US3622923A

US3622923A - Electromagnetic device for circuit breaker trip assembly unit

Info

Publication number: US3622923A
Application number: US871219A
Authority: US
Inventors: Howard R Shaffer
Original assignee: ITE Imperial Corp
Current assignee: Siemens Energy and Automation Inc; ITE Imperial Corp
Priority date: 1968-07-11
Filing date: 1969-10-03
Publication date: 1971-11-23
Anticipated expiration: 1988-11-23

Abstract

An electromagnetic device of the type having application for a circuit breaker trip unit assembly, utilizing a modified armature biasing structure as well as a means for indicating actuation of an individual magnetic assembly. The modified armature biasing structure provides a decrease of the force urging the armature away from the cooperating pole faces, as the armature gap separation decreases. By avoiding the heretofore practiced arrangement of increasing the bias force with a reduction of the gap separation, the disclosed structure permits a wider range of operation. The visual indicating means in conjunction with the trip unit assembly serves to readily indicate to the operator which pole of a multiphase device has been actuated and will require manual reset. The above noted features may be combined, and in one such combined arrangement, the armature bias force is reversed at the concluding portion of its travel, to lock the armature against the magnet pole faces until manually reset.

Description

United States Patent Inventor Appl. No.

Filed Patented Assignee ELECTROMAGNETIC DEVICE FOR CIRCUIT BREAKER TRIP ASSEMBLY UNIT 2 Claims, 16 Drawing Figs.

US. Cl 335/17, 335/174 Int. Cl. IIOIh 73/12 Field oiSearch 335/174,

Primary Examiner-Harold Broome Attorney-Ostrolenk, Faber, Gerb & Soffen ABSTRACT: An electromagnetic device of the type having application for a circuit breaker trip unit assembly, utilizing a modified armature biasing structure as well as a means for indicating actuation of an individual magnetic assembly. The modified armature biasing structure provides a decrease of the force urging the armature away from the cooperating pole faces, as the armature gap separation decreases. By avoiding the heretofore practiced arrangement of increasing the bias force with a reduction of the gap separation, the disclosed structure permits a wider range of operation. The visual indicating means in conjunction with the trip unit assembly serves to readily indicate to the operator which pole of a multiphase device has been actuated and will require manual reset. The above noted features may be combined, and in one such combined arrangement, the armature bias force is reversed at the concluding portion of its travel, to lock the armature against the magnet pole faces until manually reset.

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ELECTROMAGNETIC DEVICE FOR CIRCUIT BREAKER TRIP ASSEMBLY UNIT This application is a division of application Ser. No. 744,166 filed July 1 l, 1968 and now U.S. Pat. No. 3,505,626 relates to improved electromagnetic devices, having application in conjunction with circuit breaker trip unit assemblies.

In accordance with one aspect of my invention, the biasing force supplied to the armature of the electromagnetic structure is reduced during at least a portion of its movement towards the magnet pole faces. Although the ensuing discussion is directed to such a circuit breaker application, it should naturally be understood that this concept is not limited to circuit breakers, and such a negative force gradient characteristic device will have utilization in other applications, wherein it is desired that the armature biasing force does not progressively increase as the armature member approaches the cooperating magnetic pole faces.

In accordance with another aspect of my invention, a visual indicating means is provided to indicate actuation of the electromagnetic trip. This visual indicating means, once set responsive to magnetic actuation, will remain in this condition until manually reset, Such a visual indicating means advantageously permits the operator to distinguish from an overload fault and an instantaneous fault when a circuit breaker has tripped, and to advise the operator which of the phases of a multiphase unit has experienced the fault condition.

The invention is shown in conjunction with a circuit breaker trip unit assembly of the general type, and having application in the circuit breaker device shown and more fully described in U.S. Pat. No. 3,319,195 issued May 9, 1967 in the names of Albert Strobel and John C. Brumfield, based on an application filed June 2 I 1965 and assigned to the assignee of the instant invention. As shown therein, such automatic circuit breakers are usually provided with a trip unit assembly which includes an overload magnetic trip instantaneously responsive to a severe overload condition. The trip unit assembly may also include a thermal trip assembly responsive to a more moderate, but sustained overload condition. The instantaneous trip assembly, to which the instant invention pertains, includes a stationary magnet member and a cooperating armature member. A biasing means is provided to urge the armature away from the magnet, such that in the absence ofa predetermined fault condition the energization of the magnet member will be insufficient to overcome the biasing means and move the armature towards the magnetic'pole faces. The instantaneous trip unit assembly is adjustably calibrated in accordance with the bias force and the initial air gap separation, such that upon the occurrence of a particular fault condition, the magnetic energization will be sufficient to overcome the bias force and thereby move the armature towards the magnetic pole faces. This armature movement causes the rotation ofa tripping bar, and the associated release of a latch mechanism in conjunction with the circuit breaker operating mechanism for followup movement of the circuit breaker contacts to their tripped open position.

