US3582587A

US3582587A - Vacuum-type circuit interrupter having a stroke length dependent upon current magnitude

Info

Publication number: US3582587A
Application number: US796062A
Authority: US
Inventors: Philip Barkan
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1969-02-03
Filing date: 1969-02-03
Publication date: 1971-06-01
Anticipated expiration: 1988-06-01
Also published as: JPS4915748B1; DE2004660A1; FR2033911A5; GB1264603A; DE2004660C3; DE2004660B2

Abstract

Discloses a vacuum-type circuit interrupter comprising currentresponsive means for varying its opening stroke length in accordance with the magnitude of the current being interrupted.

Description

United States Patent Philip Barltan Media, Pa.

Feb. 3, 1969 June 1, 1971 General Electric Company lnvcmor Appl. No. Filed Patented Assignee VACUUM-TYPE CIRCUIT INTERRUPTER HAVING A STROKE LENGTH DEPENDENT UPON CURRENT MAGNITUDE 5 Claims, 5 Drawing Figs.

US. Cl 200/144, 335/40, 200/153 Int. Cl 1101b 33/66 Field ofSearch 335/16, 40, l74;200/147 C, 144.2, 148,153.20

[56] References Cited UNITED STATES PATENTS 3,050,073 10/1961 Reiss et a1 200/147(C)X 3,164,700 1/1965 Bodenschatz 200/147(C)X 3,418,439 12/1968 Casey et al ZOO/144(2) 3,492,609 1/1970 Murai et a1. 335/16 Primary Examiner-Robert K. Schaefer Assistant EgcaminerRobert A. Vanderhye Attorneys-J Wesley l-laubner, William Freedman, Frank L.

Neuhauser, Oscar B. Waddell and Melvin M. Goldenberg ABSTRACT: Discloses a vacuum-type circuit interrupter comprising current-responsive means for varying its opening stroke length in accordance with the magnitude of the current being interrupted.

/NVENTOR.' PH/L/P BAR/(AN,

ATTORNEY PATENVTED JUN 1 an SHEET 2 OF 2 PHASEM' nvvmvron PHIL/P BAR/(A N,

ATTORNEY VACUUM-TYPE CIRCUIT INTERRUPTER HAVING A STROKE LENGTH DEPENDENT UPON CURRENT MAGNITUDE This invention relates to a vacuum-type circuit interrupter and, more particularly, to a vacuum-type interrupter which has a stroke length dependent upon the magnitude of the current being interrupted.

When used in highly repetitive duty-switching applications, such as in motor control contactors, a vacuum interrupter must have an extremely long life, e.g., hundreds of thousands or even millions of operations. An important determinant of the life of a vacuum interrupter is the life of its bellows. The bellows is a flexible metal part that forms a vacuumtight seal between the movable contact rod and the evacuated envelope of the vacuum interrupter. Each time the interrupter is opened or closed, this bellows is flexed; and after many such opera tions, may develop, through fatigue, a crack which allows leakage into the evacuated envelope.

If the stroke of the vacuum interrupter used in such switching applications can be kept short, a much higher number of operations can be endured before any fatigue induced cracks will develop in the bellows. But there is one consideration which limits the extent to which the stroke can be shortened, and that is the short circuit current interrupting ability of the interrupter. In the vast majority of operations,

only relatively light currents will be interrupted by the interrupter; but occasionally the interrupter will be called upon to interrupt a short circuit current, which has a much higher magnitude. These latter interruptions require a considerably longer stroke than the light current typically interrupted, and the interrupter would be unable to handle such currents if its stroke were limited to the short length that is ideal for prolonged bellows life.

An object of my invention is to maintain the stroke of such a vacuum interrupter short in length so as to prolong the life of its bellows, yet without defeating the ability of the interrupter to handle occasional short circuit currents.

Another type of switching application that I am concerned with is that in which the vacuum interrupter is used in an infrequently operated protective circuit breaker that is relied upon for short circuit interrupting duty and for capacitance switching duty. For capacitance switching duty, it has been found that a longer stroke is needed than that which is optimum for short circuit current interruption. This longer stroke helps the interrupter to successfully withstand the higher voltages that are imposed by capacitance switching. But surprisingly, this longer stroke detracts from the short circuit current interrupting ability of the vacuum interrupter.

