US2571864A - Arc extinguishing circuit interrupter - Google Patents

Description

Oct. 16, 1951 H. w. GRAYBILL.

ARC EXTINGUISHING CIRCUIT INTERRUFTER Filed Aug. 21, 1947 INVENTOR Howard/Z Grayb/fl. 6 BY ATTORNEY WITNESSES: @477 Mafia Ma,

Patented Oct. 16, 1951 ARC EXTINGUISHING CIRCUIT INTERRUPTER Howard W. Graybill, Honey Brook, Pa., assignor to -Westinghouse Electric Corporation,, East Pittsburgh, Pa., a corporation of Pennsylvania Application August 21, 1947, Serial No. 769,910

6 Claims.

This invention relates, generally, to electric circuit interrupters and, more especially, to such interrupters which employ a material along the arc path which evolves an arc-extinguishing gas when in proximity to an electric are, for the purpose of extinguishing the arc.

In circuit interrupters, such as switches designed to open load currents, where repeated operations are required without renewal of any parts of the interrupter, interruption by the use of a blast of arc-extinguishing gas through the are, which gas is obtained from a solid gasevolving material activated by the arc, have been found to be objectionable because of the relatively short life of the gas-evolving material. The action of the are on such gas-evolving materials results in erosion of the material, and while this erosion or wear is small at first, being on the order of .001 inch per interruption, it is of importance because these interrupters depend in part for rapid and efiflcient arc extinction on the high are voltage obtained by mechanically restricting the arc in a narrow passage which is formed at least in part by the aforesaid gasevolving material. These are passages are generally made as narrow as practicable to obtain maximum arc voltage, and consequently, erosion of the gas-evolving material results in widening of the arc passage and consequent lowering of arc voltage and resultant loss in efliciency and speed of interruption. Moreover the erosion becomes progressively Worse with each interruption, because widening of the slot results in a longer arcing time and consequently a greater amount of erosion.

One object of this invention is to provide in circuit interrupters of the self-generated gas blast type, novel means for reducing erosion of any one point of the gas-evolving material so as to materially prolong the effective life of such material.

It has been found that in interrupters of the self-generated gas blast type, as they are now known, most of the erosion of the gas-evolving material occurs at a relatively small area where initial separation of the interrupter contacts occurs.

Accordingly, another object of this invention is to provide novel means in an interrupter of the type described, for distributing the major portion of the erosion occurring on successive interruptions over a relatively large area of the gas-evolving material.

A more specific object of this invention is to provide in an interrupter of the self-generated gas-blast type, novel means for continuously moving the end point locations of the are which is formed upon the separation of the interrupting contacts, during the entire period required for are extinction, and by such motion, to distribute the erosive action of the are over a relatively large area.

A still further object of this invention is to provide in a circuit interrupter of the type described, improved arc-extinguishing means.

These and other objects of this invention will become more apparent upon consideration of the following description of a preferred embodiment thereof, when taken in connection with the attached drawing, in which:

Figure 1 is a partial side elevation View, partly in section, of a switch constructed in accordance with this invention, and shows the switch having its interrupting contacts in closed circuit engagement with each other.

Fig. 2 is also a partial side elevation view similar to Fig. 1, partly in section, and shows the relative position of the interrupting contacts shortly before their separation.

Fig. 3 is a partial transverse, cross-sectional view through the arc chute substantially on the line IIIIII of Fig. 1 and illustrating the main disconnecting switch and the interrupting switch in elevation.

Fig. 4 is a view similar to Fig. 2, but of the arc chute only and with the contacts removed, to show the distribution of the erosion on the chute passage after a relatively large number of circuit interruptions.

This invention is illustrated on Figs. 1 to 4 of the drawing as being embodied in a load break disconnect switch of the general type illustrated in H. L. Rawlins Patent No. 2,308,026, issued January 12, 1943, to the same assignee as this invention. Although this invention has certain particular cooperation with a switch of the type disclosed in the aforesaid Rawlins patent, it is to be understood that the invention also may be used with other types of circuit interrupters wherein it may also find certain novel features of cooperation.

