Abstract:
In a circuit breaker undervoltage release device, a spring powered trip slide is held in a latched position by a latch lever while the plunger of a solenoid is magnetically held in a seated position against the bias of a calibrated return spring. In the event of an undervoltage condition, the spring retracts the plunger, causing the latch lever to release the trip slide, which then moves to trip the breaker. Opening movement of the breaker mechanism first actuates a reset lever to load a reset spring and then returns the slide to its latched position. As the latch lever regains latching control of the slide, the reset spring discharges to snap the plunger to its seated position.

Description:
BACKGROUND OF THE INVENTION 
     An undervoltage release (UVR) device is a well known circuit breaker accessory utilized to protect electrical equipment against potential damage from an abnormal undervoltage condition. Typically, a UVR device takes the form of a solenoid energized from the line voltage to magnetically detain its plunger in a seated position against the bias of a calibrated return spring. If line voltage drops to an undesirably low level for longer than a momentary period, the plunger detaining magnetic force decreases to the point where the return spring force becomes overpowering. The plunger thus springs to a retracted position, initiating tripping of the circuit breaker to its open circuit condition. After the undervoltage condition has been corrected, it is necessary to reset the UVR device. This reset operation entails forceably returning the plunger to its seated position in order that the magnetic force generated by the solenoid can regain control of the plunger such as to retain it in its seated position against the return spring bias. One manner of effecting this reset operation is manually by depression of a button to force the plunger back to its seated position. However, the preferred method is to utilize the opening movement of the circuit breaker operating mechanism to return the plunger to its seated position and hold it there against the return spring bias pending the return of normal line voltage. U.S. Pat. Nos. 3,162,740; 3,293,577; 3,360,751 and 3,453,568 are exemplary of this prior art approach to resetting a UVR device. 
     In the typical circuit breaker, the opening movement of its mechanism is quite violent, necessarily so to achieve the abrupt contact separation required in most applications. In order that the full impact of the breaker mechanism opening movement not be communicated to the UVR device, resilient means, typically in the form of a spring, is generally interposed between the breaker mechanism and the UVR plunger. Such resilient means yields to cushion the force of impact of the plunger upon arrival at its seated position, as well as to accommodate overtravel of the breaker mechanism in its opening movement. Thus, the resilient means also accommodates less strigent manufacturing tolerances. 
     The principle problem encountered in the field with UVR devices is their failure to reset. If the UVR device cannot be reset, its plunger remains retracted by the return spring, and thus reclosure of the breaker contacts to restore electrical service is inhibited. Reset failures are generally occasioned by the inability of the breaker mechanism acting via the cushioning means to firmly reseat the solenoid plunger and thereby render the solenoid magnetic force capable of detaining the plunger in its seated position against the bias of the return spring. It is found that in time increased frictional drag on the plunger movement caused by wear, dirt accumulation and misalignment can render the cushioning means incapable of reseating the plunger to the extent necessary to enable the magnetic force of the solenoid to overpower the return spring. 
     It is accordingly an object of the present invention to provide an improved undervoltage release device for utilization as an accessory for electric circuit breakers. 
     Another object of the present invention is to provide an undervoltage release device of the above character which is automatically reset incident to normal functioning of the breaker operating mechanism. 
     A further object is to provide an undervoltage release device of the above character which is automatically reset in an efficient and reliable manner. 
     Yet another object of the present invention is to provide an undervoltage release device of the above character which is uniquely constructed to provide long-lived, trouble-free operation. 
     Other objects of the invention will in part be obvious and in part appear hereinafter. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, there is provided an undervoltage release (UVR) accessory device for electric circuit breaker, wherein the UVR device, upon operating to trip a circuit breaker, is automatically reset incident to normal functioning of the breaker operating mechanism to open the breaker contacts. More specifically, the present invention provides an improved UVR device which is uniquely structured such that automatic resetting of the device is achieved in a more reliable manner than has been the case heretofore. 