In past trip unit assemblies, as typified by U.S. Pat. No. 3,319,195, the armature biasing means is associated with the armature movement, in a manner that will increase the biasing force as the armature moves towards its magnetic pole faces. This disadvantageously requires the magnet to operate against an increasingly greater spring bias force as the armature is moved towards the pole faces. Further, the need to provide an increasing portion of the magnetic force to overcome the armature bias spring results in a lesser force being available at the tripper bar.

Further, in such circuit breaker trip unit assemblies, it is generally required to include an instantaneous trip adjustment for selecting the magnet pickup point over a predetermined range. This permits a single trip unit assembly to have application for a range of circuit conditions, with the user selecting the desired pickup point in accordance with the circuit demands. Such a trip unit adjustment may be of the type shown in U.S. Pat. No. 3,302,140 issued Jan. 31, 1967 in the name of Albert Strobel entitled Circuit Breaker Instantaneous Trip Adjustment," based on an application filed June 21, 1965, and also assigned to the assignee of the instant application. As shown therein, and in numerous other trip adjustment structures, the magnet pickup point is modified by changing the initial air gap separation between the armature and the magnetic pole faces. As the armature is moved closer to the magnet pole faces in the nontripped position, with a lessening of the air gap separation, the reluctance of the magnetic path will be decreased and should require less magnetic energization to draw the armature towards the magnetic pole faces. Thus, the initial placement of the armature closer to the magnetic pole faces is usually associated with a lowering of the instantaneous magnetic pickup point. In such prior art devices, the movement of the armature closer to the magnetic pole faces had also been accompanied by an increase in the armature bias force. This increased armature bias force opposes the desired effect of reducing the magnetic pickup point. Since the instant invention reduces the bias force as the armature moves closer to the pole face, the change of bias force acts in cooperation with the adjustment means, rather than opposed to it, and thereby enhances the operation of the instantaneous trip adjustment. It has been demonstrated that by virtue of the improved structural arrangement of my invention, the trip unit adjustment range may be increased by at least 50 percent, and up to percent, over comparable size magnetic structures of the prior art.

In such circuit breaker units, it is normally not possible for the operator to determine whether tripping has occurred as a result of the actuation of the instantaneous trip assembly, or the overload thermal trip means. Further, there is usually no way for the operator to determine which of the phases has experienced the fault. My improved trip unit assembly includes, as an additional feature, a means for readily indicating the actuation of themagnetic trip unit assembly. In accordance with one embodiment, such movement is associated by a reversal of the armature biasing force, so as to maintain the armature against the magnetic pole faces until manually reset. In accordance with another embodiment of the invention, the visual indicating means is provided in conjunction with the trip unit calibration adjustment button. In accordance with the modified structure of the calibration adjustment button, the movement of the armature downward serves to permit similarly axially downward movement of the calibration button, and it will be maintained in this axially downward position until manually reset.

It is'therefore seen that the basic concept of the instant invention resides in providing an improved magnetic structure having utilization in conjunction with a circuit breaker trip unit assembly. The features of the magnetic structure include a negative force gradient in the interconnection means between the armature and its associated biasing means, and a visual indicator for readily apprising the operator of magnet actuation.

It is, therefore, a primary object of the instant invention to provide an improved electromagnetic device.

Another object of the instant invention is to provide an electromagnetic device wherein the armature biasing force is reduced as the armature member is drawn towards the pole faces of its cooperating magnet.

A further object of the instant invention is to provide within an electrical circuit breaker an instantaneous trip unit assembly, in which the armature biasing force is reduced as the armature moves closer to the magnetic pole faces.

An additional object of the instant invention is to provide an electrical circuit breaker device with an adjustable trip unit assembly, wherein the range of adjustment is increased by at least 50 percent over comparable magnetic assemblies hereto fore available.

Still another object of the instant invention is to provide within a circuit breaker device a magnetically actuable instantaneous trip unit assembly having a range of adjustment achieved by varying the initial position of the armature, wherein the initial movement of the armature towards the pole faces to lower the magnetic pickup point is accompanied by an associated decrease of the armature bias force.

Still a further object of the instant invention is to provide, in conjunction with a circuit breaker trip unit assembly including a magnetically actuated fault sensing means, a visual indicating means for apprising the operator of magnetic actuation.

