US1984035A - Circuit interrupter - Google Patents

Description

Dec. 11, 1934. A C. SCHWAGER 1,984,035

G IRGUI'I INTERRUPTER Filed May 8, 1934 Sheets-Sheet l Dec. ll, 1934. A. c. scHwAGi-:R 1,984,035

CIRCUIT INTERRUPTER Filed May 8, 1934 2 Sheets-Sheet 2 Patented Dec. 1i, 1934 UNITED STATES CIRCUIT INTEBRUPTEB `August C. Schwager, San lanclsco,

Calif., as-

signor to Pacific Electric Manufacturing Corporation, California San Francisco, Calif., a

corporation of Application May 8, 1934, Serial No. 724,505

5 Claims.

The present invention relates to an electric circuit interrupter, and more particularly to a circuit interrupter of the type wherein the arc between the separating contacts of the interrupter is confined within an arcing chamber, to decompose a gas producing medium, and subjected to the deionizing action of a blast of gas to extinguish the arc.

An object of the invention is to provide a new and improved circuit interrupter in which the arc between its separating contacts will be subjected to a blast of gas substantially immediately upon contact separation.

Another object of the invention is to provide an improved arc extinguishing chamber for an alternating current circuit interrupter which will subject the arc to a deionizing high velocity blast of gas at the first current zero after contact separation.

Another object of the invention is to provide an arcing chamber for an alternating current circuit interrupter which will subject the arc between the separating contacts to an elongating and deionizing blast of gas within a half cycle of current fiow.

Another object of the invention is to provide, in connection with an arcing chamber for a circuit interrupter of the gas-blast type, a means which will facilitate an elongation of the arc, under the influence of a blast of gas, independently of the contact separation.

Another object of the invention is to provide, in connection with the arcing chamber of a circuit interrupter of the gas-blast type, a means which, inv cooperation with a blast of gas from the chamber, will produce an elongation of the arc in a substantially straight line independently of the contact separation.

Other objects and advantages of the invention will be in part point-ed out and in part evident to those skilled in this art as the description thereof proceeds.

The objects of this invention are obtained by interrupting the electrical circuit in an arcing chamber in close proximity with any substance which will generate a gas upon the application of heat, such as is the case when an electrical arc is drawn between a pair of separating contacts under an insulating oil, and confining the gas generated in this way so that it cannot escape from the chamber except by subjecting the arc between the separating contacts to an elongating and deionizing action of a high velocity blast of inert gas.

,When the contacts of a circuit interrupter are (Cl. 20D-150) separated under the surface of oil or other fluid,

as is the case in an ordinary oil circuit breaker, the uid will be decomposed and form a gas bubble around the arc. If the arc is maintained, the high temperature created thereby will contin- 5 uously generate more gas at the inner surface of the bubble and as a result the bubble will rapidly increase in size. This growth of the gas bubble in the oil circuit breaker is a factor which works against the extinction of the arc, because it permits the oil boundary to move out from the arc and thus reduces the rate of decomposition of the oil.

In the earliest application of this principle the switch contacts were separated within an exl5 plosion chamber disposed below the surface of an insulating fluid and the gas generated by the arc was confined within the explosion chamber until the moving contact was withdrawn through a small throat in one end of the chamber. When the moving contact of this switch was thus withdrawn from the explosion chamber the confined gas escaped through the throat of the chamber and subjected the arc, at this point, to the deionizing effect of a longitudinal blast of the confined gas. A disadvantage of this arrangement is that the arc must be drawn through the throat in the explosion chamber and consequently the arc cannot be extinguished until after several cycles of current flow'have taken place. If the arc is con- 30 fined within the explosion chamber for a considerable length of time, the pressure generated therein will become very high. This pressure can be reduced by providing a throat opening of a larger diameter than the movable contact which passes therethrough and while such a construction is effective at high current values, it reduces the effectiveness of the switch at low current values. In the case of low current values the volume of gas generated is comparatively e I small and, therefore, if part of the gas is expelled from the chamber before the movable contact leaves the throat, the gas remaining in the explosion chamber will escape at such a low 'velocity that the arc will not be immediately interrupted, but will persist until the contact separation is sufficient to break the arc.

From the above it will be seen that when the switch is equipped with an explosion chamber of the type referred to, the circuit interruption cannot take place until after the movable contact has left the throat of the explosion chamber, as it is not until this moment that the arc extinguishing action of the vgas blast can function.