Accordingly, another object of my invention is to provide in a protective circuit breaker a vacuum interrupter which can develop a stroke long enough to perform well during capacitance switching operations, yet without impairing its ability to interrupt short circuit currents.

In carrying out the invention in one form, I provide a vacuum interrupter which has means for automatically changing the length of its stroke in accordance with the magnitude of the current being interrupted. In the first switching application referred to above, i.e., the repetitive duty application, I provide the interrupter with two stops, one of which is capable of limiting the stroke length to a short value that is especially suited for prolonged bellows life and the other of which is capable of limiting the stroke length to a longer value appropriate for short circuit interruptions. Under light current interrupting conditions, the first stop controls the stroke length; but current responsive means is provided which acts under high current conditions to disable the first stop and allow the second stop to control the stroke length.

In the second switching application referred to above, i.e., the protective circuit breaker application, first and second stops ofa similar character to those referred to in the previous paragraph are provided; but the first stop is normally disabled and the second stop normally controls the stroke length. Under high current conditions, however, current res onsive means frees the first stop from its disability and allows it to control, thus reducing the stroke length.

For a better understanding of the invention, reference may be had to the following description taken in conjunction with the accompanying drawings, wherein:

FIG. I is a sectional view partly in section showing a vacuum interrupter embodying one form of my invention.

FIG. 2 is a sectional view along the line 2-2 of FIG. 1.

FIG. 3 is a schematic showing ofa polyphase circuit breaker comprising single phase intcrrupters such as shown in FIG. 1.

FIG. 4 is a schematic showing of a modified form of the invention.

FIG. 5 is a schematic showing of another modified form of the invention.

Referring now to FIG. 1, there is shown a vacuum-type circuit interrupter 10 comprising a highly evacuated housing 11 comprising a cylindrical insulating case 12 and upper and

lower end caps

13 and 14 joined to the casing 12 by suitable vacuumtight seals. Mounted within housing 11 are two

separable contacts

16 and 17, shown in FIG. I in their engaged, or closed, position. The upper contact 16 is a stationary contact mounted on a stationary conductive rod 16a that is integrally joined to the upper end cap 13. The lower contact 17 is a movable contact that is mounted on a conductive operating rod 17a that projects freely through the lower end cap 14. A I

flexible metallic bellows 18 is joined in sealed relationship at its respective opposite ends to rod 17a and end cap 14. This flexible bellows permits vertical movement of rod without impairment of the vacuum inside housing 11. The vacuum interrupter is mounted on a stationary conductive stud 20 by means of a mounting bracket 22 suitably fixed to stud 20 and lower end cap 14. Bracket 22 carries a bearing 24 that surrounds the movable operating rod 17a and guides it for opening and closing movement.

For transmitting opening and closing motion to movable operating rod 170, I provide a conductive crossbar 26 pivotally mounted on stationary bracket 22 at 28. Crossbar 26 is rigidly attached at its free end to movable operating rod 170, and when it is pivoted in a counterclockwise direction from its position of FIG. I drives the operating rod'downwardly to separate contacts l7, 16.

For transmitting opening and closing motion to crossbar 26, l provide an actuating lever 30 that is mounted for pivotal motion on stationary pivot 28. A compression-type wipe spring 32 located between lever 30 and crossbar 26 biases these parts apart. The wipe spring 32 encircles a pull rod 34, which is pivotally mounted at 35 on the crossbar 26 and extends freely through an opening in the actuating lever 30. The pull rod 34 has a stop 36 on its lower end that is adapted to be engaged by the lower side of lever 30 on an opening operation, as will soon be described.

Actuating lever 30 is biased in a clockwise opening direction by a torsion-type opening spring 39. The actuating lever 30 is normally prevented from moving out of its position of FIG. 1 by a closing rod 40 that freely extends through an opening in the actuating lever 30 and carries a stop 42 against which lever 30 normally bears. For reasons which will soon be explained, the connection 41 between the actuating lever 30 and closing rod 40 is a lost-motion connection. Closing rod 40 is latched in its illustrated position by a suitable trip latch (shown at 43 in FIG. 3). When closing rod 40 is released for downward movement, the opening spring 39 and wipe spring 32 drive the actuating lever 30 in a counterclockwise opening direction. After a short amount of counterclockwise travel, actuating lever 30 impacts against the stop 36 on pull rod 34, and the resulting impact plus force from opening spring 39 rapidly drive thepull rod downwardly in the direction of arrow 44 (FIG. 1). This downward motion of the pull rod produces counterclockwise motion of crossbar 26, thereby driving'the operating rod 17a downwardly to separate the contacts.

