US2794881A

US2794881A - Circuit breaker operating mechanism

Info

Publication number: US2794881A
Application number: US444947A
Authority: US
Inventors: Edward J Frank
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1954-07-22
Filing date: 1954-07-22
Publication date: 1957-06-04
Anticipated expiration: 1974-06-04
Also published as: FR1137406A

Description

June 4, 1957 A E. J. FRANK 2,794,831

CIRCUIT BREAKER OPERATING MECHANISM Filed July 22. 1954 Ff J.

S I g I /9 f I V DISTANCE nventor:

I Edwa d J. Fr nk, Hf?

borneg.

Patented June 4, 1957 2,794,881 CIRCUIT BREAKER OPERATING MECHANISM Edward J-. Frank, Springfield, Pa., assignor to General Electric Company, a corporation of New York Application July 22 1954, Serial No. 444,947

12 Claims. (Cl. 200 89) This invention relates to an operating mechanism for an electric circuit breaker and, more particularly, to an operating mechanism which is capable of providing smooth and effective closing performance even though the breaker is closed against a faulted line.

When the contacts of a circuit breaker are driven toward closed position against a faulted line, at the instant fault current begins to flow between the contacts, high electromagnetic forces are abruptly established. These electromagentic forces var in magnitude in accordance with the square of the fault current and, for most contact arrangement, tend to oppose the final portion of the breaker closing stroke. At high values of fault current these retarding forces tend to stall, or even momentarily reverse, the closing motion of the breaker. and, as a result; tend to cause excessive Contact burning and other und sit-able disturbances. This problem is especially acute in those a plications where the closing device which supplies the force tor closing the breaker may lose its closin'g power at the very instant that these high retarding forces are established.

Accordingly, it is a primary object of my invention to provide a circuit breaker closing mechanism which is capable of effectively overcoming the high retarding forces which are established near the end of the contaet-closing stroke.

It is a further object of my invention to provide; in a circuit breaker mechanism, a simple and reliable energy storing means which is charged during the first por tion of the closing stroke and is discharged at the end of the closing stroke in such a manner that the stored energy is available to effectively overcome the electromagnetic retarding forces which are established at the end of the stroke.

In accordance with one form of my invention, the cir c'uit breaker operating mechanism is provided with a follower which is movable from a fully-open position to a fully-closed position as the breaker is driven through its closing stroke by suitable driving means. This follower cooperates with a holding member which is rnovable toward a mechanism-restraining position behind the follower at a predetermined intermediate point near the end of the breaker closing stroke. Biasing the holding member toward this mechanism-restraining position is an energy accumulator in the form of a heavy spring in which energy is stored during the first portion of the closing stroke. The holding member has a driving cam surface engageable with the follower and through which the stored energy of the spring is discharged to said follower as said holding member is moved toward its mechamom-restraining position. This driving cam surface is contoured in such a manner that the moving contact point between the cam surface and the follower progressively approaches said fully-closed position of the follower. As a result of this contour,- the spring, acting through the driving earn surface, is eneetive to produce a .wedgin action which materially aids in driving the follower and the associated mechanism into the fullyclosed position.

For a better understanding of my invention, reference may be had to the accompanying drawing in which Fig. 1 illustrates a circuit breaker closing mechanism embodying my invention. The fully-closed position of the mechanism is indicated in solid lines. Fig. 2 is a detailed view of a portion of the mechanism of Fig. 1. Solid lines have been used to illustrate the position of the parts at an intermediate point in the breaker closing stroke. Fig. 3 is a graphical representation of the manner in which excess energy stored during the first portion of the breaker closing stroke is made available to overcome the high magnetic opposing forces which are present at the end of the stroke.

Referring now to Fig. 1, I have illustrated my invention as being applied to a circuit breaker 10 having separable contacts 11 and 12 which are relatively movable to control a polyphase circuit including conductors 7, 8 and 9. In a conventional manner, the contacts are arranged to have a slight amount of wipe so that when the contacts 11 are moved toward closed position the dos ing stroke continues for at least a short distance beyond the point at which the contacts first touch. The contacts 11 are jointly movable from a fully-open position to the fully-closed position shown in Fig. l by means of an operating mechanism 13 actuated by a suitable closifig device such as the solenoid 14 shown. This clo'si'n'g operation is described in greater detail hereinafter. As shown in the drawing, the operating mechanism 13 is of the mechanically trip-free type and is in many respects similar to the mechanism shown in U. S. Patent No. 2,458,240 issued to R. J. Baskerville and assigned to the assignee of the present invention. The mechanism 13 comprises a toggle linkage which includes a pair of toggle links 15 and 16 pivotally joined together at the knee of the toggle by a pin 17, hereinafter referred to as a follower or a follower pin.

