US2071848A - Circuit breaker - Google Patents

Description

Patented fFeb. 23, 1937 PATENT OFFICE CIRCUIT BREAKER Ture Lindstrom,

Edgewood, Pa.,

assigner to Westinghouse Electric & Manufacturing Colnpany, a corporation of Pennsylvania Original application November 26, 1930, Serial No. 498,408, now Patent No. 2,027,238, dated January 7, 1936. Divided and this application December 24, 1935, Serial No. 55,991

9 Claims.

My invention relates to circuit breakers and particularly to circuit breakers and tripping mechanisms therefor that are current-responsive for tripping to open position under overload and short-circuit conditions.

This application is a division of my copending application, Serial No. 498,408, filed Nov. 26, 1930 now Patent 2,027,238, issued January 7, 1936.

An object of my invention is to provide a tripping device wherein a bimetal thermal element serves' to releasably retain a circuit breaker in operative closed position and deiiects to releasing position in response to predetermined current conditions, such as are caused by an overload or a short circuit.

A further object of my invention is to provide a thermal element for releasably retaining a circuit breaker in operative closed position wherein the operating characteristics of such element may be varied without altering its shape.

These and other objects that will hereinafter appear are attained by means of the apparatus hereinafter described and illustrated in the accompanying drawing wherein Figure l is an elevational view, partially in section, of a circuit breaker and trip mechanism therefor embodying features of my invention,

Fig. 2 is an end elevational view of the trip mechanismshown in Fig. l, and

Fig. 3 is a transverse section through the trip mechanism ,taken on line III-III of Fig. 2.

Referring tothe drawing, the circuit breaker to which the improved trip mechanism is applied comprises an insulating base 4 upon which is mounted a metal supporting frame 5, terminal contact 6 and a terminal 1. The movable contact arm 8 is pivotally mounted for oscillatory movement about the pivot shaft 9, and a spring-metal contact arm II is attached thereto by means of an attaching screw I2 which also serves to conneet a exible conductor I3 to the contact arm 8. The outer end of the spring member II is provided with a contact I4 that is secured to its free end by means of a rivet I which serves to clamp one end of the flexible conductor I3 between the spring member and the contact.

The contact arm 8 is tuated by means of a pair of toggle links I d I6 that are pivotally connected together by a knee pivot shaft I 1, the link I5 being pivotally connected to the contact arm 8 by a pivot shaft I8 and the link I6 being pivotally connected to a cradle I9 by means of a pivot shaft 2I.

The cradle I9 is mounted upon the frame 5 for oscillatory movement about a pivot shaft 22,

mounted on the frame 5, and is releasably retained in its operative closed position shown in Fig. 1 by means of a current-responsive trip device 23, which will be hereinafter described.

When the toggle links I5 and I6 are in the straightened position, shown in Fig. 1, they serve to retain the contact arm 8 in closd position, wherein the contact I4 engages the contact 6. 'I'he toggle links are actuated to collapsed or opened position by means of a tension spring 24 that is pivotally connected, at one end, to the knee pivot shaft I1 and, at the other end, to a pivot pin 25, carried by an operating handle 26 that is mounted for oscillatory movement about a pivot shaft 21 which is supported by the frame 5.

Clockwise movement of the operating handle 26 causes the center of the pin 25 to be moved beyond a center line of the pivot shafts I8 and 2|, which results in moving the knee pivot I'I laterally. This movement, by reason of the contraction of the spring 24, causes the toggle links to collapse and move the contact I4 to the open position shown in dotted lines in Fig. l, with a snap action. Upward movement of the operating handle 26 causes closing of the contact I4, when the center of the pin 25 has again moved about the said center line of the toggle pivots I8 and 2 I.

When the cradle I9 is released, in response to an overload or a short-circuit condition, the contraction of the spring 24 also causes collapse of the toggle when the cradle has moved the pivot pin 2I in a counter-clockwise direction beyond a center line through the knee pivots of the toggle and the pin 25. Manual operation of the contact I4 to open and to closed positions is, accordingly, accomplished through the movement of the operating handle 26, and automatic operation of the circuit breaker to open position occurs when the cradle I9 is released.

