US3505622A - Current limiting circuit breaker with collapsible cradle structure - Google Patents

Description

April 7, 1970 C I AQSTROBEL 3,505,622 CURRENT LIMITING CIRCUIT BREAKER WITH COLLAPSIBLE CRADLE STRUCTURE Fileauomzl, 1968 6Sheets-$heet1 IN VEN TOR 6 7 fifffi d N M U Aprxl 7, 1970 A. .STROBEL CURRENT LIMITING CIRCUIT BREAKER WITH COLLAPSIBLE CRADLE STRUCTURE Filed Nov. 21, 1968 I e Sheets-She et z A ril 1, 1970 COLLAPSIBLE CRADLE STRUCTURE s Sheets-Sheet 5 Filed NOV. 21, 1968 M m V NJ 1 m 1 I ML 3 Lu m mlmm April 7, 1970 I A. STROBEL I I 3,505,622

CURRENT LIMITING CIRCUIT BREAKER WI'II-I COLLAPSIBLE CRADLE STRUCTURE Filed Nov. 21, 1968 6 Sheets-Sheet 4 April 7, 1970 AQSTROBEL 3,505,622

CURRENT LIMITING- CIRCUIT BREAKER WITH COLLAPSIBLE CRADLE STRUCTURE Filed Nov. 21, 1968 e Sheets-Sheet 5 April 7, 1970 AUSTROBEL 3,

CURRENT LIMITING CIRCUIT BREAKER WITH COLLAPSIBLE CRADLE STRUCTURE Filed Nov. 21, 1968 s Sheets-Sheet e \xJ k INVENTOR. 445aerszeaaz4 United States Patent 3,505,622 CURRENT LIMITING CIRCUIT BREAKER WITH COLLAPSIBLE CRADLE STRUCTURE Albert Strobel, Cherry Hill, N.J., assignor to I-T-E Impenal Corporation, Philadelphia, Pa., a corporation of Delaware Filed Nov. 21, 1968, Ser. No. 777,821 Int. Cl. H01h 77/02 US. Cl. 335-16 5 Claims ABSTRACT OF THE DISCLOSURE In a circuit breaker device whereupon the contact blowoff forces accompanying a severe fault condition serve to collapse a two-part cradle structure, a toggle type cradle biasing arrangement is disclosed. The two portions of the cradle structure are normally maintained as a rigid integral member by a spring biased toggle linkage structure. The use of the toggle linkage for biasing the collapsible cradle permits a reduction in the biasing spring requirements, and hence an attendant reduction in the overall circuit breaker size.

My invention relates to current limiting circuit breakers of the type shown and more fully discussed in my copending US. patent application Ser. No. 777,704 filed on even date herewith and assigned to the same assignee of the present application. That patent application shows a current limiting circuit breaker device which upon the occurrence of a severe fault condition of a predetermined magnitude, utilizes the blowoff forces generated at the main contact pair to defeat the latch means of the main circuit breaker mechanism. The release of the latch means under such conditions is obtained by the provision of a collapsible portion of the operating mechanism latch train; That is, the latch train includes at least one member having a pair of relatively movable portions. These relatively movable portions are biased into a certain fixed relationship by a biasing means of a calibrated predetermined retention force. Under normal operation of the circuit breaker, as for example in the contact engaged, manual off, and the tripping of the circuit breaker upon operation of the conventional thermal or magnetic trip device, these two operative portions function as a single integral rigid member. Their integral relationship is maintained by the force of a latch retention biasing means. Upon the occurrence of a severe fault condition, the contact blowoif forces generated at the contact pair are transmitted to the collapsible portions of the latch in opposition to the latch retention biasing means. The collapse of these latch portions then serves to release the main operating mechanism latch.

As discussed in my aforementioned pending US. patent application Ser. No. 777,704, it is advisable that for most rapid operation of the circuit breaker, the collapsible portion of the latch train should be closest to the contacts, and hence the cradle is usually used. Accordingly, the principal disclosed embodiment of that application shows a two-part spring loaded collapsible cradle mechanism. The biasing of the cradle in the previous embodiments is obtained by means of a compression or tension spring directly connected to the relatively movable portion of thelcollapsible cradle. These springs on the cradle are required in addition to the biasing springs of the overcenter toggle utilized in the circuit breaker main operating mechanism. The load requirements of the auxiliary cradle spring is dependent upon the force of the main circuit breaker operating mechanism spring as well as the contact pressure maintained on the circuit breaker .contacts. At increasing load ratings of the circuit breaker,

these forces tend to correspondingly increase, thereby requiring more substantial spring forces for use in conjunction with the collapsible cradle. I have, therefore, experienced that in the larger frame size of molded case circuit breakers constructed in accordance with my invention, a substantial space may be required to physically locate the biasing spring means provided in conjunction with the collapsible cradle mechanism. This in turn increases the size of the circuit breaker mechanism and hence the overall size of the breaker.

