US2458317A - Arc extinguishing means for electric circuit breakers - Google Patents

Description

Jan. 4; 1949- D. K, TOWER ET Al. 2,458,317

ARC EXTINGUISHING MEANS FOR ELECTRIC CIRCUIT BEAKERS Filed Aug. 24, 1946 F Inventors 6 Dell KTOwef,

l Benjamin BeaH, HI.)

by M

Their` Attcrney.

Patented Jan. 4, 1949 ARC EXTINGUISHING MEANS FOR, ELEC- TRIO CIRCUIT BREAKERS Dell K. Ilower, Millbrook, N. Y., and Benjamin S.

Beall, III, Upper Darby, Pa., assignors to General Electric Company, a corporation of New York Application August 24, 1946, Serial No. 692,886

(Cl. 20G-14S) Claims. l

Our invention relates to improvements in circuit breakers of the fluid blast type wherein an arc drawn between separable contacts is extinguished by a blast of pressure fluid directed transversely at high velocity through the arc. Such circuit breakers are commonly known as cross blast breakers, one commercial type being disclosed in United States Patent 2,284,842, Prince et al., granted June 2, 19412, and assigned to the same assignee as the present application.

In the above mentioned Prince et al. breaker, the arc drawn between the contacts is blasted against and around the leading edges of a plurality oi transverse barriers which barriers radiate outwardly from the initially drawn arc within divergent are chute. More recently however, it has been found-possible to greatly reduce the volume of the arc chute by using but one transverse barrier, against and around whose .leading edge the arc is blasted. This arrangement is particularly effective when, in addition, the arm is transferred from the separable contacts to a pair of spaced stationary electrodes to provide a preferred arc gap of limited length irrespective of the continued movement toward open circuit position of the reciprocable contact blade. Such an improved arrangement is disclosed and described in Patent 2,452,953, Paul et al., issued November 2, i948, and assigned to the same assignee as the present application.

Specifically, our invention is directed to further improving the interrupting capacity of a single-barrier type of cross blast breaker operating in accordance with the precepts set forth in the above mentioned Paul et al. application. by providing a transverse arc barrier of particular cross-sectional configuration whereby the looping of the arc into the chute is impeded, thereby to more effectively cause extinguishment of the arc.

It is therefore an object of our invention to provide an improved cross blast circuit breaker having a more effective single transverse insulating arc barrier than heretofore.

It is another object of our invention to provide a cross blast circuit breaker of the fixed-gap type having a single transverse insulating are barrier of improved arc extinguishing ability.

It is a further object of our invention to provide a cross-blast circuit breaker having a single arc extinguishing barrier which impedes the passage of the are while permitting streamline flow ci the product of arcing into the arc chute.

Further objects and advantages of our invention will become apparent as the following description proceeds and the features of novelty which characterize our invention will be pointed out with particularity in the claims annexed to and forming a part of this specification,

For a better understanding of our invention reference may be had to the accompanying drawing in which Fig. 1 is a comprehensive cut-away view showing in perspective the internal construction of an interrupting device embodying our invention; While Fig. 2 is a partial sectional elevational view of the same structure which more clearly shows the precise cross-sectional configuration of the improved arc extinguishing barrier of our invention as applied to the circuit interrupting structure shown, described and claimed in the above-mentioned Paul et al. application.

Referring now to the drawing, there is illustrated an electric circuit interrupting device I comprising an arc chute 2 of box-like configuration fabricated from suitable slab-like walls of insulating material such as fibre within which, at the right hand end thereof, is disposed a fixed Contact structure 3. Cooperating with the fixed contact structure is a reciprocable blade-like contact 4 whose fragmentary lower end portion is shown separated from the fixed contact structure 3 and drawn clear from the arc chute 2 as when in the circuit open position. Guiding means and a suitable operating mechanism (not shown) provide for rectilinear closing and opening movement oi the movable blade 4, the latter preferably7 being at vall times connected by suitable means. such as a sliding contact, to an external electrical circuit conductor generally indicated at 5.

As in the above-mentioned Paul et al. application, the fixed contact structure 3 may be mounted conductingly upon la metal pedestal member 6 having a dovetailed base l whereby the interrupting unit I is clamped removably upon the cap 8 of a supporting insulator 9 by wedging member I0 under the jacking action of the single clamping screw II.