The trip device 23 for releasably retaining the circuit breaker in closed position comprises a flat strip 28 of bimetal that is connected to the terminal 'I by means of rivets 29. One end of the flexible conductor I3 is conductively connected to the bimetal element at a point between the free end thereof and its point of attachment to the terminal "I, the conductor I3 being attached to the bimetal element by screws or rivets 33 that also serve to attach a metal strap 34.

By attaching the conductor I3 to the bimetal strip 28, at a point intermediate its ends, all of the current may be made to pass through the bimetal element at any desired point between the point of attachment of the conductor i3 andthe fixed end of the strip, thus causingl the heating effect of the current to be concentrated between the point of attachment of the strip 28 to the terminal 1 and the flexible conductor I3. The maximum bending of 'the bimetal element, at that point, will, therefore, cause a relatively wide range of movement of the free end of the bimetal which carries a. latch clip 35 that is insulated from the bimetal strip by an insulating plate 36, and releasably engages the latch arm 31 of the cradle i9. The strip is provided with a plurality of perforations 40 for permitting attachment of the conductor to the strip at any desired point.

Under normal operating conditions, the bimetal strip will remain in the latch-retaining position shown in Fig. 1 and will releasably retain the circuit breaker in closed position. Under an overload condition, the bimetal element will be heated-by the excessive current passing therethrough and cause it to deflect to the ybroken-line position shown in Fig.`1, wherein the latch clip 35 is disengaged from the latch arm 31, thereby causing the circuit breaker to be released or tripped to open position, wherein the latch and cradle will occupy the positions shown in broken lines in Fig. 1.

The fact that the flexible conductor I3 is attached to the bimetal strip 28 adjacent the midportionthereof means that only the lower portion of the bimetal strip is directly heated by the current flow therein. The upper portion of the bimetal is heated only by the flow of heat from the lower portion. This requires considerable time with the result that on small overloads where the bending of the lower portion alone is not sufficient to release latch arm 31 from latch clip 35, the breaker will not trip until there has been time for heat to flow to the upper portion of the bimetal strip and cause it to bend also, but on heavy overloads or short circuits/ the breaker will trip more quickly due to the rapid heating and bending of the lower portion of the bimetal strip without the time required for heat to flow to the upper portion of the bimetal strip.

The trip mechanism, therefore, provides a time interval before opening the circuit breaker under overload conditions and by connecting the flexible conductor i3 at any one of various points between its fixed and its free ends, the time lag or the current rating of the bimetal element may be varied without altering its shape. The bimetal current-responsive element, therefore, may be calibrated by Asimply shifting the position of the flexible conductor with reference to it.

While I have illustrated but one embodiment of my invention, it will be apparent to those skilled in the art that various changes, modifications, substitutions, additions and omissions may be made in the apparatus illustrated, without departing from the spirit and scope of my invention as set forth in the appended claims.

I claim as my invention:

1. A trip device for electrical apparatus comprising a bimetal thermal strip fixed at one end and having the opposite end free for releasably retaining the apparatus in a predetermined position, and afiexible conductor adjustably connecting the strip in an electricv circuit, whereby current will flow through the strip only between a point intermediate its ends and its fixed end.

2. In a circuit breaker, a pair of relatively movable contacts, biasing means for moving one of said contacts to open the circuit, means normally opposing said movement, said means including a member of blmetallic material mounted at one end and movable at its other end, a ilexible conductor for connecting said member of bimetailic material in the circuit through the circuit breaker, and means for connecting said flexible conductor to said member of blmetallic material at any one of a plurality of points along its length.

3. In combination in an automatic circuit breaker, a contact biased for movement to break the circuit, releasable mechanisml normally holding the contact in closed-circuit position and including a blmetallic strip supported at one end and capable of deflection to cause the other end to relatively move and thereby effect the release of the mechanism, and means including a. flexible conductor for connecting the blmetallic strip into the circuit to enable it to be deflected upon the passage of excess current and thereby release the mechanism, the said flexible conductor being connectible with the strip at different longitudinally spaced positions so as to change the rate of deflection thereof.

4. In a circuit breaker, a pair of relatively movable contacts, biasing means for moving one of said contacts to .open position, means normally opposing said movement, said means including a blmetallic member, an electrical connection to one end of said blmetallic member and a flexible conductor connected to said bimetallic member adjacent the mid-portion thereof for connecting a portion of the blmetallic member in the circuit through the circuit breaker, and said blmetallic member being heated substantially entirely by the heat generated therein due to the current flow therethrough.

