US3317867A

US3317867A - Electric circuit breaker with thermalmagnetic tripping allowing for overtravel of the thermal means

Info

Publication number: US3317867A
Application number: US513204A
Authority: US
Inventors: David B Powell
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1965-12-13
Filing date: 1965-12-13
Publication date: 1967-05-02
Anticipated expiration: 1984-05-02

Description

7 6 8 7 7 1 3 C 3 I T E N G A ML um MA RR EMS ENNW VA OE H l T M %L FAB GM ENE .K I H W TD E m T l i F OF y 2, 1967 D. B. POWELL ELECTRIC CIRCUIT BREA TRIPPING ALLOW INVENTOR. DA v10 5. POWELL ATTORNEY United States Patent '0 3,317,867 ELECTRIC CIRCUIT BREAKER WITH THERMAL MAGNETIC TRIPPING ALLOWING FOR OVER- TRAVEL OF THE THERMAL MEANS David B. Powell, Bristol, Cnn., assignor to General Electric Company, a corporation of New York Filed Dec. 13, 1965, Ser. No. 513,204 Claims. (Cl. 335-37) The present invention relates to electrical control devices, and more particularly, to a novel electrical circuit breaker of the type incorporating thermal and magnetic current responsive means to cause tripping of the circuit breaker upon the occurrence of predetermined abnormal conditions in the current passing therethrough.

Thermal and magnetic current responsive means have been used for many years in electric circuit breakers to detect abnormal conditions in the current passing therethrough and to cause actuation of the circuit breaker to interrupt the electrical circuit. Prior art devices have used thermal current responsive means in combination with magnetic current responsive means by providing a bimetallic strip which is thermally actuated to trip the circuit breakers by a predetermined increase in the current passing therethrough, and by providing a field piece of magnetically susceptible metal disposed in the magnetic field of the bimetallic strip which develops suflicient magnetic strength when there is a sudden large increase in current passing through the bimetallic strip to attract a latch element and trip the circuit breaker.

In some prior art devices which failed to provide for overtravel of the bimetallic strip after it had moved to trip the circuit breaker and become engaged with the magnetic field piece, the bimetallic strip could be damaged by overstressing which causes permanent warping or other deformation of the strip as it attempts to continue bending against the surface of the magnetic field piece. In order to overcome this difficulty, it has been proposed to attach the magnetic field piece directly to the bimetallic strip but welding of the magnetic field piece to the bimetallic strip may change the characteristics of the bimetallic strip thus making it difficult to manufacture a bimetallic strip with an attached field piece with the desired predetermined characteristics.

Accordingly, it is an object of this invention to provide novel thermal and magnetic current responsive means for electrical control devices which permits overtravel of the thermally responsive means after the control device has been tripped.

It is also an object to provide such current responsive means that is simple in construction and operation and which is relatively rugged and inexpensive to manufacture.

A specific object of the present invention is to provide an improved electrical circuit breaker employing such novel thermal and magnetic current responsive means.

Other objects and advantages of the invention will be in part pointed out and in part become obvious from the following detailed description.

It has now been found that the foregoing objects and advantages can be readily attained in an electrical control device having a support and a bimetallic strip fixedly mounted on one end to the support with its other end free for movement. A magnetic field piece is mounted on the support in close proximity to the bimetallic strip so as to have a magnetic field induced therein by current passing through the bimetallic strip, and an armature or latch member is disposed adjacent to the field piece so as to be magnetically drawn thereto upon passage of a large overload current through the bimetallic strip during operation of the device. The armature or latch member is pivotably mounted on the support by mounting means and is engageable by the bimetallic strip as it elongates and bends upon occurrence of a predetermined overload current to be pivoted thereby. The mounting means provides a first pivot for initial pivotal movement of the armature or latch member relative to the field piece and a second pivot for further pivotal movement to accommodate overtravel of the bimetallic strip during elongation and avoid overstressing thereof.