With separable contact 4 moved down to closed circuit position inl which its lower end is embraced between the resilient Contact fingers I2 of fixed contact 3, the circuit to be interrupted may be considered to flow from conductor and sliding contact 5, through blade 4, fingers I2 of fixed contact 3, pedestal 6, base l, cap 8, thence out to the external circuit I3 through conductor bars I4 secured to cap 8 by connector screw I5.

It will be understood that although but a single circuit and interrupting device therefor has been illustrated, such a device in which the box-like arc chute structure 2 is comparatively flat (it Y being substantially no wider than the insulator cap 8) is particularly adapted for polyphase application in which three interrupting devices l are arranged in side by side relationship in a sheet metal cubicle structure for operation by a common actuating mechanism in the manner disclosed in Patent 2,436,190, Boisseau et al., issued February 17, 1948, and assigned to the same assignee as the present application.

The fixed and movable contacts preferably are equipped respectively with arcing ngers IB which extend above current carrying lingers I2, and a cooperating arcing tip Il projecting below the bottom edge of contact blade Il whereby, upon contact separation, a single power arc is drawn therebetween which is traversed by a cross blast of arc extinguishing fluid which is released from a supply tank in known manner such as is described, for example, in the above-mentioned Boisseau et al. application.

The fluid blast is directed into the right hand end of arc chute 2 through an insulating conduit I8 which is secured sealingly to an end wall I9 of are chute 2 by a conventional stuffing box arrangement as is clearly self-evident from the drawing, the studs providing clamping means for this purpose. End Wall I9 is provided with a blast entrance orifice 2I lying in registry with the conduit I3 and from which orifice a by-pass duct 22 connects to recesses 23 for providing an air seal around the blade 4 during the blast period as the blade moves through its guide slot 24 in the top slab of the fabricated box-like chute 2. This seal functions to conne ionized gases within the chute during the arcing period as disclosed and described in Rankin Patent 2,290,708 granted July 21, 1942, and assigned to the same assignee as the present application. It will be noted that end wall i9 is arranged in tongue and groove abutting relationship with the top slab of arc chute 2 and preferably, for ensuring gas tightness, all walls and sides of the fabricated arc chute are bolted together with tongue and groove joints, including the pedestal member E as is clearly shown in Fig. 2.

Also, for limiting the length of the arc drawn between the separable contacts, and as disclosed in the above mentioned Paul et al. application, a xed preferred arc gap 25 is defined by a pair of electrodes, one 2 being attached to thexed contact structure 3 while the other, 2l, is secured to a wiping contact structure 28 which is disposed in the arc chute for sliding engagement with the blade 4 during limited opening and lclosing movement thereof by means of spring pressed ngers 29. Accordingly, the arc drawn during separation of blade tip Il from the xed arcing contact fingers I6 transfers across the fixed electrodes 26 and 2l so that the roots of the arc' continue to adh-ere to these electrodes until the instant at which the arc is extinguished and which instant occurs before the blade 4 has passed out of wiping engagement with the ngers 29 of the contact structure 28. To the left of the gap 25 is fixedly disposed a pair of wedge-shaped insulating members 30 and 3i which define, in conjunction with a transverse barrier structure 32, a pair of widely divergent and separated expansion chambers or passages 33 and SI! for receiving the arc products of the blast and which products are cooled when encountering and passing through the spaced metallic sheets comprising the cooling units 35 and 30 which are disposed in the rectangular portions of the chute structure downstream of the wedge members 30 and 3l. For continuing the segregation of the arc products for as long as possible within the chute, a barrier extension member 31 may be provided at the downstream end of barrier 32. Beyond the barrier extension 3l the divided arc products merge together and exhaust through an appropriate cylindrical conduit 38 leading upwardly to atmosphere. The tubular exhaust conduit is clamped in sealing relationship to the arc chute 2 by a stuffing box arrangement comparable to the already described for the supply conduit I8,

1n accordance with our invention, the division barrier 32 (which, in the above mentioned Paul et al. application is a sheet of insulating material of substantially uniform thickness throughout) comprises a member whose cross-section, proceeding from its leading edge 3S directly opposite the gap 25, widens rapidly to produce a blunt wedge form which then rounds off decreasingly from its region of maximum depth to assume a constant thickness, commencing adjacent to the leading edges of the cooling units 35 and 30, for the remainder of its length. The barrier 32 then, may be considered to be a blast dividing member extending transversely across the side-walls of the arc chute Whose cross-section has the form of a blunt spear, the head d0 of which is directed upstream toward the blast with the point 39 poised at the throat defined by the narrow arc gap 25. This barrier, or at least the Spearhead portion thereof, is made from an insulating material of good gas producing characteristics when subjected to arc heat such as, for example, hard fibre or methylemethacrylate; also the adjacent wedge shaped arc chute members 30 and SI are also made from similar gas-emitting insulating material.

