US2032149A - Circuit interrupter - Google Patents

Description

Feb. 25, 1936.

H. L. RAWLINS CIRCUIT INTERRUPTER Filed Sept. 13, 1934 2 Sheets-Sheet l 5 2 i F M 3 l E 3 2 M a z 3 33 {A f INVENTOR Her-672 L. EawZz'rzs ATTORNEY WITNESSES I H. L. RAWLINS 2,032,149

CIRCUIT INTERRUPTER Filed Sept. 13, 1934 2 Sheets-Sheef 2 Maynef/c Ma/er/a/ Feb. 25, 1936.

f/erberz L. PawZz'n s.

ATTO R N E Patented Feb. 25, 1936 CIRCUIT INTERBUPTER Herbert L. Rawlins, Wilklnsburg, Pat, assignor to Westinghouse Electric is Manufacturing Company, East Pittsburgh, Pa a. corporation of Pennsylvania Application September is, 1934, Serial No. 743,845

25 Claims.

My invention relates generally to circuit interrupters and particularly to circuit breakers wherein the arc which is established incident to the opening of the controlled circuit is extinguished by the action of an expulsive blast of arc extinguishing gas. Y

Devices of this type are generally used for protecting network distribution systems, and in this service they are subjected to very exacting and somewhat conflicting operational requirements. One of these requirements is the almost imperative necessity that the devices shall be capable of efficiently extinguishing arcs of both large and small magnitude currents. This arises from the fact that the normal overload currents which flow in the ordinary network distribution system are usually of relatively small current magnitude, while the short circuit currents may reach a very large magnitude: Despite this necessity for eilicient operation over a wide range of current values, commercially successful devices must be relatively inexpensive both in first cost and in maintenance cost, due to the large numbers which are used on even a small distribution system. The devices must, of course, be absolutely reliable in operation, and it is desirable that they shall not utilize an inflammable liquid for extinguishing the arc formed during a switching operation in order that the fire hazard shall be minimized.

The principal object of my invention, therefore, is to provide an improved circuit interrupter of the expulsion type which shall be simple in design, reliable in operation, and inexpensive to manufacture and tc service.

A further object of my invention is to provide a circuit interrupting device of the above-mentioned type which shall utilize a minimum of moving parts, and which shall eiTect the extinguishment of the arc which is established.in--

cident to the opening of the controlled circuit by means of a blast of arc extinguishing gas, which is evolved from a solid material positioned adjacent the arc path.

The principal field for immediate application of my invention is in conjunction with expulsion circuit interrupting devices which utilize a partially enclosed arc passage that is lined with a solid material for evolving arc extinguishing gas during the circuit interrupting operation. The eiilciency oi. operation of these devicesdepend to a large extent upon the intimacy of contact which is achieved during the circuit interrupting operation between the arc and the gas evolving walls of the arcpassage. At first glance, it

might appear that this necessity for securing intimate contact between the arc and the gas evolving lining of the arc passage would prevent no particular difllculties, since the arc passage could .be made small enough to assure lnti mate contact between the walls thereof and the are for the lowest current magnitude arcs which the device would ordinarily be called upon to interrupt.

Unfortunately, however, the problem is not so simply solved, since it is possible to make the cross sectional area of the arc passage too small, in which case, the volume of gas generated may be sufilciently large to cause an actual rupture oi. the walls of the device, due to the pressure formed therein. It has been demonstrated in the prior art structures that a satisfactory device, which is capable of interrupting arcs of widely varying current magnitude, must utilize a plurality of arc passages. For most presentday circuits, two passages have been found sumcient, one of relatively small cross-sectional area for interrupting the low magnitude arcs and one of somewhat larger cross-sectional area for interrupting the higher magnitude arcs.

When a plurality of arc passages is used, it is necessary to provide means for assuring that the arc shall be drawn within that passage which is best suited for effecting its extinguishment, because if small current magnitude arcs are drawn within the arc passage which is capable of interrupting large current magnitude arcs, it is probable that insufllcient gas will be evolved to effect the extinguishment of that arc, and the circuit may never be interrupted at all.

Various arrangements have been proposed for assuring that thearc will be established in the proper passage, but few of these have been as simple and as rugged as might be desired, and it is a further object of my invention to provide a simple means for use with circuit interrupters having a plurality of arc passages, one of which is of greater are interrupting capacity than the other, for assuring that the arc shall be drawn within that passage which is best suited for effecting its extlnguishment.