My improved negative force gradient armature biasing means is achieved by an arrangement of levers and springs to provide an effective negative gradient force during at least a portion of the armature movement. In an illustrated embodiment, the interconnection means between the spring bias means and the armature includes a pivoted lever which establishes a moment arm for applying the spring force to the armature. As the armature moves towards its associated magnetic pole faces, the lever is pivoted in a manner to reduce the moment arm of the spring force. This reduction of the moment arm is designed to overcome the actual increased spring force as the spring expands, such that the applied product of the spring force and moment arm will be of lesser magnitude as the armature moves towards the magnetic pole faces.

In accordance with a further advantageous feature which has found applicability in conjunction with some of the forms of my invention, a counterbalance assembly may be utilized in conjunction with the interconnection of the spring bias means to the armature. This counterbalance assembly counteracts shock induced movement of the armature towards the mag net, and has demonstrated particular utility in conjunction with circuit breakers installed in environments which may be subjected to appreciable shock forces, e.g., shipboard use.

It is, therefore, still a further object of the instant invention to provide an electromagnetic device having an armature biased away from its cooperating pole faces, which is counteracted by a negative force gradient as it moves towards the magnetic pole faces.

Still an additional object of the instant invention is to provide such an electromagnetic device within a circuit breaker trip unit assembly, in which the moment arm applying the biasing spring force to the armature means experiences an effective reduction as the armature moves towards the magnetic pole faces.

Yet another object of the instant invention is to provide such an electromagnetic trip unit assembly wherein such reduction of the moment arm is accompanied by an increase in spring force, with the resultant product being a decreased magnitude.

Yet an additional object of the instant invention is to provide, withing an electrical circuit breaker, an instantaneous trip unit assembly having a negative force gradient in conjunction with the armature biasing spring, wherein the moment of the armature force reverses as the armature reaches the magnetic pole faces, so as to lock the armature in the trip position and require a manual reset.

These, as well as other objects of the instant invention, will become readily apparent upon a consideration of the following description and drawings, in which:

FIG. 1 is a plan view of a three-phase molded case circuit breaker device, utilizing one form of the instant invention, and wherein the cover, and the cover of the trip unit assembly, are partially removed to reveal the region containing the electromagnetic device of the instant invention.

FIG. 2 is a longitudinal cross-sectional view along the line 2-2 of FIG. 1, and looking in the direction of the arrows, showing the center phase and including the circuit breaker operating mechanism.

FIG. 3 is an end view of the replaceable trip unit assembly, partially cut away to show the instantaneous trip portion.

FIG. 4 is a perspective view, partially exploded, of the magnetic trip unit assembly constructed in accordance with the instant invention. and utilized in the trip unit of FIG. 3.

FIG. 5 is a cross-sectional view along the line 55 of FIG. 3, showing the details of the electromagnetic instantaneous trip assembly.

FIG. 6 is a cross-sectional view along the line 66 of FIG. 5.

FIG. 7 is a simplified view ofa portion of FIG. 5, increased in size, to show the manner in which the moment arm varies as the armature moves towards the magnetic pole faces.

FIG. 7A is a simplified schematic representation of FIG. 7, showing the basic operation of the device.

FIGS. 8 through 11 show a modification of the general form of magnetic trip unit assembly shown in FIGS. 1 through 7, in which the armature is locked in its final position, and a visual indication is provided, in conjunction with a manual reset means. FIG. 8 is a front elevational view of the modified trip assembly. FIG. 9 is a simplified end view showing the device in the tripped position. FIG. 10 shows the visual indicator in the nontrip normal position. FIG. 11 shows the manner in which the spring pivots to provide a reversal in moment for the locked-in condition.

FIG. 12 graphically represents the spring force and moment of force variation, versus armature position, corresponding to the embodiment of FIGS. 1 through 7.

FIG. 13 graphically represents the spring force and moment of force variation versus armature position corresponding to the embodiment of FIGS. 8 through 11.

FIGS. 14 and 15 show another form of the instant invention, having a modified visual indicating arrangement, in conjunction with the instantaneous magnetic adjustment button, for indicating actuation of the magnetic assembly. FIG. 14 shows the nonactuated condition, and FIG. 15 the actuated condition.

Reference is initially made to detailed FIGS. 1 through 7, and schematic representation FIG. 7A, which show electromagnetic devices built in accordance with the instant invention, installed within the replaceable trip unit assembly ofa commercial three-phase circuit breaker, of the type shown in aforementioned US Pat. Nos. 3,302,l40 and 3,3l9,l95. It should naturally be understood that the novel concepts of the instant invention may be incorporated in numerous other types of circuit breakers or other electrical switching devices, with this detailed embodiment being merely for illustrative purposes.

