US3009034A

US3009034A - Mechanically trip-free operating mechanism for an electric circuit breaker

Info

Publication number: US3009034A
Application number: US3964A
Authority: US
Inventors: Barkan Philip
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1960-01-21
Filing date: 1960-01-21
Publication date: 1961-11-14
Anticipated expiration: 1978-11-14

Description

P. BARKAN LY TRIP Nov. 14, 1961 3,009,034 MECHANICAL FREE OPERATING MECHANISM FOR AN ELECTRIC CIRCUIT BREAKER Filed Jan. 21, 1960 4 Sheets-Sheet l L ia Inventor Philip Baw karw Attorney. 3

Nov. 14, 1961 P. BARKAN 3,009,034

MECHANICALLY TRIP-FREE OPERATING MECHANISM FOR AN ELECTRIC CIRCUIT BREAKER 4 Sheets-Sheet 2 Filed Jan. 21, 1960 m Inventor:

Philip Barkan, b /mw'i'zuh...

Attorneg.

Nov. 14, 1961 P. BARKAN 3,009,034

MECHANICALLY TRIP-FREE OPERATING MECHANISM FOR AN ELECTRIC CIRCUIT BREAKER Filed Jan.. 21, 1960 4 Sheets-Sheet 3 FULLY P067770 FULLY Inventor:

Philip Bawkan,

OPE IV Attornes.

Nov. 14, 1961 P. BARKAN 3, 34

MECHANICALLY TRIP-FREE OPERATING MECHANISM FOR AN ELECTRIC CIRCUIT BREAKER Filed Jan. 21, 1960 4 Sheets-Sheet 4 I n ve n tor: P h i l ip Bar R an b5 Attorn e 5.

United States Patent 3,009,034 MECHANICALLY TRIP-FREE OPERATING MECH- ANISM FOR AN ELECTRIC CIRCUIT BREAKER Philip Barkan, Lima, Pa., assignor to General Electric Company, a corporation of New York Filed Jan. 21, 1960, Ser. No. 3,964 7 Claims. (Cl. 200-89) This invention relates to a mechanically trip-free operating mechanism for an electric circuit breaker, and, more particularly, to an operating mechanism of this type which is especially suited for high speed reclosing duty.

In certain circuit breaker applications, it is important to reclose the circuit breaker within a very short time interval after the breaker is initially tripped to open. This is a rather complex problem in most mechanically trip-free operating mechanisms because tripping of the usual trip-free latch allows the mechanism to collapse during circuit breaker opening and renders the mechanism incapable of again transmitting closing thrust until it is reset to a thrust-transmitting condition. This resetting operation ordinarily requires a considerable amount of time and, thus, necessitates a delay that tends to interfere with reclosing the breaker within the very short time available after tripping.

In order to reclose within the short time available, it is frequently necessary to reset the operating mechanism to its thrust-transmitting condition long before the breaker has had an opportunity to move through a full opening stroke.

It is therefore an object of my invention to provide a mechanically trip-free operating mechanism that is capable of resetting to a thrust-transmitting condition long before the breaker has had an opportunity to move through a full opening stroke.

Another object is to effect such high speed resetting by means of an improved resetting arrangement that does not significantly interfere with the desired high speed opening of the breaker but yet is capable of providing resetting forces which are maintained at a high level from the instant of tripping until resetting is completed.

In the circuit breaker hereinafter described, resetting forces are applied to the operating linkage by loading a predetermined part of the linkage in tension. 80 long as this part remains on one side of a predetermined dead center position, such tension forces will be in a direction to reset the linkage. But if this part moves beyond dead center, such tension forces will be in a direction to oppose resetting. Under certain conditions, a trip-free operation of the breaker will cause this predetermined part of the linkage to move beyond the predetermined dead center position, and under such circumstances, tension forces applied to the part in question would tend to oppose resetting.

Another object of my invention is to effect automatic resetting of such a linkage under these circumstances despite the presence of resetting means capable of producing only the type of forces that would tend to oppose resetting under these overcenter conditions.