In general, the particular switch illustrated in Figs. 1 to 4, comprises a pair of supporting insulators 2 and 4, such as porcelain insulators or the like, on which the switch proper is mounted. The supporting insulator 2 is illustrated as having a hinge tongue casting 6 secured thereon as by bolts 1, and the said casting is provided with an integral terminal pad 8 to which a line conductor may be secured in any desired manner.

.ative to main blade [2.

Hinge tongue 6 is apertured for the reception of a pivot bolt In for pivotally mounting a split switch blade 12. Preferably pivot bolt II! is provided at each side of switch blade l2 with spring Washers II, for the purpose of providing a predetermined contact pressure between the sides of the split blade l2 and hinge tongue 6.

Supporting insulator 4 is adapted to support a break contact tongue l4 having an integral base which is secured to insulator 4, as by bolts l5, and having an integral outwardly extending terminal pad H, to which a line conductor may be secured in any desired manner. The outer end of switch blade l2 has the sides thereof secured together by a bolt I9 having spring washers 2! thereon at the outer sides of the blade, and break contact tongue I4 is preferably provided with a slot l3 for receiving bolt [9 in the closed position of the switch illustrated in Fig. 1. An actuating handle is is adapted to be secured between the outer ends of the sides of blade l2, and is preferably provided with a hook eye l8 for the reception of a hook stick operating member or the like.

It is believed apparent that the structure thus far described is that of a conventional disconnect switch having a blade l2 pivotally mounted at one end for movement of the other end into and out of engagement with break contact tongue I4, to close the circuit when in engagement, and to provide a safe air gap in the circuit when out of engagement.

For the purpose of interrupting load currents,

switch blade I2 is provided with an auxiliary snap-acting blade 20 adapted to be mounted on one side of blade l2. The mounting for auxiliary blade 25 comprises a mounting fixture 22 which may comprise a casting having spaced 'side walls 25 (only one of which is shown), one

side wall being adapted to lie against the inner side of auxiliary blade 25 near the end thereof and be secured thereto as by screws 24; and

.32 to recei e a stop screw 34 mounted in main blade l2. The purpose of stop screw 34 is to limit pivotal movement of auxiliary blade 20 rel- A spring 36 is coiled about pivot bolt 25 and reacts between one screw 24 and stop screw 34 to normally bias auxiliary blade 29 in a counterclockwise direction about pivot bolt 26 to maintain stop screw 34 in engagement with the side 33 of notch 32, wherein the auxiliary blade lies substantially parallel to main blade i2, so as to be received in an arc chute 31 positioned at one side of break contacttongue l4.

The structure thus far described is substantially identical with that disclosed in the aforementioned Rawlins patent, and, accordingly, for a more complete description of the parts and their operation, and particularly the mounting and cooperation of auxiliary blade 20 with main blade [2, reference is hereby made to such Rawlins patent. This invention is primarly concerned with the construction of swinging contact as assembly 5| with the switch structure heretofore described.

Arc chute 31 comprises a pair of plates 38 which may be machined or molded complementary in shape. Plates 38 may be of any desired insulating material but are preferably of, or at least one of the plates has an inside lining of, an insulating material which is capable of evolving an arc-extinguishing gas when in proximity to an electric arc, such, for example, as fiber, a synthetic resin, or the like. The plates 38 are each provided with integral flange portions 40 and 42 along adjacent edges thereof, for the purpose of spacing the plates a predetermined distance part when the plates are assembled with the flanges in abutting relation and secured together, for example, as by bolts 44. Arc chute 31 is supported on the upright arm 45 of an angled supporting bracket, which is made of a conducting material suchas hard drawn copper bar, the base portion 48 of said bracket being adapted to be secured to insulator 4, between the insulator and the integral base of break contact tongue l4, by bolts l5. Bolts 41 secure arc chute 31 to upright arm 46, said bolts also cooperating with bolts 44 in securing plates 38 together.