Circuit breaker I0 is assembled in a housing comprising molded base 11, separated into compartments l2, l3 and 14, respectively, for locating the operating members of each of the phases. The adjacent compartments are separated by housing walls 15 and I6. A main cover assembly 17 and end covers 18 similarly include barriers for maintaining the longitudinally extending compartment of the housing, with end shields 19 being located at the line and load ends of the circuit breaker.

The current carrying members of all three phases are identical with the center phase, which also includes the circuit breaker operating mechanism 32. The current carrying path in each phase between the line terminal strap 20 and load terminal strap 21 is as follows. The line terminal strap 20 includes at its inward end the main and arcing stationary contacts 22, 23. With the circuit breaker in the ON condition, these contacts are in engagement with cooperating movable contacts 24, 25, respectively carried by contact arms 26 and 27. The current path then proceeds through flexible braids 28 to the contact carrier strap 29. A replaceable trip unit assembly I00, having the appropriate current ratings, and including the improved electromagnetic structure of the instant invention in each of its phases, is inserted in the circuit breaker. Trip unit assembly includes a current carrying strap 102 connected at the inward end by bolt 114 to the circuit breaker contact carrier strap 29, and connected at its outward end to the circuit breaker line terminal strap 21 by bolt members 112.

Circuit breaker 10 includes a quick make-break toggle operating mechanism generally shown as 32 for moving the contact arms 26, 27 between their engaged and disengaged positions, as is more fully discussed in aforementioned U.S. Pat. Nos. 3,302,l40 and 3,3l9,l95. For present purposes, it is sufficient to understand that the movement of the circuit breaker to the TRIP condition of FIG. 2 results from the disengagement of the cradle latch tip 34 from latching bracket extension 101 of the trip assembly 100. Such disengagement of the latch is effected by rotation of the trip unit assembly tripper bar 104 as a result of actuation of the instantaneous electromagnetic trip 200, to be subsequently discussed (or, if included, the moderate overload thermal trip 103).

The circuit breaker also includes a manual operating handle 80, which permits manual operation of the circuit breaker to the manual OFF contact disengaged condition. This movement is effected by moving the toggle overcenter, without the release of cradle latch tip 34, in the well known manner.

Although each of the three phases of the circuit breaker includes a separate current sensing apparatus, only a single overcenter-toggle operating mechanism 32 is provided in the center phase. As is well known, the operation of either the manual operating handle 80, or the movement of the tripper bar 104 (common to all three phases), serves to actuate the operating mechanism 32,- with such movement being transmitted to the other phases by virtue of tie bar 33.

Attention will now be directed to the instantaneous magnetic trip assembly, generally shown as 200, which incorporates the improvement of the instant invention. The trip unit assembly 100 also includes a moderate overload thermal trip, in the form of bimetallic element 103, in each of the phases connected to the current carrying strap l02 by shunt 100, as is the subject of U.S. Pat. No. 3,305,653 issued Feb, 21, 1967 entitled Circuit Breaker Trip Assembly with Increased Compensation for Misalignment" in the name of Albert Strobel, based on an application filed June 21 1965 and also assigned to the assignee of the instant application.

The magnetic trip assembly 200 is generally of the same structure as shown in aforementioned U.S. Pat. No. 3,319,195, except for the mounting of the armature bias means and its interconnection to the armature, as generally shown by the designation 250. That is, the magnetic trip assembly 200 includes a generally U-shaped magnet member 105 and a cooperating armature 107. The U-shaped magnet includes horizontally disposed pole faces 111, 113, respectively, at its uppermost extremes. The armature member 107 is horizontally disposed intermediate the plane of pole faces 11], 113 and the bottom surface 161 of forwardly projecting extension 154 of the mounting bracket 150. In its nonengaged condition, the armature member 107 is separated from the pole faces 111, 113 by an air gap separation of predetermined calibrated extent as shown by d, (See FIG. 7). Upon sufficient magnitizing flux, provided by current carrying strap 102 flowing through the magnet member 105, the armature member 107 is downwardly drawn towards cooperating pole faces 111, 113, as shown in the solid condition of FIG. 7. This downward movement is against the biasing force provided by bias means 250, and will provide a negative gradient force in the unique manner which constitutes the subject matter of the instant invention, and will subsequently be described.