In carrying out my invention in one form, I provide a mechanically trip-free operating mechanism for transmitting closing forces to the usual movable contact of the breaker. The operating mechanism comprises a lever connected at one end to said contact and releasable latching means for releasably restraining the other end of said lever in a latched position. Coupled to the lever is motive means efiective while said other end of the lever is restrained in latched position for driving said lever through a breaker-closing stroke. The movable contact is biased toward open position by opening spring means responsive to release of said latching means for forcing said other end of the lever out of said latched position to allow opening movement of said movable contact to occur. For resetting said other end of the lever to its latched position, improved resetting means capable of completing resetting during an opening stroke is provided. This resetting means comprises cam means operatively connected to said one end of the lever for transmitting resetting forces to the normally latched end of the lever, and resetting spring means for applying such resetting force to the lever through the cam means during an opening stroke. A circuit breaker closing operation causes forces to be transmitted through this cam means to charge the resetting spring means to a level wherein it applies to the thrust transmitting linkage a relatively high force acting in a direction to produce resetting during an opening op eration. The cam means is so shaped that it maintains the resetting force applied by the resetting spring to the thrust-transmitting linkage at a relatively high level until resetting is completed despite large amounts of opening movement of the breaker.

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

FIG. 1 shows a mechanically trip-free operating mechanism embodying one form of my invention. The mechanism of FIG. 1 is shown in the fully-open position.

FIG. 2 shows the mechanism of FIG. 1 in the fullyclosed position.

FIG. 3. shows the mechanism of FIGS. 1 and 2 in a position through which it passes immediately after being tripped to open.

FIG. 4 shows the linkage of FIGS. 1-3 in a position through which it passes during a later stage of an opening operation.

FIG. .5 is a graphical representation of certain force relationships present during an opening operation.

FIG. 6 is a view showing the mechanism in a fully-open position after having been tripped with its closing operator being held in a closed position.

Referring now to FIGS. 1 and 2, the circuit breaker shown therein comprises a set of stationary contacts 11 connected in a power circuit 10 and a movable contact member 12 that is movable between the disengaged or open position shown in FIG. 1 and the engaged or closed position shown in FIG. 2. The movable contact 12 is biased from its closed position of FIG. 2 to its open position of FIG. 1 by means of a suitable opening spring such as the tension spring schematically shown at 13. The opening spring 13 is considerably heavier and larger than the other springs shown in the mechanism but has nevertheless been shown on a reduced scale in order to simplify the drawings. This opening spring 13 is mechanically coupled to the movable contact member 12 by means of an operating rod 14 and a bell crank 16. The bell crank 16 is pivotally mounted on a stationary pivot 18 and has one arm connected to the operating rod 14- and its other arm connected to the opening spring 13. The movable contact member 12 is normally latched in the closed position of FIG. 2 by latch means which will soon be de scribed. When this latch means is released, the opening spring 13 is free to contract and thus drive the bell crank 16 in a clockwise opening direction to effect opening of the movable contact 12.

For driving the movable contact member 12 in an opposite direction, i.e., from its open position of FIG. 1 to its closed position of FIG. 2, a vertically movable actuating rod 20 pivotally connected to one arm of the bell crank 16 is provided. Downward movement of this actuating rod rotates the bell crank in a counterclock- Wise direction from its position of FIG. 1, thus driving the contact member 12 into its closed position of FIG. 2 against the bias of opening spring 13.