It is a still further obiect of my invention to eliminate any necessity for causing the arc to transfer from one passage to the other during the operation of the device the are drawing means of my invention to be responsive to the current flowing in the circuit controlled by the interrupter in order that only one are shall be drawn during the circuit interrupting operation, and that that are shall be drawn in the proper passage.

In .the following description of one embodiment of my invention, I have described how my. invention may be applied to a dry-type expulsion circuit interrupter which utilizes a pair of arc passages. It is obvious, of course, that the broad principles disclosed may be applied to numerous other structures, and it is my intention that my invention shall be limited only by what is exthe line III--III of Fig. 2;

Fig. 4 is a fragmentary perspective view showing the details of the contact structure of the device shown in Figs. 1 and 2;

Fig. 5 is a sectional view of a modified form of the circuit interrupter shown in Figs. 1 and 2;

Fig. 6 is an elevational view of the circuit interrupting device shown in Fig. 5; i

Fig. 7 is an enlarged sectional view taken on the line VII-'V'II of Fig. 5;

Fig. 8 is a fragmentary perspective view of the contact structure for the circuit interrupter shown in Figs. 5 through 7;

Fig. 9 is a fragmentary sectional view on the line IX-IX of Fig. 8;

Fig. 10 is an enlarged fragmentary sectional view on the line X-X of Fig. 5.

Fig. 11 is a modified sectional view of an arc extinguisher similar to that used in conjunction withv the circuit breaker shown in Figs. 1 through 4; and

Fig. 12 is a sectional view taken on the line XII-XII of Fig. 11.

Essentially, the preferred circuit breaker of my invention comprises a pair of stationary contact structures 3, a, movable contact structure 5, an actuating means I for moving the contacts to the open and closed circuit position, 'and a support frame I upon which the several parts of the breaker are mounted. The interrupter is of the double-break type and is provided with a suitable arc extinguishing device 9 for each of the two breaks. These are extinguishing devices include means for producing an expulsive blast of gas which is adapted to flow longitudinally through the arc during the circuit interrupting operation to eifect its extinguishment.

The frame I, as is shown particularly in Fig. 1, is provided with a guide portion II for supporting the rod member |2 which is afiixed to the movable armature |3 of the operating solenoid. This armature I3 is normally biased to the open circuit position by means of a suitable spring I5 and is held in the closed circuit position by the solenoid coil I! which may be energized by any suitable means. The right-hand end of the rod member I2 is adapted to engage the knee of a pair oftoggle links 9 and 2| which constitute the operating linkage for the breaker. The lower end of this linkage is pivotally supported on the frame I, and the upper end engages a suitable push rod 23 which in turn is aflixed to the movable contact structure 5. The motion of the rod pressly set forth in the claims and by the prior 23 is defined by a suitable guiding means 25 forming a part of the frame.

The movable contact structure 5 comprises generally a main frame member 21 of conducting material upon which are supported the two main contact rods 29 and the auxiliary contact assemblage 3|. The assemblage 3| includes two contact rods 32 and engages the frame member 21 through a lost motion connection which comprises a pair of bolt members 33, for limiting the amount of lost motion between main frame 2! and the auxiliary contact assemblage 3|, a pair of springs 35 for biasing the auxiliary contact assemblage 3| away from the main frame 21 of the contact structure, and a magnetic arrangement for rendering the lost motion connection ineffective upon the occurrence of certain predetermined conditions. This magnetic arrangement consists of a pair of U-shaped members 31 of magnetic material which are disposed about and rigidly affixed to the main frame 2'! of the contact structure and a pair of U-shaped members 39 of magnetic material which are similarly affixed. to the main bridging portion 4| of the auxiliary contact assemblage. It is apparent that these U-shaped pieces 31 and 39 of magnetic material will be attracted toward each other when the magnitude of the current flowing through the interrupter reaches avalue capable of producing sufficient magneto-motive force to overcome the action of the springs 35.

The main contact rods 29 and the auxiliary contact rods 32 are both adapted to move, during the normal operation of the breaker, within suitable arc passages 43 and 45, respectively, which are formed within the two are extinguishing devices 9. The stationary contact structure 3 for each of the two breaks of the device is supported upon the top of the cooperating arc extinguishing structures 9 and those structures in turn are supported upon the main breaker frame I.