An actuating plunger 156 is connected to the armature member 107 and moves downwardly therewith. The actuating plunger 156 includes a trip unit actuation extension 157 ad justably threaded to the upper end thereof, which engages tripper bar extension 158 to effect rotation of the tripper bar 104 and subsequent tripping of the circuit breaker upon the downward movement of the armature member 107 towards the cooperating pole faces I, 113 of magnet member 105.

The actuating rod 156 also includes a calibration extension member 195, threaded at the intermediate region thereof. Calibration adjustment member 195 establishes the initial air gap pole separation from faces 11], 113, in accordance with the rotational position of externally accessible calibration button 189, which is supported by bracket 191 and biased rod 192, in the manner fully discussed in aforementioned US. Pat. No. 3,302,140.

Reference will now be directed to the manner in which the instant invention provides a biasing force to the armature 107. The biasing means is contained withing a support bracket 252, which also serves as the support for the magnet 105. This unit is appropriately maintained withing the trip unit assembly by fastening means which enter the threaded openings 115 on the magnet arms. A support bracket 254 is fixedly mounted to this assembly by screws 256 fastened to the bottom ofthe bracket, and extending through the body portion of magnet 105. Bracket 254 extends upwardly and includes aligned apertures 258, which receive pivot pin 259. Pivot pin 259 extends through aligned apertures 26!, 263 at the intermediate region ofa pivoted lever 260, and thereby provides a stationary pivot for the lever.

One end of pivot lever 260 includes aligned

apertures

265, 267, which are connected at 269 to the'narrowed portion 272 of the armature stern extension 274 through a pair of rollers 269'. Armature stemextension 274 has an internally threaded recess 276 at its upper end, which receives the externally threaded portion 159 of the armature stem 156, and in conjunction with nut 278, provides a firm interconnection therebetween. Hence, the downward movement of armature 107, which is accompanied by similar downward movements of the armature actuating and adjustment extension 156, will similarly move the armature stem extension 274 downward. The free end of armature extension 274 includes a bulbous portion 280, which rides along the inner wall surfaces of aperture 282 within downwardly depending portion 284 of the magnet, to thereby serve as a vertical guide,

The opposite end of the pivoted lever 260 includes aligned

apertures

286, 288, which receive pin member 291, with roller 292 being located intermediate the spaced walls of lever 260.

The pin member 291 receives one end of the armature bias spring means, illusively shown as a pair of

springs

294, 296, and serves as a movable pivot therefore. The opposite ends of the springs are located within

apertures

302, 304, respectively of the stationary support bracket 252. It should be naturally understood that a pair of springs are shown for illustrative purposes only, with more or less springs being utilized, in accordance with the particular operating characteristics desired, in a specific application.

A counterweight assembly generally shown as 300 is shown connected to the opposite end ofthe bracket 290, via pin 305, to prevent accidental moving downward ofthe armature in the event of an appreciable shock load. The use of such a counterweight assembly may be deleted without detracting from the essential spirit of the invention. It has been found, however, that the utilization of such a counterweight assembly which may be readily added to the negative gradient armature biased structure hereinabove described, substantially enhances the reliability of such an instantaneous trip mechanism when utilized in environments exposed to appreciable shock forces.

Reference will now be made to FIG. 7A, which shows in substantially simplified form, the basic operation of the negative gradient mechanism hereinabove described, in which the following corresponding part designations are employed; mag net member 103A; armature member 107A; armature stem extension 156A; trip unit actuating extension 157A; trip bar extension 158A; pivotal lever 260A; the point of attachment 269A to the downwardly extending portion of the armature stem; the stationary lever pivot 259A; the stationary spring securement 302A; and the pivotal spring securement 291A. The initial position of the armature member 107A is shown in dotted lines, with there being an air gap separation al between the armature 107A and the magnet pole faces. The biasing spring 294A will be a length L providing a spring force of F,. This spring force acts to upwardly bias the armature stem extension 156A (and hence the armature 107A). This force is applied through a moment arm of length a, through the lever 260A. Hence, the effective moment of the upward force applied to the armature may be represented by the mathematical relationship The solid line representation of FIG. 7A indicates an intermediate position of the armature 107A, as it is being drawn 260A is rotated counterclockwise about its stationary pivot 259A to the position shown in solid lines. This movement serves to traverse the end of the spring along the path indicated by the arrows 250A. The spring will now be stretched to a length L thereby providing a greater spring force F However, by virtue of the pivoting movement of the lever 260A, this force is applied to the armature stem extension 156A through a smaller moment arm a Hence, the effective moment of the force provided at this instant of time may he represented by the relationship (2) F Xa By proper design, the decrease of the amount arm will more than compensate for the increased force of the spring, thereby satisfying the mathematical relationship 3 F, a, F a while the following condition exists It is therefore seen that a condition exists whereby, as the armature moves closer to the magnet pole faces, the net effective force applied by the bias means will be decreasing rather than increasing. This advantageously serves to permit an appreciable increase in the range of adjustment achieved by the initial position of the armature. In a typical commercial unit, built as shown in US. Pat. No. 3,3l9,l95, which previously had an adjustment range of 4,000 to 8,000 amperes, a comparable magnetizing circuit using the improved bias means of the instant invention has permitted an adjustment range between 4,000 to 12,000 amperes.

