US3205325A - Circuit breaker trip device - Google Patents

Description

Sept. 7, 1965 H. w. ARCHER ETAL 3,

CIRCUIT BREAKER TRIP DEVICE 3 Sheets-Sheet 1 Filed June 19, 1963 INVENTORS HARRY W. ARCHER KE/TH W. KLEIN,

FIG. '2.

p 1965 H. w. ARCHER ETAL 3,205,325

CIRCUIT BREAKER TRIP DEVICE Filed June 19, 1963 3 Sheets-Sheet 2 F IG. 4-

I I I l INVENTORS A rm Zn/Ey United States Patent Office 3,205,325 Patented Sept. 7, 1965 3,205,325 CIRCUIT BREAKER TRIP DEVICE Harry W. Archer, New Britain, Keith W. Klein, Simsbury, and Kenneth J. Stokes, Wetherslield, Conn., as-

signors to General Electric Company, a corporation of New York Filed June 19, 1963, Ser. No. 289,116 4 Claims. (Cl. 200-88) Our invention relates to electric circuit breakers of the type including separable contacts and means for causing automatic opening of the contacts upon the occurrence of predetermined electrical conditions, and more particularly, to the portions of such circuit breakers used to initiate such automatic opening, such portions being known as trip mechanisms or trip units.

Automatic electric circuit breakers of the type used to control substantial amounts of power, such for example as upwards of 100 amperes, commonly include operating mechanism for manually operating the contacts between open and closed circuit positions, the mechanism including. a member which is normally latched, but which is releasable to cause automatic opening or" the contacts. A trip mechanism or trip unit is also provided for causing release of the releasable member upon the occurrence of predetermined current conditions. For convenience of manufacture and use, the trip mechanism or trip unit is often constructed and assembled as a separate unit, so that a circuit breaker of a desired particular current rating may be provided by using a basic circuit breaker assembly and mounting therein a particular selected trip unit, having the current rating desired. Such trip units commonly include both thermal and magnetic operating tripping means. The thermal trip means provides an inverse-time characteristic such that a relatively long time-delay is provided before tripping on the occurrence of a relatively low current overload, and a relatively short time-delay is provided on the occurrence of a relatively high current overload. The magnetic operating means, on the other hand, does not incorporate any time-delay. It operates only at current overloads in the neighborhood of three to ten or more times the nominal current rating of the circuit breaker. Since it comes into operation on the occurrence of such high overload or short circuit conditions, its tripping action is substantially instantaneous.

In accordance with a particular form of prior art electric circuit breaker of the type described, the force required of the current responsive means to cause tripping is made to be substantially independent of the contactclosing force exerted by the main operating mechanism. This is accomplished by providing a secondary releasable member carried by the trip unit itself, which, when released, strikes a latch member carried by the trip unit, which latch member then releases the main operating mechanism. There is no direct physical connection between the secondary releasable member and the latch member which releases the main mechanism, and so there is no way in which force exerted by the main operating mechanism can be reflected to the secondary releasable member. A circuit breaker of the type referred to is shown in co-pending application Serial No. 192,192, filed May 3, 1962 by L. P. Koval, now Patent No. 3,179,768, issued April 20, 1965, and assigned to the same assignee as the present invention.

While mechanisms of the type shown in the aforesaid Koval application operate entirely satisfactorily in circuit breakers having short circuit interrupting ratings up to about 10,000 amperes, they exhibit certain disadvantages when used in circuit breakers applied on systems having short-circuit capacities above -20,000 amperes. This is because the use of a secondary releasable member, with its lost-motion travel, introduces a time-delay in the tripping sequence, even by the. magnetically operated trip means, of about to electrical degrees or about .2 second. In other words, after the armature of the tripping magnet has closed, about this much time is required before the primary releasable member is released. This delay does not cause any difficulty on circuits up to about 15,000 amperes short-circuit capacity. Above this level, however, the force of the current is sufiicient to blow the circuit breaker contacts apart during the period of time between incidence of the short-circuit and the time when the main operating mechanism has moved sufiiciently to cause opening movement of the contacts. This permits arcing with consequent contamination of the arc extinguishing area, leading to eventual breakdown and failure.

In addition, it has been found that at such higher current levels, because of the time-delay mentioned, above, overheating of certain portions of the electrical circuit breaker occurs, particularly the heater portion which heats the current-responsive bimetal, often causing complete burn-out.