     The UVR device of the present invention includes a solenoid which, when energized under normal line voltage conditions, is capable of magnetically detaining its plunger in a seated position against the bias of a calibrated return spring. A latch lever linked to the solenoid plunger latchably engages a trip slide to return the latter in a retracted position against the bias of actuator spring so long as the plunger remains in its seated position. If the line voltage drops to an undesirably low lever for other than a momentary period, the energization of the solenoid decreases as does the magnetic force striving to detain the plunger in its seated position. The return spring overpowers the reduced magnetic force, and the plunger is pulled out to an extended position. The latch lever releases the trip slide, and the actuating spring forces the trip slide into tripping engagement with a circuit breaker latch. The breaker operating mechanism is thus tripped and it proceeds forthwith to open the breaker contacts. 
     To reset the UVR device of the present invention after it has operated to trip the circuit breaker, the contact opening movement of the breaker mechanism is utilized. To this end, a reset pin carried by a suitable member of the breaker operating mechanism engages and pivots a reset lever incident with opening movement of the breaker mechanism. The reset lever is coupled with the latch lever by a reset spring. Pivoting of the reset lever by the reset pin loads the reset spring which then acts to bias the latch lever toward its trip slide latching position and the solenoid plunger toward its seated position. However, such movements of the latch lever and solenoid plunger are inhibited by the trip slide. Continued movement of the reset pin during concluding contact opening movement of the breaker mechanism picks up the trip slide pursuant to returning the latter to its retracted position. Upon arrival of the trip slide at its retracted position, the motional restraint on the latch lever is abruptly removed. The reset spring discharges to move the latch lever to its latching position and, at the same time, snaps the solenoid plunger to its seated position with sufficient impact to ensure firm reseating of the solenoid plunger. The return spring maintains the plunger firmly seated, permitting the magnetic force of the solenoid to readily regain control of the plunger to detain in opposition to the bias of the return spring. With the UVR device reset, the trip slide is held latched in its retracted position while the reset pin moves to a remote position incident with resetting of the breaker mechanism. The circuit breaker may then be reclosed to restore electrical service. 
     The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims. 
    
    
     For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which: 
     FIG. 1 is a plan view of an undervoltage release device constructed according to an embodiment of the present invention, the device being illustrated in its actuated or circuit breaker tripping condition; 
     FIG. 2 is a side elevational view of the undervoltage release device of FIG. 1; 
     FIG. 3 is an exploded assembly view of the undervoltage release device of FIG. 1; 
     FIG. 4 is a plan view, partially broken away, of the undervoltage release device of FIG. 1, illustrated in a partially reset condition; 
     FIG. 5 is a plan view, partially broken away of the undervoltage release device of FIG. 1, illustrated in its fully reset condition; and 
     FIG. 6 is a plan view, partially broken away, of the undervoltage release device of FIG. 1, illustrated in its latched condition. 
    
    
     Like reference numerals refer to corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     The undervoltage release (UVR) device of the present invention includes, as seen in FIGS. 1 through 3, a frame, generally indicated at 10, which serves to mount the various components of the device as well as to facilitate mounting attachment of the device to a circuit breaker (not shown). The frame is generally U-shaped having a bight portion 10a interconnecting laterally turned upper and lower legs 10b and 10c, respectively. The upper leg terminates in a tab 10d which is undercut to key it for receipt in a vertically elongated slot 12a formed in a trip slide generally indicated at 12. The lower frame leg 10c terminates in a turned back flange 10e in which is formed a tapped bore 10f in which is threadedly engaged a screw 14 extending through an elongated slot 12b also formed in trip slide 12. It is thus seen that trip slide 12 is mounted by frame 10 for vertical, reciprocating movement. Screw 14 carries a bearing ring 14a which rides in trip slide slot 12b to ensure non-binding sliding movement of trip slide 12. A washer 14b captured under the head of screw 14 further ensures reasonably free trip slide movement. 