Further, since the moment of force opposing the downward movement of the armature 107A decreases as the armature approaches the pole faces, there will be a greater proportion of the force available for engaging the trip bar extension 158A.

Referring back to FIG. 7, the conditions schematically shown in FIG. 7A are represented with the dotted position showing the initial location of the armature prior to energization, and the solid condition showing a later position of the armature. The reduction in moment arm is represented by a, and corresponding to the similar designations of FIG. 7A.

The variation of force versus armature position ofa typical assembly manufactured in accordance with the embodiment of FIGS. 1 through 7 is graphically shown in FIG. 12. Curve 350 shows the spring force versus armature position. Since the tension type spring is expanding as the armature moves closer to its cooperating pole faces, this curve, as expected, shows an increase in spring force with decreased armature position. Curve 354 shows the moment of force applied to the armature with respect to armature position. By virtue of the reduction of the moment arm, this curve shows a condition

intermediate points

355, 356, wherein the effective moment of force applied to thearmature decreases as the armature approaches its cooperating magnetic pole faces. Thus, this region has a negative force gradient at the same time that the actual spring force is shown to increase.

Reference is now made to FIGS. 8-11, which show a modified embodiment of the instantaneous trip assembly, to provide a lockout, with manual reset, and visual indication functions. The magnet, armature, armature bias means and armature plunger generally correspond to that shown in conjunction with previous FIGS. I-7, and are similarly numbered with prime designations. A manual reset and visual indicating means are provided by the indicating lever 400. Lever 400 includes an intermediate slot 402, and is mounted to the adjustment button retaining bracket 191'. by virtue of rivet member 406. A distinctive color band 408 is provided immediately below the uppermost region of the lever 400, with such region passing freely through slotted opening 410 of the trip unit housing cover. A bias spring 412 maintains the indicating lever 400 in the normal position, shown in FIGS. 8 and 10.

Under normal conditions, the color band 408 is above the trip unit cover. and indicates that the instantaneous trip has not been actuated. Upon actuation of the instantaneous trip, the armature 107 moves downward and the calibration adjustment extension 195' engages portion 401 of the indicating lever, thereby moving it downward to the position shown in FIG. 9. This downward movement serves to move the color band 408 below the surface of the trip unit housing, thereby giving a visual indication of magnetic trip. The negative gradient bias means 300' of this embodiment is designed, as will be shown in conjunction with FIGS. 11 and 13, to move overcenter during the final armature movement, thereby locking the armature in the position shown in FIG. 9. In order to reset the breaker, it is necessary that the operator pull up on the indicating lever portion 411, forcing the armature 107' back against the overcenter locked-in arrangement of the bias means 300.

FIG. 11 shows the manner in which the overcenter movement is achieved. At point A, corresponding to maximum armature position 107', the movable end of the spring at 259'-A will exhibit a maximum downward displacement from the stationary pivot 261', thereby providing a maximum moment arm. As the armature moves closer to the magnetic pole face, as indicated successively by B, C, D-the pivoted end of the spring 259' traverses a path, to reduce its downward vertical displacement from the pivot point 261', thereby decreasing the moment arm. At point F, corresponding to very small air gap separation, there will be an effective net zero force; however, the inertia of movement at this region and the magnetic force will keep the armature moving towards its final position, point G. At this point, the free end of the spring 259'-G crosses overcenter with respect to the pivot point 261', thereby reversing the application of the moment of force provided by the spring bias means, and locking the armature in its final position. This is graphically shown in FIG. 13, where FIG. 360 represents the spring force. As is expected, since the spring is increasing in length as the armature approaches the magnetic pole faces, there will be an increase in spring force with decreasing armature gap. In FIG. 13 curve 362 represents the moment of the force applied to the armature. By virtue of the decreased moment arm, this force exhibits a decrease as the armature approaches the air gap. At point 364, corresponding to position F of FIG. 11, there will be a net zero force. The subsequent overcenter movement of the spring provides a reversal of the moment, as shown by the region of the curve intermediate points 364 and 366.