The efficiency oi.' the rupturing performance of. 55

is not practical.

a gas blast circuit interrupter is directly proportional to the effectiveness of the means provided for preventing the escape of gas generated in the vicinity of the arc without passing through the arc stream. Therefore, it will be seen that tosbe most effective the circuit interrupter must be capable of drawing and maintaining an arc continually in contact with fresh oil to produce a high rate of decomposition of the oil, and that the shape and size of the arcing chamber must be such as to force all of the generated gas or other products of decomposition to pass through the arc. If these conditions are fulfilled, the rate of recovery of dielectric strength in the arc stream after a current zero will be adequate to cope successfully with the rate atwhich recovery voltage will build up across the arc terminals under any circuit conditions to be found in practical service.

-It is known that an alternating current a'rc can be extinguished at the first current zero which occurs after the contacts of the interrupter have separated. However, since the current to be interrupted will have a zero value every half cycle, during the continuance of the arc, it will be seen that a number of half cycles of current flow will occur within an arcing chamber of the above type before the moving contact can be withdrawn from the explosion chamber and subjected, at a zero current value, to the deionizing action of a blast of gas escaping from the explosion chamber. This condition can be remedied by causing the moving contact to travel at a high rate of speed, but an increase in the operating speed of the contact requires additional operating force and results in unduly increased mechanical stresses and Therefore, it may be said that a further object of the present invention is to provide ina circuit interruptenof the gas-blast type, a means which will cause the arc to travel along va conducting surface in a direction opposite to the direction of travel of the moving contact, whereby the arc will be more rapidly elon-v gated without increasing the speed of travel of the moving contact.

For a better understanding of this invention reference should be had to the accompanying drawings wherein there are shown, by way of illustration and not of limitation, several embodiments thereof.

In the drawings, wherein like numerals refer to v like parts throughout the several views;

Figure 1 is a vertical sectional view taken centrally through an explosion chamber, for a conventional drop bar type of oil circuit breaker, constructed in accordance with this invention,

Figure 2 is a sectional view taken along line II--II of Figure l, looking in the direction of the arrows,

Figure 3 is a perspective view of the explosion chamber lining member shown in Figure 1,

Figures 4 and 5 are fragmentary sectional views showing modifications of the structure illustrated in Figure 1,

Figure 6 is a sectional view of an explosion chamber, for a so-called rotary type of circuit interrupter, embodying the present invention,

Figure I is a diagrammatic plan view showing the manner of arranging the explosion chambers illustrated in Figure 6 when used with a multiple break rotary type of circuit interrupter,

'Figure 8 is a perspective View of the arcing chamber lining member illustrated in Figure 6,

Figure 9 shows a detail of one of the parts, and

Figure 10 is a fragmentary sectional view showing a modified form of the structure illustrated in Figure 6. I

The embodiment of the invention chosen for illustration on Sheet 1 of the drawings is particularly adapted to a circuit interrupter of the so-called double break type in which the cooperating contacts are disposed within an insulating uid containing receptacle and separate by a downward movement or dropping o f a cross bar, the ends of which carry a moving contact. In such an interrupter the contacts for each break and their associated elements are identical. Therefore, a showing of only one set of cooperatingcontacts and a single explosion chamberis thought sufficient.

In Figure '1 of the drawings, the numeral 10 designates a tank which is adapted to contain an insulating fluid 11. Projecting downwardly into the tank 10 and terminating below the level of the insulating fluid 11, there is a supporting insulator 12. Extending through the insulator l2 is a conductor 13 which is adapted to connect the interrupting contacts with an external circuit. vThe end of the conductor 13 carries a member 14 which forms the upper end of an explosion chamber designated generally by the numeral 15. In addition to the member 14, the explosion chamber 15 comprises a cylindrical member 16, having a strength suilcient to withstand high internal pressures, and a plug like member 17 which is firmly secured in the lower end thereof. Mounted upon the inside of the member 14 and disposed at the upper end of the explosion chamber 15, there is a stationary contact 18 which will be described in more detail hereinafter. Projecting through the plug like member 17, at the bottom of the explosion chamber 15, and in line with the stationary contact 18, is a vertically movable contact 19 which is carried by a drop bar 20, the movement of which is controlled by the switch operating mechanism.