Each of the stationary contact structures 3 includes a metal plate 41 which forms one of the terminals of the device, and a pivotally supported contact member 49 which is adapted to cooperate with one of the main contact rods 29. Springs 5| are provided for biasing these contact members 49 in the direction of the cooperating moving contact rods 29, in order to assure adequate contact pressure between the engaging contact surfaces of those members when the breaker is in the closed circuit position. The auxiliary contact rods 32 engage suitable holes 53 formed within the conducting plates 41 which comprise the terminals of the device. A molded member 55 of insulating material having two raised portions 51 for accommodating the pivotally mounted contact members 49 is rigidly affixed to the top of the two arc extinguishing devices 9 in order that the upper end of each of the arc passages 43 and 45 shall be closed during the circuit interrupting operation. This molded-member has a tie portion 59, likewise of insulating material, which extends across the top of the device in order to give the structure increased rigidity.

The are extinguishing devices 9 are exactiysimilar in construction and are built up of a plurality of circular plates 5|, each of which has four equally spaced openings I53 therein for accommodating the through bolts 55 which serve to hold the arc extinguishing devices together. In addition, each of the plates BI is provided with a pair of openings for defining the two are passages 43 and 45. The lower plate 51, which, similarly to the upper molded member 55, extends across both of the devices, is considerably thicker than the plates 6i which define the main portion of the arc passages. A suitable opening 59 is provided in the two contact plates 41 for defining a continuation of the larger of the two are passages 43 in order that the main contact rods 29 may extend therethrough while engaging the pivoted contact members 49. All of the centrally disposed plates Bi which define the walls of the arc passages 43 and 45 are preferably formed of fibre or some other material which is capable ofevolving an arc extinguishing gas when placed in proximity to an electric arc. This assures an adequate supply of arc extinguishing gas during the circuit interrupting operation.

The breaker is shown in the closed circuit position in Fig. 2. To open the circuit, the holding coil ll of the actuating solenoid is deenergized by some suitable means whereupon the spring i5 initiates the movement of the actuating toggle linkage toward the collapsed position. If the magnitude of the current flowing in the circuit controlled by the interrupter is incapable of producing sufficient magnetic energization of the two magnetic circuits formed by the U-shaped magnetic members 31 and 39 to overcome the biasing action of the springs 35, the initial portion of the opening movement is effective merely to move the main contact rods 29 out of engagement with the cooperating members 49 of the stationary contact structures 3. All of the electric current then flowing through the breaker is carried by the auxiliary contact rods 45, and as the opening operation progresses, an arc is established within each of the two are passages 45 wherein those rods move. These smaller arc passages 45 are so proportioned that they cause an intimate engagement of even low magnitude current arcs with the evolving walls thereof, and by virtue of the fact that they are closed at the upper end produce a blast of arc extinguishing gas which flows downwardly through the arc while venting. In the open circuit position, both the auxiliary and the main contact rods are completely out of engagement operation with the arc passages.

If the magnitude of the overload current is sufficientto cause the auxiliary contact assemblage 3i to be attracted to the frame 21 of the main contact members 29, the arcs which are estab- 'iished incident to the opening of the circuit controlled by the device will be initially established and subsequently drawn within the larger arc passages 43. These passages 43, while incapable of interrupting low magnitude arcs, are capable of interrupting large magnitude arcs with a high degree of efliciency. The gas evolved from the iining of both are passages during the circuit interrupting operation, must vent at the lower portion of the device, due to the enclosing of the upper end of each of the arc passages by the molded member 55.

It will thus be seen that I have provided a circuit interrupting device which is capable of eflicient operation over a wide range of current values. My improved interrupter comprises a. pair of arc passages, one of which is capable of interrupting large current magnitude arcs but is incapable of interrupting small current magnitude arcs, and the other of which is capable of interrupting small current arcs, and means wherebyonly one are is created during the circuit interrupting operation, that are being'initially established and subsequently drawn within the passage which is best suited for effecting its extinguishment.

The walls of the arc extinguishing devices 01' the interrupter described above are defined by a plurality of superposed plate sections. This, or course, is merely one of the arrangements which may be used. Figs. 11 and 12 illustrate a modifled structure which has also been found to be particularly effective for accomplishing the objects of my invention. This modified structure differs from the arrangement shown in Figs. 1 through 3 only in that it comprises a tubular outer member ii of considerable mechanical strength and a cylindrical inner member 13 which is formed of compressed boric acid, this inner member having a pair of cylindrical openings 15 and 11 therein for defining the walls of the two are passages. Compressed boric acid is a particularly satisfactory material for this use; it may readily be compressed into solid blocks of considerable physical strength, and in addition it evolves avery considerable quantity of water vapor, a particularly effective are extinguishing gas, when exposed to an electric arc. Boric acid has another advantage in that the surface thereof does not become conducting during the arc extinguishing operation. Further, the fact that the gas is entireiy inorganic in nature and noninfiammable adds much to the safety and reliability of operation of the device when this form of arc extinguishing structure is utilized.