The power for producing downward closing motion of the actuating rod 21) is derived from a suitable closing device such as indicated at 25 in FIG. 1. This closing device can be of any suitable form but is preferably a fluid motor of the general design desribed and claimed in application Serial No. 856,122, Coggeshall et al., now Patent No. 2,972,337, filed November 30, 1959, and assigned to the assignee of the present invention. Since the details of this motor 25 form no part of the present invention, the motor has been shown in schematic form only. This motor 25 includes a vertically movable piston 26 that is driven downwardly from its position of FIG. 1 by pressurized fluid supplied to the space above the piston through a suitable three-way controlling valve, schematically shown at 27, when it is desired to close the breaker. Such downward motion of the piston drives the piston rod 28 coupled to the piston in a downward direction, and this downward motion of the piston rod 28 is transmitted to the actuating rod 29 through a mechanically trip-free linkage 30 to efiect circuit breaker closing. When the circuit breaker reaches its closed position the controlling valve 27 is quickly moved to a position that shuts 01f the flow of pressurized fluid to the motor 25 and causes the space above the piston 25 to be quickly vented to atmosphere. Any suitable conventional controlling means can be used for effecting this operation of the valve 27, and for this reason this controlling means has not been shown in the drawings. For an example of suitable controlling means, reference may be had to the aforesaid Coggeshall et al. application.

The mechanically trip-free linkage 36 for transmitting closing force from the motor 25 to the movable contact 12 comprises a main thrust transmitting lever 32 that is pivotally connected to the piston rod 28 by a connecting link 33. This connecting link 33 is pivotally connected at its respective

opposite ends

33a and 33b to the lever 32 and the piston rod 28, with the connection to the lever 32 being located intermediate the ends of the lever 32. The lever 32 is pivotally connected at one end to the actuating rod 23 by means of a pivot 34 and is pivotally mounted at its other end on a guide link 36 by means of a pivot 38. The guide link 36 is pivotally mounted on a stationary pivot 40 and is normally latched in the position of FIG. 1 by latching mechanism 41.

The latching mechanism 41 comprises a latching toggle 42 and a conventional trip latch 43. The trip latch is pivotally mounted on a stationary pivot 44 and is biased in a counterclockwise direction about pivot 44 by means of a torsion spring 44a. A stop 44b limits counterclockwise movement of the trip latch past the position of FIG. 2. The latching toggle 42 that cooperates with the trip latch 43 comprises a pair of

toggle links

45 and 46 pivotally joined together by a knee pin 47. The lower toggle link 45 is pivotally mounted at its lower end on a stationary pivot 50, and the upper toggle link 46 is pivotally connected at its upper end to the pivot 38. When the latch mechanism 41 is in its latched condition of FIG. 2, the toggle links 45 and 46 are prevented from collapsing from the under-center position of FIG. 2 by the restraining action of the trip latch 43 acting on a latch roller 52. This latch roller 52 is mounted on the knee pin 47 and rests on a stop 53 when the unloaded parts are in their fully-open but latched position of FIG. 1. The restraint of the trip latch 43 can be removed by rotating the trip latch in a clockwise direction about its stationary pivot 44. This allows the latching toggle 42 to collapse into the tripped position generally shown in FIG. 3, as will be described in more detail hereinafter.

During the time that the tripping latch 43 is maintained in its latch position of FIGS. 1 and 2, the pivot 38 supporting the left hand end of the main thrust transmitting lever 32 is fixed in its position of FIG. 1. Since the trip latch 43 will remain in its position of FIG. 1 during a closing operation, the pivot 38 may be considered to be fixed during a closing operation. Accordingly,

when the piston rod 28 is driven downwardly from its position of FIG. 1, it acts through the connecting link 33 to pivot the lever 32 in a clockwise direction about its pivot 38. This clockwise motion of lever 32 pulls the actuating rod 20 downwardly against the opposition of closing spring 13, thus driving the movable contact 12 through a closing stroke to produce engagement between the contacts 12 and 11. The position of the various parts at the end of such a closing operation is illustrated in FIG. 2, which shows the breaker in its closed position. As soon as the breaker is driven into its closed position of FIG. 2, the application of closing force from the motor 25 is terminated by suitable control means (not shown), which operates the valve 27 to a position that allows for venting or dumping of the space above piston 26.