In order to secure an early interruption of the arc established by a separation of the contacts 18 and 19 in interrupting a high tension circuit, it is important that the explosion chamber 15 be so proportioned that only suflicient fluid will be contained therein to produce a violent explosion and consequently a high velocity flow of arc interrupting gases. Therefore, the cylindrical member 16 is provided with a lining member 21 which serves to take up considerable of the space therein and thus reduce the size of the explosion chamber 15. This lining member 21, as shown in Figure 2 of the drawings, forms what may be termed a long narrow explosion chamber rather than a cylindrical one, such as would be provided if it were omitted. As shown in this latter figure of the drawings, the stationary contact 18 is disposed at one side of the explosion chamber 15 to provide room for a gas discharge outlet 22 through the member 14.

In Figure 3 of the drawings, the lower end of the lining member 21 .is illustrated as having a. key-way 23, by means of which it may be keyed against rotation within the cylindrical member 16 and at its upper end, in order to provide a clearance for the stationary contact 18 and the gas discharge outlet 22, it is cut away so as to form two semi-cylindrical projections 24 which extend upwardly along each side of the stationary contact 18 and engage the under side of the member 14. Disposed beneath the lining member 21 are two transversely extending discs 25 which are held apart by a. spacing ring 26. The discs 25 and thespacing ring 26 are also keyed within the cylindrical member 16. The discs 25 form an auxiliary compartment which will contain a reserve supply of the insulating iiuid 11 for the generation of additional arc extinguishing gas should the arc continue after the end of the movable contact 19 has moved through this auxiliary compartment.

To properly direct the gas generated by an arc formed between the contacts 18 and 19, so that it will travel at a high velocity in an effective manner through and/or against the'arc, the gas discharge outlet 22 is located with its inner end disposed closely adjacent the initial arc forming zone within the explosion chamber 15. This is accomplished, in the embodiment of the invention illustrated in Figure 1 of the drawings. by projecting an insulating tube 27 through the member 14 so that its inner end extends into the explosion chamber 15 to a point adjacent the lower end of the stationary contact 18. As a further assurance that the gases generated, within the explosion chamber 15 by an electric arc, will be effectively directed through the arc, the stationary contact 1B is provided with an arcing tip 28 which is so shaped that the arc between the separating contacts will be initially drawn at a point closely adjacent the inner end of the insulating tube 27. At this point, it should be stated that the stationary contact 18 comprises, in addition to the arcing tip 28, three contact making tips 29 which are supported upon stili.' springs 30 extending outwardly from a supporting boss 31. To provide a low resistance path for the current from the arcing tip 2B and the contact making tips 29, each tip has a laminated conductor 32 which extends therefrom to the supporting boss 31.

With the above arrangement, it will be seen that upon the interruption of a circuit an arc will be formed between the end of the movable contact 19 and the arcing tip 28 and that as gas is generated thereby, within the explosion chamber 15, the arc will be blown into the gas stream, where it will be subjected to the deionizing action of the gas, as it exhausts from the explosion chamber 15 through the gas discharge outlet 22. Under these conditions the arc root upon the arcing tip 28 will be carried toward the inner end of the insulating tube 27. As a further and important aspect of the present invention there is provided, within the gas discharge outlet 22, an auxiliary current carrying conductor 33 which is connected to the stationary contact 18 at a point externally of the explosion chamber 15. This auxiliary current carrying conductor 33 extends through the insulating tube 27 so that its lower end will be located closely adjacent the arcing tip 28 of the stationary contact 18.

If the gas discharge outlet 22 is formed with an insulating tube 2'7, as suggested above, and the auxiliary conductor 33 is omitted, the upper root of the arc established by a separation of the contacts will always remain upon the arcing tip 28, but where the auxiliary conductor 33 is provided the exhausting gas will carry the upper root of the arc over to the auxiliary conductor 33 where it wi be blown into the gas discharge outlet 22 and finally extinguished.

It is well known that if the arc root is caused to travel along a cool metal surface its temperature will be kept low and an interruption thereof will be facilitated. Therefore, it will be seen that in the arrangement above described the arc interrupting means will become effective to extinguish the arc substantially immediately upon contact separation. It will also be seen that as the upper root of the-` arc is blown out along the auxiliary conductor 33 the length of the arc will be increased independently of the travel of the moving contact 19.