The modified form of my invention which is shown in Figs. 5 to 10, inclusive, does not difier in its principles of operation from the structure shown in the other figures of the drawings. The device includes means for defining the walls of a pair of arc passages 8i and 83, one of which 8i is capable of interrupting arcs of large current magnitude but is incapable of interrupting arcs of small current magnitude, and the other of which 83 is capable of interrupting arcs of low current magnitude. The are passages are both of the so-cailed narrow-slot type, the structural features and operational characteristics of which have been rather completely described in the patent application of Joseph Slepian, Serial No. 715,817, which was filed on March 16, 1934 and which is assigned to the assignee of this invention.

This modified .form of my invention utilizes a.

lost motion connection between the are drawing means for the two are passages, and it likewise utilizes a magnetic means for rendering this lost motion connection inoperative upon the occur rence of certain predetermined conditions.

Referring more particularly to the drawings, it will be seen that this modified form of my invention comprises a base 85 of insulating material upon which the other structural features of the interrupter are supported, a pair of main stationary contact members 81, a bridging member 89 for completing the electrical circuit between the main stationary contact members, an are extinguishing device 9| which includes means for defining the two narrow slot arc passages BI and 83, auxiliary contact means 93 for drawing an arc in either of those passages, and an actuating means 95 for the are drawing contacts and the main bridging member 89. The main and the auxiliary moving contacts are supported upon link members 91 and99 which are pivotally fastened to the main supporting base I of the interrupter.

The actuating mechanism 95 is so arranged that the main bridging member 89 is always moved to the open circuit position before the electrical circuit through the auxiliary contacts parts in their proper relationship.

is broken. This means for accomplishing this consists essentially in a link member |0I (shown particularly in Fig. 10) which is provided with a slot I03 wherein the support link 99 for the auxiliary contact members moves, a suitable spring I05 being positioned within this slot I03 for biasing the auxiliary contacts into engagement with the cooperating stationary contact members therefor. The outer end of the link IOI pivotally engages an operating link I01 which is connected to the remainder of the actuating mechanism (not shown).

The auxiliary contact structure is shown particularly in Figs. 5, 8, and 9, and comprises in general a pair of hammer-shaped members I09 and III, one of which (I09) is considerably thicker than the other. The thicker of these two members is welded or otherwise rigidly affixed to the upper end of the auxiliary contact support link 99, and the thinner of the two members is pivotally supported upon the link 99 in order that it shall be relatively movable therewith. The limits of this relative motion is defined by a lost motion connection, as in the previously described structure.

The auxiliary contact members I09 and I I I are adapted to cooperate with L-shaped arc horns I I3 and H5 disposed within each of the two are passages 8| and 83 in order to complete the electrical circuit through the device. One of the arcing horns I I3 and one of the arcing horns I I5 is electrically connected to one of the stationary contacts 87 and the other of each of the two pairs of arcing horns H3 and II5 is electrically connected to the moving contact assemblage. Thus during the circuit interrupting operation the arc is established between one of the arcing horns within one of the arc passages within the arc extinguishing device and the cooperating moving contact I09 or I I I and is then transferred to the two arcing horns within that passage. The arcing horns H3 and H5 are so shaped that the arc is moved by virtue of the magnetic reactions set up therein.

The are extinguishing device 9| is shown particularly in Figs. 5 and 7 and includes a pair of fiat members II! of insulating material for defining the outer walls thereof, and a. centrally disposed member H8, likewise of insulating material, for defining an inner wall which is com-.- mon to both of the two are passages 8| and 83. Spaced members 9 of insulating material and bolts |2| are provided for assembling the various It will be seen that both of the arc passages 8| and 83 comprise narrow slots, the dimensions of which are defined by a pair of substantially parallel wall members of considerable surface area. 4

Both of the arc passages 8| and 83 are lined with a plurality of members I23 of a solid material which is capable of evolving an are extinguishing gas when placed in proximity to an electric arc. These members are shaped and disposed like tile and are cemented or otherwise rigidly affixed to the wall defining members I I7 and H8 and are preferably of compressedboric acid. During the operation of the breaker they serve to provide a blast of arc extinguishing gas for extinguishing the arc formed incident to the opening of the controlled circuit.