For maintaining the breaker in its closed position of FIG. 2 against the opening bias of opening spring 13, a hold-closed prop 60 mounted on a stationary pivot 62 is provided. This prop 60 i biased in a clockwise direction about its pivot 62 by suitable means such as the torsion spring 63. When the parts are in the position of FIG. 1, the prop 60 is held against a suitable stop 64 by means of the torsion spring 63. When the main lever 32 is driven in a clockwise direction from its position of FIG. 1 toward its position of FIG. 2, a roller 66 carried on the pivot pin 34 engages the prop at an intermediate point in the closing stroke, brushing the prop aside against the bias of spring 63. When the lever 32 has been driven through its full closing stroke to complete the closing operation, the prop 60 is driven back into its position of FIG. 2 behind the roller 66 by means of torsion spring 63. In this position, the prop 60 is capable of holding the breaker closed against the bias of spring 13 and any other forces tending to produce opening of the breaker, even though closing force is no longer being supplied to the thrust-transmitting lever 32 from the motor 25.

Referring to FIG. 2, the prop 60, in blocking upward breaker-opening movement of the actuating rod 20, converts a portion of the upward opening force into a component tending to force the main thrust-transmitting lever 32 to the left. This follows from the fact that the active face 68 of the prop is acting on a portion of the periphery of rollers 66 disposed to the right of the vertical line of action of the opening forces. This component of opening force that tends to force the thrust-transmitting lever 32 to the left is opposed by the latching means 41, which holds the pivot 38 in its fixed position of FIG. 2 against this component of opening force.

Opening of the circuit breaker is effected by releasing the latch mechanism 41. This is accomplished by energizing a suitable tripping solenoid 69. Typically, such energization is effected in response to operation of a suitable fault-responsive relay (not shown) which operates in response to a fault on the power circuit 10. The solenoid 69 responds to such energization by driving the trip latch 43 clockwise about its pivot 44 out of restraining relationship with the latch roller 52. This frees the latching toggle 42 to collapse toward its position of FIG. 3 and thus renders the latching toggle 42 incapable of continuing to hold the pivot 38 in its position of FIG. 1. The pivot 38 being thus released, the previously-described component of opening force urging the lever 32 to the left is then free to drive the lever 32 to the left. This leftward movement of lever 32 is controlled by means of the guide link 36, which forces the pivot 38 to follow an arcuate path about the pivot 40 as a center of curvature. Such movement collapses the latching toggle into the position shown in FIG. 3 and, most important, moves the prop roller 66 to the left out of restraining relationship with the prop 60. When the restraint of prop 60 is thus removed, the opening spring 13 is free to drive the actuating rod 20 upwardly and to rotate the bell crank 16 clockwise to produce contact opening.

In many circuit breaker applications, the circuit breaker must be capable of reclosing within a very short time after it is first tripped to open. For example, in one typical application, my circuit breaker is required to reclose within fifteen cycles after the usual tripping impulse is first supplied to the solenoid 69. To enable this requirement to be met, it is necessary that the latching mechanism 41 of my circuit breaker be restored from its collapsed condition of FIG. 3 to a latched condition depicted in FIG. 4 long before the breaker has had an opportunity to reach its fully-open position of FIG. 1. Until the latching mechanism 41 is so reset, the trip-free linkage 30 is incapable of transmitting closing thrust from the motor 25 to the movable contact member 12. Applying such closing thrust to the link 30 before resetting would simply produce further collapse of the latching mechanism without imparting closing thrust to the movable contact.

For resetting the latch means 41 at the required high speed, a cam type resetting arrangement 70 constructed in accordance with the present invention is provided. This cam type resetting means 70 comprises a cam member 72 rigidly attached to the actuating rod 20 at its lower end, a bell crank 74 coacting with the cam member 72, and a compression spring 76 acting on the bell crank 74. The bell crank 74 is pivotally mounted on a stationary pivot 77 and has a roller 78 on one of its arms for engaging the active surface 79 of the cam 72. The compression spring 76 is disposed between the other arm of the bell crank 74 and a suitable carrier 75 pivotally mounted on the stationary pivot 80. When the parts of the breaker are in the closed position of FIG. 2, the resetting spring 76 is in a compressed condition and is forc ing the roller 78 in a clockwise direction into engagement with the cam surface 79.