     A solenoid, generally indicated at 16, is affixed atop upper frame leg 10b by suitable means such as screws (not shown). The solenoid includes a magnetic frame 16a which serves to mount a coil 16b and a reciprocating plunger 16c. A laterally extending post 18, mounted by the frame bight 10a, receives a hub 20 affixed to a latch lever, generally indicated at 22, pursuant to pivotally mounting the latch lever to the frame. Fitted over the latch lever hub 20 is a hub 24 affixed to a reset lever, generally indicated at 26. Pin 18 thus serves to independently pivotally mount latch lever 22 and reset lever 26 to the frame, the pivotal mountings being preserved by a clip 19. A torsion spring 28 is assembled with its coil mid-section supported on hub 24 of reset lever 26. One end of 28a of this spring acts against a laterally turned actuator arm 26a, integrally formed with reset lever 26, while the other end 28b is hooked on the edge of a projection 22a integrally formed with latch lever 22. 
     An upstanding arm 22b of latch lever 22 is received in a slot 16d formed in solenoid plunger 16c, with a pin 30 inserted through a transverse bore 16e in the solenoid plunger and a vertically elongated slot 22c in this upstanding arm to link together the solenoid plunger and latch lever. 
     A calibrated return spring 32 has its upper hooked end 32a engaged in a hole 26b in reset lever actuator arm 26a and its lower end threadedly engaged by a screw 34 which passes through an opening 10g in the lower frame leg 10c. It is seen that by adjustably threading screw 34 into the lower end of spring 32, the appropriate spring force acting on reset lever 26 may be conveniently established. 
     To power the trip slide, a tension spring 36 has its upper end 36a hooked in an opening 12c in the trip slide and its lower end 36b hooked in an opening 10h formed in the frame lower leg 10c. 
     Finally, a shouldered latch pin 38 is mounted by the trip slide 12 for lateral extension inwardly toward latch lever 22. To sustain the trip slide in its retracted position, the terminal end portion of latch pin 38 is engaged by a latch shoulder 22d carried by a depending leg 22e of the latch lever. 
     In its normal condition, the various parts of the undervoltage release device of the present invention are in their positions shown in FIG. 6. Thus, trip slide 12 is held in its retracted or inactive position against the bias of spring 36 by the engagement of latch pin 38 with latch shoulder 22d of trip lever 22. This clockwise-most trip slide latching position of the trip lever is sustained by solenoid 16 acting in response to normal line voltage energization to maintain its plunger 16c in its innermost seated position against the bias of calibrated return spring 32. It is seen that the return spring 32 acts to bias reset lever 26 in the counterclockwise direction. The reset lever includes an arm 26c which terminates in a laterally turned tab 26d positioned to engage the edge of latch lever projection 22a of the latch lever, and thus spring 32 also biases the latch lever in the counterclockwise direction via the reset lever. Torsion spring 28, acting between the reset and latch levers sustains the relative angular orientations shown in FIG. 6 with latch lever projection 22a abutting reset lever tab 26d. 
     While the trip side is latched in its retracted, inactive position against the bias of spring 36, a laterally extending arm 12c is held poised above a trip lever 40 included in a circuit breaker trip mechanism (not shown). The trip lever is normally biased to an elevated, non-tripping position by a spring 42. When the line voltage falls to an abnormally low level for longer than a momentary interval, the magnetic force developed by the solenoid striving to hold the plunger in its seated position decreases to the point where return spring 32 becomes overpowering. Reset lever 26 is thus pivoted by this spring in the counterclockwise direction, and the reset lever tab 26d picks up the latch lever, pivoting it also in the counterclockwise direction to a position determined by abutment of projection 22a with upper frame leg 12a. The latch shoulder 22d is thus swung to the right as seen in FIG. 6, releasing trip slide 12. Spring 36 pulls the unlatched trip slide downward, bringing arm 12c into tripping engagement with the circuit breaker latch 40. 