By substituting the uniquely configured spear head type barrier 32 of our invention for the former flat barrier, we have been enabled thereby to increase the interrupting rating of the same arc chute from 500,000 kva. to 1,000,000 kva, in one case and in another from 1,000,000 to 1,500,n 000 kva. The following explanation is believed to account for this phenomenal improvement.

The arc, initially drawn by the blade tip I'I separating from the arcing fingers I6, is subjected to a blast stream of pressure gas issuing from the right through orifice 2l thereby transferring it across the gap 25. The transferred arc, with its roots adhering to the gap electrodes 2E and 2l, is then forcibly impressed against the blunt wedgelike Spearhead of the barrier 32. The arc, driven loopingly into the narrow slot-like passages di and d2 defined by the slant sides of the wedge members 30 and 3l and the divergent leading slopes of the Spearhead portion 'l0 of the barrier 32, will then assume the configuration indicated by the dotted lines 33 and ill in Fig. 2. Accordingly, the looped arc or the greater portion there of is subjected to a very effective cooling process whereby it is extinguished, for the leading slopes of the Spearhead barrier arrest and hold it directly in the way of the blast stream issuing from behind, while the surfaces of these leading slopes emit numerous small jets of gas which assault the arc coolingly from ahead. However, a high current arc, which expands to a comparatively large diameter, is not likely to emerge into the expansion spaces 33 and 31% for it becomes squeezed and tends to short out within the narrow elongated passages ill and 42. Hence, in these extreme cases, additional amounts of arc extinguishing gas are automatically produced due to the arc squeezing itself effectively against the gasA emitting slant surfaces of Wedge members.

33 and 31|; so. that the arc extinguishing arrangen ment of our invention is'very adaptable' for interrupting currents over a much higher interruptingv signe'eas` the present application, in which a barl rier of Wedge shaped cross4 section opposingly confronts an arc produced across preferred gap electrodes. In the Areferred to circuit breaker however, each of the two separate' exhaust passages which are initiated by the intervention of the Wedge barrier continue in a straight line to diverge outwardly; whereas in accordance with` our invention, the exhaust passages from their inception in the expansion spaces 33 and 34 respectively are caused to flare smoothly toward one another by virtue of the diminishing crosssection of the barrier 32 which constitutes the rear or downstream part of the Spearhead portion 40. In thismanner we contrive to retain all the advantages attributable to freely exhausting outwardly divergent passages whilekeeping the arc chutestructure confined within. small rectangularv limitsi Accordingly', the incandescent gaseous ar'c products emanating from the effective arcing zoney in the elongated passages 4| and 42 are permitted to dilate rapidly in thev two separated widely flaring expansion spaces 33 and 34 so. that they flow' toward and immediately encounter the heat-absorbing units 35` and 33 which cool the separated gases toA a safe temperature before they merge into a common stream beyond barrier extension 31 to exhaust to atmosphere through conduit 38. It therefore will be appreiciated that the Spearhead portion 40, whose thickness progressively increases then decreases, cooperates with the slant sides of wedge members 30- an'd 3| to produce a pair of branching narrow elongatedA arcing passages 4| and 42v each of which. flares smoothly and widely to form the divergent expansion spaces 33 and 34- adjacent thecooling units 35 and 38.

Although it might be supposed that the efficiency of the cooling units, and hence that of the interrupter, might be reduced by our positioni-ng of the impeding Spearhead portion 40 obstructingly in their way, this is not so. Photographs of acolored blast taken through a transparent chute side reveal that the separated streams effectively wash the downstream contours of the Spearhead 40, so that, on the contrary, it is believed that the exhaust gases are distributed even more uniformly, than with the prior at barrier, over the full cooling area of the units by means of the streamlined barrier of our invention, the total eectiveness of which isV more than amply substantiated by interrupting tests. which have demonstrated the already referred to phenomenal increase in interrupting capacity.