In accordance with a highly effective type of construction for electrical circuit breakers and the like, at least one pair of cooperating contacts are mounted on the support and are relatively movable between open and closed circuit positions. The latch member or armature is connected to at least one of the contacts by movable means which is operated by movement of the latch member or armature to move the contacts from closed to open position. Generally, the movable means is a spring-biased mechanism which is held in latched position by the latch member or armature but which rapidly pivots upon re lease to open the contacts such as the releasable cradle type which is widely employed and which also includes an operating handle on the housing for manually moving the contacts relative to each other.

The magnetic field piece is desirably channel-shaped and is disposed to the side of the bimetallic strip opposite from the latch member so that it partially surrounds the bimetallic strip and has the ends of the leg portions thereof providing the surface against which the latch member is magnetically drawn. Lugs on the ends of the leg portions near the end of the field piece adjacent the fixed mounting of the bimetallic strip provide the first pivot. The surfaces of the ends have a first portion tapering. away from the lugs to provide the surface against which the latch member is drawn and which permits the latch member to pivot freely by action of the elongating bimetallic strip. A second surface portion on the ends tapers more steeply away from the first surface portion with the juncture therebetween or apex providing the second pivot to accommodate the overtravel of the strip during continuing elongation of the strip.

The latch member has an aperture adjacent the end thereof opposite that pivotably mounted on the lugs, and the second pivot is located between the aperture .and first pivot. The bimetallic strip extends through the aperture and bears against the surface of the latch member bounding the aperture spaced from the movable means. In this manner, the high expansion side thereof causes the strip to bow and bear against the latch member to produce pivoting about the other end, thereby releasing the operable means and opening the contacts.

The armature or latch member is rotatable upon the first pivot point when a sudden large overload current occurs and the generated magnetic field in the field piece engages and draws the armature or latch member against the first surface portion to trip the circuit breaker or electrical control device. When a small predetermined overload current occurs, the high expansion side of the bimetallic strip elongates to produce bending and mechanical engagement and movement of the armature or latch member to the tripped position against the first surface portion of the magnetic field piece. When the overload current causes continuing bending of the bimetallic strip, the armature or latch member slides on the lugs of the field piece forming the first pivot and pivots about the second pivot formed at the apex of the inclined surfaces of the field piece so that the bimetallic strip is free to continue to bend in order to prevent overstressing so that warping or similar damage does not occur. Thus, by providing a mounting of the armature or lat-ch member and a configuration of the field piece adapted to provide two pivot points about which the armature or latch member may pivot, the thermally actuated bimetallic strip has a free end which may continue to deflect due to overload current without damage by warping or permanent deformation.

The invention will be more fully understood from the following description and its scope Will be pointed out in the appended claims.

In the drawings:

FIGURE 1 is a side elevational view of an electrical circuit breaker embodying the present invention with a side of the insulating casing removed to show internal construction;

FIGURE 2 is a fragmentary side elevational view thereof with the elements thereof illustrated in the tripped position by magnetic action and with a portion of the trip cradle shown both in the tripped position in solid line and in the latched position in phantom line;

FIGURE 3 is a similar fragmentary side elevational view thereof with elements thereof illustrated in the tripped position by thermal action and with a portion of the trip cradle illustrated in phantom line in the latched position.

FIGURE 4 is a view similar to FIGURE 3 with the elements illustrated in the overtravel position of the bimetallic strip; and

FIGURE 5 is a fragmentary perspective view to an enlarged scale of the operating elements of the current responsive means of the circuit breaker of FIGURE 1 with the parts illustrated in the latched position.

Referring now in detail to the attached drawing, the invention is shown as incorporated in an electric circuit breaker having a basic support comprising a generally rectangular insulating casing generally designated by the numeral 2 provided by a body portion 3 and side wall portions 4. Mounted in a cooperatively configured recess 6 in the casing 2 is a stationary line terminal member 8 which is generally U-shaped and adapted to receive a blade-type terminal (not shown). The terminal member 8 has an integral projecting portion 10 with a stationary contact 12 thereon which cooperates with a movable contact 14 at one end of the contact arm 16. At its other end the contact arm 16 is pivotally mounted at the point 17 on the operating handle 18, which in turn is pivotally supported in the casing 2 by seating of its integral hub portion 20 in recesses in the side wall portions 4.

