US2989605A - Bi-metal actuated bi-metal shunt - Google Patents

Description

June 20, 1961 J. H. LEONARD 2,989,605

BI-METAL ACTUATED BI-METAL sHUNT Filed June 5, 1958 2 Sheets-Sheet 1 June 20, 1961 J, H, LEONARD 2,989,605

BJI-METAL ACTUATED BI-METAL SHUNT Filed June 5, 1958 2 Sheets-Sheet 2 United States Patent O 2,989,605 BI-METAL ACTUATED BI-METAL SHUNT James H. Leonard, Philadelphia, Pa., assignor to I-T-E 'Circuit Breaker Company, Philadelphia, Pa. Filed June 5, 1958, Ser. No. 740,041 3 Claims. (Cl. 200'88) My invention relates to circuit breakers in general and is more particularly directed to a novel shunting means for by-passing the bimetal time delay trip element of the circuit breaker upon the occurrence of a severe overload condition.

Molded case circuit breakers are provided with a time delay trip unit usually in the foirn of a bimetallic element and an instantaneous trip element which is in the form of a yoke armature combination. On the occurrence of an overcurrent, the deflection of the bimetal will be effective to delatch the cradle mechanism and on the occurrence of a fault current the magnetic yoke will be sufiiciently energized to attract its armature thereby resulting in delatching of the cradle mechanism to effect contact disengagement.

-It has been found that the bimetal will be permanently deformed if it is subjected to excessive currents. Some circuit breakers of the prior art have included circuits which shunt current so as to by-pass the bimetal upon the actuation of the instantaneous trip unit. In this way the bimetal is protected from excessive current from the movement that the armature is attracted by the yoke. However, the armature is of a substantial mass so that its operating time is not instantaneous.

It has also been found that upon the occurrence of a short circuit condition the bimetal shunt circuit is not actuated by the instantaneous trip unit in a sufficiently short interval of time so as to prevent burn-out or distortion due to excessive heating in the case of a directly heated bimetal. The problem is particularly severe in circuit breakers having a low continuous circuit rating, hence a high resistance bimetal.

The circuit breaker of the instant invention is provided with a shunting circuit which is actuated by the bimetal itself. That is, the free end of the bimetal carries a contact which upon suicient deection of the bimetal, engages a contact in a shunt circuit which is completed when the two contacts are in engagement. The shunt circuit is not complete during normal heating of the bimetal but is closed when there is over-heating of the bimetal but is closed when there is over-heating at a time before burn-out or distortion set in. Thus the shunt does not carry current for an extended period of time but merely for some time less than it takes the circuit breaker to open after being hit by a short circuit or severe lfault condition. The bimetal actuated shunt, in addition to its superior electrical qualities over that of the instantaneous trip operated shunt, offers the advantages of compactness Iand fewer number of parts.

The shunt comprises a member which is securely fastened at one end and extends parallel to the bimetal. A contact is secured to the shunt at its free end and is positioned to be engaged by a contact carried by the bimetal, at the free end thereof, when the deflection of the bimetal reaches a predetermined point.

In order to prevent a reverse deflection of the bimetal under extremely high current conditions, the shunt is constructed of a yieldable material. However, the material is sufficiently resistant to deflection to prevent contact rebound and maintain contact pressure sufficient to establish a low resistance juncture.

Accordingly, a primary object of the instant invention is to provide -a novel shunting circuit for the thermal time delay tripping element of a circuit breaker.

ICC

Another object of this invention is to provide a directly heated thermal time delay trip element and a shunt therefor which are both mechanically independent of the instantaneous trip device although both act on the same common tripper bar.

Still another object is to provide a bimetal actuated bimetal shunt for the directly heated bimetallic element of an instantaneous trip unit of a molded case circuit breaker.

These as Well as other objects of the instant invention shall become readily apparent after reading the following description of the Vaccompanying drawings in which:

FIGURE l is a top view of a three pole circuit breaker, including my novel bimetal actuated bimetal bypass, with the cover removed.

FIGURE 2 is a side sectional view of the circuit breaker taken along line 2 2 of FIGURE l, and illustrates the operating mechanism after the circuit breaker has been tripped due to an overcurrent.

FIGURE 3 is a perspective view illustrating the mechanical independence of the time delay bimetal and its shunt from the instantaneous trip unit.