For aiding interruption by preventing arc restrikes due to high rates of rise of recovery voltage, there may be provided a resistor, a fragment of which is indicated. in Fig. 1 by 45,-whi'ch functions inthe manner clearly set forth in the aforementioned Prince et al. patent. This resistor preferablyv is constructed as a molded slab-like unit which is attached to they side of the arc chute in the mannerv disclosedv in the copending application Serial No. 586,893, Bold, led. April 6, 1945, and assigned to the same assignee as' the present application. Electrical connection. from the resistor to the interrupter contact structure is afforded by a threaded connector 46, proceeding from one resistor terminal which, as indicated by a projection line therefrom, may screw into one of the xed gap electrodes 2'6 or 21; while the other resistor terminal is electrically connected by another threaded connector 4l which screws into a conducting member' 48 which is embedded in the barrier member 32. A conductor rod 49 extends longitudinally within the barrier 32 for electrically connecting the conducting member 48 to an electrode whose tip 50 emerges above the surface of the Spearhead portion 40.

For optimum resistor performance, the positioning of the electrode tip 50 is quite important, for in accordance with the precepts set forth in the aforementioned Prince et al patent, it is desirable for the electrode tip to be positioned so asto provide a gap in the resistor circuit which will not break down prior to arc interruption, but which becomes subject to breakdown after extinguishment through the intervening ionized gasesV for establishing a weak parallel current path through the resistor before the recovery voltage has reached a value such as would have caused an arc to restrike across the separated contacts without the resistor. As already pointed out, the spaces 4I and 42 define an effective arcing zone, so that by positioning the electrode tip 50 just beyond this zone,viz. at one of the sides of the Spearheadportion 40 of the barrier 32 as depicted in the drawing, the resistor 45 is prevented from being subjected to the voltage of the arc of interruption prior to its extinguishrnent. Accordingly, the barrier construction of our invention is particularly suited for supporting the resistor spark gap electrode and the conductoring members 48 and 49 thereto, with the electrode tip 50 emerging at the most appropriate point for ensuring optimum performance of the arc interrupting device.

Having described the operation of the interrupter of our invention in detail during +he progress of the foregoing description, only the merest recapitulation of that operation is thought to be necessary and which is as follows: With the circuit breaker in closed position completing the external circuit 5 and I3, the blade 4 is in the down position embraced between contact fingers I2 of fixed contact 3. When tripped to open, a blast of pressure fluid is released from a suitable source such as a storage tank by the opening of a suitable blast valve which blast is directed into the arc chute 2 through conduit i8. Substantially simultaneously, the blade 4 is caused to move upwardly at high speed causing an arc to be drawn between the blade tip I'l and the arcing fingers i6, which arc is transferred by the blast to the preferred gap 25 across the fixed spaced electrodes 25 and 21. The transferred arc, with its roots adhering to the spaced electrodes, is extended and driven forcibly against the upstream surfaces of Spearhead portion 40V of the dividing barrier 32, in which position it is momentarily held in the effective arcing Zone constituted by the narrow passages 4! and 42 where it is subjected to the cooling effect of the fluid blast and by the gas generated and ejected from the confining surfaces of the passages 4l and 42 whereby the arc is extinguished. In applications involving high rates of rise of recovery voltage where a resistor 45 is provided, a light current arc may reappear across the breakdown gap provided by the internal electrode 50 and fixed electrode 21 which will be extinguished by the blast without causing an arc to re-establish across the separated contacts. The gaseous products of arcing ow expandingly from the passages 4l and 42 in two separated streams, being permitted free dilation at the downstream end of the Spearhead portion 40 in the expansion chambers 33 and 34 whereby they encounter over a broad front the cooling devices 35 and 36. Being cooled by their passage through the cooling `devices, these separated gases are permitted to re-unite for exhausting to atmosphere through the common conduit 38.

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

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

1. An electric circuit breaker of the fluid blast type comprising an arc chute, a pair of relatively separable contacts arranged to draw an arc adjacent the entrance of said arc chute, means for directing a blast of iiuid under pressure transversely across the arc gap formed between the contacts upon separation thereof, the structure of said arc chute defining a pair of conning walls proceeding diver-gently from said gap, cooling means disposed in said chute downstream from said gap, an insulating barrier extending transversely across the interior of said chute having its leading edge closely adjacent to said gap, the thickness of said barrier progressively increasing from its leading edge to a region of maximum thickness intermediate said gap and said cooling means then decreasing therefrom toward said cooling means whereby the surfaces of said barrier cooperate with the surfaces of said divergent walls to define a pair of narrow arcing passages each of which flares widely toward said cooling means, an electrode embedded in said barrier arranged with its tip projecting through the surface of said barrier in said region of maximum thickness for providing a breakdown spark gap in said arc chute, a resistance associated with said circuit breaker, and means for electrically connecting one terminal of said resistance to one of said contacts and the other terminal of said resistance to said electrode.