The arc passage 83 is considerably narrower than the other passage 8| in order that that passage shall be capable of extinguishing arcs of small current magnitude. The other are passage 8| is particularly adapted for extinguishing arcs of large current magnitude and is, in fact, incapable of extinguishing arcs of small current magnitude, due to its inability to effect an intimate contact between the arc and the gas evolving lining thereof.

In order that the low current magnitude arcs shall be drawn only within the smaller capacity are passages 83, a lost motion connection is provided between the main actuating link 99 for the are drawing means and the narrower of the two arc drawing members. This lost motion connection is shown particularly in Figs. 8 and 9, and comprises a U-shaped member I25 of magnetic material rigidly affixed to the wider arc drawing member I09 (the one which is in turn rigidly affixed to the actuating link 99 for the are drawing contact structure), an armature member I2? likewise of magnetic material rigidly aifixed to the narrower arc drawing members III, a bolt I 29 for limiting the'relative motion of the two arc drawing members, and a spring I3I for biasing the narrower member III away from the wider member I 09 in the direction of the cooperating arcing horn I I 5. By this arrangement, the circuit is always finally interrupted, and the arc incident to that interruption, is always initially drawn within the narrower arc passage 83 unless the current magnitude is sufiiciently largev to cause the arc drawing members I09 and III to move as a unit, in which case it is drawn within the wider arc passage M.

The operation of this modified form of my invention is practically identical with the operation of the previously described embodiment. As the operating mechanism moves the main actuating link I01 toward the open circuit position, the bridging member 89 is moved out of engagement with the cooperating stationary contact members 81, and all of the current flowing through the device is then caused to fiow through the auxiliary contact structure. If the current magnitude is low, the thicker auxiliary contact member I09 is next moved out of engagement with its cooperating arcing horn I I3, and subsequently, the time depending upon the amount of lost motion in the lost motion connection, the auxiliary contact I disengages its cooperating arcing horn I I5 and causes the arc incident to the opening of the control circuit to be drawn within the narrower arc passage 83.

Shortly thereafter, the end of the arc which has previously existed upon the narrow contact member I is transferred to the other arcing horn 5, that horn being electrically connected to the moving contact structure, as illustrated diagrammatically in Fig. 5. The arrangement of the arcing horns is such that the arc is moved upwardly within the narrow slot passage 83 by the magnetic reactions set up, and by virtue of the intimate engagement produced between the arc and the lining members I23 of the passage, a large quantity of vapor is evolved. This vapor in venting flows outwardly through the arc in a lateral direction and efiects its extinguishment within a very short period of time.

If the current magnitude in the controlled cir- Y by being caused to flow through the arc in venting 'eii'ects the extinction thereof within a very short period of time, usually at the next zero point in the current wave' if an alternating cur rent arc is being interrupted.

In the foregoing, I have described how my invention may be applied to two particular forms of dry-type circuit interrupting devices which utilize a plurality of arc passages of different are extinguishing capacity for extending the eifective range over which such devices may be used. I have shown how a simple structure which utilizes a lost motion connection and a magnetic means responsive to the current flowing in the controlled circuit for rendering that connection inoperative upon the occurrence of predetermined conditions may be utilized for assuring that the arc incident to the opening of the controlled circuit shall be established within that are passage which is best suited for efiecting its extinguishment. The advantagesoi this arrangement in simplicity and in making possible .a more reliable and less expensive deviceare obvious.

Moreover, I have shown how the features of my invention may be readily applied to certain existing forms of circuit interrupting devices, thereby effecting a considerable improvement in the operational characteristics thereof. In addition, I have disclosed certain preferred structural arrangements which are particularly suitable for carrying out the objects of my invention.

It will be apparent to those skilled in the art that numerous modifications of my invention will be possible without departing from the broad features thereof, audit is my desire that the language of the accompanying claims shall be accorded the broadest reasonable construction. For example, it is my wish that these claims should cover devices wherein only a single arc extinguishing device is used, and devices which utilize a liquid for securing the blast oi are extinguishing gas during a circuit interrupting operation.

