US2847532A

US2847532A - Circuit breakers

Info

Publication number: US2847532A
Application number: US590584A
Authority: US
Inventors: Paul M Christensen; Bryan John
Original assignee: Federal Pacific Electric Co
Current assignee: Federal Pacific Electric Co
Priority date: 1956-06-11
Filing date: 1956-06-11
Publication date: 1958-08-12
Anticipated expiration: 1975-08-12

Description

Allg# 12, 1958 P.- `M. HRxsTNsE-N ET AL 2,847,532

CIRCUIT BREAKERS Filed June l1, 1956 INVENTORS PA UL M. CHR/s rE/vs EN dof/BRYAN 4Z ATTORNEY United States Patent O CIRCUIT BREAKERS Paul M. Christensen, West Orange, and John Bryan, Newark, N. J., assignors to Federal Pacic Electric Company, a corporation of Delaware Application June I1, 1956, Serial No. 590,584

6 Claims. (Cl. 200-88) This application relates to automatic circuit breakers and in particular it relates to circuit breakers having provision for thermal tripping, magnetic tripping, and cornpensation for variations in ambient temperature.

In application, Serial No. 590,684, filed concurrently herewith by Paul M. Christensen, there is disclosed a circuit breaker having a combined latch and armature that has a pivot at a position closely adjacent but separated from a current-responsive bimetal. This combined latch and armature unit has a shoulder which is rockably received in a notch, forming a readily separable pivot. The combined armature and latch unit is firmly pressed against the bottom of the notch by the circuit-breakeropening mechanism which the latch arrests or, in the case of an overload, which the latch releases. In order that the latch may remain physically assembled between the time that the circuit breaker is tripped and until it is reset, and in addition, in order that the latch may be returned to the position in which it obstructs the releasable element of the circuit breaker opening mechanism, spring bias means is required. Two separate functions are to be accomplished, namely: The biasing of the latch in the direction to prevent release of the circuit breaker and the biasing of the latch in its seat.

An object of the present invention is to provide a combined thermal and magnetic latch assembly for circuit breakers having novel, effective biasing means for holding the latch in the assembly, and for biasing the latch toward its circuit-breaker-latching position. A further object is to provide such apparatus of a form to be readily manufacturable.

In carrying out the foregoing objects, and in achieving further advantages and features of the present invention, the illustrative embodiment of the invention detailed below has been provided. This embodiment has a currentresponsive bimetal electrically connected in series with a coil which, with a magnetic core structure, forms an electromagnet. The core structure and the bimetal are united at a common point, forming part of the electrical circuit through the bimetal. The latch is formed of a bimetal for compensating for the effects of ambient temperature on current-responsive bimetal. The currentresponsive bimetal bears laterally against the latch member to produce latch-releasing deflection in response to thermal over load currents. The latch pivot to the core structure causes the latch to operate at the same potential as the fixed end of the bimetal. An insulating element is interposed between the free, movable end of the current-responsive bimetal and the latch member to avoid forming an electrical path through the latch member and its support, which electrical path would shunt the path through the current-responsive bimetal. Normally, there is only a very small Voltage drop in the current-responsive bimetal, but it is nevertheless important to avoid such shunt path. For one reason, the shunt path resistance is likely to be erratic, and would prevent the circuit breaker from tripping consistently at its rated thermal current level. Furthermore, in the event of a 2 short circuit in the protected load, virtually the full voltage of the source is momentarily impressed on the bimetal. It is important that such voltage shall not be developed in any circuit involving the latch pivot which, in the event of a sort circuit, might weld.

