US2522236A - Zero current, auto exhausting, vacuum circuit interrupter - Google Patents

Description

Sept. 12, 1950 w. 5. PAUL ZERO CURRENT, AUTO EDKHAUSTING vAcuuI CIRCUIT INTERRUPTKR 3 Sheets-Sheet 1 Pilot! Sept. 15, 1948 Inventor: William E. Paul,

His Attorney.

Sept. 12, 1950 w. E. PAUL 2,522,236

- zmo cumm'r, AUTO manusnm,

vacuum cmcurr mmnur'rm Filed Sept. 15, 1948 3 Sheets-Sheet 2 I hventor William E. Paul,

His Attorney.

Sept. 12, 1950 w. E. PAUL mo cunxsu'r, AUTO mus'rmc, vncuuu cmcurr mmnum Filed Sept. 15, 1948 3 Sheets-Sheet 3 Invet or: wnnam E. Paul,

His Att orrwey- Patented Sept. 12, 1950 ZERO CURRENT, AUTO EXKAUSTING, VACUUM CIRCUIT IKTERRUPTER William E. Paul, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application September 15, 1948, Serial No. 49,376

14 Claims.

This invention relates to electric circuit breakers and more particularly to a method and apparatus for drawing an arc. to be extinguished in a vacuum. Where inflammable gases are likely to be present, such as in mines or explosive manufacturing plants, it is desirable that circuit interrupters be provided which would completely isolate the are from the surrounding atmosphere so that fires and explosions due to ignition of these gases by the arc would be prevented. Also, where space is limited and where potential hazards due to fires exist, such as in seagoing vessels and in aircraft, it is vital that suitable circuit breakers be provided which will guard against such hazards.

Heretofore, attempts to provide suitable vacuum-type breakers have involved cumbersome and expensive vacuum-maintaining apparatus which functioned as auxiliary equipment to the circuit breaker itself. Maintenance costs as well as initial costs for such equipment have generally proved prohibitive. Furthermore, the evolution of profuse metallic and other vapors within the arcing chamber due to the eflect of the are on the contacts has caused breakdown of such breakers where the magnitude oi the current is large. Also, as pointed out in the W. K. Rankin Re-issue Patent No. 21,087, which is assigned to the same assignee as the present invention, the interrupting ability of a vacuum switch is limited because of the emission of ionized metallic vapor from the cathode spot on the parted contacts if the switch opens at the instant when an appreciable instantaneous value of current is flowing therethrough.

A principal object, therefore, of my invention is the provision of a vacuum-type circuit interrupter wherein the breaker structure itself is adapted to produce a vacuum within the interrupting' chamber each time a circuit interrupting operation is performed thereby necessitating no auxiliary vacuum producing equipment.

Another object of my invention is to provide an improved self-contained interrupter wherein the arc is completely isolated at all times from the surrounding atmosphere. Still another object of my invention is the provision of an alternating current vacuum-type interrupter adapted to part its contacts at the zero point of the alternating current wave in order that large quantities of vapor will not be produced within the interrupting chamber during interruption.

A further object of my invention is to provide an interrupter which is particularly adapted for high current and relatively low voltage applications and which requires no liquid or gas blast to aid in performing the interrupting operation.

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

For a better understanding of myinvention, reference may be had to the accompanying drawings in which Fig. 1 is a side view partially in section showing schematically one embodiment of my invention wherein the contacts are shown in the closed position; Fig. 2 is a view similar to Fig. 1 wherein the various parts are shown in the positions which they occupy just after the breaker has completed an opening operation; Fig. 3 represents schematically a modification 0f the arrangement shown in Figs. 1 and 2; while Figs. 4, 5, and 6 show diagrammatically the various parts of Fig. 3 in the closed, opening, and fully opened positions respectively.

In accordance with my invention, which is an improvement over the vacuum-type circuit interrupter disclosed in the above Rankin patent, I minimize or eliminate the generation of metallic or other objectionable vapors by the steps of just ensuring that the interrupting contacts are surrounded by a vacuum and thereafter causing the contacts to separate either at or near a current zero of the alternating current circuit controlled by the switch.