Closing is performed after the above-described opening operation by moving the closing rod 40 in an upward direction, thus driving stop 42 against lever 30 to move lever 30 clockwise toward its position of FIG. I. Such a clockwise motion is transmitted to crossbar 26 through compression spring 32, thus driving the crossbar 26 clockwise toward its position of FIG. I. This clockwise motion of crossbar 26 continues until the contacts engage. Clockwise motion of actuating lever 30 continues for a short additional travel after the contacts engage, thereby partially compressing the wipe spring 32. This additional travel, which compresses spring 32, is referred to as contact wipe. At the end ofa closing stroke, latch 43 of FIG. 3 resets and holds the closing rod 40 in its elevated position of FIG. I.

For carrying current between the stud 20 and conductive operating rod 170 I provide a short length of conductive braid 50. This braid has ferrules at both ends, one of which is joined to the stud 20 and the other of which is joined to operating rod 17a via crossbar 26. The braid may be thought of as being ofa generally L-shape. Current through the breaker, when it is in the closed position shown, follows a path depicted by the dotted line arrows 54. This path extends from stud 20 through

parts

50, 26, 17a, l7, l6. and 16a to the upper terminal 55 of the breaker.

For controlling the length of the opening stroke of the vacuum interrupter, I provide two

stops

60 and 62. The first stop 60 is a movable stop which normally predominates in controlling the stroke length. This stop 60 can be disabled, as will soon be described, to allow the second stop 62 to control. The second stop 62 is a fixed stop that is rigidly secured (by means not shown) to the stationary bracket 22.

The first stop 60 is a lever of magnetizable material that is pivotally mounted on a fulcrum 65 secured to bracket 22. The lever 60 is normally maintained in its position of FIG. I by a reset spring 68 which biases lever 60 counterclockwise into its effective position shown. When the stop lever 60 is in its effective position of FIG. I, it will engage the outer end portion of the crossbar 26 when the crossbar enters its dotted line position 70 during an opening operation, thereby limiting the opening stroke to a relatively small value.

When the current through the interrupter exceeds a predetermined value, the stop 60 is rapidly withdrawn from its effective position of FIG. I and thus is rendered ineffective to control the opening stroke. This permits the vacuum interrupter to have a longer stroke inasmuch as the crossbar 26, during its opening travel, will now be able to move past the dotted line position 70 into a position of greater contact separation, where it will encounter the second stop 62.

For withdrawing the stop lever 60 in response to high current through the interrupter, I provide a U-shaped magnetic core 72 that partially surrounds the conductive braid 50 and is fixed to the stud 20. When the current through the braid 50 exceeds a predetermined value, there is a high enough attractive force between the core 72 and the stop lever 60 to drive the stop lever counterclockwise about its pivot 65 into engagement with the end faces 75 f the magnetic core. The current level at which this motion of the stop lever 60 takes place is determined by the size of reset spring 68. In one embodiment of the invention, the reset spring is of such a size that this motion occurs only when a current of short circuit magnitude passes through braid 50.

The interrupter of FIG. I is especially adapted for highly repetitive switching applications, where the required life span of the interrupter typically is many hundreds of thousands of operations. As pointed out hereinabove, an important determinant of the life span of such interrupter is the life of its bellows. Each time the interrupter opens or closes, this bellows is flexed, and this subjects the bellows to repeated stresses which, through fatigue, can ultimately cause cracks to develop in the bellows.

For reducing the severity of these stresses, thus prolonging the bellows life, I normally limit the stroke of the vacuum interrupter to a relatively short value. This is done with the first stop 60, as above described. This short stroke is adequate for the vast majority of the switching operations inasmuch as these involve only relatively light current, which can be interrupted with a short stroke. Occasionally, however, it will be necessary to interrupt short circuit currents, and this will require a longer stroke to insure successful interruption.

By quickly disabling the first stop 60 in response to short circuit currents, thus allowing the second stop 62 to control, I am able to provide the necessary increased stroke length needed for interrupting short circuit currents. When the interrupter is closed following a short circuit current interruption, the reset spring 68 quickly returns the stop 60 to its effective position of FIG. 1, thus once again restoring the short stroke for normal interrupting operations.