Each plate 38 is provided with a fan-shaped recess 55 to accommodate the swinging contact assembly 5|. Swinging contact assembly 5| 'is pivotally mounted on the central shaft portion of bolt 52. Bolt 52 is made from a conducting material, which may be a high conductivity, precipitation hardened copper-chromium alloy, and is preferably soldered to bracket arm 46, as with a lead-tin solder, where it passes through aperture 53 in arm 46, in order to provide a good electrical connection between these two parts. Swinging contact assembly 5| comprises (1) a pair of contact arms 54, which are made of a good electrical conducting material, such as hard drawn copper bar, (2) a pair of arcing tips 55, which are made of a conducting arc-resisting material, such as a copper-tungsten alloy, (one arcing tip being silver soldered, as with a silvercopper-zinc alloy, to the adjacent sides of each contact arm 54 near the outer ends thereof), (3) a torsion spring 58 and (4) a pair of fiat backup springs 65. The edges of abutting arcing tips 56 are tapered inwardly, and thereby serve as guides for the entry of auxiliary contact 20 when it engages said arcing tips prior to passing therebetween. Contact arms 54 are pivotally mounted on bolt 52 by apertures in said contact arms which receive the bolt. Flat backup springs 60, which may be made from any resilient material, such as a spring temper tin-bronze or a beryllium copper alloy which has been heat treated to a suitable spring temper, are also pivotally mounted by means of apertures therethrough, on the shaft portion of bolt 52. Spacing washers 62 serve to centrally locate swinging contact assembly 5| with respect to the width of the opening, delineated by recesses 50 in arc chute, 31. The described assembly of the swinging contact on bolt 52 is such that the backup springs 66 normally urge arcing tips 55 into abutting relationship with each other. Torsion spring 58 which is preferably, though not necessarily, designed so that it is substantially weaker in torsion than torsion spring 35, is wound around the shaft portion of bolt 52 ill the Space on said shaft between contact arms 5 -61, and has one end in engagement with :an edge 86 "of recess 50 and the other end looped over a pin 64 which passes through apertures in contact arms 54 and backup springs '68, said pin 64 also serving, by passing through said apertures in backup springs 60, to maintain the backup springs in alignment with the contact arms; and thus the spring 58 reacts to normally bias swinging contact assembly 5! against side 81 ofrecesses $9. The "inside diameter ofspacing washers 62 are ?'in press-fit relationship with the shaft of bolt 52 to provide good electrical contact therewith. Torsion spring 58 also acts "as a compression spring in that it biases con-v 'ta'ct arms 54 and backup springs '60 against their respective spacing washers 62, for good electrical contact therewith.

In the operation of the :switch, and assuming it is desired to open the circuit by moving the switch from the "closed circuit position shown in Fig. l, a hook stick "or other operating memher is inserted in hook eye t8, and main "blade I2 is pulled away from break contact tongue HI.

Auxiliary blade 2%} is initially prevented from "passing between arcing tips "56 by the action of the flat backup springs 65 upon the contact arms 54 in maintaining frictional engagement between the abutting faces of arcing tips 56. However, as the auxiliary blade 29 rotates on pivot bolt 26 and stresses spring 36, the said auxiliary blade simultaneously moves swinging contact assembly '51 so that it pivots around bolt 52 until restrained from further motion when the arcing tips 56 engage the edge 63 f recess 59. R0- tation of the auxiliary blade '29 on pivot bolt 1 continues until main switch blade i2 is separated a substantial distance from break contact tongue H, and the side 18 of notch 32 engages stop :screw 34, whereupon continued opening move- .ment of main switch blade l2 causes auxiliary blade 26 to pass between the abutting faces of arcing tips 56 and upon passage therethrough, escape frictional engagement therefrom. Fig. 2 shows the positions of auxiliary blade 26 and swinging contact assembly 5! shortly before a circuit interruption, with the auxiliary blade 20 shown as having moved, by engagement with the arcing tips 55, the swinging contact assembly 5i to the edge 58 of recess '50. Further opening movement of switch blade I2 causes auxiliary blade 28, as pointed out above, to pass between the abutting faces of arcing tips 56. As soon as auxiliary blade 2-8 escapes frictional engagement with the abutting faces of arcing tips 56, the spring 36 of the auxiliary blade 26 acts to rapidly move the auxiliary blade relative to main blade 12 in a pivotal manner about bolt 26 to restore it to the relative position with the main blade shown in Fig. '1, where it lies alongside the main blade. As auxiliary blade 20 escapes engagement with the arcing tips 58, the torsion spring 58 of the swinging contact assembly '5! acts to rapidly return the swinging contact assembly to its normal closed circuit position of bias against edge '6! of recess 5i).