It is also known that the velocity of a gas under pressure through a cylindrical tube cannot exceed a velocity in excess of the sound velocity of the particular gas under the conditions of temperature and pressure then existing. However, ii the gas discharge outlet 22 is shaped as a nozzle with a flaring end the velocity of the escaping gas will be in excess of its sound velocity. Therefore, the gas discharge outlet 22 may, if desired, be constructed as illustrated in Figures 4 and 5 of the drawings. In Figure 4 of the drawings, the gas discharge outlet 22 is formed by a funnel like member 34 which has a slightly Iiared portion 35 adjacent the arcing tip 28 and a longer Ilared portion which extends outwardly from a throat 36. Disposed within the funnel like member 34, there is an auxiliary conductor 37 which extends fron. a pointadiacent the arcing tip 28 to a point external to the explosion chamber 15 where it is secured in electrically connected relation with the base of the stationary contact 18 by means of a screw 38.

InFigure 5 of the drawings, there is shown a variation of the last above described arrangement wherein the gas discharge outlet 22 is provided by forming a ared outlet opening in the member 14, the lower end of the opening being carried down to a point adjacent the arcing tip 28 by casting a tubular extension 39 upon the under side of the member 14.

Reference is now made to Sheet 2 of the drawings where, in Figure 6, there is illustrated a modification of the present invention that is particularly adapted to a multiple break circuit interrupter of the so-called rotary type. In this gure of the drawings, the numeral 40 designates an insulating support which is adapted'to hold a stationary contact designated generally by thenumeral 41. 'Ihe stationary contact 41 is carried by a suitable insulator engaging member 42 and is disposed beneath the level of an insulating iluid as is the case in the structure previously described. This stationary contact 41 comprises three spring pressed contact making members 43 and an arcing tip 44. Mounted to travel in an arcuate path and in cooperating relation with the stationary cont-act .41, there is a movable contact 45.

As shown in Figure 7 of the drawings, the movable contact 45 is disposed upon the end of a rotatable cross arm 46 and cooperates with a second similar movable contact 45 to provide a double break in the circuit when the interrupter is in its open position. In this type of circuit interrupter the rotatable cross arm 46 is generally mounted upon a vertically disposed rotatable and insulated support 47 which is controlled by a suitable operating mechanism. Secured upon the insulator engaging member 42 and disposed about the stationary contact 41 is a member 48 which supports acylindrical member 49. The cylindrical member 49 which is of insulating material extends outwardly over the stationary contact 41 and the movable contact 45 to form a confined space or explosion chamber 50 about the ends of the contacts 41 and 45 when they are in engagement with each other. At the lower end of the cylindrical member 49, there is a plug like member 51 having an aperture therein through which the movable con- Clt tact extends into the explosion chamber 50. In this embodiment the explosion chamber is restricted in size by the insertion of a lining member 52.

As shown in Figure 8 of the drawings, the lining member 52 is slotted across its top to provide a 'clearance for the contact making members 43 and the arcing tip 44 of the stationary contact 41. 'This forms two semi-cylindrical upwardly projecting portions 53 which serve to space the lining member 52 axially within the cylindrical member 49. The lining member 52 is also shown as having one side thereof cut away as at 54 to provide for an accumulation of insulating uid directly below the arcing tip 44 of the stationary contact 41. A key-way 55 is provided along one side of the lining member 52 for securing it against rotation within the cylindrical member 49. Two disc like members 56, having a spacing sleeve 5'7 therebetween, are disposed beneath the lining member 52 to provide an auxiliary insulating fluid chamber at the lower end of the explosion chamber 50. In this embodiment of the invention, instead of providing a restricted gas discharge outlet at the end of the explosion chamber 50, the Vmember 48 is formed withv a gas discharge outlet 58, through which the gases generated within the explosion chamber 50 may exhaust when an arc is produced within the chamber by a separation of the contacts. With this arrangement there is provided an auxiliary conductor 59 which extends from the base of the stationary contact 41 to a point closely adjacent the back of the arcing tip 44. In order to restrict the exhaust of gas, from the explosion chamber 50, to a path along the outside of the arcing tip 44, the auxiliary conductor 59 is formed, as shown in Figure 9 of the drawings, with a width and shape which, in conjunction with the member 48, will substantially close the remaining portion of the opening through the member 48. This auxiliary conductor 59 is located in spaced relation with the arcing tip supporting spring so that it will not interfere with the free normal exing thereof. Disposed within the gas discharge outlet 58 and partially surrounding the stationary contact 41, there is an insulating bushing 60. This bushing 60 serves to insulate the member 48 and insures that the arc will travel along the outer surface of the auxiliary conductor 59 when its upper root is blown into the gas discharge outlet 58.