A feature of some significance is that my stroke varying means can be used in a polyphase circuit breaker to change the stroke length of the interrupter in one phase without affecting the stroke length of the interrupters in the other phases. This will be apparent from the schematic diagram of FIG. 3. Here the closing rods that extend to the interrupters of each phase are designated 40, 40a and 40b. The actuating levers for the respective phases are designated 30, 30a and 30b. A lost-motion connection 41, 4111 or 41b is present between each of these actuating levers and its associated closing rodv The actuating levers are coupled to the interrupters in the respective phases by pull rods 34, 34a and 34b. The actuating levers are respectively biased in a counterclockwise opening direction by opening

springs

39, 39a and 39b, but are normally prevented from so moving by shoulders 42, 42a and 42b on their associated closing rods.

Parts

30, 34, and 39-42 are the identically designated parts of FIG. 1. Their counterparts in the other two phases bear the same reference nu merals but with the suffixes a or b." Each of the closing rods 40, 40a, 40b is pivotally connected at its lower end to a crank I00, a or 100b, which, in turn, is keyed to a rotatably mounted shaft 104 common to all three phases and tying the cranks together. Crank 100 has a downwardly projecting arm that carries a latch roller 106 cooperating with a trip latch 43 common to all three phases. When trip latch 43 is in a position of FIG. 3, the roller I06 bears against latch 43, thereby holding all the parts in their closed position of FIG. I. When latch 43 is tripped by a tripping solenoid 108, the cranks I00, 100a and l00b are free to move in a clockwise opening direction. The opening springs 39, 39a, 39b respond by driving the respective actuating levers 30, 30a, and 30b in a counterclockwise opening direction, thus opening the interrupters in the three phases.

Stops

60 and 62, corresponding to stops with the same reference numerals in FIG. 1, determine the length of the opening stroke in phase I. Similar stops with corresponding reference numerals determine the length of the opening stroke in each of the other phases.

It will be apparent that the length of the opening stroke in any one phase will be determined by the stops in that particular phase and will not be affected by the stops in the other phases. For example, if it is assumed that short-stroke stop 60 of phase I has been disabled, then the stroke in phase I will be determined by stop 62 and will be relatively long. If the short stroke stops 60a and 60b in the other two phases are still operative, they will determine the stroke in these particular phases, and accordingly the stroke in these phases will be relatively short. The lost motion connection 41, 41a or 41b between each actuating lever and its closing rod allows the actuating lever to be blocked in a given phase by the shortstroke stop in that phase without interfering with the continued opening movement of the closing rods in the other phases.

The polyphase arrangement of FIG. 3 readily accommodates a circuit condition where short circuit current might flow through one of the phases of the circuit while the other phases are carrying normal low currents. In response to such a condition, the stroke-control means of the phase carrying short circuit current disables its short-stroke stop 60, allowing a long stroke in that phase, thus permitting effective interruption of the high current therein. The interrupters of the other phases, which are seeing low current, do not need the long stroke and operate with their usual short stroke.

At the end of such an opening operation, cranks 100, 100a and 100!) will be in their dotted line position of FIG. 3. A closing roller I12 carried by crank 100 will be located adjacent the armature of a closing solenoid 114. Closing of the threephase circuit breaker is affected by operating solenoid 114 to lift its armature and return closing roller 112 to its solid line position. This returns the three cranks I00, 100a and 1001; to their solid line positions of FIG. 3, simultaneously lifting rods 40, 40a and 40b through a closing stroke. During this closing stroke, the actuating lever 30, which had previously moved through a long opening stroke will first be picked up by its closing rod 40; and after additional closing travel, the other actuating levers 30a and 30b, which had moved through short operating strokes, will be picked up by their respective closing rods 40a and 40b. The movable contacts of the interrupters in all three phases reach their closed position at substantially the same time.

Another type of switching application that I am concerned with is one in which the vacuum interrupter is used in a protective circuit breaker that is relied upon for short circuit interrupting duty and capacitance switching duty. For capacitance switching duty, it has been found that a longer stroke is needed than that which is optimum for short circuit interruptions. This longer stroke helps to withstand the higher voltages that are imposed by capacitance switching duty; but, surprisingly, it detracts from the short circuit current interrupting capability.