As was pointed out hereinabove, when the trip latch 43 is tripped, the opening spring 13 responds by driving the thrust-transmitting lever 32 to the left from its position of FIG. 2 to that of FIG. 3. This movement is opposed by the resetting spring 76, but the resetting spring is much smaller than the opening spring 13 and thus does not significantly interfere with the desired movement of the thrust-transmitting lever 32 to the left. The cam surface 79 is so shaped that during movement of the parts from FIG. 2 to FIG. 3, the spring 76 is maintained in a highly charged condition. As a matter of fact, this movement charges the spring by slight additional amount. As soon as the thrust-transmitting lever 32 is moved sufficiently to the left to allow the roller 66 to clear the prop 60, the opening spring 13 no longer tends to drive the lever 32 to the left and thus the highly-charged resetting spring 76 becomes effective to drive the lever 32 back toward the right as the right hand end of the thrust-transmitting lever 32 moves generally upward. These forces for driving the thrust-transmitting lever 32 to the right are supplied to the thrust-transmitting lever 32 through the roller 78 and the cam surface 79. Such movement of the thrust-transmitting lever 32 to the right continues until the latching mechanism 41 has been reset to its latched position. The solenoid 69 does not interfere with such resetting inasmuch as it was deenergized shortly after the contacts parted, in a conventional manner (not shown). When latch resetting has been completed, the parts are passing through the position of FIG. 4. When the trip latch '43 resets into this position of FIG. 4, it closes a latch-checking switch 85 that completes an energizing circuit for the control means of the controlling valwe 27 of the fluid motor 25. The controlling valve 27 responds by quickly admitting pressurized fluid to the motor 25, causing the piston 26 of the motor 25 to move rapidly downward. Such downward movement of piston 26 terminates counterclockwise opening motion of the thrust-transmitting lever 32 about its pivot 38 immediately after the parts pass through the position of FIG. 4 and immediately thereafter forces the lever 32 in an opposite or closing direction, thereby reclosing the breaker.

Inasmuch as the resetting spring 76 is in a highly charged condition when the breaker is in its fully-closed position of FIG. 1, a high resetting force is applied to the thrust-transmitting linkage 32 from the very instant that the trip latch 43 is released to initiate opening. This high initial resetting force contributes to high speed resetting because there is no delay required for building up resetting forces after opening is initiated. Another factor contributing to high speed resetting is that the cam surface 79 is so shaped that movement of the parts from the fullyclosed position of FIG. 2 through that of FIG. 3 to that of FIG. 4 does not appreciably discharge the resetting spring 76. Through all of this opening travel of the parts, the resetting spring 76 is continuing to apply a high resetting force through the cam 79, so as to force the thrust-transmitting lever 32 to the right to reset the latching mechanism 41 after the parts pass through the position of FIG. 3. This high resetting force accelerates resetting action and thus decreases the time required for resetting. A graphic representation of this resetting force is shown in FIG. 5 where resetting force is plotted against opening travel of the actuating rod 20. It wil be observed from the graph that the resetting force is at a high level when the breaker is initially tripped from its fully closed position of FIG. 2, increases slightly during movement from the fully closed position to the position of FIG. 3, and then decreases slightly during movement from the position of FIG. 3 to the fully reset position of FIG. 4. Since these variations are relatively slight, the resetting force may be thought of as remaining at roughly its high initial level until resetting is completed. It will therefore be apparent that my resetting arrangement 70 not only initially applies a high resetting force to the linkage 30 but continues applying a high resetting force to the linkage until the latch means 41 is reset despite large vertical displacements of the actuating rod 20 in an opening direction.