2. An electrode circuit breaker of the fluid blast type comprising a pair of separable contacts, a pair of electrodes defining a xed arc gap associated with and arranged adjacent to said contacts for maintaining the arc gap length constant following a predetermined separation of said contacts, an arc chute of substantially rectangular box-like form fabricated from slablike wall sections, the xed one of said contacts and said electrodes being disposed therein at one end thereof, means for -directing a blast of fluid under pressure through the entrance to said arc chute transversely across the path of separation of said contacts and through said xed gap upon separation of said contacts, an insulating partition for dividing said arc chute downstream from said gap into two exhaust passages of similar cross-section, cooling means `disposed in each of said passages, and means disposed in said chute intermediate said gap and said cooling means for producing a pair of similar narrow elongated arcing passages diverging from said gap, each of which flares widely and expansively toward said cooling means, the walls of said passages being composed of gas evolving insulating material.

3. An electric circuit breaker of the fluid blast type comprising an arc chute, a pair of relatively separable contacts arranged to draw an arc adjacent the entrance of said arc chute, -meansl for ldirecting a blast of fluid under pressure transversely across the arc gap formed between the contacts upon separation thereof, means defining a, fixed arc gap associated with said contacts for maintaining the arc gap length constant following a predetermined separation of said contacts, the structure of said arc chute defining a pair of confining walls proceeding divergently from said xed gap, an insulating barrier extending transversely across the interior of said chute having its leading edge closely adjacent said fixed gap for separating said chute into two passageways, the thickness of said barrier progressively increasing from its leading edge to a region of maximum thickness between said gap and the opposite edge of said barrier` and then decreasing therefrom in the direction of fluid flow whereby to produce cooperatively with said divergent conning walls a pair of narrow elongated arcing passages branching from said xed gap each of which passages flares widely and expansively in a downstream direction and an insulating partition disposed in said arc chute downstream from said barrier for dividing the downstream portion of said arc chute into two exhaust passages.

4. An electric circuit breaker of the fluid blast type comprising a pair of separable contacts, a pair of electrodes defining a xed arc gap associated with and arranged adjacent to said contacts for maintaining the arc gap length constant following a predetermined separation of said contacts, an arc chute in which at one end thereof said contacts separate and said electrodes are disposed, means for directing a blast of fluid under pressure through said are chute transversely across the path of separation of said contacts and through said fixed gap upon separation of said contacts, a fixed insulating body adjacent the downstream side of said xed gap in vsaid chute for producing with the surfaces of said arc chute a pair of narrow elongated arcing passages, each of which diverges gradually from said fixed gap a predetermined amount and then flares quickly smoothly and widely in a downstream direction andan insulating partition disposed in said arc chute downstream from said insulating body for forming with the surfaces of said arc chute an exhaust passage for each of said arcing passages.

5. An electric circuit breaker of the uid blast type comprising an arc chute, a pair of relatively movable contacts arranged to draw an arc adjacent the entrance of said arc chute, means for directing a blast of fluid under pressure transversely across the arc gap formed between said contacts upon separation thereof, an insulating barrier extending transversely across the interior of said chute and having its leading edge closely adjacent said gap, an electrode embedded in said 2,458,317 9 10 barrier and arranged with its tip projecting REFERENCES CITED through the surface of said barrier at a point spaced from the leading edge of said barrier for providing a breakdown spark gap in said arc The following references are of record in the le of this patent:

chute, and a resistance electrically connected be- 5 UNITED STATES PATENTS tween one of said contacts and said electrode for Number Name Date limiting the current across the breakdown spark 2,234,842 Prince et a1 June 2, 1942 gan 2,298,859 Allan et a1. Oct. 13, 1942 DELL K. TOWER. 10 FOREIGN PATENTS BENJAhmI S' BEALL In Number Countr57 Date 181,356 Switzerland Mar. 2, 1936 539,236 Great Britain Sept. 2, 1941

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