FIG. 4 shows a circuit breaker which can provide a shorter stroke under short circuit interrupting conditions than under capacitance switching conditions. In passing, it should be noted that this short stroke in FIG. 4 corresponds to the long stroke in FIG. 1, whereas the long stroke in FIG. 4 is of still greater length. The circuit breaker of FIG. 4 comprises a vacuum interrupter which is substantially the same as that of FIG. 1 and thus has its parts designated by corresponding reference numerals. In addition, the interrupter of FIG. 4 is provided with an opening spring 80 which drives the movable contact 17 downwardly when released by a trip latch 82. The trip latch 82 is operable by solenoid 83 which is connected in a trip circuit 85. Trip circuit 85 can be completed either by a manually controlled switch 86 or a switch 88 which is operated to closed position by suitable means (not shown) responsive to overcurrent in the circuit through the interrupter. Completion of trip circuit 85 operates the tripping solenoid 83 to release latch 82, thus allowing opening spring 80 to drive the movable contact 17 downward through an opening stroke.

The length of the opening stroke is determined by either one of two

stops

90 and 91. Stop 91 is a stationary stop disposed in the path of the movable contact operating rod 17a. Under low current conditions, this stop 91 will determine the length of the opening stroke. This stop is so located that it permits a relatively long opening stroke before being engaged by operating rod 17a. Since capacitance switching operations are low current interruptions, a relatively long stroke will be provided for capacitance switching, thus facilitating such operatrons.

The other stop 90 is normally inactive, but it is brought into operation in response to a high current through the interrupter. This stop 90 is controlled by solenoid 93 that has its coil 94 connected in series with circuit 92 through the interrupter. A reset spring 95 normally maintains the stop 90 in its inactive position. When current exceeding a predetermined magnitude passes through the circuit 92, solenoid 93 responds by quickly driving the stop 90 into its dotted line position. This occurs before actual opening movement of the movable contact operating rod 17a begins. Accordingly, when movable contact operating rod 17 moves downwardly during an immediately following high current opening operation, it encounters stop 90 and is thus prevented from moving through its full opening stroke. Solenoid reset spring 95 is of such a size that the stop 90 is made operative for currents of short circuit magnitude. Thus under short circuit interrupting conditions, the desired shorter stroke is provided.

After an interrupting operation, the solenoid 93 will be deenergized. During the early stages of a subsequent closing operation, the reset spring 95 will restore the stop to its ineffective position as soon as the operating member lifts it off the stop 90 to free it for reset motion.

During low current interruptions, solenoid 93 will be ineffective to move stop 90 into its effective position. Thus, during low current interruptions, the movable contact can quickly move through its desired relatively long stroke without any interference from stop 90.

FIG. 5 shows a modification of the general arrangement shown in FIG. 4. Here the stop 90 is biased toward its effective position by a spring 96 that is normally prevented from moving stop 90 into its effective position by a latch 97 controlled by a solenoid 98 connected in series with the circuit 92 through the interrupter. When current of short circuit magnitude flows through circuit 92, the solenoid 98 operates its latch 97, thus permitting spring 96 to drive the stop 90 into its effective position where it is can provide the desired reduction in stroke length.

A reset member 99, attached to operating rod 17a, is used for returning stop 90 to its normal position when the operating rod 17a is lifted (by suitable closing means, not shown) during a closing operation. This reset member 99 will prevent the stop from being operated during an opening operation prior to initial contact movement. But immediately following initial contact movement, reset member 94 moves out of the way of stop 90, allowing stop 90 to immediately move into its effective position if it has been released to do so by solenoid 98.

It is to be understood that the three-phase arrangement of FIG. 3 can be used in either of the above two switching applications. Whether the short-stroke stop (60 of FIG. 3) is normally active (as in FIG. 1) or normally inactive (as inFIGS. 4 8L 5), there is still independence between the interrupters in the various phases as a result of the lost-motion connections 4!, 41a, 41b. Thus, the stroke-control means in each phase can change the stroke length in that phase in response to current therethrough without affecting the stroke length in the other phases. One type of switching duty where this ability is important to a circuit breaker is that involved when the circuit breaker is performing a line-dropping operation on two phases and is interrupting a short circuit current on the remaining phase. The line-dropping operation is a light current capacitance switching operation, and the interrupters in these phases retain their relatively long stroke since their associated stops 90 of FIG. 4 or 5 remain inactive. But the interrupter in the short-circuited phase has a reduced length stroke (as a result of its associated stop 90 being activated), which facilitates interruption of the short circuit current.