FIGURE 4 is an end view of the overcurrent device.

FIGURE 5 is a side view of the novel bimetal actuated bimetal shunt.

FIGURE 6 is a view taken in the direction of the arrows 6-6 of FIGURE 5.

FIGURE 7 illustrates a modification of this invention wherein a moving shunt is carried by the bimetallic element.

Referring first to FIGURES l and 2 showing a three pole embodiment of a circuit breaker in which my invention can be adapted, the housing 20 of the circuit breaker 10 is preferably made of a plastic substance and is provided with appropriate openings 21 and 22 through which the circuit breaker terminals 25-26, respectively, `are substantially brought out of housing 20 to be engaged by the line terminals of the line to be protected. This circuit breaker may be of the type shown in U.S. Patent 2,673,908 to I. C. Brumfield entitled Instantaneous Trip Circuit and assigned to the assignee of the instant application.

The housing 20 consists of two sections, a base 20a is a section of the housing 20 on which the various components of the circuit breaker 10 are mounted as hereinafter described and a cover 20b which completely closes the circuit breaker 10 by tightly engaging the base 20a.

In the three pole circuit breaker 10 which is being considered for this example, there will be three sets of circuit breaker terminals 25 and 26. However, for the sake of clarity, only the center phase B of the three pole circuit breaker 10 having phases A, B and C will be described.

`Considering then this center phase B of the three pole circuit breaker 10, the circuit breaker terminal 25B rests against an extending shoulder 28B of molding 20a. Shoulder 28B is perforated to receive threaded insert 29B which eventually receives a bolt (not shown) to secure 'the line terminal (not shown) to circuit breaker terminal 25B. As previously mentioned, circuit breaker terminal 25B extends through opening 21B into base 20a. Circuit breaker terminal 25B is shaped like -an angle, one side 30B of the angle being used to receive a line terminal (not shown), while the other side 31B is soldered or in any other way connected to a pigtail or conductor 35B.

Pigtail 35B is rigidly secured to cross member 300B mounted to bimetal 38B at the calibration screw 43B. As best seen in FIGURES 3 through 6, the L-shaped thermal responsive means 38B has one leg thereof positioned on top of the substantially U-shaped magnetic yoke 200. A screw 201 is passed through the leg of fixed shunt member 301B, through one leg of the bimetal 38B through magnet-ic yoke 200 into the molding 20a. Thus, the screw 201 secures both the bimetallic element 38B and the magnetic yoke 200 to the base molding 20a and also serves to electrically connect the terminal 48B to the bimetallic element 36B. Big-tail 52B is soldered or otherwise Vsecured to the diagonally extending tip 48B of shunt member 301B. Thus, a com plete current path is -provided from the pigtail 52B to the terminal 48B and out the pigtail 35B to thereby form a single turn for the energization of the magnetic yoke 200.

A pivotally mounted shaft 203 mounted in bearings 204, 205 contains wire spring 206. A barrier plate 209 positioned Within appropriate recesses of the groove in base molding 20a for the overcurrent device serves as a stop for one end of the wire spring 206.

The armature 211 is secured to the rotatably mounted shaft 203 at the area which contains the wire spring 206 land serves as a stop for the opposite end of this Wire spring. It will be noted that the wire spring 206 may be mounted on either side of lthe armature 211 rather than being mounted in the center as shown in FIGURE 3. With only one end of the spring 206 engaging the armature 211, it will not be necessary to reduce the crosssectional `area of the shaft 203 to mount the spring. Thus, as best seen in FIGURE 5, the armature 21.1 is biased in a counterclockwise direction around the shaft 203 due to the wire spring 206. The bottom ledge of the barrier 209 serves as ya stop to limit the counterclockwise rotation of the armature 211.

The enlarged magnetic section 213 of the armature 211 is positioned abovethe pole faces 214 and 215 of the magnetic yoke 200. On the occurrence of a fault current, the single turn comprising the current ow through the bimetal 38B will sufficiently energize the magnetic yoke 200 so that the portion 213 of the armature 211 will be attracted toward the pole faces 214 and 215. That is, the armature 211 will be rotated in a clockwise direction against `the bias of the wire spring 206, The protruding portion 21B of the armature 211 will then be against the protrusion 60B of the common tripper bar 65.

As will be apparent, the counterclockwise rotation of the common tripper 4bar 65 will effect disengagement of the latch 147B--152B to thereby effect disengagement of the cooperating contacts 77-85.