Reference is now made to FIGS. 14 and 15, which show a modified arrangement for visually indicating the operation of the magnetic trip assembly. The instantaneous trip assembly, which is generally shown as 200, includes magnet and a cooperating armature 107. An actuating plunger 156 is secured to the armature 107 and includes threaded

members

157, 195, corresponding in operation to identically numbered components of FIGS. 1-7. The instantaneous trip adjustment 500 is, however, of a different construction, generally conforming to that shown in Us. Pat. No. 3,201,659. The armature adjustment button 501 is rotatively maintained within bracket 502, mounted to the trip unit housing. The button 501 includes a transversely extending pin 504, with a spring member 506 being located intermediate the pin 504 and the underside 505 of the bracket support, thereby biasing the button 501 downward. The bottom of the button includes a cam surface 510, which, upon rotation of button 501 (typically by a screwdriver within slot 512), cooperates with adjustment extension of the plunger 156, for establishing the initial gap separation between the armature 107 and the pole face of the magnet 105. In accordance with my invention, the button 501 also serves as the visual indicating means of magnet actuation. When the magnet is actuated, resulting in movement ofthe armature 107 downward to the condition shown in FIG. 15, button 501 moves downward under the influence of spring 506. As the button 501 moves down, the end 507 of spring 506 will snap into one ofthe grooves 513. This prevents the button 501 and the armature 107 from moving upward, after the circuit breaker trips open, thereby removing the energizing source for the magnetic trip assembly 200.

The axially downward movement of the trip adjustment button 501 serves to give the operator a visual indication of magnet actuation. In order to reset the instantaneous feature, the operator must rotate button 501 to a reset position. That is, a partial turn of button 501 will allow the armature biasing means to force the armature 107 and the adjustment button 501 upward to the position shown in FIG. 14. The operator will then set the instantaneous trip adjustment button 50l to the desired calibration point, and the breaker is reset for subsequent use.

It is therefore seen that the instant invention provides an electromagnetic device of improved operating characteristics. In accordance with one aspect, the armature biasing means exhibits a decrease in net effective force as the armature is drawn towards the cooperating magnetic pole faces. The various illustrative embodiments are particularly directed to the instantaneous magnetic trip portion of an electric circuit breaker. Where a plurality of instantaneous magnets are utilized, as in a multiphase unit, another aspect of the invention is directed to a visual indicating means for apprising the operator which of the electromagnetic devices has been actuated. It is to be understood, however, that the invention is not to be limited to such described preferred embodiments, but is defined by the appended claims.

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows:

1. A multiphase circuit breaker comprising at least the pair of cooperating contacts for each phase;

contact operating means for moving all of said contact pairs between an engaged and disengaged position; v

latch means cooperating with said operating means for maintaining all of said contact pairs in their engaged positions under normal load conditions;

a trip unit including a housing substantially enclosing said unit, an individual current sensing means for each phase, operatively responsive to the current flow through the individual phase circuit, and including means for releasing said latch means responsive to a predetermined fault condition in any individual phase;

handle means for operating said contact operating means under normal current conditions in all of said phases;

said handle means being movable to off and on" positions to respectively cause said contact operating means to open and close said contact pairs, and also being movable to a tripped position, intermediate said on" and said off' positions. by said contact operating means, when said latch means is released;

each of said individual current sensing means also including a thermal trip means,

a magnetic trip means having cooperating magnet and armature means,

support means for mounting said armature means for movement towards and away from the pole faces of said magnet means,

bias means for normally urging said armature means in a first direction away from said pole faces, towards a first position whereat said armature means is spaced from said pole faces,

means for energizing said magnet means to attract said armature means and move said armature means in a second direction, towards said pole faces. to a second position responsive to an individual phase fault condition,

a combined visual indicia means and manual reset means passing through an opening of said housing. operable by said armature as it moves to its said second position and remaining inactive upon actuation of said thermal trip means. whereby said combined means provides a readily discernible indicator portion for indicating the faulted phase armature means movement to said second position,

and a manually actuated reset portion for returning said armature means of the faulted phase to said first position.