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.

lclaim:

1. A vacuum-type circuit interrupter for highly repetitive switching duty comprising:

a. a highly evacuated housing,

b. a pair of relatively movable contacts within ,said housing that have a position of engagement,

c. an operating member projecting into said housing from the exterior thereof and coupled to one of said contacts,

d. means comprising said operating member for moving said one contact through an opening stroke that separates said contacts and interrupts the circuit therethrough,

e. a flexible metal bellows providing a vacuumtight seal between said operating member and said housing,

f. and stroke-length control means responsive to current through said contacts for varying the length of said open ing stroke in accordance with the magnitude of said current, said stroke-length control means causing the length of said opening stroke to the greater for short circuit current interruptions than for light-current interruptions,

thus allowing light-current interruptions to be effected with a reduced flexure of said bellows, said stroke-length control means comprising:

i. a first stop for limiting the opening stroke to a relatively short length,

ii. a second stop effective when said first stop is disabled for limiting the opening stroke to a greater length, and iii. current-sensitive means for disabling said first stop when the current through said contacts exceeds a predetermined value, thereby rendering said second stop effective to govern the stroke length.

2. A vacuum-type circuit interrupter for interrupting short circuit currents and capacitive currents comprising:

a. a highly evacuated housing,

b. a pair of relatively movable contacts within said housing that have a position of engagement,

c. an operating member projecting into said housing from the exterior thereof and coupled to one of said contacts, d. means comprising said operating member for moving said one contact through an opening stroke that separates said contacts and interrupts the circuit therethrough,

c. a flexible metal bellows providing a vacuumtight seal between said operating member and said housing,

f. and stroke-length control means responsive to current through said contacts for varying the length of said opening stroke in accordance with the magnitude of said current, said current-responsive control means causing the length of said opening stroke to be greater for lightcurrent interruptions than for heavy current interruptions, thus providing a stroke of greater length for capacitance switching operations than for short circuit current interruptions.

3. A vacuum-type circuit interrupter as defined in claim 2 in which said stroke-length control means comprises:

a. a first stop that is normally disabled but which is effective upon removal of said disability to limit said opening stroke to a relatively short value,

b. a second stop that limits said opening stroke to a greater length when said first stop is disabled,

c. and current-sensitive means for removing said disability when the current through said contacts exceeds a predetermined value, thereby rendering said first stop effective to govern the stroke length on short circuit current interruptions.

4. In a polyphase vacuum circuit breaker comprising a plurality of vacuum interrupters for the respective phases of the circuit, each vacuum interrupter comprising:

a. a highly evacuated housing,

f. and stroke-length control means responsive to current through said contacts for varying the length of said opening stroke in accordance with the magnitude of said current, the stroke-length control means of each phase being operable independently of the stroke-length control means of the other phases for varying the stroke length of the interrupter in any one phase in accordance with the current in that phase without affecting the stroke length in the other phases.

5. In a polyphase vacuum circuit breaker comprising a plurality of vacuum interrupters for the respective phases of the circuit, each vacuum interrupter comprising:

a'. a highly evacuated housing,

b. a pair of relatively movable contacts within said housing that have a position of engagement, c. an operating member pro ecting into said housing from the exterior thereof and coupled to one ofsaid contacts,

. and stroke-length control means responsive to current through said contacts for varying the length of said opening stroke in accordance with the magnitude of said current; the combination of:

g. a linkage connected to the interrupters in all phases for imparting closing motion thereto after an opening operation,

h. latching means for holding said linkage in an operated position after a closing operation to hold said interrupters closed,

i. said latching means being releasable to permit opening of said interrupters,

j. a plurality of opening operators respectively biasing the interrupters toward open position and operable upon release of said latching means to separate the contacts of their respective interrupters, and

k. a lost-motion connection between said linkage and each interrupter which allows the opening stroke in the associated interrupter to be terminated at a relatively short value by said stroke-length control means without blocking continued opening travel in the other interrupters.