With reference to Fig. 1, a circuit interrupter embodying my invention is shown in which the retractable contacts I and 2 are disposed within the interrupting chamber 3 filled with liquid, such as mercury, water, carbon tetrachloride, or other suitable material. The chamber 3 comprises a metallic closure member 4 and an annular metallic member 5 to which the closure member 4 is secured as by welding so as to form a fluid-tight seal. Disposed within the annular metallic member 5 is a pair of relatively large openings 6 through which the relatively small contact rods I and 2 are slidable. Mounted about each of the contact rods i and 2 is a Sylphon bellows 1 constructed of rubber or other suitable, yieldable, insulating material. The bellows I are sealed in a fluid-tight manner to the annular member 5 at their outer ends and to the contact rods l and 2 respectively at their inner ends. If desired the bellows I could be constructed of-metal and the annular member 5 could be constructed of suitable sturdy insulating material. The closure member 4, of course. could be constructed of insulating material. The Sylphon bellows 8 is secured by a fluid-tight seal to the lower edge of the annular member 5 so that the space within the bellows 8 is coniinuous with the space enclosed by the annular member 5 and the closure member 1. The bellows 2 may be constructed of any suitable material but preferably should be of metallic construction in order to withstand the various forces applied thereto during the operation of the circuit breaker. The lower extremity of the bellows 8 is constructed of a relatively sturdy metallic closure member 9 on which is mounted the sole noid armature l9. Disposed about the lower extremity of the armatur I0 is an operating sole noid coil ll. Should objectionable vapor pressure tend to build up within the interrupting chamber, cooling means of a conventional type may be utilized to minimize this tendency. When coil H is energized, as by closing the manually operable switch l2 or by the equivalent energizetion of relay [3 by current transformer H upon the occurrence of an excessive current condition through line IS, the armature l 0 will move downwardly and hence will elongate the bellows 8, inasmuch as the interrupting chamber 3 is mounted on a fixed supporting structure not shown. This elongation of the bellows I increases the volume of the space inside the bellows and the liquid within the interrupting chamber promptly assumes a lower level due to the action of gravity thereon. Downward displacement of the liquid creates a vacuum in the upper portion of the interrupting chamber in the region surrounding the contacts I and 2, as best seen in Fig. 2. Because this armature movement also effects the opening of the contacts, it will be seen that, in accordance with my invention, means operable by the breaker operating mechanism are utilized to establish a vacuum about the contacts each time a circuit interruption is performed, and that by this construction all the advantages which are to be obtained by utilizing a vacuum-type interrupting chamber are achieved without the necessity for using separate auxiliary vacuum maintaining apparatus, such as pumps and the like. Also, as will become evident, difficulties of sustaining a vacuum over long periods are eliminated, for the vacuum need be maintained only during the interrupting process.

As is known in the art, the ability for vacuumtype breakers to withstand the recovery voltage following an interrupting operation is due to the fact that, because of the vacuum, the arc is not produced in an easily ionized or combustionsupporting medium such as is the case in oil or air circuit breakers. This advantageous feature is partially offset, however, by the fact that the interrupting chamber is completely enclosed, and hence, the ionized metallic vapors or gases which are liberated from the contacts due to the action of the are are retained within the interrupting chamber and of necessity will tend to weaken the dielectric strength of the space between the separated contacts. The extent to which these undesirable metallic and gaseous vapors are generated is largely determined by the magnitude of the current interrupted. Thus, particularly for alternating current vacuum-type breakers, it would be advantageous to provide means for parting the contacts at or near the zero point of the alternating current wave so that the liberation of ionized gases is thereby reduced to a practicable minimum.