It will be noted that the movement of the Aarmature 211 when attracted by the magnetic pole 200 is completely independent of the movement of the bimetal 38B and hence, clockwise rotation thereof will result in la hammer blow on the protrusion 60B of the common tripper bar 65 to effect contact disengagement. The portion 66B of `the common tripper bar 65 is positioned in alignment with the adjustment screw 43B of the thermal element 38B. Thus, on the occurrence of an overcurrent, the bimetal 38B will deflect to the right in the conventional manner as seen in FIGURE 2, to thereby engage the portion 66B and cause counterclockwise rotation of the common tripper bar 65. It will be noted that when the circuit breaker is tripped due to the occurrence of an overeurrent condition, the bimetallic element 38B will deflect to the right `and its 4movement will be independent and unaffected by the instantaneous magnetic trip means 2011-211.

The common tripper bar 65 provided Aat phase B as above noted has an extending member having portions 60B and 66B which are respectively engaged by the portion 216 of the armature 211 `and the adjustment screw 43B of the bimetal 38B.

The pigtail 52B to the fault current responsive means 38B and 211 is electrically connected to the arm 71B at the end 70B thereof. Movable contact `arm 71B is pivoted by means of the pivot pin 72B engaging `aligned openings 73B of the metallic `frame or support 75B. Contact arm 71B is provided at its other end with a substantially rectangular shaped contact slab 77B. Contact slab 77B made of good conducting material is rigidly secured to cont-act arm 71B by means of a rivet 78B or in any other suitable way.

Stationary contact 80B consists of a rectangular section metallic member 81B having at the end nearer to contact arm 71B a stationary contact slab JSSB'rigidly secured to member 80B. Member 81B is secured to housing 20a of the circuit breaker through a screw 86B and 1a washer 87B. Stationary contact V'80B is lalso provided with `a terminal extension 26, yan integral part of metallic member 81B, which extends yfor 4a portion 90B out of housing 20a to permit by means of screw means (not shown) the connection of a line terminal .to circuit breaker terminal 26. Stationary contact 80B is further provided with an yarc extinguishing chamber B or `arc chute having a number of arc extinguishing plates 96B so that at ,the opening portion of the circuit breaker the arc existing between contact slab 77B and contact slab 85B is extingiished before producing damage to the contact slabs 77B and 85B.

The operating mechanism of the circuit breaker, which forms no part of my present invention, is described in the aforementioned U.S. Patent 2,673,908.

T-member `B is provided at its upper portion 122B with a substantially rectangular extension 131B. Upper portion 122B of T-member 120B is slotted in its mid portion and provided with raised member 132B cutout from the upper portion 122B of T-member 120B which serves to be engaged by a plastic operating handle 135B tor manually opening and closing the circuit breaker, as hereinafter described. One leg 155B of the V-shaped cradle B is shaped as shown in FIGURE 2 to engage a latch 147B. Latch 147B is provided with a slot 148B engaged by pin 150B around which latch 147B can rotate and can also have translational motion. Latch 147B is provided with a pointed end 151B latched under norm-al conditions by a latch surface 152B on the tripper bar 65.

Latch surface 152B is composed of a thin strip of material on tripper bar 65 supporting the latch 147B. The leg 157B of Vshaped member 145B is provided with a cylindrical hole engaged by a pivot pin l106B secured to the raised portion B of frame 75B. Leg 157B 0f V-shaped member 145B is provided at the bottom of the V with a shoulder extension 166B. Raised portion 165B of frame 75B is provided with an opening through which passes contact slab 77B of movable contact arm 71B and provides a stop `for V-shaped cradle 145B.

Near the end 70B of movable contact arm 71B at which pigtail 52B is connected, `an essentially rectangular section bar is rigidly secured to movable contact arm 71B in any suitable way. Shaft or tie bar 1180 is common to all three phases A, B and C of the three-pole circuit breaker, being rigidly secured to the ends 70 of the movable contact arm 71 of every phase so that if one mov-able contact, for example, 71B, is moved whether opened or closed, the other two movable contact arms 71A and 71C will simultaneously perform the same movements. The circuit breaker 10 is also provided, in the vicinity of are chute 95B, with an insulation 185B for completely insulating arc chute 95B.