It is an object of the present invention to provide an automatic electrical circuit breaker including a trip unit which maintains the thermal tripping means independent of the loading of the main operating mechanism, and which nevertheless, does not introduce a time delay for operation of the magnetic tripping means.

It is a further object of the invention to provide an electric circuit breaker of the type described which is compact in size, and economical to manufacture.

In accordance with the invention in one form, anelectrics circuit breaker is provided of the type including at least one pair of separable contacts and operating mechanism for manually operating the contacts between open and closed circuit positions, the operating mechanism including a primary releasable member and separable trip means for causing release of the releasable member upon the occurrence of predetermined current conditions in the circuit. The separable trip means includes a primary latch member which normally engages and restrains the primary releasable member. The trip unit also carries a secondary releasable member which is normally held against movement by a secondary latch member, disposed and arranged to be engaged by a thermal current responsive element. The secondary releasable member has lostmotion travel between it and the primary latch member, so that no force is reflected from the primary latch member to the secondary releasable member. In addition, magetic tripping means is provided including a magnet and an armature, and means directly connecting the armature to the primary latch member, whereby movement of the magnetic armature is immediately accompanied by movement of the primary latch member with no timedelay.

In addition, in accordance with another aspect of the invention, means is provided for indicating following a tripping or automatic opening operation, whether such automatic opening operation has occurred by reason of thermal tripping or by reason of magnetic tripping.

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

In the drawings,

FIGURE 1 is a side elevation view, with part of the casing broken away, of an automatic electric circuit breaker incorporating the invention.

FIGURE 2 is a side elevation view, on enlarged scale, of a portion of the circuit breaker of FIGURE 1, showing the trip mechanism, portions of the trip unit casing being broken away;

FIGURE 3 is a view similar to FIGURE 2, but show- 3 ing only the thermally operated tripping means, in tripped condition;

FIGURE 4 is a view similar to FIGURE 3, showing only the magnetically operating trip means, in tripped condition;

FIGURE 5 is a top plan view of the tripping mechanism of FIGURES 1 through 4, and

FIGURES 6 and 7 are fragmentary views of a portion of the indicating mechanism of FIGURE 5.

In the drawings, the invention is shown as incorporated in an electric circuit breaker comprising a generally rectangular insulating casing including a base 11 and a cover 11. Three pairs of relatively movable contacts 12, 13 (only one pair shown), are provided in the base 10. Each stationary contact 13 is connected to a corresponding line terminal 14 by a line terminal strap 13A. Each movable contact 12 is carried by a contact arm 15. The movable contact arms 15 are adapted to be operated in unison between open and closed circuit positions by means of an operating mechanism, including a manually engageable handle member 16, projecting through an opening, not shown, in the casing cover 11. The operating mechanism includes a releasable member 17 and a pair of toggle links 17A and 17B, interconnected by a knee pin 17C. The toggle is adapted to be operated by the handle 16 by means of an overcenter spring 170. The operating mechanism shown is more fully described in Patent No. 2,921,169, E. B. Judd et al., issued January 12, 1960, and assigned to the same assignee as the present invention.

For the purpose of holding the member 17, and releasing it upon the occurrence of predetermined current conditions through any of the three pairs of contacts 12, 13, tripping mechanism is provided comprising a trip unit designated generally at 18.

The trip unit 18 comprises a first insulating casing part 20 and a second insulating casing part 21. The casing parts 20, 21 cooperated to form a closed box-like enclosure for the tripping mechanism.

A first set of three terminal members 22 is provided projecting through openings in the casing part 21. A second set of three terminal members 25 is also provided projecting through openings in the casing part 20. Each pair of terminal members 22, 25, is connected to opposite ends of an intermediate conductor 24. Each conductor 24 includes a generally U-shaped intermediate portion 28 of smaller cross-section than said end portions, adapted to act as a heater.

The casing part 20 includes, adjacent each of the conductors 24, a pair of abutments or bosses, 29, positioned respectively at opposite sides of each conductor 24. A generally U-shaped magnet 30 is supported adjacent each strap 24 in such a way that its bight portion rests against two corresponding abutments 29. The side portions of each magnet 30 extend on opposite sides of one leg of the intermediate U-shaped portion 28 of one of the conductors 24.