Pivotally supported in the casing 2 on the pivot pin 22 is a generally U-shaped releasable cradle or support 24 which has a lug portion 26 engageable by the projecting portion 28 of the operating handle 18. A tension-type operating spring 30 is interconnected between the contact arm 16 and an aperture 32 in the cradle 24. Rotation of the handle 18 about its hub portion 20 in the casing 2 moves the pivoted end of the contact arm 16 back and forth across the line of action of the tension spring 30 and moves the contact arm 16 between open and closed circuit positions with respect to the stationary contact 12 with a snap-action.

The end portion 34 of the releasable cradle or support 24 which is remote from the pivot pin 22 is releasably latched in the position shown in FIGURE 1 by currentresponsive means to be described hereinafter so that movement of the contact arm 16 is effected only by the operating handle during normal operation of the circuit breaker. However, when the contact arm 16 is in closed circuit position with the movable contact 14 against the stationary contact 12 and the end portion 34 of the cradle 24 is released by the current-responsive means, the tension spring 30 acts on it to cause rotation in clockwise direction as viewed in FIGURE 1. Clockwise rotation of the cradle 24 moves the anchor point or aperture 32 of the spring 30 across the pivot point 17 of the contact arm 16, thereby reversing the bias of the spring 30 on the contact arm 16 and moving the contact arm 16 to automatically opened or tripped position.

Following tripping action, the parts may be returned to the olf position as indicated in FIGURE 1 by rotating the handle 18 clockwise about its hub portion 20 back to its FIGURE 1 position. This causes the projecting portion 28 of the handle 18 to engage pin or lug portion 26 on the releasable cradle 24 and to rotate it in a counterclockwise direction about its pivot pin 22 to the latched position as shown in FIGURE 1.

It should be understood that the particular operating mechanism utilized may be of any suitable type including a member which is moved to cause automatic opening, and that the particular mechanism illustrated herein is chosen merely as an example. The construction and operation of the mechanism illustrated are more specifically described in copending application Ser. No. 405,757, filed on Oct. 22, 1964, and assigned to the same assignee as the present invention.

Current responsive means For the purpose of normally restraining the releasable support or cradle 24 and for releasing it upon the occurrence of predetermined conditions in the current flowing through the circuit breaker in accordance with the invention, current responsive means is provided which will now be described.

An elongated bimetallic strip 36 is rigidly attached to the bentover, generally U-shaped end portion 38 of the terminal strap member 40 by any suitable means such as welding. Intermediate its length, the terminal strap member 40 is fixedly attached to the casing 2 by suitable means such as the fastener 42, and at its outer end is provided a V threaded fastener 44 forming the load terminal.

For the purpose of adjustably positioning the bimetallic strip 36, a calibrating screw 46 is provided which is threadedly engaged in a nut 48 trapped in a conforming recess 50 in the casing 2. The inner end of the screw 46 extends in a notch 52 formed in part of the end portion 38 and bears on terminal portion thereof attached to the bimetallic strip 36 so that adjustment of the screw 46 causes more or less bending of the strap member 40 intermediate the end portion 38 and the fastener 42, thereby changing the angle of the bimetallic strip 36 in the casing 2. The other end portion 54 of the bimetallic strip 36 is free or movable and is electrically connected to the movable contact member 14 by means of a flexible conductor 56. Thus, the current path through the circuit breaker is from the line terminal member 8, to the stationary contact 12 to the movable contact 14, to the flexible conductor 56, to the free end portion 54 of the bimetallic strip 36 to the terminal strap member 40, and to the load terminal 44.