The present invention is directed to an improved means of biasing the collapsible cradle in conjunction with a toggle mechanism, thereby utilizing the mechanical advantage of the toggle mechanism to reduce the required spring size. Basically, the manner in which the toggle mechanism operates in conjunction with its associated biasing means permits the use of a substantially lower biasing force than previously required in the structures of aforementioned US. patent application Ser. No. 777,- 704. The biasing meansis illustratively shown as a spring, whose principal purpose is to hold the toggle mechanism of the cradle against a stop. In the illustrative embodiment a torsion spring is shown, located about the toggle knee. However, this is done for illustrative purposes only, with it being understood that an appropriately located tension or compression spring may also be utilized, with such tension or compression spring being of significantly lesser force (and hence size) than the springs necessitated by the previous embodiments. The toggle knee is operatively connected to the movable contact, as by a hook-like member intermediate the contact carrier arm and the toggle knee. In the event of contact arm movement caused by blowoff, the hook-like lever moves the toggle knee overcenter with respect to its biasing spring, thereby collapsing this latch retention toggle mechanism. The collapse of the latch retention toggle mechanism is accompanied by the collapse of the cradle. This results in the movement of the cradle portions to effect release of the operating mechanism latch, and hence movement of the main circuit breaker overcenter toggle mechanism to the contact disengaged condition.

It is, therefore, a principal object of the present invention to provide an improved biasing arrangement in conjunction with a collapsible cradle structure of a current limiting circuit breaker.

A further object of the present invention is to provide, in conjunction with a current limiting circuit breaker having a collapsible cradle, an improved retention arrangement for the collapsible cradle, which comprises an overcenter toggle means.

Another object of my present invention is to provide a spring biasing arrangement in conjunction with a collapsible cradle, which utilizes the mechanical advantage of a toggle structure to reduce the requisite spring forces.

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

FIG. 1 shows a current limiting circuit breaker, constructed in accordance with my invention, in the contact engaged condition.

FIGS. 2 and 3 sequentially show the operation of the circuit breaker of FIG. 1 upon the occurrence of a moderate overload or fault condition, causing operation of the conventional type of overload trip unit mechanism.

FIG. 4 shows initial movement of the circuit breaker mechanism upon the occurrence of a severe short circuit condition, with the contacts being separated by blowoff forces to obtaincurrent limiting action and the cradle being collapsed thereby releasing the operating mechanism latch.

FIGS. 5 and 6 sequentially follow FIG. 4, and show release of the circuit breaker operating mechanism by the auxiliary latch, and ultimate operation of the main circuit breaker toggle.

Referring to the figures, circuit breaker is of the same general type discussed in conjunction with my aforementioned US. patent application No. 777,704 and includes a molded housing having a main body portion 12 and cover 14. The circuit breaker includes at least one pair of contacts for each phase, having a stationary contact 22 connected to line terminal 24. The cooperating movable contact 26 is mounted on a contact arm 28, which in turn is pivotally mounted at 30 to contact carrier 32. Contact pressure forces for urging the cooperating contact pair 22, 26 in good intimate electrical engagement are obtained by the spring force of the contact operating mechanism 50 and the contact pressure means 34. The contact carrier 32 is pivotally mounted to an operating mechanism frame (not shown) at pivot 36. The circuit breaker 10 may typically be a multi-phase device, with the various phases interconnected by tie bar 38, for coordinated multi-phase operation, in the well known manner.

The movable contact arm 28 is electrically connected to the trip unit assembly by means of an appropriate conductor means, generally simplified by the braid 40. In actual practice, the trip unit assembly 20 which is typically an integral and replaceable assembly is connected to the contact arm 28 by separate contact carrier straps, which are bolted together during the insertion of the trip unit assembly. Trip unit assembly 20 includes a magnetically actuated fault conditioned responsive means 41 including a stationary magnet 42 and cooperating armature 44. The trip unit assembly 20 may also include the wellknown type of thermally responsive bimetal element (not shown), responsive to a sustained moderate overload condition. Upon the occurrence of a predetermined overload fault condition, the armature 44 moves toward the pole face of magnet 42 as shown in FIG. 2, thereby moving the armature stem 46 downward and rotating the tripper bar 48 counterclockwise. This serves to defeat the latching engagement between the tripper bar 48 and latch member 45.