The leg of the intermediate U-shaped portion of the conductor 24 which passes through the magnet 30 is rigidly anchored to the casing part 20 by means of a screw 31. Each screw 31 passes through an opening in the casing part 20, through an enlarged clearance hole 32 in one leg of the intermediate portion 28 of the conductor 24, through a clearance hole in the bight portion of the magnet 30, and into threaded engagement with the other leg of the intermediate portion 28. Thus the screw 31 serves to press one leg of the portion 28 of the conductor 24 against the bight portion of the magnet 30 and this in turn against the abutments 29 of the casing part 20. The other leg of the portion 23, however, extends freely and with ample clearance through the space provided between the magnet 30 and the outer wall of the casing part 20.

Thermal tripping structure For the purpose of causing automatic opening in response to predetermined current overload conditions which are relatively low in magnitude but of relatively long time duration, a bimetallic strip 34 is provided at each pole of the circuit breaker, rigidly attached at one end thereof to the intermediate conductor 24 adjacent one end of the U-shaped intermediate heater portion 28. Current flow through the portion 28, therefore, causes heating in the intermediate portion 28 because of its restricted cross-section. This heat is transmitted by conduction to the bimetallic strip 34, causing deflection thereof. Each of the bimetallic strips 34 carries an adjusting or calibrating screw 35 adjacent its free end which, when the bimetallic strip deflects, engages a thermal trip bar 36 and causes it to rotate in a clockwise direction, as viewed, about the pivot pins 37.

The parts of the mechanism which operate when thermal tripping occurs are shown particularly in FIGURE 3, the parts being shown in the condition which they occupy immediately after tripping has occurred.

The trip bar 36 carries an ambient compensating bimetallic strip 52 rigidly attached thereto at one end, the strip 52 having its other end disposed and arranged to engage a secondary latch member 38, see FIGURES 2 and 3. The secondary latch 38 serves to restrain a secondary releasable member 39 from movement. The secondary latch member 38 is always biased toward latching position by means of spring 38A, and the secondary releasable member 39 is contantly biased for rotation in counterclockwise direction by means of the spring 40.

When the secondary releasable member 39 is released by the latch member 38, it therefore rotates in counterclockwise direction, causing the projecting portion 41 thereof to engage a portion 42 of the primary latch member 43 which is pivotally supported on a pin 44. This releases the primary latch member 17 and permits automatic opening of the contacts.

It will be observed that since the trip bar 36 extends across all three poles of the circuit breaker and can be engaged by the calibrating screw 35 of each of the bimetallic strips 34 in each of the poles, thermal tripping as described will occur upon sufiicient deflection of the bimetallic strip 34 in any one of the poles.

Following release of the secondary releasable member 39 by the latch member 38, some time is required for it to rotate far enough to engage the portion 42 of the primary latch member 43 and to move this far enough to initiate tripping.

Magnetic tripping structure In accordance with the invention, magnetic tripping means is also provided, comprising the three magnets 30 with energizing conductors 28, previously described, and also three pivotally supported magnetic armatures 45 pivotally supported on the pivot pins 37. Also supported on the pivot pin 37 is a generally channel-shaped member 47, which has connected thereto an elongated sliding link or hook 48 having a hook-like projection 49 at the other end thereof. The member 48 is guided for sliding movement on a pin 50 which extends through a slot 48A. The member 47 also carries a side-wise extending magnetic trip bar 51 having portions extending across all three poles of the circuit breaker. Upon the occurrence of high short-circuit currents, one or more of the armatures 45 is attracted to its magnet 30, causing the extension 45A of the armature 45 to engage the magnetic trip bar 51, causing rotation of the member 47 and moving the link 48 to the left as viewed in FIGURE 2. This causes the hook portion 49 of the link 48 to engage the bent-over portion 42 of the primary latch 43, thereby releasing the primary releasable member 17.

It will be noted that this tripping action by the magnetic tripping means takes place without movement of the secondary latch member 38 or the secondary releasable member 39.

Each of the armatures 45 is biased toward non-operated position by means of a return spring 45A which is adjustably positioned by an adjusting lever 61 carried by an adjusting screw 61A which is pivotally supported on an abutment 62 of the circuit breaker casing.

The parts which operate when magnetic tripping occurs are shown particularly in FIGURE 4, the parts here also being shown in the position which they occupy at the instant when tripping occurs.