An insulating tensioner is provided in the illustrative embodiment between the latch-and-armature unit and the current-responsive bimetal; and this tensioner is disposed to apply two components of force, one toward the pivot seat of the latch member and the other toward the current-responsive bimetal. More specifically, a band of silicone rubber encircles the latch member and the bimetal and engages longitudinally offset abutments 0n the latch member and the bimetal to produce the dual tensions described. The silicone rubber is an insulator and thus meets the requirement that there be no shunt path formed by the tensioner to a part of the current-responsive bimetal. The band, when extended in all directions, may be readily slipped over both the latch and the current-responsive bimetal and then allowed to snap into place. Thus, during assembly, the latch and the tensioner of the latch may both be moved along the current-responsive bimetal, moving from the free end of that bimetal towards its fixed support. This simplicity of assembly of the novel construction is an important factor in the practicality oi the construction. The silicone rubber is of long life and of stable characteristics despite occasional high operating temperatures of the bimetal. Furthermore, the band may be disposed quite close to the very pivot of the latch and consequently it may be quite a strong element without producing an excessive moment of force that must be overcome by the current-responsive bimetal or by the electromagnet in the circuit breaker for tripping the circuit breaker.

The nature of the invention and its further novel features will be better appreciated from the following detailed disclosure thereof. The illustrative embodiment is shown in the accompanying drawings, forming part of this disclosure, wherein:

Fig. l is a side view of an assembled circuit breaker with one part of a two-part enclosure of insulation removed to reveal the internal construction;

Fig. 2 is a fragmentary end view of certain parts in Fig. l viewed from the line 2-2;

Fig. 3 is a fragmentary cross-section along the line 3--3 in Fig. l; and

Fig. 4 is an enlarged portion of Fig. l.

Referring now to the drawings there is shown in Fig. 1 a circuit breaker assembly including a fixed contact it) carried by one terminal member 12 and a movable contact member 14 carried by movable contact arm 16. Contact arm 16 is pivoted on a helical spring 13 whose axis extends perpendicular to the drawing and whose ends are received in recesses in the side walls of the two-part enclosure, only one part 2@ being shown in the drawing. A metal actuator 22 has a metallic pivotal connection to the right-hand extremity of moving contact arm 16. That a metal pivot rather than an insulated pivot may be employed at this point is significant because it facilitates the problem of holding close tolerance at this relatively critical part of the mechanism. A handle 24 of insulation is pivoted in the side walls of the insulated housing and is connected by a link 26 to operate actuator 22. Member 26 is lJ-shaped with one leg (perpendicular to the drawing) received in a hole in handle 24 and the other -leg of the U being received in a bearing in actuator 22.

Moving contact arm 16 has a downward extension formed as a rivet 28 to unite latching assembly 3G to the moving contact arm, in position normally to obstruct and thereby to latch actuator 22.

A spring 32 is held in compression between handle 24 and moving contact arm 16.

Contacts

10 and 14 are shown closed, and handle 24 is in the closed position. If handle 24 is operated clockwise from the position shown, the handle shifts link 26 so that the link and actuator 22 (which constitute a toggle) tend to swing actuator 22 counterclockwise and to allow spring 32 to drive moving contact arm 16 counterclockwise. When this occurs, assuming handle 24 is retarded, spring 32 is also effective to drive the handle clockwise all the way to its oli position in readiness for renewed closing of they circuit breaker.

When handle 24 is operated in the counterclockwise direction (Fig. l) from its oft position, link 26 drives actuator 22 against the end of the latching assembly 30 to be arrested there. Further counterclockwise operation of the handle drives the moving contact arm 16 into contacts-closed position. Spring 18 allows the relatively

rigid members

24, 20, 26 and 16 to complete their operation into on configuration even though moving contact 14 engages fixed contact 10 shortly before the handle completes its on stroke. V-shaped member 34 coacts With casing formations and with springs 18 and 32 to irst arrest contact arm 16 and then release it for contact-closing with snap action.

Latch assembly 30 includes a current-responsive bimetal 36 secured by integral rivet 28 to moving contact arm 16 mechanically and electrically. This integral rivet also secures a magnetic core structure 38 flxedly to moving contact arm 16.

Member 38 has a connecting portion through which rivet 28 extends (Fig. 2) and a pair of side walls extending therefrom to incorporate a two-part curved core 40 about which a coil 42 as of copper wire is wound. One terminal of this coil is welded to the right-hand extremity of current-responsive bimetal 36 while the other terminal of the coil is joined to iexible copper braid 44 for connection to external terminal 46.