To this end I have provided suitable means for selecting a point at or near the zero point of the alternating current wave as the particular point when the contacts are to be parted. For example, the zero selector units generally designated by the numerals l6 and H may be employed. These units l6 and H as such are identical with the zero selector units disclosed and claimed in my Patent 2,436,665 granted February 24, 1948, and assigned to the same assignee as this application. However, for convenience, a description of these units is recapitulated here. Each of the structures l6 and I1 comprises an insulating supporting member 18 which is pivotally mounted at the fixed fulcrum l9. Because units it and Il are identical, unit IE only will be described. With reference to unit IS, an oval coil wound from flat copper strip indicated by dotted lines and designated by the numeral 22 is supported within the member I8. One terminal of the coil 20 is connected as indicated at 2| via the pivot pin [9 to the circuit controlled by the breaker, while the other terminal of the coil 20 is connected to the lower end of a relatively stiff but resilient contact carrier arm of conducting material 22. The arm 22 is rigidly fastened at its lower end into support ll but is permitted by mechanical deflection of the upper end within an appropriate oval cone space within the coil 20. Accordingly, the unit 16 may be pivoted a few degrees counterclockwise about the pin is without necessitating a corresponding movement to the left of contact I which is mounted and electrically connected at the upper end of the resilient arm 22. Thus, it will be seen that the circuit through the interrupter comprises the line IS, the coil 20, the contact arm 22, contacts I and 2, through unit ll in the same manner as in unit I6, and isolative switch 23 to line 24. The arm 22 is held in the closed position shown in Fig. 1 by the latch 25 which is pivotally mounted to the fixed pivot 26. A suitable compression spring 21 exerts a turning moment on the latch 25 so as normally to maintain the latch in engagement with th cooperating arm 22, as well as biasing the pivoted units IE or H inwardly.

The selector units [6 and i1 operate to select contact opening at a zero point of the alternating current wave because of the interaction of magnetic forces exerted between the coils 20 and the arms 22 which forces are strong enough to maintain the contacts I and 2 in engagement against a contact opening force provided the instantaneous current through coil 20 is of sufficient magnitude. More specifically, at a particular instant, incoming current from line Ii would flow upwardly in unit ii in those portions Of coil 20 which are to the right of contact arm 22 and downwardly in those portions of coil 2| which are to the left of arm 22 while current in arm 22 would flow upwardly. Thus, in accordance with well-known principles, an attractive force would be exerted between the arm 22 and the right-hand side of coil 20 and a repulsing force would be exerted between the arm 22 and the left-hand side of coil 20. This attraction and repulsion between the coil 22 and the arm 22 will result in a force which tends to rotate the selector unit ii, for instance, in a counterclockwise direction about the pivot II and also causes a moment to be exerted on the arm 22 which tends to cause this am to move clockwise asaaaae about its lower end which, as pointed out above. is fixed while the upper end thereof is capable of limited movement from right to left. With the latches 26 of units I6 and I! in engagement with the flexible arms 22, the contacts I and 2 are maintained in engagement. The magnetic forces between the strips 22 and the coils 26 of units It and I! probably would not be sumcient to trip the latches 26 by forcefully rotating selector units against projection 25a of the latch 23 under ordinary fault current conditions. For this reason mechanical means to be described hereinafter are provided to trip the latches 25 coincident with the outward rotation of the selector units. When selector unit I6, for example, is rotated counterclockwise about pivot I2 by mechanical means, the latch 26 is moved out of engagement with the arm 22 due to forcible engagement between unit I6 and projection 26a of the latch 25. The magnetic force tending to rotate unit I6 counterclockwise and the strip 22 clockwise will tend to maintain contacts I in engagement withcontact 2, while the mechanical force rotating unit I6 counterclockwise will bow the arm 22 since the upper end of the arm is fixed in position by the latch 25. If the instantaneous current is above a predetermined value, the contacts will be held in engagement but if the instantaneous current is below a predetermined value, the bowed arms 22 will snap apart and separate the contacts. Thus contacts I and 2 are caused to separate at or near the zero point of the alternating current wave.

For the purpose of causing the selector units I6 and Il to move in the contact opening direction by mechanical means referred to above, a pair of side links 23 are provided which are secured to the closure member 9 at their lower ends and which at their upper ends are provided with a lost-motion slot 23. Cooperating with each slot 29 is a pin 30 which forms the knee of toggle means comprising the links 3I and 32 which are pivotally connected at 33 and 34 to the selector units I6 and I1 respectively.