In accordance with the invention, the two systems, one thermal and the other magnetic, for causing release of the primary latch member 43, operate independently of each other. Thus instantaneous release of the primary latch member 17 is provided, even though the thermal tripping means is isolated from the primary latch member and even though a short time delay is involved when such thermal tripping occurs.

In accordance with another aspect of our invention, means is provided for indicating the occurrence of magnetic tripping as distinguished from thermal tripping. For this purpose, an indicator 39A is provided on the secondary releasable member 39, and a bracket 55 is provided on the trip unit casing part 21, hearing the markings magnetic and thermal. The indicator 39A is normally positioned adjacent the word magnetic, and only when the member 39 is released by the secondary latch member, does it move to the thermal position. When magnetic tripping occurs, therefore, the indicator 39A does not move, but remains adjacent the Word magnetic." When the user observes that tripping has occurred, such tripping being indicated, for example, by the movement of the operating handle 16 to trip indicating position as is well known in the prior art, he needs only to look at the indicator 39A to observe that such tripping occurred because of a sudden high overload rather than a sustained slow overload.

Likewise, if tripping occurs by reason of a slow, sustained overload, the member 39 will be released to cause tripping, thereby moving the indicator 39A to the thermal indicating position.

The trip indicating pointer 39A may be observed by removing the casing cover 11, or if desired, by providing an opening, not shown, in the casing cover, through which the indicator may be observed.

In a series of tests on a circuit capable of delivering 50,000 amperes at 240 volts, the average interrupting time in terms of electrical degrees of a particular prior art circuit breaker was 204 degrees from the incidence of the short circuit. With the same circuit breaker, modified to incorporate the present invention, the interrupting time on the same test was 131 electrical degrees. The time required for interruption of the short circuit in the above tests was therefore reduced 73 electrical degrees out of a total of 204 electrical degrees, or a reduction of about 36%. When dealing with short circuit currents of this magnitude, a reduction of this nature, of over /3 of the arcing time, significantly prolongs the life of the circuit breaker and significantly reduces the likelihood of failure of the breaker to interrupt.

While the invention has been disclosed in only one particular embodiment, it will be readily apparent that many modifications may readily be made, and I therefore intend by the appended claims, to cover all such modifications as fall within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An electric circuit breaker comprising:

(a) a generally rectangular insulating main casing;

(b) at least two separable contacts;

(c) operating mechanism for moving said separable contacts between open and closed circuit positions;

(d) said operating mechanism including a primary releasable member movable when released to cause automatic opening of said contacts;

(e) a primary latch normally engaging and restraining said primary releasable member;

(f) a removable trip unit mounted in said main casing;

(g) a secondary releasable member carried by said trip unit and movable when released to cause releasing movement of said primary latch member;

(h) said trip unit including a secondary latch member normally engaging and restraining said secondary releasable member;

(i) said trip unit including a thermal current responsive means responsibe to current passing through said separable contacts for causing release of said secondary latch member;

(j) at least one electromagnet carried by said trip unit;

(k) said trip unit including means for energizing said electromagnet in response to current flowing through said separable contacts;

(I) said trip unit including a magnetic armature disposed and arranged to be attracted to said electromagnet upon the occurence of predetermined energization of said electromagnet;

(m) a releasing member pivotally connected to said armature;

(11) means slidably guiding said releasing member for reciprocating movement in response to pivotal movement of said armature;

(0) said releasing member having a hook portion disposed and arranged to engage said primary latch member to positively move said primary latch member to releasing position when said armature moves to attracted position.

2. An electric circuit breaker comprising:

(a) a generally rectangular insulating main casing;

(b) at least two separable contacts;

(0) operating mechanism for moving said contacts between open and closed circuit positions;

(d) said operating mechanism including a primary releasable member movable when released to cause automatic opening of said contacts;

(e) a primary latch member normally engaging and restraining said primary releasable member;

(f) a removable trip unit comprising an insulating casing mounted in said main casing;

(g) at least one electromagnet mounted in said trip unit casing;

(h) means for energizing said eelctromagnet in response to current flowing through said separable contacts;

(i) a magnetic armature disposed and arranged to be attracted to said electromagnet upon the occurrence of predetermined current energization of said electromagnet;

(j) a releasing member slidably mounted on said trip unit casing and including a hook portion disposed and arranged to engage said primary latch member;

(k) connecting means connecting said armature memher to said releasing member whereby movement of said armature to attracted position positively moves said primary latch member to releasing position.