It will be apparent that the cam surface 79 is so shaped that forces applied from the resetting spring 76 through the roller 79 have little or no vertical component tending to drive the cam 72 upwardly. Practically the entire force applied to the roller 78 is acting to force the cam 72 and, hence, the thrust-transmitting lever 32 to the right rather than in an upward direction. Accordingly, I am using the force output of spring 76 primarily for resetting purposes rather than for aiding in opening.

In the above discussion of resetting action, it has been stated that the resetting spring 76 is in a highly charged condition when the breaker is in its fully closed position of FIG. 2. The spring 76 is charged to this relatively high force level by the action of cam surface 79 acting on roller 78 of the bell crank 74 during a closing operation involving movement of the parts from the position of FIG. 1 to that of FIG. 2. More specificially, when the parts are in the fully opened position of FIG. 1, the reset spring '76 is in a discharged condition, but when the parts are driven from the position of FIG. 1 to that of FIG. 2 the cam surface 79 engages the roller 78, forcing the bell crank 74 in a counterclockwise direction and thus compressing the spring 76, as is shown in FIG. 2. When the breaker is in the closed position of FIG. 2, the prop 60 and the latching mechanism 41 hold the resetting spring 76 charged.

A situation which my linkage 30 must be capable of accommodating is one in which the breaker is called upon to open despite the fact that the piston rod 23 of the fluid motor 25 is being held in its lowermost, or closed, position of FIG. 1. Ordinarily, the piston rod 28 will be free to move upwardly with the thrust-transmitting lever 32 and the actuating rod 20 during an opening operation inasmuch as the pressure above piston 26 is normally relieved immediately after closing is completed. However, if for some remote reason, this pressure above piston 26 is not immediately relieved, the piston rod 28 will be held in its lowermost position of FIG. 2. This situation might possibly arise if the breaker is closed on a fault which results in immediate tripping of the trip latch 43 (i.e., a

trip-free operation), but the controlling valve 27 is delayed in opening to relieve the pressure above piston 26, thus holding the piston rod 28 in its lowermost position. Despite the inability of the piston rod 28 to move upwardly, the linkage 30 must allow the breaker to open under these conditions. The disclosed linkage is capable of meeting this requirement inasmuch as the opening spring can first drive the parts into the position of FIG. 3 without lifting the piston rod 23 and inasmuch as further opening movement simply pivots the thrust-transmitting lever 32 in a counterclockwise direction about the pivot 33a, While producing further collapse of the tripping mechanism 41, eventually collapsing the latching mechanism 41 into the position of FIG. 6.

In moving into the position of FIG. 6, it will be noted that the guide link 36 and the lever 32 will pass through a dead center position wherein the line a-a drawn through through the axis of pivots 38 and 4t) and the line b-b drawn through the axis of

pivots

33, 34 will be aligned. Up to this point, any tension forces on the link 32, i.e., forces urging the link 32 to the right, would be in a direction to reset latching mechanism 41. However, after the parts move through this dead center position, as has occurred in FIG. 6, any tension forces applied to the thrust-transmitting lever 32 would act in a direction to produce further collapse of the latching mechanism 41 and therefore to oppose resetting. It therefore follows that if the resetting spring 76 were allowed to continue acting on the thrust-transmitting lever 32 after the dead center position was passed, it would tend to oppose, rather than produce, resetting.

In order to prevent the resetting spring from so preventing resetting of the latching mechanism 41, I have designed the cam 72 in such a manner that it separates completely from the roller 78 as the parts approach their fully open position of FIG. 6. When the cam and its roller separate, the resetting spring 76 no longer applies a tension force to the lever 32 and thus is no longer capable of blocking resetting. This separating action is illustrated in the graph of FIG. 5 by the sharp drop in force occurring at the right hand side of the curve of FIG. 5. Resetting is accomplished under these circumstances by an auxiliary resetting spring in the form of a light torsion spring 90 that drives the guide link 36 in a clockwise direction about its pivot 40. FIG. 6 illustrates the parts just prior to such resetting under the influence of auxiliary resetting spring 90. The resetting spring 90, being a light one, this resetting is accomplished at a relatively low speed, but this is no significant disadvantage because no high speed reclosing would ordinarily be required under these circumstances. In this regard, in most circuit breaker applications, if a breaker is closed on a fault and trips open immediately in response thereto, as has just been described, no efiort is ordinarily made to follow this opening operation with a high-speed reclosing operation.