The current responsive means also includes an elongated, generally channel-shaped magnetic field piece, generally designated by the numeral 58, which forms a recess of generally -U-shaped cross section in which the bimetallic strip 36 is disposed. The field piece 58 is mounted in a recess in the casing 2 by any suitable means and the leg or side wall portions 60 thereof have ends which provide lugs 62 at the end adjacent the strap member 40. The ends are configured to provide upper inclined surfaces .64

in one plane tapering away from the lugs 62 toward th free endportion 54 of the bimetallic strip 36 and lower inclined surfaces 66 in another plane tapering away from the lugs 62 at a greater angle, the

inclined surfaces

64 and 66 meeting in anap'ex 68.

Pivotably supported on the lugs 2 of the field piece 58 is an armature or latch member generally designated by the numeral 70 which has notches 72 on either side adjacent one end thereof seating the lugs 62. The armature or latch member 70 is biased for clockwise rotation as viewed in FIGURE 1 about its pivotal support on lugs 62 by one end of a compression spring 74 which has its op posite end abutting against the projection 76 on the casing 2. Adjacent the opposite end thereof the armature or latch member 70 has an aperture through which the free end portion 54 of the bimetallic strip 36 extends. A latch projection or bent-out tab portion is formed on the latch member 70 adjacent the aperture 78 for engaging and retaining the end portion 34 of the releasable cradle 24 when the latch member 70 illustrated in FIGURE 1.

The current responsive means operates to cause release or tripping of the circuit breaker in either one of two ways, depending upon the magnitude of the excess current, that is, either magnetically or thermally. Magnetic tripping takes place upon the occurrence of an extremely high overload current, such as those of short-circuit value, which produces a magnetic field of such strength in the magnetic field piece 58 that is able to draw the latch member 70 against the pressure of the spring 74. As the latch member 70 is drawn toward the surface portion 64, the latch member 70 is pivoted about the lugs 62 and the latch projection 80 is withdrawn from engagement with the end portion 34 of the releasable cradle 24, thereby causing tripping of the circuit breaker.

' Thermal tripping takes place upon the occurrence of electrical currents which are above the normal or rated value of the circuit breaker and below the excessively high or short-circuit values which cause magnetic tripping. Such intermediate overload currents cause bending of the bimetallic strip 36 due to greater elongation of the highly expansive side thereof so as to move the free end portion 54 away from the cradle 24. As the strip 36 deflects, it bears upon the portion of the latch member 70 bounding the aperture 78 through which it extends to move the end portion away from the cradle end portion 34. This pivoting of the latch member 70 against the biasing pressure of the spring 74 causes the latch projection 8t) to disengage from the cradle end portion 34 and trip the circuit breaker.

As illustrated in FIGURE 3, when the armature or latch member 70 is moved by either the bimetallic strip 36 acting thereon in the aperture 78 or by magnetic attraction of the field piece 58, the latch member 70 is rotated about its first pivot on the lugs 62 so that it closes the main magnetic gap and moves into engagement with the upper inclined surface portion 64. As illustrated in FIGURE 4, when continued bending of the bimetallic strip 36 occurs due to a continuing overload current, the latch member 70 is free to pivot about thesecond pivot provided by the apex 68 at the juncture of the

inclined surface portions

64, 66 as the notches 72 and lugs 62 are dimensioned and configures so that the latch member 70 is slidable on the lugs 62 as it pivots on the apex 68. Thus, the bimetallic strip 36 is free to continue bending against the force of the spring 74 about the apex 68 so as to prevent bimetallic overstressing of the bimetallic strip 36 which could cause damage by permanent deformation or warping thereof.

Thus, by providing the current responsive device of the present invention, overtravel of the bimetallic strip 36 is accommodated and damage by overstressing of the strip is prevented. The magnetic field piece need not be attached to the bimetallic strip and is simple in construction and relatively inexpensive to manufacture with portions providing two pivot points for two independent movements of the armature-latch. The structure and operation of the current responsive device are rugged and simple providing for reliable operation with a minimum number of parts.