I claim as my invention:

1.In a device for interrupting an electrical circuit; means for defining the walls of a pair of arc passages; one of said are passages being capable of extinguishing arcs of large current magnitude but being incapable of extinguishing arcs of small current magnitude, and the other of said passages being capable of extinguishing arcs of small current magnitude; and electro-responsive' means for causing the are which is established incident to the opening of said circuit by said interrupter to be initiated and then drawn only within that passage which is best suited for effecting its extinguishment.

2. In a device for interrupting an electrical circuit; means for defining the walls of a pair of arc passages; one of said are passages being capable of extinguishing arcs of large current magnitude but being incapable of extinguishing arcs of small current magnitude, and the other of said passages being capable oi extinguishing arcs of small current magnitude; and means for drawing the are which is established incident to the opening of the circuit controlled by said device within only one of said passages, said are passages; one of said arc passages being capable of extinguishing arcs of large current magnitude but being incapable of extinguishing arcs of small current magnitude, and the other of said passages being capable of extinguishing arcs of small current magnitude; and means for drawing the are which is established incident to the opening of the circuit controlled by said device within only one of said passages; said are drawing means including conducting means movable through each of said passages during the circuit opening operation, means for actuating said conducting means, and magnetic means responsive to the current flowing in the circuit controlled by said device for causing arcs of large current magnitude to be initially drawn within said passage of large arc interrupting capmity and for causing arcs of small current magnitude to be initially drawn within said passage which is capable of extinguishing arcs of small current magnitude.

4. a device for interrupting an electrical circuit; means of a solid material which is capable of evolving an arc extinguishing gas when placed in proximity to an electric arc for defining the walls of a pair of arc passages; one of said passages being so proportioned that it is capable of extinguishing arcs of large current magnitude but is incapable of extinguishing arcs of small current magnitude, the other of said passages being capable of extinguishing arcs of small current magnitude; and electro-responsive means for causing the are which is established incident to the opening of said circuit by said device to be established only within that passage which is best suited for efiecting its extinguishment.

5. In a device for interrupting an electrical circuit; means of a solid material which is capable of evolving an arc extinguishing gas when placed in proximity to an electric arc for defining the walls of a pair of arc passages; one of said passages being so proportioned that it is capable of extinguishing arcs of large current magnitude but is incapable of extinguishing arcs of small current magnitude, the other of said passages being capable of extinguishing arcs of small current magnitude; and means for causing the arc which is established incident to the opening of the circuit controlled by said device to be drawn within only one of said passages; said are drawing means including conducting means movable through each of said passages duringthe circuit opening operation and magnetic means responsive to the current flowing through the circuit controlled by said device for assuring that said arc is initially established and is drawn only within that passage which is best suited for effecting its extinguishment.

6. In a device for interrupting an electrical circuit, means defining a pair of arc passages, actuating means for said device, and means whereby the arc which is established incident to the opening of the circuit controlled by said device is initially drawn within one of said passages provided that the magnitude of the current flowing in the circuit controlled by said device does not exceed a predetermined value and is initially drawn within the other of said passages if the magnitude of said current exceeds said predetermined value.

7. In a device for interrupting an electrical circuit, means defining a pair of arc passages of different are interrupting capacity, conducting means movable through each of said passages during the operation oi said device, a single actuating means for said conducting means, and means whereby the are which is established incident to the opening of the circuit controlled by said device is initially drawn within one of said passages provided that the magnitude of the current flowing in the circuit controlled by said device does not exceed a predetermined value, and is initially drawn within the other of said passages if the magnitude of said current exceeds said predetermined value.

8. In a device for interrupting an electrical circuit, means defining a pair of arc passages of different arc interrupting capacity, conducting means movable through each of said passages during the operation of said device, a single actuating means for said conducting means, and magnetic means responsive to the current flowing in the circuit controlled by said device for causing the are which is established incident to the opening of said circuit to be initially established and subsequently drawn within the arc passage of lesser arc interrupting capacity provided that the magnitude of said current does not exceed a predetermined value, and if the magnitude of said current does exceed said predetermined value to cause said are to-be initially established and subsequently drawn within the arc passage of greater are interrupting capacity.

9. In an expulsion device for interrupting an electrical circuit, means defining the walls of a pair of arc passages, at least a portion of the inner surfaces of said wall defining means being lined with a solid material that is capable of evolving an arc extinguishing gas when exposed to an electric are; means for closing one end of said are passages during the circuit interrupting operation, the other end of said passages being open during the circuit interrupting operation; actuating means for said device; and means whereby the are which is established incident to the opening of the circuit controlled by said device is initially drawn within one of said passages provided that the magnitude of the current flowing in the circuit controlled by said device does not exceed a predetermined value, and is initially drawn within the other of said passages if the magnitude of said current exceeds said predetermined value.