     The tripping condition of the UVR device is shown in FIG. 1, with trip slide 12 in its lowermost, tripping position, determined by abutment of latch pin shoulder 38a against the upper edge of frame flange 10e. It is seen that trip slide arm 12c  engages and holds the circuit breaker latch 40 in its depressed, tripped position, thus preventing the circuit breaker operating mechanism (not shown) from being reset pursuant to reclosure of the breaker contacts. Latch lever 22 and reset lever 26 coupled together by reset spring 28 are jointly pivoted to their counterclockwise-most positions by return spring 32, with the latch lever pulling solenoid plunger 16c out to its extended position. 
     During opening movement of the breaker mechanism, a pin 44 carried by an element of the breaker mechanism, such as the mechanism cradle, moves upwardly and slightly to the right in an arcuate path into engagement with actuating arm 26a of reset lever 26. Continued upward movement of pin 44 pivots the reset lever around in the clockwise direction. By virtue of torsion spring 28, the clockwise pivotal movement of reset lever 26 is communicated to latch lever 22. However, the latch lever only moves through a small arc in the clockwise direction before a flat nose 22f carried by the latch lever arm 22e immediately below latch shoulder 22d encounters latch pin 38 of trip slide 12. Consequently, continued pivotal movement of the reset lever in the clockwise direction by pin 44 is not accompanied by continued clockwise pivotal movement of latch lever 22, and the reset spring 28 becomes loaded. With the nose 22f of the latch lever abutting the trip slide latch pin, solenoid plunger 16c is constrained from further movement toward its seated position. The positions of the various parts with the device in this intermediate reset condition are seen in FIG. 4. 
     Turning to FIG. 5, with continued upward movement of pin 44, an ear 12d extending laterally from the upper left corner of trip slide 12 is picked up by the reset pin, raising the trip slide upwardly toward its retracted position. Latch pin 38 rides upwardly along nose 22f, and upon reaching latch shoulder 22d, it is seen that latch lever 22 is then suddenly released for clockwise pivotal movement by reset spring 28. Plunger 16c is abruptly and forcefully propelled to its seated position concomitantly with the clockwise pivotal movement of the latch lever. This snap action ensures that the solenoid plunger is firmly reseated under conditions that have heretofore defeated the resetting of prior art UVR devices. Moreover, with the parts in their positions shown in FIG. 5, reset spring is not fully discharge and thus is effective to hold the plunger in its seated position pending restoration of normal line voltage. 
     With the resetting of the breaker operating mechanism, reset pin 44 moves downwardly to its position shown in FIG. 6, thus releasing the trip slide and the actuator arm of reset lever 26. If the undervoltage condition has not been corrected, release of the actuator arm by pin 44 will allow return spring 32 to pull the solenoid plunger out of its extended position, thereby pivoting latch lever 22 in the counterclockwise direction to release trip slide 12. The trip slide immediately moves downwardly to trippingly engage the circuit breaker latch 40 and resetting of the breaker mechanism is defeated. However, if the undervoltage condition has been corrected, the magnetic force of the solenoid 16 will retain plunger 16c in its seated position against the bias of return spring 32, and latch lever 22 remains in its clockwise-most position with latch shoulder 22d latchably engaging latch pin 38 to hold the trip slide in its retracted position. Arm 12c of the trip slide is thus held out of tripping engagement with the circuit breaker latch 40, and the breaker mechanism can then be reset pursuant to reclosure of the breaker contacts. 
     From the foregoing description, it is seen that the construction of the present invention accommodates considerable overtravel of reset pin 44 in resetting the undervoltage release device. Specifically, FIG. 5 illustrates an appreciable degree of reset pin overtravel which simply results in further elevation of the trip slide; such further slide movement being readily accommodated by the elongation of slots 12a, 12b. Moreover, it is seen that actuator arm 26a is at this point oriented almost tangential to the reset pin path of movement, and thus reset pin overtravel results in very little additional clockwise pivotal movement of the reset lever; such additional movement simply serving to increase the force of spring 28 holding the plunger in its seated position. 
     It will thus be seen that the objects set forth above, among those made apparent in the preceding description, are efficiently attained and, since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.