For transmitting movement from this toggle linkage to the movable contacts 11, there is provided an output crank 18 and an operating rod 19 suitably coupled tog'ether by a pin 20. The output crank 18, which is pivotally mounted about fixed shaft 21, is pivotally joined at 22 to one end of the toggle link 16, whereas the opcrating rod 19 is suitably coupled to movable contacts 11. The other toggle link 15 is pivotally connected at 23 to a guide link 24 which, in turn, is pivotally mounted about a fixed supporting pin 25.

The contacts 11, 12' are biased toward open position by means of a suitable opening spring 30, but are relea'sably latched in the closed position shown by means of a suitable trip latch 31. As shown in Fig. l, the trip latch 31 is biased by spring 32 in a counterclockwise direction about a fulcrum pin 31a and into a latching position against a latch roller 33 mounted about the pivot pin 23.

Suitable stops

33a and 34 respectively retain the latch and the roller in the latch-closed position of Fig. 1.

When the mechanism is latched in this position; it is prevented from collapsing at the knee of toggle 15, 16 by means of a prop 41 which support the follower pin 17. This prop, or holding member, 41 is pivotally mounted about a shaft 42 and is biased into the mechanismrestraining position of Fig. 1 by means of a strong coil spring 43. A stop 44 prevents the prop from being moved counterclockwise past the mechanism-restraining position of Fig. 1.

For releasing the trip latch 31 so as to trip the breaker, there is provided a tripping solenoid 35 comprising a coil 36 and a plunger 37 biased into a normal position By a return spring 38. Although the coil 36 may be energized in accordance with any desired electrical con dition, I have shown it connected as a series coil which is responsive to overcurrent in one of the power lines 9. Thus, when the current in line 9 exceeds a predetermined value, the plunger 37 overcomes the bias of spring 38 and moves to the left thereby to drive the latch 31 counterclockwise to a tripped position. This tripping movement of the latch 31 immedaitely renders the mechanism 13 inelfective to restrain the opening spring 30, and as a result, the opening spring rapidly drives the contacts 11 upwardly through an opening stroke. During this contact opening stroke the opening spring 30 drives the unlatched guide link 24 counterclockwise about its support pin 25, and as a result, the follower pin 17 moves leftwardly off of the supporting surface of prop 41, and the toggle 15, 16 collapses downwardly at its knee. As the opening stroke is completed, the mechanism is reset for a subsequent closing operation by a suitable resetting spring 39 which is shown coiled about the pivot 25. The resetting spring 39 carries out this resetting operation by returning the guide member 24 to the latched position shown in Figure l with the trip roller 33 resting upon the support stop 34. The position of toggle linkage 15, 16 when the mechanism has been tripped and subsequently reset is indicated by the dotted line of Fig. 1. With the mechanism thus reset, it is in a condition for transmitting thrust from the closing device 14 to the movable contact 11.

The mechanism as described up to this point is similar to the conventional form of circuit breaker operating mechanism illustrated in the above-mentioned Baskerville patent. Since the essence of my invention resides in the improved closing performance of the circuit breaker mechanism, it is believed that the novel structure which produces this improved performance can be best understood from a description of a closing operation. Such a closing operation may be initiated at any time after the mechanism has been reset to the thrust-transmitting condition described above.

Closing of the breaker is accomplished by driving the knee of the toggle 15, 16 from the dotted-line, fully-open and reset position of Figs. 1 and 2 upwardly toward the solid-line, fully-closed position shown in Fig. 1. The solenoid 14, which supplies the motive power for this closing operation, comprises a reciprocable plunger 46 which is moved upwardly by energization of a coil 47. This upward closing movement of the plunger is transmitted to the mechanism 13 by means of a suitable roller 48, which is supported about the knee pin 17'and against the outer surface of which the upwardly moving plunger bears in driving relationship.

When the contacts of a circuit breaker are driven toward closed position, at the instant that current begins to flow between the contacts, high-electromagnetic forces are abruptly established. Since these magnetic forces vary in magnitude in accordance with the square of the current, it will be apparent that they will reach an extremely high value if the breaker is closed against a fault, or a short circuit. For a conventional contact arrangement, such as shown in Fig. 1, these electromagnetic forces act in a direction to oppose the breaker closing action. For many circuit breaker applications, these forces are of suflicient magnitude to stall, or even momentarily reverse, the closing motion of the breaker. As a result, these retarding forces tend to cause excessive contact burning and other undesirable disturbances which impair the reliability of the breaker.