The side walls of magnetic structure 38 have notches 48 formed therein, opening toward actuator 22 pivotally or rockably supporting a latch member 50 by Virtue of the shoulders 52 thereof. Armature 54 is united to the left-hand extremity of latch member 50. As shown in Fig. 4, this latch member has one arm which substantially occupies the space between the side walls of magnetic member 38 in the region of notches 48, this arm moving laterally along those magnetic side walls when coil 30 is appropriately energized. Armature 54 also has an arm extending downward and opposite the end of core 40. It is evident that a highly efficient magnetic circuit isformed of core 4t) and the side walls of magnetic structure 38 which embrace the first-mentioned arm of armature S4. Consequently the current that flows through the circuit breaker energizes coil 40 and exerts a comparatively strong attraction for armature 54, and this in turn produces a tripping force exerted clockwise to swing latch member S out of the path of actuator 22 when the predetermined level of magnetic-tripping current flows.

Members t) and 54 which are secured together as a combined latch-and-armature unit, are biased to the left and counterclockwise in Fig. 4 by a band 56 that is of insulation and acts as a spring. A lance 58 projects upward from bimetal 36 to prevent the upper part of band 56 from sliding to the right (Fig. l) on the bimetal'. Armature 54 is a corresponding formation on latch-and'- armature unit 50-54 that prevents the lower part of band 56 from shifting to the left (Fig. l). In this way band 56 retains assembly Sil-54 into its supporting notches 48, and band 56 also biases latch 50 in the reset vor latching direction, that is, in the direction for operative engagement with bimetal 36.

In the extreme counterclockwise position of member 50 as illustrated, it bears against a button 60 of insulation carried by current-responsive bimetal 36. Core 40 is coated with insulation 51, and, as noted, band 56 is of 4 insulation. Thus, the coil 42 and the movable end of bimetal 36 are insulated from core structure 38 that is united electrically to the contact arm 16 and is therefore at the same potential as the fixed end of bimetal 36.

The operation of the above tripping mechanism may now -be described. Current flowing from one terminal 46 and braid 44 through coil 42 travels along currentresponsive bimetal 36, to moving contact arm 16, through

contacts

14 and 10, to opposite terminal 12. For small levels of current, the current-responsive bimetal 36 deects downward only slightly, and the magnetic field produced by coil 42 and core 40 is inadequate to cause tripping. Before tripping can occur, latch 50 must be pressed down through a sufiicient distance to clear actuator 22. Bimetal 36 is required to overcome the latch friction of latch 50 wiping across the latching end of actuator 22, this deflecting force requiring a much lower order of strength or stiffness than would be required of it if it were also to resist the endwise force applied by actuator 22 against the end of latch 50. Because only a low order of detiecting force is needed bimetal 36 can be made ofrelatively slender proportions so that its resistance can be relatively high and consequently tripping heat can be developed in response to low values of rated tripping current. In other words high thermal sensitivity can be realized.

When the current rises to a sufiicient level, and for a suicient period of time for the bimetal temperature to rise and cause sufiicient deflection, thermal tripping takes place. Button 60 of insulation pushes latch 50 down out of the path of,v actuator 22. The latter swings clockwise quickly and spring 32 is then enabled to drive contactY arm counter-clockwise. If handle 24 is not held, it is also returned to ot position at this time by spring 32,. The

linkage

26, 22 is then in condition for renewed closingy of' the circuit breaker. If handle 24 is later released, spring 32 effects resetting of the circuit breaker in condition for reclosing.

Thermal tripping requires some short delay-time during whichy the current-responsive bimetal is heated by the current through the circuit breaker. Magnetic tripping involves no such delay, but magnetic tripping is commonly desired to operate at a level of 6 to 10 times the thermal tripping level in order that the circuit breaker shall notopen. in response to safe surge currents such as the in-rush current of a cold tungsten lamp load, which, when heated, draws a muchk lower operating current. In order to achieve magnetic tripping of 6 to l0 times the thermal tripV rating, especially for small values of rated current, the present circuit breaker construction provides excellent sensitivity without an undue, massive number of turns in coil 42. Low mass is important for a minimum of inertia of parts carried by the moving contact arm, such inertia having a retarding effect on opening of the contacts after tripping occurs.