Attention is now directed to the manner of securing the cylindrical member 49 to the supporting member 48 and also closing the lower end thereof. This is important as the cylindrical member 49 is constructed of insulating material, such as iibre or the like, which does not have the strength of metal. At its upper end the cylindrical member 49 projects inside of an annular ange 61 formed upon the member 48 and it has a metallic ring 62 fitted tightly within its end. This makes it possible to firmly secure the cylindrical member 49 to the member 48 by a plurality of screws 63 which pass through the flange 61 and are threaded into the metallic ring 62. These screws 63 may be placed at properly spaced points about the end of the outwardly extending cylindrical member 49. At its lower end the cylindrical member 49 is provided with a reduced annular portion 64 having a metallic ring 65 disposed around its outside and a second metallic ring 66 extending about its inside. The second ring 66 serves to secure the discs 56 in place and with the ring 65 it reinforces the reduced annular portion 64 of the cylindrical member 49. After the rings 65 and 66 have been assembled, as above, the plug like member 51 is inserted in the end of the cylindrical member 49 and screws 67 are then inserted through the ring 65 and threaded into the 'ring 66. The screws 6'7 have projecting ends 68 which extend into the plug like member 51 and thus firmly secure the parts together. As an additional element, there is an outer cylindrical tube 69 of insulating material which is slipped over the whole assembly and secured into place by a single screw 70.

The modification illustrated in Figure l0 of the drawings is similar to that illustrated in Figure 6 of the drawings, except that a member Fl1, which supports the stationary contact 41, is substituted for the vmember 48. This member '71 has a restricted gas discharge outlet 72 which is disposed at one side of and outwardly beyond the end of the explosion chamber, rather than about the stationary contact 41.

The operation of a circuit interrupter constructed in accordance with this invention should be evident from the above. However, the following additional description is thought desirable:

When the contacts 18 and 19 are separated, as when interrupting an electrical circuit, an arc will be established between the upper end of the movable contact 19 and the arcing tip 28 of the stationary contact 18. This arc will decompose the surrounding oil or other insulating fluid and generate a gas within the explosion chamber 15. As the gas is generated it will form a continually expanding bubble which will create a pressure within the explosion chamber 15 and as a result the uid located within the gas discharge outlet 22 will move outwardly, as a piston of uid, to permit the escape of the gas therethrough.

The movement of this so-called piston of fluid, within the gas discharge outlet 22, will be comparatively slow and as a result a high gas pressure will be established within the explosion chamber 15. As soon as the iluid has been completely displaced from the gas discharge outlet 22 the gas will exhaust through this outlet at a high velocity. In other words, the piston of uid, within the gas discharge outlet 22, will serve to delay the discharge of gas therethrough sufficiently to permit the building up of a high pressure within the explosion'chamber 15 so that immediately upon a clearing of the gas discharge outlet 22 the gas will exhaust at a high velocity. As previously stated, in the preferred arrangement the diameter and length of the insulating tube 27, which forms the gas discharge outlet 22,*are so proportioned that the iluid located therein will be discharged therefrom, to provide a free passage for the gas, during the first half cycle of arc duration. Under these conditions the are wm be armed by the exhausting gas from the arcing tip 28 to the auxiliary conductor 33 and blown there along until it is nally extinguished. If the arc persists until the upper end of the movable contact 19 has been drawn into the auxiliary compartment, formed between the discs 25, the iiuid contained therein will be decomposed and produce an additional quantity of arc extinguishing gas.

The operation of the modifications illustrated in Figures 4 and 5 of the drawings is the same as above described, except that in these modified embodiments of the invention the fiarng character of the gas discharge outlet 22 will permit a more rapid-discharge of the fluid piston therefrom.

In the embodiment of the invention illustrated in Figures 6 and 10 of the drawings, the gas will be initially formed within the explosion chamber 50 at a point immediately below the arcing tip 44 of the stationary contact 41 and since the gases will follow the line of least resistance, in their lexhaust from the explosion chamber 50, they will pass around the outside of the arcing tip 44 and thus carry the upper root of the arc to and along the auxiliary conductor 59 until the arc is extinguished.