When a, short circuit occurs to produce automatic tripping, the relay I3 will be actuated by current transformer I4 in a well-known manner to energize the solenoid I I. Energization of solenoid II will pull armature I downwardly which in turn will elongate the bellows 8 and establish a vacuum within the fixed upper portion of the interrupting chamber as already explained. Continued downward motion of armature III then causes lost motion slots 29 to pick up the pin 36 at the knee of the toggle comprising the links 3i and 32. Further downward motion of the armature I0 causes the toggle links 3I and 32 to rotate or tilt the selector units I6 and I1 outwardly. When these units engage the latch extensions 25a, the arms 22 and their contacts I and 2 will be freed to spring apart to their open position in the vacuum as soon as the instantaneous value of the alternating current approaches or is at or below the predetermined value as already explained.

It is preferable that means be provided to prevent separation of the contacts before the liquid has assumed a level well below the contacts. To this end a stop member 36 may be disposed below the armature III for producing a brieii pause in the solenoids operating stroke. Stop member 36 is provided with an armature 31 which cooperates with a solenoid coil 36. A compression spring 39 biases the armature 31 and stop member 36 to the position shown against the fixed stop 46. The stop 33 is spaced from the lower end of the armature It a, distance approximating the length of the lost motion slot 23 in the upper end of the links 23. After a predetermined downward opening movement of the armature It to lower the liquid level, stop 36 will be encountered before any movement has been imparted to the selector units I6 and I1 by the toggle links 3I and 32. Thus a vacuum is formed about the contacts I and 2 before the selector units I6 and II can move to release the latches 26.

In order to move the stop 36 after an appropriate pause out of the path of movement of the armature III, a time-delayed relay 4Ia is provided which will not operate to close its contacts until a predetermined time after the energization of solenoid II. At the end of the pause, the relay 4Ia will close its contacts and will thus energize coil 33 which in turn will move the arms.- ture 31 and stop 36 to the right to permit armature III to complete its downward opening travel. It will be appreciated that any equivalent temporary stop means, e. g., a dashpot, could be employed in place of the above-described magnetic stop for ensuring any desired delayin effect dur-. ing the breaker opening stroke. As the armature Ill completes its downward travel, the selector units I6 and I1 will be rotated outwardly about the fixed pivots I9 to complete an interrupting operation by the contacts I and 2 as explained above.

After the circuit is interrupted, the breaker will reclose automatically. This reclosing operation is accomplished by the spring action of the bellows 3 and also by the vacuum in the upper end of the arcing chamber. After the links 3i and 32 break their toggle springs 21 will aid in completing the reclosing operation.

Because the circuit breaker embodying my invention recloses automatically after an interrupting operation, suitable means must be provided for isolating the circuit. To this end the actuating lever H and link 42 are provided which constitute an operating linkage between the armature I0 and an isolating switch blade 23 arranged in series with the interrupting device. Thus, when armature Ill nears the end of its downward circuit breaker opening movement, the lower end thereof will engage the lever 4I to swing it downward about its pivot 43 thereby rotating the switch blade 23 about its fixed pivot 44 to the open position from its terminal stud 45 as shrown in Fig. 2.

In order to reclose the isolating switch 23, an armature 46 and a coil 41 may be provided. Energization of manually operable switch 48 will cause armature 46 to move upwardly against the arm H to close the isolating switch blade 23 thereby re-establishing contact between the blade 23 and the terminal stud 45. The isolating switch comprising the blade 23 and the terminal stud 45 is shown schematically as a conventional airbreak disconnect, although it will be understood that this isolating switch might assume equivalent appropriate forms such, for example, as an oil immersed or other totally enclosed disconnecting unit arranged for operation in accordance with the opening stroke of the armature II).