When the instantaneous current through the circuit breaker exceeds the magnetic tripping level, armature.

54 swings clockwise and pulls latch 50 away from button 60 and out of latching engagement with actuator 22. Contact opening after magnetic tripping is the same as in connection with thermal tripping described above, but

magnetic tripping involves no such delay as that oc-l casioned by heating of the bimetal.

In they event of a short circuit being imposedv on the circuit protected by the circuit breaker, a high instantaneous voltage develops between the wire of coil 42 and the metallic assembly 16-38-40. For this reason it is desirable to coat either or both of members 40 and 2 with insulation as, for example, an insulating enamel 51 on core 40; This insulation, and button 60 and band 56 of insulation prevent any portion of the normal circuit breaker current from by-passing bimetal 36 and the insulation also prevents occasionally heavy currents from flowing from the movable end of bimetal 36 to latch 50,

toiron structure 3S joined to the fixed end of bimetal 36. Sparking or welding at the latch pivot might otherwise result in extreme condititfns.

Member 50, described as a latch, is formed as a bimetal and arranged to curve in the reverse direction, compared to bimetal 36. The low-expansion sides of those bimetals face each other. Insulation button 60 bears against bimetal 50 between the ends thereof and, when bimetal 36 curves downward, not in response to current but in response to an ambient temperature rise, bimetal 50 compensates by curving downward. In the embodiment illustrated, insulating button 60 engages bimetal latch S closer to the latching point than to latch pivot 52. This is of particular advantage in circuit breakers of low current ratings, where weak current bimetals may be expected. The force developed by Ibimetal 36 for tripping the breaker is required to overcome resistance to unlatching movement of the latch, developed at the point of engagement with actuator 22. This frictional resistance is developed at the end of the full length of lever 5t), where the unlatching force developed yby bimetal 36 is applied to lever S0 at a fraction of its length. This ratio of lever lengths is a disadvantage to circuit breakers that depend on weak current-responsive bimetals; and the mechanical disadvantage in such breakers can be minimized by arranging effective coaction between the bimetals to be at a point of compromise between the ends of the compensating bimetal nearer to actuator 22 than to pivot 48--52 It has been noted that band 56 is an insulated tensioner between the bimetal 36 and the latch 50. In the circuit breaker this tensioner is required to serve reliably for an indefinitely long period, and it is also subject to the elevated temperatures that may develop in current-responsive Ibimetal 36 due to overload. This band S6 is particularly effective when made of silicone rubber which has the properties of sustained resilience over long periods of time and of stable characteristics at normal and elevated temperatures, and is thus of special value in the organization described.

Tensioning band 56 is effective to bias the combined armature and latch unit 50-54 against the left-hand extremity the bottom of notch 4S. It also biases member 50 against the top edge 48a of notch 48, and against button 60 carried by bimetal 36. Because of the few dimensional variables in the unity core structure 38 and in the latch-and-armature unit 50, the orientation of latch member 50 is quite stable when once calibrated. This factor is of great importance in the routine production of circuit breakers which are to have and retain consistent characteristics. A further factor in this consistency is that, even with relatively strong ybands 56 and iirm, possibly variable tensions developed by the several bands 56 in many circuit breakers made in production, the magnetic tripping sensitivity is high and con sistent. This tensioning band applies its force close to the pivot point of latch Sil, that is, close to shoulder 52, and the distance between the band and that shoulder can readily be held to a consistent dimension, so that the counterclockwise tensioning moment is small. Magnetic tripping force must overcome latch friction and little more. Consequently the magnetic tripping sensitivity as previously noted remains consistent from each breaker to the next in mass produced circuit breakers, and the sensitivity is high.

The initial calibration of the circuit breaker is achieved as in a widely used circuit breaker of this type by driving a wedge in the calibrating notch in arm 16 between pivot 18 and actuator 22 when the bimetal 36 has been heated by carrying rated current for a rated time interval. The wedge is then driven into the notch sufficiently to cause latch 5t) to move relatively down and out of obstructing position at the end of latch 22, and the Calibrating wedge is removed.