While I have, for the sake of clearness and in order to disclose my invention so that the same can be readily understood, described and illustrated specific devices and arrangements, I desire to have it understood that this invention is not limited to the specific means disclosed, but may be embodied in other ways that will suggest themselves to persons skilled in the art. It is believed that this invention is new and it is desired to claim it so that all such changes as come within the scope of the appended claims are to be considered as part of this invention.

Having thusdesc'ribed my invention, what I claim and desire to secure by Letters Patent is- 1. In an explosion chamber for a fluid-break type of circuit interrupter, the combination of. a metallic contact supporting member, a stationary contact upon said supporting member, a tubular member of insulating material secured at one end to said supporting member and extending over the stationary contact supported thereby, a metal ring tted tightly Within the other end of said tubular member, a plug like member extending into said metal ring and having a flanged portion' extending outwardly thereover forming with said tubular member an enclosed explosion chamber, and securing means extending radially through said tubular member and said metal ring and projecting into said plug like member for securing said members together:

2. In a high tension circuit interrupter of the fluid-break type, the combination of a tank containing an insulating-huid, an elongated cylindrical member forming an arc enclosing and gas generating chamber submerged in said insulating fluid, a ilxed contact disposed within and at one end of said chamber, a moving contact adapted to `extend into the other end of said chamber and engage said ilxed contact, a gas discharge outlet in the end of said chamber adjacent said xed contact for the gases generated within said chamber by an arc when the contacts separate, and a plurality of battles within the other end o! said chamber cooperating with the insulating tluid therein to provide a 'substantially gas tight seal about said moving contact until said moving contact has been withdrawn from said chamber.

3. In an explosion chamber for a circuit interrupter of the fluid-break type. the combination ot a stationary contact supporting member, a stationary contact upon said supporting member and projecting outwardly therefrom, an outwardly disposed annular iiange carried by said contact supporting member and extending in spaced relation around said stationary contact, an open ended tubular member of insulating material mounted upon said annular ange and extending outwardly beyond said stationary contact, a movable contact adapted to extend into said tubular member and cooperate with said stationarycontact, and means comprising a plurality of baille like members at the outer end of said tubular memberv providing a liquid seal about said movable contact when submerged in an insulating fluid, whereby gases generated by an arc within said tubular member upon a separation of said contacts will be caused to exhaust from the interior of said tubular member through said annular flange and in a direction opposite to the direction of travel ot said movable contact.

4. In a circuit interrupter of the fluid-break type, the combination of a contact supporting member adapted to be submerged in an insulating fluid, an outwardly disposed annular flange forming an opening through which fluid may circulate, a stationary contact mounted upon said supporting member and extending into the opening provided in said annular flange, an open ended tubular member of insulating material secured to said annular flange and extending outwardly from said stationary contact to form an arc extinguishing chamber, a movable contact extending into the outer end of said tubular member and adapted-to cooperate with said stationary contact, closure means at the outer end of said tubular member having a central opening through which said movable contact moves and cooperating with said movable contact to substantially close the outer end of the arc extinguishing chamber formed by said tubular member, and a baille forming means adiacent said stationary contact extending into said tubular member and adapted to partially close the opening in said annular ilange to provide a gas discharge outlet from said arcing chamber at one side of said stationary contact.

5. In a circuit interrupter of the iluid-break type, the combination of a contact supporting member adapted to be submerged in an insulating duid, an outwardly disposed annular ilange forming an opening through which iiuid may circulate, a stationary contact mounted upon said supporting member and extending into the opening provided in said annular flange, an open ended tubular member of insulating material secured to said annular iiange and extending 'outwardly from said stationary contact to form an arc extinguishing chamber, a movable contact extending through the outer end of said tubular member Vand adapted to cooperate with said stationary contact, closure means at the outer end of said tubular member having a central opening through which said movable contact moves and cooperating with said-movable contact to substantially close the outer end of the arc extinguishing chamber formed by said tubular member, and an auxiliary conductor extending into said tubular member and partially closing the opening through said annular flange adapted to conduct an' arc formed within said chamber away from said stationary contact and into the gas discharged from said chamber by a decomposition of the insulating iluid therein.-

AUGUST C. SCHWAGER.

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