2. A multiphase circuit breaker comprising at least the pair of cooperating contacts for each phase;

contact operating means for moving all of said contact pairs between an engaged and disengaged position;

latch means cooperating with said operating means for maintaining all of said contact pairs in their engaged position under normal load conditions;

a trip unit including an individual current sensing means for each phase, operatively responsive to the current flow through the individual phase circuit, and including means for releasing said latch means responsive to a predetermined fault condition in any individual phase;

said current sensing means including a magnetic trip assembly having cooperating magnet and armature means;

support means for mounting said armature means for movement towards and away from the pole faces of said magnet means;

bias means for normally urging said armature means in a first direction away from said pole faces, towards a first position whereat said armature means is spaced from said pole faces;

means for energizing said magnet means to attract said armature means and move said armature means in a second direction, towards said pole faces, to a second position responsive to an individual phase fault condition;

a housing substantially enclosing said trip unit;

a combined visual indicia means and manual reset means passing through an opening ofsaid housing;

said combined means providing a readily discernible indicator portion for indicating the faulted phase armature means movement to said second position, and a manually actuated reset portion for returning said armature means of the faulted phase to said first position;

said combined means further including an adjustment surface for adjusting the initial surface for adjusting the initial location of said armature means relative to said magnet means in the absence of magnet energization;

said combined means being a rotatable member extending outward of said trip unit housing;

said combined means including a plurality of circumferentially spaced positions for establishing a selected one ofa similar plurality ofinitial armature locations;

means for displacing said rotatable member in the axial direction responsive to magnet actuation and maintaining said rotatable member in the axially displaced location;

said reset portion permitting the axial return of said rotatable member to the nonactuated condition;

said axial displacement providing a readily discernible visual indication offault induced magnet actuation.

Claims

1. A multiphase circuit breaker comprising at least the pair of cooperating contacts for each phase; contact operating means for moving all of said contact pairs between an engaged and disengaged position; latch means cooperating with said operating means for maintaining all of said contact pairs in their engaged positions under normal load conditions; a trip unit including a housing substantially enclosing said unit, an individual current sensing means for each phase, operatively responsive to the current flow through the individual phase circuit, and including means for releasing said latch means responsive to a predetermined fault condition in any individual phase; handle means for operating said contact operating means under normal current conditions in all of said phases; said handle means being movable to ''''off'''' and ''''on'''' positions to respectively cause said contact operating means to open and close said contact pairs, and also being movable to a tripped position, intermediate said ''''on'''' and said ''''off'''' positions, by said contact operating means, when said latch means is released; each of said individual current sensing means also including a thermal trip means, a magnetic trip means having cooperating magnet and armature means, support means for mounting said armature means for movement towards and away from the pole faces of said magnet means, bias means for normally urging said armature means in a first direction away from said pole faces, towards a first position whereat said armature means is spaced from said pole faces, means for energizing said magnet means to attract said armature means and move said armature means in a second direction, towards said pole faces, to a second position responsive to an individual phase fault condition, a combined visual indicia means and manual reset means passing through an opening of said housing, operable by said armature as it moves to its said second position and remaining inactive upon actuation of said thermal trip means, whereby said combined means provides a readily discernible indicator portion for indicating the faulted phase armature means movement to said second position, and a manually actuated reset portion for returning said armature means of the faulted phase to said first position.

2. A multiphase circuit breaker comprising at least the pair of cooperating contacts for each phase; contact operating means for moving all of said contact pairs between an engaged and disengaged position; latch means cooperating with said operating means for maintaining all of said contact pairs in their engaged position under normal load Conditions; a trip unit including an individual current sensing means for each phase, operatively responsive to the current flow through the individual phase circuit, and including means for releasing said latch means responsive to a predetermined fault condition in any individual phase; said current sensing means including a magnetic trip assembly having cooperating magnet and armature means; support means for mounting said armature means for movement towards and away from the pole faces of said magnet means; bias means for normally urging said armature means in a first direction away from said pole faces, towards a first position whereat said armature means is spaced from said pole faces; means for energizing said magnet means to attract said armature means and move said armature means in a second direction, towards said pole faces, to a second position responsive to an individual phase fault condition; a housing substantially enclosing said trip unit; a combined visual indicia means and manual reset means passing through an opening of said housing; said combined means providing a readily discernible indicator portion for indicating the faulted phase armature means movement to said second position, and a manually actuated reset portion for returning said armature means of the faulted phase to said first position; said combined means further including an adjustment surface for adjusting the initial location of said armature means relative to said magnet means in the absence of magnet energization; said combined means being a rotatable member extending outward of said trip unit housing; said combined means including a plurality of circumferentially spaced positions for establishing a selected one of a similar plurality of initial armature locations; means for displacing said rotatable member in the axial direction responsive to magnet actuation and maintaining said rotatable member in the axially displaced location; said reset portion permitting the axial return of said rotatable member to the nonactuated condition; said axial displacement providing a readily discernible visual indication of fault induced magnet actuation.