The circuit breaker operating mechanism 50 includes an overcenter toggle means having a lower toggle link 52, upper toggle link 54 and spring biasing means 56. Spring biasing means 56 is connected at its lower ends to the toggle knee 68, and at its upper end to the manual operating handle 15. A latchable cradle is provided which comprises two relatively movable portions 58 and 60, pivoted about upper toggle bearing 62.

In accordance with the present invention, the relatively movable portions 58, 60 of the cradle are maintained in the position shown in FIG. 1 by a latch retention means, including toggle linkages 80 and 82. One end of toggle linkage 80 is pivotally mounted to the cradle portion 58 at 81. The opposed end of toggle linkage 82 is similarly pivotally mounted to the cradle portion 60 at 83. The

toggle links are connected together at the toggle knee 84 which also serves to mount the torsion type biasing spring 86. The auxiliary toggle linkage 80, 82 therefore serves to move the cradle portion 58, 60 apart about their pivot 62, as limited by the stop 61. As long as the toggle 80, 82 is maintained as shown in FIG. 1, it will serve as a retention arrangement to maintain the cradle portions 58, 60 as a single rigid member.

The means for moving the toggle linkages 80, 82 overcenter and collapsing the cradle is provided by the hookshaped lever 90, which is connected at one end 91 to the contact arm 28. The opposite end of the lever includes the hook-shaped portion 92, which operatively engages extension lever 94, mounted to the toggle link 82.

The operation of the circuit'breaker will now be discussed:

Reference is now made to FIG. 2, which illustrates the condition upon the occurrence of a moderate overload or fault current condition above the normal load carrying 4 capacity of the circuit breaker but within its conventional trip rating. The magnetic fault responsive operating means 41 of the trip unit 20 has been actuated, thereby rotating the tripper bar 48 counterclockwise and releasing the tip 51 of the latch lever 45. This, in turn, serves to permit rotation of auxiliary latch 66 releasing latch tip 65 of the cradle portion 58. The cradle assembly (comprising portion 58, 60, toggles 80, 82 and their biasing spring 86), now rotates as a single integral rigid member about pivot 83. Referringnow to FIG. 3, the main mechanism toggle linkage 52, 54 has now moved overcenter with respect to the main operating spring 56, at which point the rigid cradle assembly has completed its movement to the cradle stop 67 and the contacts have completely parted. It should be noted that the latch train comprising elements 48, and 56 have now returned to their Original positions (as shown in FIG. 1) under the influence of appropriate biasing means, and the tripping cycle has been completed. Following the sequence from FIGS. 1-3, it should again be recognized that the two-part cradle 58, and its associated toggle mechanism 80, 82 has moved as an integral member following the actuation of the trip unit assembly 20. Similarly, the cradle portions 58, 60 will be maintained as an integral member should the circuit breaker be moved to the manual OFF position (not shown).

Reference is now made to FIGS. 4-6, which sequentially indicate the operation of the circuit breaker when subjected to a severe fault condition, substantially in excess of that discussed in conjunction with the operation of FIGS. 2 and 3. The magnitude of the severe fault condition causes a rapid initial contact blowoff as shown in FIG. 4, resulting in the pivoting of contact arm 28 about its pivot 30. This in turn causes downward movement of hook type lever 90 mounted to the rear of the contact arm. The hook end 92 engages toggle linkage lever 94, thereby moving the cradle biasing linkage 80, 82 overcenter with respect to the condition shown in FIG. 1. Mechanical forces pushing upward at the cradle pivot 62 serve to pull the latched portion 94 outward from underneath the hook tip 92. This in turn causes relative movement of the cradle portions 58, 60, such that the cradle tip is released from latching portion 63 of the auxiliary latch 66. The cradle, once freed, continues to rotate clockwise about pivot 83 to the condition shown in FIG. 5. As shown therein, the toggle linkages 80, 82 of the cradle assembly are still held below their locked-in center by the hook lever 92. Referring sequentially to FIG. 6, the cradle has completed its movement to the cradle stop 67 and the contacts are fully opened, with the main toggle mechanism 52, 54 having been moved to overcenter with respect to its spring 56. The extension lever at the auxiliary toggle knee 94 has ben released from the hook 92, thereby permitting the cradle toggle 82 to move back into the locked-in position under the influence of biasing spring 86. The tripping cycle is now completed, and it should be recognized that the condition of the circuit breaker of FIG. 6 corresponds to that shown in FIG. 3.