In accordance with my invention, these high magnetic retarding forces which are abruptly established near the end of the closing stroke are effectively overcome by utilizing the prop 41 and its associated spring 43 asa means which, after having extracted and stored a desired amount of energy from the solenoid for the first portion of the closing stroke, returns this energy to the mechanism near the end of the stroke in such a manner that it is avail- I stroke.

To facilitate an understanding of the manner in which energy is transferred to and from the spring as the circuit breaker moves through its closing stroke, reference may be had to Fig. 3. In this figure the curve A represents the solenoid force curve as the magnetically-actuated plunger moves through its upward stroke, the stroke being initiated at the left-hand end ofthe abscissa and terminating at the right-hand end thereof. The area B represents energy extracted from the closing thrust during the first portion of the stroke when the circuit breaker opposing forces are low. This energy is stored within the spring for subsequent release at a point C, where it is returned in the form of a concentrated block of energy represented by the area B1. This block of energy 81 is available to overcome the high opposing forces at the end of the stroke, and as may be seen from the graph, the force derived from this block B1 may be substantially in excess of that yielded by the solenoid magnetic effort alone. For effecting this transfer of energy, the prop is provided with a driven cam surface 50 and a driving cam surface 51 which are arranged to engage the follower pin 17 as it moves upwardly through its closing During the first portion of this upward closing stroke the pin 17 engages the driven cam surface 50 and, because of the cam contour, is effective to drive the prop clockwise against the spring 43 thereby storing excess energy from the solenoid in the spring As this upward movement continues, the energy stored within the spring 43 progressively increases until finally the pin 17 passes above thecrown 52 which joins the two cam surfaces 50 and 51. The position of the operating parts at this instant isshown in solid lines in Fig. 2. At this instant, the energy stored within the spring is released and becomes effective to drive the prop 41 counterclockwise behind the upwardly moving follower pin 17. In accordance with my invention, the upper cam surface 51 is contoured in such a manner that this counterclockwise prop movement is effective to produce a wedging action which materially aids in driving the follower pin 17 and the associated mechanism 13 upwardly into the fully closed solid-line position. Stated otherwise, this wedging or spring-discharging action of prop 41 materially aids in driving the moving contacts 11 past the point of initial contact engagement, through their wiping travel, and into the fully-closed position. To describe the contour of this driving cam surface 51 more specifically, it may be said that, proceeding in a clockwise direction from the crown 52, incrementally spaced points on the cam surface are disposed at progressively greater distances from the pivot axis of the prop, as a result of which, the moving contact point between the cam sur face 51 and the follower pin 17 approaches the fullyclosed solid-line position of the pin 17 as the prop is driven into it solid-line mechanism-restraining position underneath the pin 17 The extent of this upward driving movement of pin 17 by the cam surface 51 is limited by the engagement of stop 44 with a suitable extension or arm of the prop 41.

In the preferred form of my invention crown 52 is so located that the upward wedging action of the prop is initiated at an intermediate point in the closing stroke just prior to the instant at which current begins to 110W between the contacts 11, 12; since it is at this instant that the electromagnetic retarding forces are abruptly ini-' tiated. It is at this instant that the added closing energy is needed to drive the contacts to fully-closed position without stalling. Since thereis almost always a short arc established just prior to the instant in which the closing contacts touch, the position of the mechanism atthe instant which current begins to flow between the contacts may be termed the pre-arc position." Thus,-in the pre-' ferred form of my invention, the cam surfaces of the prop are so contoured that the counterclockwise wedging action of the prop 41 is initiated prior to the mechaable to eifectively overcome these high retarding forces. nism having reached theme-arc posi ion... 5 11 91 811 such a relationship is the preferred one, for some applications the kinetic energy stored within the moving mechanism permits this wedging action to be initiated at a slightly later intermediate point in the closing stroke.

It will be apparent from the above description that the spring 43 should be sufiiciently large so that it is capable of storing enough energy to provide a closing force which is effective to overcome the peak retarding forces without stalling of the moving contacts. More particularly, the spring, in discharging, should be capable of supplying, through the driving cam surface 51, an instantaneous force which is at least equal to the difference between the peak contact-retarding force and the sum of the instantaneous output of solenoid plus the force derived from the kinetic energy stored within the moving parts of the circuit breaker.