10. In an expulsion device for interrupting an electrical circuit, means defining the walls of a pair of arc passages of difiering arc interrupting capacities, at least a portion of the inner surfaces of said wall defining means being lined with a solid material that is capable of evolving an arc extinguishing gas when placed in proximity to an electric a3; means for closing one end of each of said are passages during the circuit interrupting operation, the other end of said passages being open during the circuit interrupting operation; and electro-responsive means for causing the are which is established incident to the opening of said circuit by said device to be initially established only within that passage which is best suited for effecting its extinguishment.

11. In an expulsion device for interrupting an electrical circuit, means defining the walls of a pair of arc passages of difi'ering arc interrupting capacities, at least a portion of the inner surfaces of said wall defining means being lined with a .solid material that is capable of evolving an arc extinguishing gas when placed in proximity to an electric are; means for closing one end of each of said are passages during the circuit interrupting operation, the other end of said passages being open during the circuit interrupting operation; and magnetic means responsive to the current flowing in the circuit controlled by said device for causing the arc which is established incident to the opening of said circuit to be initially established and subsequently drawn within the arc passage of lesser arc interrupting capacity provided that the magnitude of said current does not exceed a predetermined value, and if the magnitude of said current does exceed said predetermined value to cause said are to be initially established and subsequently drawn within the arc passage of greater are interrupting capacity.

12. In a device for interrupting an electrical circuit; means for defining the walls of a pair of arc passages; one of said arc passages being capable of extinguishing arcs of large current magnitude but being incapable of extinguishing arcs of small current magnitude, and the other of said passages being capable of extinguishing arcs of small current magnitude; at least a portion of each of said are passages being lined with a solid material consisting chiefly of boric acid, and electro-responsive means for causing the arc which is established incident to the opening of said circuit by said interrupter to be initiated and then drawn only within that passage which is best suited for eiiecting its extinguishment.

13. In a device for interrupting an electrical circuit; means for defining the walls of a pair of arc passages; one of said arc passages being capable of extinguishing arcs of large current magnitude but being incapable of extinguishing arcs of small current magnitude, and the other of said passages, being capable of extinguishing arcs of small current magnitude; at least a portion of each of said arc passages being lined with a solid material consisting chiefly of boric acid; and means for drawing the are which is established incident to the opening of the circuit controlled by said device within only one of said passages, said are drawing means including conducting means movable through each of said passages during the circuit opening operation, means for actuating said conducting means, and magnetic means responsive to the current flowing in the circuit controlled by said device for causing arcs of large current magnitude to be initially drawn within said passage of large are interrupting capacity and for causing arcs of small current magnitude to be initially drawn within said passage which is capable of extinguishing arcs of small current magnitude.

14. In a device for interrupting an electrical circuit; means for defining the walls of a pair of arc passages; one of said arc passages being capable of extinguishing arcs of large current magnitude but being incapable of extinguishing arcs of small current magnitude, and the other of said passages being capable of extinguishing arcs of small current magnitude; at least a portion of each of said are passages being lined with a solid material consisting chiefly of boric acid; and means for causing the arc which is established incident to the opening of the circuit controlled by said device to be drawn within only one of said passages; said are drawing means including conducting means movable through each of said passages during the circuit Opening operation, and magnetic means responsive to the current flowing through the circuit controlled by said device for assuring that said are is initially established and is drawn only within that pas- 7 said are to be established within that passage which is best suited for effecting its extinguishment.

16. In a circuit interrupter, means defining a plurality of wall members of considerable surface area, meansfor spacing said wall members in proximity to each other to define the opposed walls of a pair of narrow arc passages, at least a portion of each of said are passages being lined with a solid material that is capable of evolving an arc extinguishing gas when placed in proximity to an electrical are, one of said are passages having a greater arc interrupting capacity than the other of said passages, separable contact means for opening and for closing the electrical circuit through said interrupter, and electroresponsive means for causing the are which is established incident to' the separation of said separable contact means to be established within that passage best suited for effecting its extinguishment.

17. In a circuit interrupter, means defining a plurality of 'wall members of considerable surface area, means for spacing said wall members in proximity to each other to define the opposed walls of a pair of narrow arc passages, one of said are passages having a greater are interrupting capacity than the other, means for drawing the are which is established incident to' the opening iof the circuit controlled by said device within only one of said passages, said are drawing means including conducting means movable through each of said passages, and magnetically responsive means for so controlling the movement of said conducting means that said are is initially established in that passage which is best, suited for efi'ecting its extinguishment.