It will be apparent from the above description that the speed of the interrupting operation will be limited by the time required for gravity to displace the fluid within the arcing chamber 3 down to a safe level below the contacts I and 2 before permitting them to separate. Thus, in

asaaase order to reduce the duration of the circuit interrupting operation, it may be desirable to cause the contacts I and 2 to emerge from the liquid and to form the vacuum at an acceleration greater than that due to gravity by exerting an upward pull on the upper end of the arcing chamber, rather than upon the lower end as in Fig. 1, while the lower end of the arcing chamber comprising the bellows 8 would remain fixed in position. If desired, the lower end could be arranged simultaneously to move downwardly. In this way the time required to establish a suitable vacuum around the contacts I and 2 would not be limited by the acceleration due to gravity. An arrangement adapted to decrease the interrupting time in accordance with these principles is shown schematically in Figs. 3-6 and represents a modification of my invention.

The elements of Fig. 3 which correspond to the elements of Figs. 1 and 2 are designated by the same numerals. In the arrangement of Fig. 3, the lower end of the bellows 8 is secured to a fixed support 50. The interrupting chamber 3 is shackled for upward movement by some suitable means such as a pair of lugs 5I attached thereto and the cooperating yoke or beam 52. Pivotally connected at either end of the beam 52 is a downwardly extending push rod 53, the lower ends of which are pivotally connected to a pair of mutually operable levers 54 which in turn are mounted on the fixed pivots 55. The slotted inner ends of the levers 54 are coupled to the crosshead pin 55 which is secured to and hence movable with the armature extension 51. The outwardly extending ends of the levers 54 are coupled to the levers which are coupled to selector units I6 and IT at 60. Thus, it will be seen that energization of coil I I will cause armature Ill and armature extension 51 to move downwardly thereby elevating the upper end of the arcing chamber due to the action of the levers 54, while simultaneously elevating the selector units I8 and I1 through the corresponding action of the levers 58.

For the purpose of guiding the selector units I6 and Il during their vertical travel, the rollers GI and 62 are provided. Rollers 6| are mounted on fixed supports whereas rollers 62 are mounted on the selector units and are arranged to roll up along the fixed inclined surfaces 63 for producing the outward tilting action required by the units I6 and I! as explained in the case of Fig. 1.

Because during the opening operation the selector units I6 and ll of Fig. 3 move vertically, different latches than of Fig. 1 must be used to accommodate such movement. To this end the latch members 64, mounted to fixed pivots 65, cooperate with the pair of vertical auxiliary latch arms 66, the lower ends of which are mounted on fixed pivots 61. The latch arms 65 and the latches B4 are biased to their latching position as shown by their respective compression springs 68 and II. The contacts I and 2 are provided at their outer ends with rollers 69 which are arranged to track along the parallel latch arms 66. Thus, as selector units I6 and I! move upwardly during an opening operation from the position shown in Fig. 4 to the position shown in Fig. 5, contacts I and 2 are maintained in engagement because the rollers 69 are travelling along the vertical parallel paths provided by the fixed arms 66 even though the selector units themselves are tilting outwardly due to the divergent path of rollers 62 up on the inclined surfaces it. During this initial travel of the selector units It and II, the resilient contact arms 22 are bowed inwardly within their respective coils in preparation for their zero-selecting separating movement as shown in Fig. 5. After a predetermined upward travel of the selector units It and I1, a tripping shoulder 12 provided on each of the selector units engages a corresponding projection 10 of each latch 64 thereby causing the latter to release the contact-holding auxiliary latch arms 55 so that the contacts I and 2 can snap apart at the next current zero as illustrated diagrammatically in Fig. 6. This interrupting portion of the opening operation will be followed by the final sequential isolating portion as explained in the case of Fig. l. I

In view of the above description of the arrangement shown in Figs. 3 to 6, it is clear that the speed of the interrupting operation is not limited to the speed of travel of a freely falling body because the vacuum is established by mechanical means independent of gravitational conditions. With this construction a time-delayed relay for delaying the instant of tripping until after the vacuum is established is not necessary.