The problem of contact stalling is especially acute in those applications in which the closing solenoid is energized as shown in the drawing. More specifically, in the drawing the closing coil is connected across the power lines 8, 9 and is controlled by a switch 60 which may be operated either manually or automatically in accordance with any desired condition. Assume now that the circuit breaker first is in its open position and the switch 60 is then closed to energize the solenoid 14 and thereby to drive the breaker toward closed-contact position. If it so happens that there is a fault, such as a fault to ground, present on the line 8 or 9 when the contacts 11, 12 reach the pre-arc position, current will instantly flow through the contacts and into the fault, thereby depriving the solenoid 14 of closing power at the very instant that it is most needed. The hazards of such a situation are effectively avoided in a mechanism constructed in accordance with my invention because the closing energy of the then discharging spring 43 is available at this critical instant not only to compensate for the loss, which may be total, of solenoid power but also to provide the added energy which is necessary to overcome the peak electromagnetic retarding forces which are abruptly initiated at this instant.

If the circuit breaker is closed on an unfaulted line, it will be apparent that the electromagnetic retarding forces are very low in comparison to those present when the breaker is closed on a faulted line. To insure that excessive closing power will not be delivered to the mechanism for such a closing operation, the stroke of the solenoid is preferably arranged to be less than the full closing stroke of the breaker. This permits the prop mechanism 41, 43 alone to provide the closing power for the final portion of the stroke for all closing operations.

The necessity of avoiding stalling during a contactclosing or reclosing stroke is especially important in those circuit breaker applications in which the tripping action is deliberately retarded, say, in a system wherein several associated circuit breakers are arranged for coordinated tripping and reclosing. Obviously, it is most hazardous for the movable contacts to remain stalled at an intermediate arcing position for an appreciable portion of the time interval during which tripping is retarded. It is to be understood that my invention is equally applicable to such time-delayed, or retarded, tripping arrangements as it is to instantaneous tripping arrangements.

While I have shown and described a preferred embodiment of my invention, it will be obvious to those skilled in the art that various modifications may be made without departing from my invention in its broader aspects. I therefore aim 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. A circuit breaker closing mechanism comprising a follower which is movable from a fully-open position to a fully-closed position as said breaker is moved through its full closing stroke, actuating means operable to drive said follower from said fully-open position toward said fully-closed position, a holding member movable toward a mechanism-restraining position behind said follower at a predetermined intermediate point in said closing stroke, spring means from which stored energy is releasable to drive said holding member into said mechanism-restraining position, means responsive to movement of said follower through a first portion of said closing stroke for storing energy in said spring means, a driving cam surface on said holding member through which said stored energy is releasable to said follower as said holding member is moved toward its mechanism-restraining position, said driving cam surface being shaped so that the moving contact point between said follower and said cam surface gradually approaches said fullyclosed position as said holding member moves into its mechanism-restraining position whereby said holding member movement pr'o vides a wedging action which effectively aids in driving the breaker through the last portion of its full closing stroke.

2. A circuit breaker closing mechanism comprising a follower which is movable from a fully-open position to a fully-closed position as said breaker is moved through its full closing stroke, actuating means operable to drive said follower from said fully-open position toward said fully'closed position, a holding member movable toward a mechanism-restraining position behind said follower at a predetermined intermediate point in said closing stroke, spring means from which stored energy is releasable to drive said holding member into said mechani'sm-restraining position, means responsive to movement of said follower through a first portion of said closing stroke for storing energy in said spring means, a driving cam surface on said holding member through which said stored energy is releasable to aid in driving said follower toward fullyclosed position in response to movement of said holding member toward its mechanism-restraining position.

3. The closing mechanism of claim 1 in which said predetermined intermediate point is located ahead of the pre-arc position at which the circuit breaker first reestablishes an electrical circuit.

4. A circuit breaker having a closing mechanism which is subjected to high electromagnetic retarding forces when closed on a fault, said closing mechanism comprising a follower which is movable from a fully-open position to a fully-closed position as said breaker is driven through its full closing stroke, actuating means operable to drive the follower from said fully-open position toward said fully-closed position, a holding member movable toward a mechanism-restraining position behind said follower at a predetermined intermediate point in said closing stroke, spring means from which stored energy is releasable to drive said holding member into said mechanism-restraining position, means responsive to movement of said follower through a first portion of said closing stroke to store a predetermined amount of energy in said spring means, a driving cam surface on said holding member through which said stored energy is releasable to said follower as said holding member is moved toward its mechanism-restraining position, said cam surface being shaped so that the moving contact point between said follower and said cam surface gradually approaches said fully-closed position as said holding member moves into its mechanism-restraining position, said predetermined amount of stored energy being of suflicient magnitude to permit the spring means when released to overcome, without stalling, the peak retarding forces initiated when the breaker is closed on a fault.

5. The combination of claim 4 in which said predetermined amount of stored energy provides a closing force which exceeds the difference between the peak retarding force and the sum of the instantaneous output force of the actuating device plus the force derived from the kinetic energy stored in the moving parts of said circuit breaker.