The are extinguishing act-ion of the circuit interrupter described is due (1) to the rapid elongation of the are by the snap movements of auxiliary blade 2!! and of swinging contact assembly 5! in substantially opposite directions, which rapidly increases the arc voltage; (2) to physical confinement of the arc in the narrow space between the arc chute plates 38; and finally, 3) to the action of arc-extinguishing gas evolved from the material of plates '38 if the latter, be of gas evolving material, which acts to supply a blast of un-ionized gas through the chute and out the open sides of arc chute 31 to further increase the resistance of the arc 'path at current zero by replacing'the ionized particles in the arc path by the un-ionized particles of the evolved :gas. These several arc extinguishing actions jointly produce extremely efficient arc-extinguishing action. The space or slot defined between arc chute plates 38 is made as smallas possible, being limited only by the thick- :ness of auxiliary blade 20 and, with respect to the recess 50, being limited by the thickness of swinging contact assembly 5|.

"Ilhis "invention provides an arc extinguishing action superior to that of the switch disclosed in the above mentioned Rawlins Patent 2,308,206

because of the snap movements of both of the interrupting contacts in substantially opposite directions; which movements continuously change the location of both, rather than only -one, 'of the end point locations of the arc during the entire arc extinction period and "thereby reduce the stability of the arc. Continuously changing both end point locations of the arc during the arc extinction period results in exposing the arc to continuously different parts of the gas evolving material of the plates 38 thus exposes the arc to a greater volume of cooler gas than is possible where only one of the arc end point locations is changed during the arc extinction period. This greater volume of cooler gas is eifective to more rapidly increase the arc voltage and hence is more e'fiective in extin uishing the arc.

After the circuit has been opened in the manner described above and it is desired to close the switch, -main blade [2 is rotated in the opposite 'or clockwise direction about its pivot bolt l0 by means of hook eye 18, and this carries auxiliary blade '28 along with it into arc chute 31. Further movement causes main blade I2 and auxiliary blade 20 to engage their respective contacts until the .fully closed position shown in Fig. '1 is attain'ed.

When the switch is closed, the main current path is through break contact tongue 14 and main blade 12. When the circuit is opened and main blade 12 has just been pulled away from break contact tongue I4, the current path may then largely be traced through ('1) the base portion 48 "and upright arm "46 of the angled supporting bracket, (2) the bolt 52, (3) the spacing washers 62, (4) the back up springs 68, (5) the contact arms 54, (6) the arcing tips 56, (7) the auxiliary blade '28, and (8) the main blade I2. The latter current path is in parallel circuit relationship with the main current path when the switch is closed; accordingly, the circuit is required to be interrupted in the arc chute when the main current path is opened.

Each time the circuit is opened, the action of the arc on the gas evolving plates 38 of the arc chute 31 has an eroding effect thereon, so that the width of the slot in which the arc is drawn is very slightly increased. Such erosion of course, increases with the value of the current interrupted and with the length of time the arc is maintained. In a switch constructed without the use "of this invention but employing a stationary interrupting contact in the arc chute, tests have shown that such erosion is very much greater at a point closely adjacent the point of initial contact separation than elsewhere, so much so that erosion at a point an inch or more away from such point of initial contact separation is comparativelynegligible. Erosion is most severe at the point of initial contact separation because at that point the arc is relatively stationary, whereas over the remainder of its length,