It is well understood that various changes in the details, materials, and arrangement of parts, which have is in the latched position been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the claims.

Having thus described the invention, I claim: 1. In a thermal and magnetic current responsive device, the combination comprising:

(a) a support; (b) an elongated bimetallic strip fixedly mounted at one end on said support and having its other end movable; (c) a magnetic field piece mounted on said support in close proximity to said bimetallic strip; (d) an armature adjacent to and magnetically engageable by said field piece during operation of the device upon passage of a large overload current through said bimetallic strip; and (e) mounting means pivotably mounting said armature on said support, said armature being engageable by said bimetallic strip during operation of the device upon occurrence of a predetermined overload current to produce pivotal movement of said armature upon elongation of the high expansion side of said bimetallic strip and resultant bending thereof, said mounting means providing a first pivot for initial pivotal movement of said armature relative to said field piece and a second pivot for further pivotal movement of said armature relative to said field piece to accommodate overtravel of said bimetallic strip. 2. The current responsive device of claim 1 wherein said armature has an aperture therein through which said bimetallic stn'p extends and wherein said bimetallic strip bears against a portion of the armature defining said aperture upon a current overload condition to provide the operative engagement thereof.

3. The current responsive device of claim 1 wherein said pivotal mounting means is provided by portions of said field piece.

4. The current responsive device of claim 1 wherein said magnetic field piece partially surrounds said bimetallic strip, and has lug portions providing said first pivot and converging surface portions providing said second pivot spaced from said first pivot toward said movable end of said bimetallic strip.

5. An electrical control device comprising:

(a) a support;

(b) at least one pair of cooperating contacts mounted on said support and relatively movable between open and closed circuit positions;

to) a latch member;

(d) movable means connecting said latch member to at least one of said contacts to move said contacts from said closed to said open position uponpredetermined movement of said latch member;

(e) an elongated bimetallic strip adjacent said latch member fixedly mounted at one end on said support and having its other end movable;

(f) a magnetic field piece mounted on said support in close proximity to said bimetallic strip, said field piece having the major portion thereof disposed substantially to the side of said strip opposite from said latch member, said latch member being magnetically engageable by said field piece during operation of the device upon passage of a large overload current through said bimetallic strip; and

(g) mounting means pivotably mounting said latch member on said support, said latch member having a portion thereof engageable by said bimetallic strip during operation of the device upon occurrence of a predetermined overload current to produce pivotal movement of said latch member upon elongation of the high expansion side of said bimetallic strip and resultant bending thereof, said mounting means providing a first pivot for initial pivotal movement of said latch member to an unlatched position for actuating said movable means and thereby said contacts to said open circuit position and a second pivot for subsequent pivotal movement of said latch member to accommodate overtravel of said bimetallic strip and avoid overstressing thereof.

6. The electrical control device of claim 5 wherein said latch member has an aperture therein through which said bimetallic strip extends and said latch portion defines a portion of said aperture, said bimetallic strip bearing against said latch portion upon bending to provide the operative engagement thereof.

7. The electrical control device of claim 5 wherein said latch member is pivotably mounted adjacent one end thereof on said field piece to provide said first pivot,

and wherein said portion of said latch member engageable with said bimetallic strip is adjacent the other end thereof, said field piece being configured to provide said second pivot between said first pivot and said latch member portion, said latch member having another portion adjacent said engageable portion engageable with said movable means in the latched position thereof and disenagageable therefrom upon movement in response to magnetic engagement by said field piece or to bending of said bimetallic strip.