- whereby said actuating means drives the mechanism through only a portion of its stroke.

7. The combination of claim 4 in which said actuating means is a solenoid having a plunger which has a stroke less than the travel of said follower during said full breaker closing stroke, whereby said plunger drives the mechanism through only a portion of its full closing stroke.

8. A circuit breaker closing mechanism comprising a follower which is movable from a fully-open position into a fully-closed position as said breaker is driven through its full closing stroke, actuating means operable to drive said follower from said fully-open position toward said fully-closed position, a holding member movable toward a mechanism-restraining position behind said follower at a predetermined intermediate point in said closing stroke, spring means from which stored energy is releasable to drive said holding member into said mechanism-restraining position, a first cam surface on said holding member through which closing movement of said actuating means is transmitted to store energy in said spring means,

' a second cam surface on said holding member through which said stored energy is imparted to said follower as said holding member is moved toward its mechanismrestraining position behind said follower, said second cam surface being shaped so that the moving contact point between said follower and said cam surface gradually approaches said fully-closed position as said holding member moves toward its mechanism-restraining position, whereby said holding member movement provides a wedging action which is effective to drive the breaker through the last portion of its closing stroke' 9. A circuit breaker closing mechanism comprising a follower which is movable from a fully-open position into a fully-closed position as said breaker is driven through its full closing stroke, actuating means operable to drive said follower from said fully-open position toward said fully-closed position, a holding member movable about a pivot axis toward a mechanism-restraining position behind said follower at a predetermined intermediate point in said closing stroke, spring means from which stored energy is releasable to drive said holding member into said mechanism-restraining position, means operable in response to movement of said follower through a first portion of said closing stroke to store energy in said spring means, a driving cam surface on said holding member through which said stored energy is imparted to said follower as said holding member is moved toward its mechanism-restraining position behind the follower, said cam surface being contoured to contact said follower at incrementally spaced points disposed at progressively greater distances from the pivot axis of said holding member whereby said holding member movement provides 'a wedging action which is effective to drive the breaker through the last portion of its closing stroke;

10. A circuit breaker closing mechanism comprising a follower which is movable from a fully-open position into a'fully-closed position as said breaker is driven through its full closing stroke, actuating means operable to drive said follower from said fully-open position toward said fully-closed position, a holding member movable about a pivot axis toward a mechanism-restraining position behind said follower at a predetermined intermediate point in said closing stroke, spring means from which stored energy is releasable to drive said holding member into said mechanism-restraining position, said holding member having a pair of cam surfaces successively engageable with said follower and intersecting at a crown, the first of said cam surfaces constituting a driven cam surface through which closing movement of said actuating means operates to store energy in said spring means, the second of said cam surfaces constituting a driving surface through which said stored energy is imparted to said follower as said holding member is moved toward its mechanism-restraining position, said second cam surface being contoured so that, proceeding from said crown, incrementally spaced points on said second surface are at progressively greater distances from the pivot axis of the holding member.

11. In a circuit breaker having a circuit-controlling contact, a collapsible linkage coupled to said contact and including a follower portion movable from a fully-open position into a fully-closed position as said contact is driven through its full closing stroke, actuating means operable to supply closing thrust to said linkage, a trip latch operable in a latching position to render said linkage effective to transmit closing thrust to said contact and movable toward a tripped position to render said linkage ineffective to transmit closing thrust to said contact, a holding member movable into a mechanism-restraining position behind said follower as said follower is moved beyond a predetermined intermediate point in said closing stroke, spring means from which stored energy is releasable to drive said holding member into said mechanism-restraining position, means responsive to closing movement of said actuating means for storing energy in said spring means, a driving cam surface on said holding member through which said stored energy is imparted to said follower as said holding member moves toward its mechanism-restraining position, said cam surface being shaped to gradually approach said fully-closed position as said holding member moves into its mechanism-restraining position, whereby said holding member movement provides a wedging action which aids in driving the breaker through its full closing stroke.

12. In a solenoid actuated circuit breaker mechanism comprising an actuating plunger, a toggle-linkage mechanism including a tripping latch and holding prop member for said linkage, an energy accumulator the discharge of which urges said prop into its holding position, means associated with said plunger for progressively charging said accumulator during the actuating stroke of said plunger, and means associated with said prop for discharging said accumulator whereby to materially aid in completing an actuating stroke of said mechanism.

References Cited in the file of this patent UNITED STATES PATENTS 1,827,626 Thumim Oct. 13, 1931 1,953,789 Thurnin Apr. 3, 1934 1,988,287 Thumin Jan. 15, 1935 2,152,453 Atwood et a1 Mar. 28, 1939