Thus, it will be seen that when either the time delay or instantaneous overcurrent means rotates the common tripper bar 65, in a clockwise direction, both the latch Y147B and 187B will be released and hence, spring 118 will drive the contacts '77 to 4disengaged' position.

As heretofore noted this trip of the circuit'breaker to the position indicated in FIGURE Zby the releaseof the 'two latches can .be achieved by either an overcurrent which will cause delico-tion .of the bimetal 38B to the right and result in engagement of the adjustment ,screw 43B with the protmsion 66B to cause counterclockwise rotation of the tripper bar 65 or due to a fault current condition wherein the single turn of the bimetal y38B will sutciently energize the magnetic pole 200 to thereby rotate the armature 211 in a clockwise direction yagainst: its bias aosaeo 206 thereby bringing its extension 216 into engagement with the protruding portion 60B to rotate the tripper bar in a counterclockwise direction.

Thus, it will be seen that with the novel overcurrent device of my invention, the instantaneous trip means comprising the armature 213 and the m-agnetic yoke 200 are mechanically independent of the time delay thermal means 38B and hence, the occurrence of a fault current or an overcurrent will result in a blow or force in one direction on the tripper bar 65 to result in the tripping of the circuit breaker.

Fixed shunt member 310B is generally L-shaped with the upwardly extending arm thereof being positioned generally parallel to the upwardly extended leg of bimetal 38B when it is not deflected. A fixed shunt contact 302B issecured to the upper end of shunt member 301B and is positioned for engagement by movable contact 303B carried by the bimetal cross-member 300B.

When shunt contacts 302B and 303B are engaged a complete current path between pigtails 43B and 52B which by-passes bimetal 38B is formed. This current path ex* tends from pigtail 35B, through cross-member 300B, through shunt contacts 302B and 303B, through llow resistance fixed shunt 301B to pigtail 52B. Current flow is shunted through this path since fixed shunt 301B is of a much lower electrical resistance than bimetal 38B.

Upon the occurrence of a mere overload condition the upper end of bimetal 38B will slowly deflect to the right until adjusting screw 43B engages portion 66B of tripper bar 65 and the cooperating contacts 77B, 85B will be parted before shunting contacts 302B, 303B become engaged.

Upon the occurrence of a short circuit or other severe fault instantaneous trip means 200-211 will act before screw 43B has engaged tripper bar 65. However, circuit interruption is not instantaneous so that bimetal 38B is deflected beyond the point where screw 43B engages tripper bar 65 under mere overcurrent conditions. Bimetal 38B will continue to deflect until movable shunt contact 303B engages fixed shunt contact 302B and the major portion of the circuit current now passes through shunt 301B rather than bimetal 38B. The spacing between shunt contacts 302B and 303B is such that they will be engaged before burn-out or distortion of bimetal 38B can take place.

FIGURE 7 illustrates a variation of the bimetal shunting circuit hereinbefore described. This latter circuit comprises a movable shunting member 400 secured at one end. 401 to the free end of bimetal 38B and carrying movable shunt contact 402 at its other end. Movable shunt con. tact 402 as positioned to engage fixed shunt Contact 403 and when so engaged most of the phase current will bypass bimetal 38B by following through stationary shunt 404 and movable shunt 400 now connected in series.

Shunts 400 and 301B are both constructed of a low resistance material which is sufliciently yieldable so as to prevent reverse deflection of bimetal 38B when it is subjected to currents of high magnitude. Further the material of shunts 400 and 301B is suiciently rigid so as to prevent contact rebound and maintain high contact pressure to provide a low resistance joint.

In the foregoing, I have described my invention only in connection with preferred embodiments thereof. Many variations and modifications of the principles of my invention within the scope of the description herein are obvious. Accordingly, I prefer to be bound not by the specific disclosure herein but only by the appending claims` I claim:

l. A circuit breaker having a pair of cooperable contacts; one of said contacts being biased to open position; a thermally responsive element comprising a bimetal; one end of said bimetal being rigidly supported and the other end flexing when heated; said thermally responsive element being connectible into an electric circuit to be protected by said circuit breaker; an electromagnet connected in electrical series with said thonmally responsive element; a trip latch engaging said biased contact to maintain said contact -in its contact engagement with the other of said cooperable contacts; the flexible portion of said bimetal when operated to a first predetermined position operating said trip latch to release said contact for operation by its bias; an amature operated by said electromagnet when fault current flows through said electric circuit and energizes said electromagnet; said armature when oper-ated operating said trip latch; said circuit comprising a fixed shunt contact and a movable shunt contact; said movable shunt contact being carried by said bimetal and being operatively positioned to engage said fixed shunt contact when said bimetal is operated to said second position; a shunt circuit also including an L-shaped shunt member; one leg of said shunt member being rigidly supported; said fixed shunt contact being mounted near the free end of the other leg of said shunt member; said member being comprised of a material having sufficient rigidity to prevent rebound of said shunt contacts and to maintain con* tact pressure between said shunt contacts; said member being sufliciently yieldable to prevent a reverse deflection of said bimetal; said circuit breaker having the elements thereof operatively arranged so that the free end of the other leg of said shunt member is free to be deflected a substantial distance.

2. A circuit breaker having a pair of cooperable contacts; one of said contacts being biased to open position; a thermally responsive element comprising a bimetal; one end of said bimetal being rigidly supported and the other end flexing when heated; said thermally responsive element being connectible into an electric circuit to be protected by said circuit breaker; an electromagnet connected in electrical series with said thermally responsive element; a trip latch engaging said biased contact to maintain said contact in its contact engagement with the other of said cooperable contacts; the flexible portion of said bimetal when operated to a first predetermined position operating said trip latch to release said contact for operation by its bias; an armature operated by said electromagnet when fault current flows through said electric circuit and energizes said electromagnet; said armature when operated operating said trip latch; said circuit comprising a fixed shunt contact and a movable shunt contact; said movable shunt contact being carried by said bimetal and being operatively positioned to engage said fixed shunt contact when said bimetal is operated to said second position; a shunt circuit also including an L-shaped shunt member; one leg of said shunt member being rigidly supported; said fixed shunt contact being mounted near the free end of the other leg of said shunt member; a first member mounted to the other leg of said bimetal near the free end thereof and extending transverse to the plane of movement of said bimetal; said movable shunt contact being mounted to said first member; said member being comprised of a material having suflicient rigidity to prevent rebound of said shunt contacts and to maintain contact pressure between said shunt contacts; said member being sufficiently yieldable to prevent a reverse deflection of said bimetal; said circuit breaker having the elements thereof operatively arranged so that the free end of the other leg of said shunt member is free to be deflected a substantial distance.

3. A circuit breaker having a pair of cooperable contacts; one of said cont-acts being biased to open position; a thermally responsive element comprising a bimetal; one end of said bimetal being rigidly supported and the other end flexing when heated; said thermally responsive ele rnent being connectible into an electric circuit to be protected by said circuit breaker; an electromagnet connected in electrical series with said thermally responsive element; a trip latch engaging said biased contact to maintain said contact in its contact eng-agement with the other of said cooperable contacts; the flexible portion of said bimetal when operated to a first predetermined position operating said trip latch to release said contact for operation by its bias; an armature operated `by said electromagnet when fault current flows through said electric circuit and energizes said electromagnet; said armature when operated operating said trip latch; a circuit comprising a fixed shunt contact and a movable shunt contact; said movable shunt contact being ycarried by said bimetal and being operatively positioned to engage said Xed shunt contact when said bimetal is operated to said second position; said shunt circuit also including .a shunt member secured at one end thereof `to said other end of said bimetal and extending toward said one end of said bimetal; said movable shunt contact being secured .to a second end of said shunt member; said member being comprised of a material having suciently rigidity to prevent rebound of said shunt contacts and to maintain contact pressure between said shunt Acont-acts; said member being sufciently yieldable `to prevent a reverse deflec- 8 tion of said bimetal; said shunt member being connected into said electric circuit only when said shunt contacts are in engagement; said circuit breaker having the elements thereof operatively arranged so that the free end of 4the other leg of said shunt member is free to be deflected -a substantial distance.

References Cited in the tile of this patent UNITED STATES PATENTS 1,966,444 Guett July 17, 1939 2,328,458 Jackson Aug. 31, 1943 2,357,151 Von Hoor-n Aug. 29, 1944 2,362,855 Stimson Nov. 14, 1944 2,491,959 Dyer Dec. 20, 1949 2,754,392 Bendik July Al0, 1956 2,764,650 Hodson Sept. 25, 11956 2,845,507 Brumfield July 29, 1958

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