Although there has been described a preferred embodiment of this novel invention, many variations and modifications will now be apparent to those skilled in the art. Therefore, this invention is to be limited, not by the specific disclosure herein, but only :by the appending claims.

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

1; In a circuit breaker comprising at least one cooperating pair of stationary and movable contacts;

an operating mechanism connected to said movable contact for moving said movable contact between an engaged and disengaged condition relative to said stationary contact; said operating mechanism including a latchable cradle and first biasing means tending to move said cradle towards a contact disengaged condition; said cradle including a latchable tip normally in latched engagement with a latching member during contact engagement;

said latchable tip, when disengaged from said latching member, allowing movement of said cradle under the influence of said first biasing means to the contact disengaged condition;

a first fault responsive operating means responsive to overload currents of a first predetermined nature for automatically moving said latching member out of latched engagement with said cradle tip for defeating said latched engagement. and permitting movement of the cradle to the contact disengaged condition;

a second fault responsive operating means responsive only to fault currents of a second predetermined nature substantially in excess of said first predetermined nature, for automatically moving said latchable tip out of latched engagement with said latchable member and permitting movement of the cradle to the disengaged conditions;

said second fault responsive operating means constructed to respond to its operative fault current condition and defeat said latched engagement in a substantially more rapid manner than required for the operation of said first fault responsive means;

said cradle having first and second relatively movable operative elements, one of which includes said latchable tip;

a latch retention means urging said operative elements to a first position whereby said-cradle operatively functions as a single integral member under conditions of contact engagement and the movement of said contacts other than by said second fault responsive means;

said latch retention means including a second biasing 0 means;

said second biasing means urging said operative cradle elements towards said first position;

said second fault responsive operating means generating a latch release force in opposition to said second biasing means for causing said one operative cradle element to move relative to 'the other element into a release position, serving to move said latchable cradle tip out of latched engagement with said latching member;

said second fault responsive operating means utilizing the blowoif forces at the contact pair to provide said latch release force;

said contact pair being urged together in the engaged condition by a predetermined contact pressure force;

said predetermined contact pressure force operatively related to a specific magnitude of the blowoff forces accompanying fault current magnitudes of said second predetermined nature, such that the blowoff forces will be insuflicient to overcome said contact pressure force and second biasing means until the fault current magnitude reaches said second predetermined nature;

the improvement comprising:

said latch retention means including an overcenter toggle means including first and second toggle links;

each of said links having opposed first and second ends;

the first end of said first toggle link connected to said first cradle operative element;

the first end of said second toggle link connected to said second cradle operative element;

the second ends of said toggle links connected together to form a toggle knee;

force directing means directing said latch release force to said toggle knee to move said toggle means overcenter with respect to said second biasing means;

said overcenter movement of said toggle knee moving said one operative cradle element from said first position to said release position, thereby serving to release the latched engagement of said latchable cradle tip.

2. In a circuit breaker, as set forth in claim 1:

said second biasing means being a spring means operating about said toggle knee.

3. In a circuit breaker, as set forth in claim 1:

said force directing means including a direct linkage member between said movable contact and said toggle knee;

said direct linkage member moving responsive to the blowoff induced movement of said movable contact to directly translate said toggle knee overcenter.

4. In a circuit breaker, as set forth in claim 1:

said movable contact carried by a pivotally mounted contact arm;

said force directing means including a direct linkage member between said movable contact arm and said toggle knee;

said direct linkage member moving responsive to the blowofi induced movement of said movable contact arm to directly translate said toggle knee overcenter. 5. In a circuit breaker, as set forth in claim 2: said spring means being a torsion spring positioned about said toggle knee.

References Cited UNITED STATES PATENTS 3,251,232 5/1966 Harper 335174 3,384,845 5/1968 Johnson 33516 3,384,846 5/1968 Heft 335-16 BERNARD A. GILHEANY, Primary Examiner H. BROOME, Assistant Examiner US. Cl. X.R.

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