18. In a circuit interrupter, means defining a plurality of wall members of considerable surface area, means for spacing said wall members in proximity to each other to define the opposed walls of a pair of narrow arc passages, one, of said arc passages having a greater arc interrupting capacity than the other, and means for drawing the arc which is established incident to the opening of the circuit controlled by said device within only one of said passages, said arc drawing means including conducting means movable through each of said passages during the circuit opening operation, means for actuating said conducting means, and magnetic means responsive to the current flowing in the circuit controlled by said device for causing arcs of large current magnitude to be initially drawn within said passage of large arc interrupting capacity and for causing arcs of small current magnitude to be initially drawn within said passage which is capable of extinguishing arcs of small current magnitude.

19. In a device for interrupting an electrical circuit, means defining a pair of arc passages, conducting means movable in one of said passages, a second conducting means movable in the other of said passages, a single actuating means for said conducting means, a lost motion mechanical connection between one of said conducting means and said actuating means, and means responsive to the current fiowing in the circuit controlled by said device for rendering said lost motion connection inoperative upon the occurrence of predetermined conditions, the arc which is formed incident to the opening of the circuit controlled by said device being initially established and extinguished within one of said passages when said lost motion connection is operative, and being initially established and extinguished within the other of said passages when said lost motion connection is rendered inoperative.

20. In a device for interrupting an electrical .circuit, means comprising a plurality of superposed plates at least some of which are of insulating material for defining the walls of a pair of arc passages of different are interrupting capacity, and means for causing the are which is formed incident to the opening of the circuit controlled by said device to be initiated and then drawn only within that passage which is best suited for effecting its extinguishment.

21. In a device for interrupting an electrical circuit, means comprising a stack of superposed plates for defining the walls a pair of arc passages of different arc interrupting capacity, at least some of said plates being formed of a material which is capable of evolving an arc extinguishing gas when exposed to an electric arc, and means for causing the are which is formed incident to the opening of the circuit controlled by said device to be initiated and then drawn only within that passage which is best suited for efiecting its extinguishment.

22. In electrical circuit interrupting apparatus, a pair of circuit interrupting devices of different are extinguishing capacities, each of which is movable to an open and to a closed circuit position, means for electrically connecting said devices in parallel, actuating means for said apparatus, which means causes both of said devices to move to the open circuit position during each circuit interrupting operation of said-apparatus, and magnetic meansfor controlling the sequence of operation of said devices so that the electrical 'circuit through said apparatus shall always be opened by the device best suited for extinguishv ing the are formed incident thereto.

23. In electrical circuit interrupting apparatus, a pair of circuit interrupting devices of difiering circuit interrupting capacity, each of said devices including contact means movable to an open and to a closed circuit position, means for electrically connecting said devices in parallel, actuating means for said apparatus, which means causes both of said devices to move to the open circuit position during each circuit interrupting operation of said apparatus, and elec-' tro-responsive means for controlling the sequence of operation of said devices in order that the circuit controlled by said apparatus shall finally be interrupted by that device which is best suited for effecting such interruption.

24. In electrical apparatus, a pair of circuit interrupting devices of different circuit interrupting capacity, one of said devices being capable of extinguishing arcs of large current magnitude but being incapable of extinguishing arcs of small current magnitude, the other of said devices being capable of extinguishing arcs of small current magnitude, and electro-responsive means for causing the are which is established incident to the opening of the electrical circuit through said apparatus to be initiated and then drawn by that device which is best suited for effecting its extinguishment.

25. In electrical circuit interrupting apparatus, a pair of circuit interrupting devices of different circuit interrupting capacity, one of said devices being capable of extinguishing arcs of large current magnitude but being incapable of extinguishing arcs of small current magnitude and the other of said devices being capable of extinguishing arcs of small current magnitude, each of said devices including a pair of separable contacts, means for-electrically connecting said devices in parallel, actuating means for said apparatus which causes both of said pairs of contacts to move to the open circuit position during each circuit interrupting operation of said apparatus, and electro-responsive means for controlling the sequence of separation of said pairs of contacts in order that the-circuit controlled by said apparatus shall be initially opened and finally interrupted by that device which is best 10 suited for efiecting such interruption.

HERBERT L. RAWLINS.

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