3. An electric circuit breaker comprising:

(a) a generally rectangular insulating casing;

(b) at least three pairs of separable contacts mounted in said insulating casing;

(c) operating mechanism mounted in said insulating casing for moving said separable contacts in unison between open and closed circuit positions;

(d) said operating mechanism including a primary releasable member movable when released to cause automatic opening of all of said contacts;

(e) a primary latch member normally engaging and restraining said primary releasable member;

(f) a removable trip unit comprising a generally rectangular insulating casing, receivable in said main circuit breaker casing;

(g) at least three electromagnets in said trip unit casing, each of said electromagnets corresponding to one of said pairs of separable contacts;

(11) means for energizing each of said electromagnets in response to current flowing through said corresponding pair of separable contacts;

(i) a magnetic armature for each of said electromagnets disposed and arranged to be attracted to said corresponding electromagnet upon the occurrence of predetermined energization of said electromagnets;

(j) a member pivotally supported in said trip unit cas- (k) a trip bar carried by said pivotally supported member and having portions extending adjacent each of said magnetic armatures, whereby movement of any of said armatures towards its corresponding electromagnet causes movement of said pivotally supported member;

(1) means directly connecting said pivotally supported member to said primary latch member, whereby movement of any of said magnetic armatures to attracted position with respect to its corresponding electromagnets positively causes releasing movement of said primary releasable member.

4. An electric circuit breaker as set forth in claim 3 said circuit breaker also comprising:

(in) thermal current responsive means carried by said trip unit corresponding to each of said pairs of separable contacts;

(n) a secondary releasable member carried by said trip unit casing;

(o) a secondary latch member carried by said trip unit casing and normally engaging and restraining said secondary releasable member;

(p) said thermal current responsive means being disposed and arranged to engage said secondary latch member to cause releasing movement of said secondary latch member upon the occurrence of predetermined current conditions through any one of said pairs of separable contacts, and

(q) said thermal current responsive means and said magnetic current responsive means acting independently of each other on said primary latch member to cause releasing of said primary latch member.

References Cited by the Examiner UNITED STATES PATENTS 2,419,125 4/47 Dorfman et a1. 2,821,596 1/58 Bires et a1. 2OO88 2,981,811 4/61 Steven et al. 20088 BERNARD A. GILHEANY, Primary Examiner.

Claims (1)

1. 2. AN ELECTRIC CIRCUIT BREAKER COMPRISING: (A) A GNERALLY RECTANGULAR INSULATING MAIN CASING; (B) AT LEAST TWO SEPARABLE CONTACTS; (C) OPERATING MECHANISM FOR MOVING SAID CONTACTS BETWEEN OPEN AND CLOSED CIRCUIT POSITIONS; (D) SAID OPERATING MECHANISM INCLUDING A PRIMARY RELEASABLE MEMBER MOVABLE WHEN RELEASXED TO CAUSE AUTOMATIC OPENING OF SAID CONTACTS; (E) A PRIMARY LATCH MEMBER NORMALLY ENGAGING AND RESTRAINING SAID PRIMARY RELEASABLE MEMBER; (F) A REMOVABLE TRIP UNIT COMPRISING AN INSULATING CASING MOUNTED IN SAID MAIN CASING; (G) AT LEAST ONE ELECTROMAGNET MOUNTED IN SAID TRIP UNIT CASING; (H) MEANS FOR ENERGIZING SAID ELECTROMAGNET IN RESPONSE TO CURRENT FLOWING THROUGH SAID SEPARABLE CONTACTS; (I) A MAGNETIC ARMATURE DISPOSED AND ARRANGED TO BE ATTRACTED TO SAID ELECTROMAGNETIC UPON THE OCCURRENCE OF PREDETERMINED CURRENT ENERGIZATION OF SAID ELECTROMAGNET; (J) A RELEASING MEMBER SLIDABLY MOUNTED ON SAID TRIP UNIT CASING AND INCLUDING A HOOK PORTION DISPOSED AND ARRANGED TO ENGAGE SAID PRIMARY LATCH MEMBER; (K) CONNECTING MEANS COPNNECTING SAID ARMATURE MEMBER TO SAID RELEASING MEMBER WHEREBY MOVEMENT OF SAID ARMATURE TO ATTRACTED POSITION POSITIVELY MOVES SAID PRIMARY LATCH MEMBER TO RELEASING POSITION.

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