In this circuit breaker, actuator applies an endwise,

6 compressional force on latch 5t) toward the latch pivot, being the principal force holding the latch in its separable pivot or hinge seat 48-5'2 when the circuit breaker is closed. Viewed otherwise, the latching end of acuator 22 moves in the direction along which latch 50 extends, at the instant of release of the actuator. When the circuit breaker is open, band 56 holds latch 50 in its seat.

It will be appreciated that the illustrative embodiment employs various features of the invention in exemplary fashion, but that certain features may well be applied to other types of circuit breakers than that illustrated; and consequently this invention should be broadly construed in accordance with its spirit and scope.

We claim:

l. in a circuit breaker having separable contacts, manually operable mechanism for opening and closing the contacts, and a latching assembly causing automatic opening of the contacts in response to fault currents, said latching assembly including a current-responsive bimetal arranged to carry circuit breaker current, a latch extending generally along said bimetal and having a latching end and having a separable pivot at the opM posite end, thereof, said pivot being separable in the direction toward said latching end, and an insulating tensioner connected between said current-responsive bimetal and said latch, biasing the latch both endwise towards its pivot and pivotally into cooperation with the current-responsive bimetal.

2. Apparatus in accordance with claim l wherein said current-responsive bimetal and said latch co-act with each other through an interposed element of insulation and wherein said tensioner engages said latch member between said element of insulation and said pivot.

3. Apparatus in accordance with claim 2 wherein said tensioner is an elastic band encircling said latch and said current-responsive bimetal, and wherein portions of the band engage formations on the bimetal and the latch and are thus held offset from cach other longitudinally of the latch and the bimetal.

4. In a circuit breaker having separable contacts, manually operable mechanism for opening and closing the contacts, and a latching assembly causing automatic opening of the contacts in response to fault currents, said latching assembly including a current-responsive bimetal arranged to carry circuit breaker current, a latch extending generally along said bimetal and having a latching portion at one extremity thereof and having a pivot at the opposite end thereof, said latching assembly also having a notch formed as a pivotal seat for rockably receiving said latch, said seat being disposed adjacent the current-responsive bimetal, said seat opening toward said latching portion of the latch, and an insulating tensioning band of silicone rubber about said currentresponsive bimetal and said latch, said tensioning band being positioned by formations. on the latch and on the current-responsive bimetal disposed to bias the latch both towards its seat and pivotally into cooperation with current-responsive bimetal.

5. A circuit breaker including separable contacts manual mechanism for opening and closing the contacts, a releasable member effective to hold the contacts closed, and a latching assembly for providing automatic release of the releasable member in response to current overload, said latching assembly including a currentresponsive bimetal, a magnetic core structure having a coil thereon connected electrically in series with the current-responsive bimetal, and a combined latch-andarmature unit having shoulders rockably received in corresponding notches in the magnetic core structure, and an insulating tensioner connected between said latch and said current-responsive bimetal disposed to bias said unit both toward said current-responsive bimetal for mechanical co-action therewith and toward said seat, for remaining in assembly therewith.

6. A circuit breaker having separable contacts, a movable arm carrying one of said contacts, manually operable mechanism to operate said arm into open and closed positions, a releasable member carried by sai'd' Contact arm and effective when released to initiate opening operation of the contact arm, and a latching assembly carried by said contact arm, said latching assemblyincluding a current-responsive bimetal and a magnetic core structure both mechanically and electrically joined at a common point to said Contact arm, said currentresponsive bimetal having a movable end, a coil carried by said core structure and connected to said movable bimetal end for passing said current through the bimetal and for magnetizing said core structure, a combined latch-and-armature unit forming a separable pivotal connection to an open seat in the magnetic core structure,

and an elasticy insulating tensioner connected between said unit and said bimetal for maintaining assembly of,

the latchand-armature unit in the open set and for biasing thev latch intomechanical co-action with the current-responsive bimetal without however providingv a shunt electricalvpath through the tensioner.

yReferences Cited in the file of this patent UNITED STATES PATENTS