5. In a circuit breaker, a base having mounted thereon a pair of line terminal members, a portion of one o f said terminal members forming a fixed contact, a strip of blmetallic material having one end xedly mounted on the other said terminal member, said strip of blmetallic material having at its other end a straight portion which is freely movable laterally, a switch arm movable to make and break connection with said fixed contact, a flexible conductor connected at one end to the movable switch arm and at its other end to the movable portion of the strip of bimetallic material, said strip of blmetallic material being heated substantially entirely by the current flow therein, means biasing said switch arm to move to break connection with said fixed contact, and said strip of blmetallic material normally opposing said movement with a reaction force substantially longitudinally of the straight portion thereof.

6. In a circuit breaker, a movable contact member biased in the circuit-opening direction, a stationary electric contact engageable by the movable contact,Y an actuator movable when released to cause circuit-opening movement of the contact member, a thermostatic blmetallic strip rigidly mounted at one end and engaging the actuator at the other end so as to serve as a connecting l latch adapted to release the actuator upon electro-thermal deflection, a flexible conductor electrically connected with the strip at a point substantially spaced from the point of engagement with the actuator and serving to complete the circuit through a part of the strip, whereby the said strip is automatically deflected rapidly upon the attainment of an excessive overload condition therein and is automatically deflected very slowly upon the attainment of a moderate overload condition therein.

7. In a circuit breaker, a movable contact member biased in the circuit-opening direction, a stationary electric contact engageable by the movable contact, an actuator movable when released to cause circuit-opening movement of the contact member, a thermostatic bimetallic strip rigidly mounted at one end and engaging the actuator at the other end so as to serve as a connecting latch adapted to release the actuator upon electrothermal deflection, a exible conductor electrically connected with the strip at a point substantially spaced from the point of engagement with the actuator and serving to complete the circuit through a part of the strip, whereby the said strip is automatically deflected rapidly upon the attainment of an excessive overload condition therein and is automatically denected very slowly upon the attainment of a moderate overload condition therein,'and means for changing the position of the connection of the flexible conductor to the strip to change the rates of deflection under excessive and moderate overload conditions.

8. In a circuit breaker, a base having mounted thereon a pair of line terminal members, a portion of one of said terminal members forming a fixed contact, a strip of bimetallic material having one end fixedly mounted on the other said terminal member, said strip, of bimetallic material havingl only a single leg with a latch portion at its other end which is freely movable laterally of the length of the strip, a switch arm movable to make and break connection with said fixed contact, a flexible conductor connected at one end to the movable switch arm and at its other end to the movable portion of the strip of' bimetallic materlal, said strip of bimetallic material being trav- 40 ersed by all of the current through the circuit breaker and being heated substantially entirely by the current flow through the strip, means biasing said switch arm to move to break connection with said xed contact. and said strip of bimetallic material normally opposing said movement with a reaction force substantially longitudinally of the strip.

9. In a circuit breaker, a base having mounted thereon a pair of line terminal members, a portion of one of said terminal members forming a fixed contact, a strip of bimetallic material having one end xedly mounted on the other said terminal member, said strip of bimetallic material having only a single legl with a latch portion at its other end which is freely movable laterally of the length of the strip, a switch arm movable to make and break connection with said fixed contact, a flexible conductor connected at one end to the movable switch arm and at its other end to the movable portion of the strip of bimetallic material, said strip of bimetallic material being traversed by all of the current through-the circuit breaker and being heated substantially entirely by the current fiowthrough the strip, an operating mechanism for the circuit breaker including means biasing said switch arm to move to break connection with said fixed contact, a latch portion for controlling the switch arm normally engaging said latch portion on the strip of bimetallic material and said strip of bimetallic materlal normally opposing said movement with a reaction force substantially longitudinally of the strip, a handle member operable to both open and close the circuit breaker without breaking the engagement ot said latch portions, and said strip when heated by the current fiow therethrough disengaging said latch portions and causing opening of the circuit breaker irrespective of the position in which said handle member may be held. TURE LINDSTROH.

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