It is assumed in the above description of a resetting operation by auxiliary reset spring 9t) that the controlling valve 27, though delayed in'operating to vent the fluid motor 25, has finally effected such venting to allow piston 26 to be moved upwardly by the auxiliary resetting spring 90.

There are some relatively rare circuit breaker applications that require that a trip-free operation be followed by a high speed reclosing operation. It is to be understood that my breaker can readily be applied in such applications inasmuch as it is normally capable of resetting at the required high speed even after a trip-free operation. It is only in the remote event of a malfunction in valve 27 that high speed resetting could not occur.

While I have shown and described a particular embodiment 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 movable contact and a mechanically trip-free operating mechanism for transmitting closing force to said movable contact, said operating mechanism comprising a lever connected at one end to said contact, releasable latching means for releasably restraining the other end of said lever in a latched position, means coupled to said lever and effective while said other end is restrained in latched position for driving said lever from a first to a second position to produce closing of said contact, opening spring means responsive to release of said latching means for forcing said other end of said lever out of said latched position to allow opening of said movable contact to occur, resetting means for resetting said other end of said lever to said latched position during an opening stroke, said resetting means comprising cam means coupled to said one end of said lever for transmitting resetting forces to said other end of said lever, and resetting spring means for applying said resetting force to said lever through said cam means during an opening stroke.

2. The circuit breaker of claim 1 in combination with prop means coacting with said lever to hold said movable contact closed while said other end of the lever is held in said latched position, said prop means acting upon release of said latching means to convert force from said opening spring means into a force component acting in a direction to drive said other end of said lever out of said latched position.

3. An electric circuit breaker comprising a movable contact and a mechanically trip-free operating mechanism for transmitting closing force to said movable contact, said operating mechanism comprising a lever connected at one end to said contact, releasable latching means for releasably restraining the other end of said lever in a latched position, means coupled to said lever and effective while said other end is restrained in latched position for driving said lever from a first to a second position to produce closing of said contact, opening spring means responsive to release of said latching means for forcing said other end of said lever out of said latched position to allow opening of said movable contacts to occur, resetting means for resetting said other end of said lever to said latched position during an opening stroke, said resetting means comprising cam means coupled to said one end of said lever for transmitting resetting forces to said other end of said lever, and resetting spring means for applying said resetting force to said lever through said cam means during an opening stroke, means for charging said resetting spring means from a first force level to a second force level during closing motion of said lever from said first to said second position, said cam means being so shaped that the resetting force supplied by said resetting spring means to said lever through said cam means remains at a level substantially higher than said first force level during substantially the entire resetting operation.

4. An electric circuit breaker comprising a movable contact and a mechanically trip-free operating mechanism for transmitting closing force to said movable contact, said operating mechanism comprising a lever connected at one end to said contact, releasable latching means for releasably restraining the other end of said lever in a latched position, means coupled to said lever and effective While said other end is restrained in latched position for driving said lever from a first to a second position to produce closing of said contact, opening spring means responsive to release of said latching means for forcing said other end of said lever out of said latched position to allow opening of said movable contacts to occur, resetting means for resetting said other end of said lever to said latched position during an opening stroke, said resetting means comprising cam means coupled to said one end of said lever for transmitting resetting forces to said other end of said lever, and resetting spring means for applying said resetting force to said lever through said cam means during an opening stroke, and means for charging said resetting spring means from a first force level to a second force level during closing motion of said lever from said first to said second position.