Claims

1. A vacuum-type circuit interrupter for highly repetitive switching duty comprising: a. a highly evacuated housing, b. a pair of relatively movable contacts within said housing that have a position of engagement, c. an operating member projecting into said housing from the exterior thereof and coupled to one of said contacts, d. means comprising said operating member for moving said one contact through an opening stroke that separates said contacts and interrupts the circuit therethrough, e. a flexible metal bellows providing a vacuumtight seal between said operating member and said housing, f. and stroke-length control means responsive to current through said contacts for varying the length of said opening stroke in accordance with the magnitude of said current, said strokelength control means causing the length of said opening stroke to the greater for short circuit current interruptions than for light-current interruptions, thus allowing light-current interruptions to be effected with a reduced flexure of said bellows, said stroke-length control means comprising: i. a first stop for limiting the opening stroke to a relatively short length, ii. a second stop effective when said first stop is disabled for limiting the opening stroke to a greater length, and iii. current-sensitive means for disabling said first stop when the current through said contacts exceeds a predetermined value, thereby rendering said second stop effective to govern the stroke length.

2. A vacuum-type circuit interrupter for interrupting short circuit currents and capacitive currents comprising: a. a highly evacuated housing, b. a pair of relatively movable contacts within said housing that have a position of engagement, c. an operating member projecting into said housing from the exterior thereof and coupled to one of said contacts, d. means comprising said operating member for moving said one contact through an opening stroke that separates said contacts and interrupts the circuit therethrough, E. a flexible metal bellows providing a vacuumtight seal between said operating member and said housing, f. and stroke-length control means responsive to current through said contacts for varying the length of said opening stroke in accordance with the magnitude of said current, said current-responsive control means causing the length of said opening stroke to be greater for light-current interruptions than for heavy current interruptions, thus providing a stroke of greater length for capacitance switching operations than for short circuit current interruptions.

3. A vacuum-type circuit interrupter as defined in claim 2 in which said stroke-length control means comprises: a. a first stop that is normally disabled but which is effective upon removal of said disability to limit said opening stroke to a relatively short value, b. a second stop that limits said opening stroke to a greater length when said first stop is disabled, c. and current-sensitive means for removing said disability when the current through said contacts exceeds a predetermined value, thereby rendering said first stop effective to govern the stroke length on short circuit current interruptions.

4. In a polyphase vacuum circuit breaker comprising a plurality of vacuum interrupters for the respective phases of the circuit, each vacuum interrupter comprising: a. a highly evacuated housing, b. a pair of relatively movable contacts within said housing that have a position of engagement, c. an operating member projecting into said housing from the exterior thereof and coupled to one of said contacts, d. means comprising said operating member for moving said one contact through an opening stroke that separates said contacts and interrupts the circuit therethrough, e. a flexible metal bellows providing a vacuumtight seal between said operating member and said housing, f. and stroke-length control means responsive to current through said contacts for varying the length of said opening stroke in accordance with the magnitude of said current, the stroke-length control means of each phase being operable independently of the stroke-length control means of the other phases for varying the stroke length of the interrupter in any one phase in accordance with the current in that phase without affecting the stroke length in the other phases.

5. In a polyphase vacuum circuit breaker comprising a plurality of vacuum interrupters for the respective phases of the circuit, each vacuum interrupter comprising: a. a highly evacuated housing, b. a pair of relatively movable contacts within said housing that have a position of engagement, c. an operating member projecting into said housing from the exterior thereof and coupled to one of said contacts, d. means comprising said operating member for moving said one contact through an opening stroke that separates said contacts and interrupts the circuit therethrough, e. a flexible metal bellows providing a vacuumtight seal between said operating member and said housing, f. and stroke-length control means responsive to current through said contacts for varying the length of said opening stroke in accordance with the magnitude of said current; the combination of: g. a linkage connected to the interrupters in all phases for imparting closing motion thereto after an opening operation, h. latching means for holding said linkage in an operated position after a closing operation to hold said interrupters closed, i. said latching means being releasable to permit opening of said interrupters, j. a plurality of opening operators respectively biasing the interrupters toward open position and operable upon release of said latching means to separate the contacts of their respective interrupters, and k. a lost-motion connection between said linkage and each interrupter which allows the opening stroke in the associated interrupter to be terminated at a relatively short value by said stroke-length control means without blocking continued opening travel in the other interrupters.