The coils 20 of the selector units I6 and II also serve as magnetic blowout means to aid in extinguishing the are drawn between contacts I and 2. Assuming that the instantaneous current is flowing into the interrupter from the line I5 of Fig. 1, for example, the magnetic field would be in a direction from the rear to the front of coils 20 and from front to rear across contacts I and 2. With current flowing from contact I to contact 2 an upward force would be exerted on the contacts. Upon separation of contacts I and 2 the are drawn therebetween would be blown upwardly by the magnetic field. With the reversal of the instantaneous current, i. e., when flowing to the interrupter from line 24, the magnetic field across the contacts I and 2 and the direction of current flow would both reverse simultaneously so that the are still would be blown upwardly.

While I have shown and described particular embodiments of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects and I, therefore, intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

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

1. An electric circuit breaker comprising a deformable substantially fluid-tight interrupting chamber, a liquid in said chamber, a pair of relatively movable interrupting contacts disposed within said chamber, means operable during a circuit opening operation for deforming said chamber to increase the volume therein so as to form a vacuum in the region of said contacts and above the level of said liquid, and means for separating said contacts after the formation of the vacuum.

2. An electric circuit breaker comprising a substantially fluid-tight interrupting chamber constructed of deformable material, a liquid in said chamber substantially filling said chamber under normal conditions, a pair of relatively movable contacts disposed in the upper end of said chamber and normally immersed in said liquid, means operable in response to the initiation of a circuit opening operation for elongating said chamber so as to form a vacuum in the upper end thereof above the level of said liquid in the region surrounding said contacts, and means for separating said contacts after the formation of the vacuum.

3. An alternating current electric circuit breaker comprising a substantially fluid-tight interrupting chamber constructed of deformable material, a liquid in said chamber substantially fllling said chamber under normal conditions, a pair of relatively movable contacts disposed in the upper end of said chamber and normally immersed in said liquid, means operable in response to the initiation of a circuit opening operation for elongating said chamber so as to form a vacuum in the upper end thereof above the level of said liquid in the region surrounding said contacts, and means including a pair of selector units operable after a predetermined elongation of said chamber for separating said contacts at a predetermined point on the alternating current wave.

4, An alternating current electric circuit breaker comprising a substantially fluid-tight interrupting chamber constructed of deformable material, a liquid in said chamber substantially filling said chamber under normal conditions, a pair of relatively movable contacts disposed in the upper end of said chamber and normally immersed in said liquid, means operable in response to the initiation of a circuit opening operation for elongating said chamber so as to form a vacuum in the upper end thereof above the level of said liquid in th region surrounding said contacts, and means including a selector unit operable after a predetermined elongation of said chamber for separating said contacts near a current zero point of the alternating current wave.

5. An electric circuit breaker comprising a deiormable substantially fluid-tight interrupting chamber, a liquid in said chamber, a pair of relatively movable interrupting contacts disposed within said chamber, means operable during a circuit opening operation for deforming said chamber to increase the volume therein so as to form a vacuum in the region of said contacts and above the level of said liquid, means for separating said contacts, and time delay means for preventing the separation of said contacts until after the establishment of the vacuum.

6. An electric circuit breaker comprising a de- .formable substantially fluid-tight interrupting chamber, a liquid in said chamber, a pair of relatively movable interrupting contacts disposed within said chamber, means operable during a circuit opening operation for deforming said chamber to increase the volume therein so as to form a vacuum in the region of said contacts and above the level of said liquid, means for separating said contacts, time delay means for preventing the separation of said contacts until after the establishment of the vacuum, and isolating contacts in series with said interrupting contacts and operable after operation of said interrupting contacts.

7. An electric circuit interrupter comprising a deformable substantially fluid-tight interrupting chamber. a liquid in said chamber substantially fillinsaid chamber under normal conditions, a pair of relatively movable interrupting contacts disposed within the upper portion of said chamber and normally immersed in said liquid, means for deforming said chamber so as to increase the volume therein during a circuit interrupting operation to cause said liquid to vacate the space l 10 within the upper portion of said chamber in the region of said contacts due to the action of gravity on said liquid, and means for separating said contacts after said liquid has moved out of the region of said contacts.