5. An electric circuit breaker comprising a movable contact and a mechanically trip-free operating mechanism for transmitting closing force to said movable contact, :said operating mechanism comprising a lever connected at one end to said contact, releasable latching means for releasably restraining the other end of said lever in a latched position, means coupled to said lever and effective while said other end is restrained in latched position for driving said lever from a first to a second position to produce closing of said contact, opening spring means responsive to release of said latching means for forcing said other end of said lever out of said latched position to allow opening of said movable contacts to occur, resetting means for resetting said other end of said lever to said latched position during an opening stroke, said resetting means comprising cam means coupled to said one end of said lever for transmitting resetting forces to said other end of said lever, and resetting spring means for applying said resetting force to said lever through said cam means during an opening stroke, means for charging said resetting spring means from a first force level to a second force level during closing movement of said lever from said first to said second position, said cam means being so shaped that the resetting force supplied by said spring means to said lever through said cam means remains at approximately said second force level during substantially the entire resetting operation.

6. An electric circuit breaker comprising a movable contact and a mechanically trip-free operating mechanism for transmitting closing force to said movable contact, said operating mechanism comprising a lever connected at one end to said contact, releasable latching means for releasably restraining the other end of said lever in a latched position, means coupled to said lever and efiective while said other end is restrained in latched position for driving said lever from a first to a second position to produce closing of said contact, opening spring means responsive to release of said latching means for forcing said other end of said lever out of said latched position to allow opening movement of said movable contacts to occur, guide means for guiding said other end of the lever during movement thereof While out of its latched position, main resetting means for applying to said one end of said lever a resetting force that loads said lever in tension, said guide means being so constructed that tension force applied to said lever acts to return said one end of the lever toward said latched position so long as said lever is located on one side of a predetermined dead center position with respect to said guide means but acts to move said one end away from said latched position when said lever is located on the opposite side of said dead center position, means responsive to a predetermined mechanically tripfree operation of said breaker for moving said lever into a position at said opposite side of said dead center position during an opening operation, means for disengaging said main resetting means from said lever in response to movement of said lever into said position at said opposite side of dead center thereby rendering said main resetting means incapable of opposing return of said one end of said lever to latched position, and auxiliary resetting means coupled to said lever for restoring said other end of said lever to said latched position when said main resetting means is disengaged from said lever.

7. An electric circuit breaker comprising a movable contact and a mechanically trip-free operating mechanism for transmitting closing force to said movable contact, said operating mechanism comprising a lever connected at one end to said contact, releasable latching means for releasably restraining the other end of said lever in a latched position, means coupled to said lever and effective While said other end is restrained in latched position for driving said lever from a first to a second position to produce closing of said contact, opening spring means responsive to release of said latching means for forcing said other end of said lever out of said latched position to allow opening of said movable contact to occur, resetting means for resetting said other end of said lever to said latched position during an opening stroke, said resetting means comprising cam means coupled to said one end of said lever for transmitting reset-ting forces to said other end of said lever, and resetting spring means for applying said resetting force to said lever through said cam means during an opening stroke, the resetting force applied by said resetting means to said lever loading said lever in tension, guide means for guiding said other end of said lever during movement thereof while out of its latched position, said gmide means being so constructed that tension force applied to said lever acts to return said one end of the lever toward said latched position so long as said lever is located on one side of a predetermined dead center position with respect to said guide means but acts to move said one end away from said latched position when said lever is located on the opposite side of said dead center position, means responsive to a predetermined mechanically trip-free operation of said breaker for moving said lever to said opposite side of said dead center position during an opening stroke, means for rendering said cam means incapable of transmitting tension force to said lever in response to movement of said lever to said opposite side of dead center, thereby rendering said resetting means incapable of opposing return of said one end of the lever to latched position, and auxiliary resetting means coupled to said lever for restoring said other end of said lever to said latched position when said cam means is disabled.

References Cited in the file of this patent UNITED STATES PATENTS 2,150,587 Peterson Mar. 14, 1939 2,570,153 Phillips Oct. 2, 1951 2,730,589 Perry et a1 Jan. 10, 1956 2,794,881 Frank June 4, 1957