the arc is in continuous erratic motion. With such a switch not using this invention, it is possible to interrupt a given value of current at a given voltage very efiectively at the end of the first half cycle, when the arc chute is new. However, after 100 or more operations at the same current and voltage, the chute will show erosion of from one-eighth to one-fourth of an inch, in depth over a roughly circular area about onehalf of an inch in diameter radiating from the point of contact separation. Moreover, after this number of operations, the arc during interruption will continue, for as many as four to six half cycles due to the decrease in efiectiveness of the arc extinguishing action resulting from widening of the arc chute, with a resulting erosion five to ten times that occurring when the chute is new. This becomes progressively worse as the number of operations is increased, and eventually reaches a point where the arc is not extinguished within the chute, but is drawn outside the chute, resulting in a fiashover and failure. My invention greatly reduces the foregoing diificulty and greatly increases the effective life of an arc chute by providing swinging contact assembly instead of a normally stationary con-- tact located within the arc chute, which contact assembly moves rapidly and continuously during the entire period required for are extinction and is effective thereby to distribute the erosive action of the arc over a comparatively largearea. In other words, I replace a stationary contact with its attendant local erosion of the arc chute, with a moving contact which distributes the erosion of the arc chute over a much greater area. Figure 4 shows generally how the erosive effect of the arc is widely and uniformly distributed in a switch employing this invention. As contrasted with this an arc chute having a stationary contact would exhibit, as above mentioned, erosion confined to and concentrated in a roughly circular area about onehalf of an inch in diameter radiating from the point of initial contact separation.

Having described a preferred embodiment of the invention in accordance with the patent statutes, it is desired that this invention should not be limited to the particular embodiment of circuit interrupter disclosed, because it will be obvious, particularly to persons skilled in the art, that many modifications and changes may be made therein, and that the invention is adapted for use with other types of circuit interrupters. Accordingly, it is desired that the invention be interpreted as broadly as possible in accordance with the following claims.

I claim as my invention:

1. A circuit interrupter including means of insulating material defining opposed inner wall portions of a narrow slot arc passage, said material of at least one inner wall portion being capable of evolving an arc-extinguishing gas when in proximity to an electric arc to aid in extinguishing the arc, a pair of separable contacts when in engagement being located in said are passage, each of said contacts being pivotally mounted on separate spaced axes for pivotal movement in different directions upon separation of the contacts, said pivotal axes being disn posed on opposite sides of the pointof separa-3 tion of said contacts, respectively, and means for separating said contacts in said are passage and causing simultaneous movement of said contacts in the aforesaid different directions through the arc passage.

2. A circuit interrupter including means of insulating material defining opposed inner wall portions of a narrow slot arc passage, said material of at least one inner wall portion being capable of evolving an arc-extinguishing gas when in proximity to an electric arc to aid in extinguishing the arc, a pair of separable contacts when in engagement being located in said slot arc passage, each of said contacts being mounted to move in different directions upon separation of the contacts, one of said contacts being mounted so that its path of movement intersects only the first part of the path of the circuit opening movement of the other of said contacts and at the closed circuit position is located aheadpf said other contact, means for moving said other contact so that it moves said one contact,during the aforesaid first part of a circuit opening operation and then disengages it, and means biasing said one contact to return to move it in the opposite direction upon disengagement from the other contact.

3. A circuit interrupter including means of insulating material defining opposed inner wall portions of a narrow slot arc passage, said material of at least one inner wall portion being capable of evolving an arc extinguishing gas when in proximity to an electric arc to aid in extinguishing the arc, first and second separable contacts when in engagement being located in said slot arc passage, each of said contacts being pivotally mounted to move in diiferent directions upon separation of said contacts, said pivotal mountings being disposed on opposite sides of the point of separation of said contacts and said first contact being positioned in the path of circuit opening movement of said second contact and having its path of movement intersecting only the first part of the circuit opening path of movement of the second contact, and, means for moving said Second contact during a circuit opening operation in a circuit opening direction, said means including a stop portion engageable by said first contact during its circuit openin movement for limiting the movement of said first contact by said second contact.

4. A switch comprising a support, a disconnect contact, are passage means and a first interrupting contact all mounted in proximity on said support, with said first interrupting contact mounted fOr limited pivotal movement within said passage means and electrically connected with said disconnect contact, a switch blade mounted for movement on said support into and out of engagement with said disconnect contact, a second interrupting contact pivotally mounted on said blade for movement to and away from said passage and through said passage into and out of engagement with said first interrupting contact, said arc passage means including spaced walls defining an arc passage therebetween at least when an arc is struck in said passage, the space between said walls. being relatively small so that said walls will be in close proximity to arcs struck upon separation of said interrupting contacts, at least inner surfaces of said walls being of an insulating material and at least one inner wall of said passage comprising at least in part insulating means which is capable of evolving an arc-extinguishing gas when in proximity to an electric are, said first interrupting contact being positioned in the first part of the path of the circuit opening movement of said second interrupting contact, means responsive to circuit opening movement of said blade for causing pivotal movement of said second interrupting contact which in turn moves said first interrupting contact during the first part of a circuit opening operation, and thereafter said interrupting contacts separate, and means responsive to such separation of the interrupting contacts to cause pivotal movement thereof in opposite directions with a snap action irrespective of the rate of circuit opening movement of said blade.