8. An alternating current electric circuit breaker comprising a deformable substantially fluidtight interrupting chamber, a liquid in said chamber substantially filling said chamber under normal conditions, a pair of relatively movable interrupting contacts disposed within the upper portion of said chamber and normally immersed in said liquid, a selector unit cooperating with at least one of said contacts and responsive to instantaneous current through said unit for causing separation of said contacts under predetermined conditions, and means operable during a circuit opening operation of said breaker for elevating the upper portion of said chamber, said contacts and said selector unit so as to form a vacuum in said chamber in the region surrounding said contacts.

9. An alternating current electric circuit breaker comprising a deformable substantially fluidtight interrupting chamber, a liquid in said chamber substantially filling said chamber under normal conditions, a pair of relatively movable interrupting contacts disposed within the upper portion of said chamber and normally immersed in said liquid, a selector unit cooperating with at least one of said contactssand responsive to instantaneous current through said unit for causing separation of said contacts under predetermined conditions, means operable during a circuit opening operation of said breaker for elevating the upper portion of said chamber, said contacts and said selector unit so as to form a vacuum in said chamber in the region surrounding said contacts, and a pair of isolating contacts in series with said interrupting contacts for isolating the circuit associated with said interrupter after operation of said interrupting contacts.

10. An alternating current electric circuit breaker comprising a deformable substantially fluid-tight interrupting chamber, a liquid in said chamber substantially filling said chamber under normal conditions, a pair of relatively movable interrupting contacts disposed within the upper portion of said chamber and normally immersed in said liquid, a selector unit cooperating with at least one of said contacts and responsive to instantaneous current therethrough for causing separation of said contacts under predetermined conditions, said selector unit having a coil disposed with respect to said contacts so as magnetically to blow the arc drawn between said contacts in a predetermined direction, and means operable during a circuit opening operation of said breaker for elevating the upper portion of said chamber, said contacts and said selector unit so as to form a vacuum in said chamber in the region surrounding said contacts.

11. An electric circuit interrupter comprising a vertically disposed substantially fluid-tight interrupting chamber constructed of deformable material, a liquid in said chamber substantially filling said chamber under normal conditions, a pair of relatively movable contacts disposed in the upper end of said chamber and normally immersed in said liquid, means operable in response to the initiation of a circuit interrupting operation for elongating said chamber so as to form a vacuum in the upper end thereof above the level of said liquid in the region surrounding asaaasc said contacts, means for separating said contacts after the formation of the vacuum, and magnetic blowout means for blowing the are drawn between said contacts in a direction away from said liquid.

12. In an electric circuit interrupter, a tubular substantially fluid-tight interrupting chamber, constructed of deformable material, a liquid in said chamber substantially filling said chamber under normal conditions, means for securing one end of said chamber in position, means for applying a force to the other end of said chamber so as to elongate said chamber and establish a vacuum therein above the level oisaid liquid, a pair of relatively movable contacts so disposed in said chamber as to be immersed in said liquid under normal conditions but above the level thereof when said chamber is elongated, and means for separating said contacts after elongation of said chamber.

. 13. An electric circuit breaker including a sealed interrupting chamber having relatively separable electrodes disposed therein, a liquid in said chamber means for increasing the size of said chamber thereby to produce a vacuum in said chamber above the level of said liquid, means for establishing an interrupting gap between said electrodes, a common actuating device for operating both said above-mentioned means, and

means cooperating with said common actuating device for preventing the establishment of the gap until after the formation of the vacuum.

14. An alternating current electric circuit breaker including a sealed interrupting chamber having relatively separable electrodes disposed therein, a liquid in said chamber, means for increasing the size of said chamber thereby to produce a vacuum in said chamber above the level of said liquid, means for causing an interrupting gap between said electrodes, means for preventing the formation of the gap except when the instantaneous current is below a predetermined value, and a common actuating device for operating said three above-mentioned means.

WILLIAM E. PAUL.

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

UNITED STATES PATENTS Cramblet Dec. 5, 1933

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