8. An electrical circuit breaker assembly comprising:

(a) a support;

(b) at least one pair of cooperating contacts mounted on said support and relatively movable between open and closed circuit positions; a

(c) a manually operable member on said support for moving said contacts to said open and closed positions;

(d) an automatically releasable member on said support for moving said contacts to said open position;

(e) a latch member;

(f) movable means connecting said latch member to at least one of said contacts to move said contacts from said closed to said open position upon predetermined movement of said latch member;

(g) an elongated bimetallic strip adjacent said latch member fixedly mounted at one end of said support and having its other end movable;

(h) a magnetic field piece mounted on said support in close proximity to said bimetallic strip, said field piece having the major portion thereof disposed substantially to the side of said strip opposite from said latch member, said latch member being magnetically engageable by said field piece during operation of the device upon passage of a large overload current through said bimetallic strip; and

(i) mounting means provided by portions of said field piece, pivotably mounting said-latch member on said field piece, said latch member having a portion thereof engageable by said bimetallic strip during operation of the assembly upon occurrence of a predetermined overload current to produce pivotal movement of said latch member upon elongation of the high expansion side of said bimetallic strip and resultant bending thereof, said mounting means providing a first pivot for initial pivotal movement of said latch member to an unlatched position for actuating said movable means and thereby said contacts to said open circuit position and a second pivot for subsequent pivotal movement of said latch member to accommodate overtravel of said bimetallic strip and avoid overstressing thereof.

9. The electrical circuit breaker assembly of claim 8 wherein said latch member has an aperture therein through which said bimetallic strip extends and said latch portion engaged by said strip bounds said aperture, said himetallic strip bearing against said latch portion upon bending to provide the operative engagement thereof.

10. The electrical circuit breaker assembly of claim 8 wherein said latch member is pivotably mounted adjacent one end thereof on said field piece to provide said first pivot, and wherein said portion of said latch member engageable with said bimetallic strip is adjacent the other end thereof, said field piece being configured to provide said second pivot between said first pivot and said latch member portion, said latch member having another portion adjacent said engageable portion engageable with said movable means in the latched position thereof and disengageable therefrom upon movement in response to magnetic engagement by said field piece and to bending of said bimetallic strip.

References Cited by the Examiner UNITED STATES PATENTS 1/1957 Thomas 33537 X 200-116 X 3,162,739 12/1964 Klein et al.

Claims

1. IN A THERMAL AND MAGNETIC CURRENT RESPONSIVE DEVICE, THE COMBINATION COMPRISING: (A) A SUPPORT; (B) AN ELONGATED BIMETALLIC STRIP FIXEDLY MOUNTED AT ONE END ON SAID SUPPORT AND HAVING ITS OTHER END MOVABLE; (C) A MAGNETIC FIELD PIECE MOUNTED ON SAID SUPPORT IN CLOSE PROXIMITY TO SAID BIMETALLIC STRIP; (D) AN ARMATURE ADJACENT TO AND MAGNETICALLY ENGAGEABLE BY SAID FIELD PIECE DURING OPERATION OF THE DEVICE UPON PASSAGE OF A LARGE OVERLOAD CURRENT THROUGH SAID BIMETALLIC STRIP; AND (E) MOUNTING MEANS PIVOTABLY MOUNTING SAID ARMATURE ON SAID SUPPORT, SAID ARMATURE BEING ENGAGEABLE BY SAID BIMETALLIC STRIP DURING OPERATION OF THE DEVICE UPON OCCURRENCE OF A PREDETERMINED OVERLOAD CURRENT TO PRODUCE PIVOTAL MOVEMENT OF SAID ARMATURE UPON ELONGATION OF THE HIGH EXPANSION SIDE OF SAID BIMETALLIC STRIP AND RESULTANT BENDING THEREOF, SAID MOUNTING MEANS PROVIDING A FIRST PIVOT FOR INITIAL PIVOTAL MOVEMENT OF SAID ARMATURE RELATIVE TO SAID FIELD PIECE AND A SECOND PIVOT FOR FURTHER PIVOTAL MOVEMENT OF SAID ARMATURE RELATIVE TO SAID FIELD PIECE TO ACCOMMODATE OVERTRAVEL OF SAID BIMETALLIC STRIP.