5. A switch comprising a support, a disconnect contact, are passage means and a first interrupting contact all mounted in proximity on said support, with said first interrupting contact being limited' y movably mounted within said passage means and electrically connected with said disconnect contact, a switch blade mounted for movement on said support into and out of engagement with said disconnect contact, a second interrupting contact limitedly pivotally mounted on said blade for movement therewith to and away from said passage and through said passage into and out of engagement with said first interrupting contact, said are passage means including spaced walls defining an arc passage therebetween at least when an arc is struck in said passage, the space between said wal s being relatively small so that said walls will be in close proximity to arcs struck upon 1 separation of said interruptin contacts, at least inner surfaces of said walls being of an insulating material and at least one inner wall of said passage comprising at least in part insulating means which is capable of evolving an arc-extinguishing gas when in proximity to an electric arc, said first and said second interrupting contacts each being mounted to move in different directions upon separation of the contacts, means biasing said interrupting contacts to normal positions, said first interrupting contact being positioned in the first part of the path of the circuit opening movement of said second interrupting contact so as to be moved by said second interrupting contact during circuit opening movement of said blade up to a predetermined limit while its biasing means is stressed and at the same time said second interrupting contact moves pivotally relative to the blade while stressing its biasing means, and both of said interrupting contacts being returned to their normal positions with a snap action by their respective biasing means after the separation of said interrupting contacts, and means for moving said switch blade and said second interrupting contact during a circuit opening operation in a circuit opening direction 6. A switch comprising a support, a disconnect contact, are passage means and a first interrupting contact all mounted in proximity on said support, with said first interrupting conill) 10 tact being mounted for limited pivotal movement within said passage means and electrically connected with said disconnect contact, a switch badc mounted. for movement on said support into and out of engagement with said disconnect contact, a second interrupting contact lim itedly pivotally mounted on said blade for movement therewith to and away from said passage and through said passage into and out of engagement with said first interrupting contact, said passagemeans including spaced walls defining an arc passage therebetwee-n at least when an arc. is struck in said passage, the space between said walls being relatively small so that said. walls will be in close proximity to arcs struck upon separation of said interrupting contacts, at least inner surfaces of said walls being of an insulating material and at least one inner wall of said passage comprising at least in part insulating means which is capable of evolving an arc-extinguishing gas when in proximity to an electric arc, said pivotal mounting of said first interrupting contact being arranged to permit said first interrupting contact to move in a direction different than that of said second interrupting contact upon separation of the contacts, with said pivotal mountings of said interrupting contacts being disposed on opposite sides of the point of separation of said interrupting contacts, means biasing said interrupting contacts to normal positions, said first interrupting contact being positioned in the first part of the path of the circuit opening movement of said second interrupting contact so as to be moved by said second interrupting contact during circuit opening movement of said blade up to a predetermined limit while its biasing means is stressed and at the same time said second interrupting contact moves pivotally relative to the blade while stressing its biasing means, and both of said interrupting contacts being returned to their normal positions with a snap action by their respective biasing means after the separation of said interrupting contacts, and means for moving said switch blade and said second interruptin contact during a circuit opening operation in a circuit opening direction.

HOWARD W. GRAYBILL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 477,374 Klein June 21, 1892 681,112 Dolier Aug. 20, 1901 1,026,296 Badeau May 14, 1912 2,239,224 Goldner Apr. 22, 1941 2,308,026 Rawlins Jan. 12, 1943 2,404,957 Graybill July 30, 1946 FOREIGN PATENTS Number Country Date 690,910 Germany May 10, 1940

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