means of a pair of clamping bars 42 suitably secured to the sidewalls. If desired, an appropriate barrier 43 of insulating material may be disposed between each group of plates, and one such barrier may be disposed between each of the outer groups of plates 38a and 38b and the adjoining transverse member 24 of the arc chute 11.

,From the foregoing description of the stack of arcchopping metal plates, it can be observed that a nonuniform distance or spacing is maintained between adjacent plates. The spacing between adjacent plates in groups 37a and 37b is twice as great as the spacing between adjacent plates in groups 36a and 36b, and the spacing between adjacent plates in the outer groups 38a and 38b is three times the spacing used in the central groups 36a and 36b. This progressive change in spacing provides for a greater venting ratethat is, a greater rate of flow or volume per unit time of the are products being vented-'between adjacent plates in groups 38a than between adjacent plates in group 37a, and similarly a greater venting rate between adjacent plates in group 37a than in group 36a. In other words, the effective venting area between adjacent plates has been varied so that the groups of plates locatedat the opposite ends of the stack provide lower fiuid resistance than the groups of plates located nearer to the center of the stack.

The advantages obtained in accordance with the abovedescribed structure can best be understood by considering first the action in the arc chute 11 during a circuit opening operation by the illustrated interrupter. Upon separation of the arcing contacts 14 and 16 during an arc-back condition, an electric arc is initiated. The movable arcing contact 16 transfers its terminal of the arc to the arc runner 31, and the arc proceeds to move through the generally divergent body of the arc chute toward the outlet or exhaust end. The stream of ionized gases forming the arc is extremely hot, and the surrounding atmospherein the arc chute is rapidly heated. In addition, vaporization takes place at the surface of the arc runners 30 and 31, and additional gases are evolved in the arc chute. Since the arcing area is relatively confined, there is a rapid increase in the pressure of the various gases which are generated as a result of the arc, known as the are products. The pressure is greatest where the arc is most active and where the gases are most confined, and in the illustrated embodiment of my invention both of these conditions are most prevalent in the arcing regions adjacent to the outer or divergent ends of the arc runners. This is shown pictorially in Fig. 5 where the broken line 44 outlines the pattern of discharged incandescent products of the arc during a circuit interrupting operation of a circuit interrupter having an arc chute that was not provided with the arc-chopping metal plates 34. Accordingly, I have provided the greatest venting area between adjacent metal plates 34 located closest to the outward ends of the arc runners 30 and 31 so that a larger volume of are products can be expelled per unit time from the arc chute in these areas.

Since the pressures of the are products generated in the arc chute are not uniform across the outlet of the chute, it is my purpose to provide a stack of metal plates arranged so that the venting areas between adjacent plates are varied to accommodate for the varying pressures and consequently volumes of are products to be expelled. In the illustrated embodiment of the invention, the groups of plates 38 and 38b located nearest to the outward ends of the arc runners 30 and 31 have the greatest interplate spacings and hence the least fluid resistance, and accordingly these groups can rapidly exhaust all of the arc products generated in the adjoining areas or regions of the arc chute. Conversely, the groups of plates 36a and 36b nearest. tothe point of arc initiation have venting areas that are relatively small and hence have relatively high fluid resistance, but the volume of are products generated in the area adjoining these groups is relatively less. In other words, the venting areas are least where the amount of are products. to be exhausted are least. a As a result of the arrangement described above, relatively high-pressure pockets of are products that might otherwise be formed are rapidly relieved and exhausted, and; the stream of ionized gases comprising the arc, which stream is moving behind the arc products, will quickly reach the lower exposed edges of all of the metal plates 34 substantially simultaneously. This enables each pair of adjacent plates to be utilized efiiciently, and optimum interrupting ability is realized. The initial voltage drop in the stack of plates will comprise an aggregate uniformly distributed across substantially all of the adjacent pairs of plates. Thus, the broken line 45 in Fig. represents the pattern of incandescence are products discharged during an actual circuit interrupting operation by a circuit interrupter having an arc chute provided with the arcchopping metal plates in accordance with my invention. While I have shown and. described a preferred form of my invention by way of illustration, many modifications will occur to those skilled in the art. I therefore contemplate by the claims which conclude this specification to cover all such modifications as fall within thev true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In an electric arc extinguisher having spaced-apart sidewalls defining an arcing area and an outlet for the arc products, means for initiating an arc at a predetermined point within the extinguisher and for subsequently propelling the arc toward the outlet, and a plurality of metal plates stacked across the outlet in spaced-apart planes disposed generally perpendicular to the sidewalls and the arc, the spacing between adjacent planes being varied so that the effective venting. area between the adjacent plates nearest to said predetermined point is smaller than .the effective venting area between adjacent plates more remotely located;

2. An arc extinguishing device having in combination: an arc chute provided with a pair of opposing sidewalls having transverse members mounted therebetween; a pair of arc runners mounted on the inner sides of said transverse members, respectively, and disposed to extend divergently outward from the arc initiating end of the chute toward the discharge end thereof; and a plurality of groups of transversely extending spaced-apart metal plates stacked in series relation across the discharge end of the chute, the plates in the groups located nearest to the outwardv ends of the arc runners, respectively, being disposed to provide between adjacent plates spacings that are relatively great with respect to the spacings between adjacent plates in the other groups.

3. An electric circuit interrupter, comprising: means for drawing an arc and an arc chute for receiving the are at one end and exhausting the arc products at another end thereof, said chute comprising a plurality of spacedapart metal plates mounted to extend transversely of the arc intermediate the are drawing means and the, exhaust end of the chute, the plates located most remotely from the are drawing means being disposed to provide between adjacent plates an effective venting area substantially larger than the venting area between adjacent plates located closer to said are drawing means.

4. in a circuit interrupter including contact structure separable to establish an arc, an arc chute comprising a pair of spaced sidewalls for enclosing the arc, means disposed in the arc chute for directing the arc between the sidewalls toward an exhaust end of the chute, and a plurality of spaced-apart metal plates spanning the sidewalls to chop the are into a family of serially related a-rclets, the plates located closer to the contact structure being spaced at shorter intervals from adjacent plates than the plates further removed from the contact structure are spaced from adjacent plates.

5. A circuit interrupter including contact structure separable to establish an arc, an arc chute comprising a pair of spaced sidewalls for enclosing the arc, means including a pair of arc runners disposed in the arc chute for directing the arc from the vicinity of the contact structure outwardly toward an exhaust end of the chute, and a plurality of spaced-apart metal plates stacked across the exhaust end of the chute to chop the arc into a family of serially related arclets, the plates located nearest to the outer ends of the arc runners, respectively, being dis posed to provide greater venting area between adjacent plates than the plates located further from said outer ends are disposed to provide.

6. An electric circuit interrupter, comprising: an arc chute having a relatively small openingat one end thereof, a generally divergent body portion for enclosing anelectric arc, and a relatively large exhaust opening'at the opposite end thereof; means associated with the arc chute for directing the are through said body portion toward said exhaust opening; and a plurality of arc-chopping metal plates mounted in variable spaced-apart relation intermediate said openings, said plates being disposed so that those located relatively close to relatively high-pressure arcing regions enclosed by the body portion of the arc chute are separated from their adjacent plates by spacings that are greater than the spacings maintained between adjacent plates located closer to relatively lowpressure arcing regions in the chute.

References Cited in the file of this patent UNITED STATES PATENTS Atwood et al. Feb. 1', 1949'

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